A flame-retardant coating and its application in preparing a flame-retardant coating on the surface of a polylactic acid substrate

Abstract

The application discloses a kind of flame-retardant coating and its application in the surface of polylactic acid substrate preparation flame-retardant coating, belong to polylactic acid material technical field.The flame-retardant coating includes flame-retardant coating, it includes A component and B component, A component includes film-forming resin and at least one flame retardant, wherein, the film-forming resin includes modified alkyd resin, the hydroxyl value of the modified alkyd resin is 50~150mg KOH / g, and acid value is 3~10 mg KOH / g;The B component includes curing agent, and the curing agent is isocyanate curing agent.The coating formed by the flame-retardant coating of the application on the surface of PLA substrate not only has strong adhesion, but also can effectively bear and disperse high content of flame-retardant filler, so as to consider high adhesion and high flame retardancy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polylactic acid materials, in particular, the present application relates to a kind of flame-retardant coating suitable for polylactic acid base material and its application in the preparation of flame-retardant coating on the surface of polylactic acid base material. BACKGROUND

[0002] As an important biodegradable material, polylactic acid (PLA) has a wide application prospect in electrical enclosures (such as electrical energy metering box), packaging, automotive interior, etc. However, PLA itself is flammable, and the surface energy is low, which leads to poor adhesion of conventional coatings (according to GB / T 9286 standard test, the adhesion of untreated is often only 3-4 grade or even lower), thus limiting the application of PLA in occasions with high requirements for safety and surface performance.

[0003] In order to improve the flame retardance of PLA, the existing technology usually adopts the following ways:

[0004] Bulk flame-retardant modification: adding flame retardant during PLA melt blending, but this flame-retardant modification method easily affects the mechanical properties and processing properties of PLA, and the cost is high.

[0005] Multi-layer coating system: first spray a layer of adhesion promoting primer on the surface of PLA, and then spray a layer of flame-retardant topcoat. Although this method can take into account the adhesion and flame retardance, the process flow is complex (at least twice spraying and possible intermediate drying), which increases the production cost and time, and the interlayer bonding will become a potential weak point, which has the risk of delamination. For example, in the early scheme, a combination of polyurethane modified acrylic primer and oil-based cable fire retardant topcoat was used, which could achieve the target, but the process was complicated.

[0006] Single-layer flame-retardant coating: adhesion and flame retardance are realized by a single coating, but the existing single-layer coating cannot take into account both flame retardance and coating adhesion. Specifically, in order to achieve flame retardance, a high proportion of flame retardant needs to be added, which will significantly reduce the interfacial bonding force between the coating resin matrix and the PLA substrate, resulting in a decrease in adhesion. Therefore, in order to pursue high flame retardance by adding a large amount of flame retardant, the adhesion between the coating and the PLA substrate is sacrificed; on the other hand, in order to ensure adhesion, the amount of flame retardant is limited, making it difficult to achieve high flame retardance.

[0007] Therefore, the existing single-layer flame-retardant coating of PLA substrate cannot meet the dual requirements of adhesion and flame retardance. SUMMARY

[0008] In view of the problem that the coating formed by the existing flame-retardant coating on the surface of PLA substrate cannot take into account both adhesion and flame retardance, the present application provides a flame-retardant coating and its application in forming a flame-retardant coating on the surface of PLA substrate.

[0009] In a first aspect of the present application, there is provided a fire-retardant coating comprising an A component and a B component, the A component comprising a film-forming resin and at least one fire-retardant agent, wherein the film-forming resin comprises a modified alkyd resin, the modified alkyd resin being formed by:

[0010] (1) introducing a monomer or oligomer containing a polar functional group for copolymerization modification during the polyesterification reaction for forming the alkyd resin; or

[0011] (2) copolymerization modification after pre-polymerization of the alkyd resin;

[0012] the modified alkyd resin having a hydroxyl value of 50-150 mg KOH / g and an acid value of 3-10 mg KOH / g; and the B component comprising a curing agent, the curing agent being an isocyanate curing agent.

[0013] In some embodiments of the first aspect of the present application, the modified alkyd resin is formed by copolymerization modification by introducing a hydroxyl-terminated poly-caprolactone diol PCL-diol during the polyesterification reaction for forming the alkyd resin.

[0014] In some embodiments of the first aspect of the present application, the modified alkyd resin is formed by copolymerization modification by introducing an amide group-containing diol during the polyesterification reaction for forming the alkyd resin.

[0015] In some embodiments of the first aspect of the present application, the amide group-containing diol comprises N,N-bis(2-hydroxyethyl)acetamide.

[0016] In some embodiments of the first aspect of the present application, the modified alkyd resin is formed by copolymerization modification by introducing a hydroxyl-terminated oligomeric lactic acid after pre-polymerization of the alkyd resin.

[0017] In some embodiments of the first aspect of the present application, the hydroxyl-terminated oligomeric lactic acid has a number average molecular weight Mn of 1000-1500 g / mol.

[0018] In some embodiments of the first aspect of the present application, the modified alkyd resin has a solid content of 15-35 parts by weight based on 100 parts by weight of the total weight of the A component.

[0019] In some embodiments of the first aspect of the present application, the modified alkyd resin has a hydroxyl value of 80-120 mg KOH / g and an acid value of 3-8.5 mg KOH / g.

[0020] In a second aspect of the present application, there is provided use of the fire-retardant coating according to the first aspect of the present application in preparing a fire-retardant coating layer on a polylactic acid substrate.

[0021] In a third aspect of the present application, a flame-retardant coating is provided, which is formed on the surface of a polylactic acid substrate using the flame-retardant coating according to the first aspect of the present application.

[0022] In a fourth aspect of the present application, a method for forming a flame-retardant coating on the surface of a polylactic acid substrate is provided, which uses the flame-retardant coating according to the first aspect of the present application.

[0023] The present application has the following beneficial technical effects relative to the prior art:

[0024] The flame-retardant coating of the present application uses a specific modified alkyd resin as a film-forming material in component A, which is modified on the basis of a conventional alkyd resin and has its hydroxyl value and acid value controlled within a suitable range (i.e. a hydroxyl value of 50-150 mg KOH / g and an acid value of 3-10 mg KOH / g), so that the flame-retardant coating formed by the A component containing the modified film-forming resin and the B component containing the isocyanate curing agent forms a coating on the surface of a PLA substrate with low surface energy, which not only has strong adhesion, but also can effectively carry and disperse a high content of flame-retardant fillers and form a dense and tough coating through high-efficiency crosslinking with the curing system, thus achieving both high adhesion and high flame retardancy for the coating.

[0025] For the adhesion of the coating, due to the dense and tough crosslinking network formed by the PLA-philic groups / segments introduced in the molecular structure of the modified alkyd resin and the isocyanate curing agent, the coating forms a strong interfacial bonding force with the PLA substrate, and in an exemplary embodiment, the adhesion of the coating is as high as 0 or 1 level according to GB / T9286-2021 standard, which is much better than the common 3-4 level in the prior art, effectively solving the problem of coating adhesion caused by the low surface energy of PLA.

[0026] For the flame-retardant performance, under the condition of the glow wire test (750℃±15℃ or 650℃±15℃), the coating sample shows no obvious flame and sustained combustion phenomenon, and is completely extinguished within 30 seconds after the glow wire is removed, the underlying tissue paper does not ignite, and the pine board does not burn, achieving excellent flame-retardant effect. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a grid test result diagram of the flame-retardant coating formed on the surface of a PLA substrate by the coating of Example 1.

[0028] Figure 2 is a result diagram of the sample after the flame-retardant coating formed on the surface of a PLA substrate by the coating of Example 1 is subjected to the glow wire test. DETAILED DESCRIPTION

[0029] The various aspects of the present application will be described in detail with reference to specific embodiments and exemplary examples, which are merely illustrative of the present application and do not limit the scope of the present application.

[0030] The fire-retardant coating of the present application employs a modified alkyd resin as the film-forming resin in its A component, which is modified on the basis of a conventional alkyd resin and has its hydroxyl value and acid value controlled, so that the coating employing the modified film-forming resin not only has strong adhesion to a PLA substrate of low surface energy, but also effectively bears and disperses a high content of fire-retardant fillers and highly efficiently crosslinks with a curing system to form a dense and tough coating layer, thus making the coating layer have both strong adhesion and high fire retardancy.

[0031] Specifically, the modified alkyd resin of the present application can be obtained by copolymerization modification of a monomer or oligomer containing a polar functional group of a specific structure during the synthesis of a conventional alkyd resin (prepared by reaction of a polyol, a polyacid and a fatty acid / oil), or by post-reaction modification of a pre-prepared alkyd resin. The modification aims to:

[0032] a) increase the affinity to the PLA substrate: for example, introduction of a functional group (such as an additional hydroxyl group, an amide group, a carbamate group, or a short-chain polyester fragment, etc.) capable of forming hydrogen bonds or dipole-dipole interactions with the ester groups or terminal hydroxyl / carboxyl groups on the surface of the PLA.

[0033] b) optimize the crosslinking reaction activity: ensure that the resin molecular chain contains a sufficient number of active groups (mainly hydroxyl groups) and a reasonable distribution, so as to highly efficiently react with the isocyanate curing agent to form a dense crosslinking network.

[0034] c) improve the wetting and coating of the fire-retardant fillers: the modified alkyd resin structure helps to better disperse and coat the fire-retardant filler particles, reducing the risk of cohesion loss and adhesion loss of the coating layer due to a large amount of fillers.

[0035] The modified alkyd resin in the present application can be obtained by partially using a polyol containing an additional hydroxyl group in the polyesterification reaction of the alkyd resin; alternatively, the modified alkyd resin in the present application can also be obtained by introducing a small amount of a diacid capable of enhancing polarity (such as a diacid containing an ether bond or an amide bond); in addition, the modified alkyd resin in the present application can also be realized by grafting a short-chain, hydroxyl-terminated oligomer similar in structure to PLA, such as a hydroxyl-terminated oligomeric lactic acid or oligomeric caprolactone.

[0036] The hydroxyl value of the modified alkyd resin obtained in this invention can be controlled to be 50-150 mg KOH / g, preferably 80-120 mg KOH / g; the acid value of the modified alkyd resin can be controlled to be 3-10 mg KOH / g, preferably less than 9.5 mg KOH / g.

[0037] In one exemplary embodiment of the present invention, the basic components of the alkyd resin are pentaerythritol, glycerol, phthalic anhydride, and soybean oil fatty acids. During the polyesterification reaction of these basic components, terminal hydroxyl polycaprolactone diol (PCL-diol) is introduced as a comonomer, and the ratio of polyol (molar ratio of pentaerythritol to glycerol) and anhydride is adjusted so that the hydroxyl value and acid value of the finally synthesized modified alkyd resin 1 are controlled within the required range. The mass fraction of PCL-diol can be 5-10% of the total solid mass of the alkyd resin, and the number average molecular weight Mn of PCL-diol can be 500-1000 g / mol.

[0038] In another exemplary embodiment of the present invention, the basic components of the alkyd resin are pentaerythritol, glycerol, phthalic anhydride, and soybean oil fatty acids. During the polyesterification reaction of these basic components, itaconic acid and amide monomers are added for copolymerization to form a modified alkyd resin. The amide monomers can be diols containing amide groups (e.g., N,N-bis(2-hydroxyethyl)acetamide), so that the hydroxyl value and acid value of the final modified alkyd resin 1 are controlled within the required range. The amount of itaconic acid used is 8-15 mol% of the total acid components, and the mass fraction of the diol containing amide groups is 3-10% of the total solid mass of the alkyd resin.

[0039] In another exemplary embodiment of the present invention, the basic components of the alkyd resin are pentaerythritol, glycerol, phthalic anhydride, and soybean oil fatty acids. During the polyesterification reaction of these basic components, terminal hydroxyl oligolactic acid (PLA-OH) is introduced as a copolymer-modified oligomer to generate stronger physical entanglement and interfacial affinity with the PLA substrate. The mass fraction of terminal hydroxyl oligolactic acid is 10-12% of the total solids mass of the alkyd resin, and its number-average molecular weight Mn is 800-1500 g / mol.

[0040] The flame retardant in component A of the flame-retardant coating of the present invention can be one or more flame retardants known in the art suitable for polylactic acid-based materials, including but not limited to the following flame retardants:

[0041] Intumescent flame retardants: such as ammonium polyphosphate (APP) combined with charring agents (such as pentaerythritol) and foaming agents (such as melamine), which form an intumescent char layer when heated;

[0042] Phosphorus-containing flame retardants: In addition to APP, phosphorus-containing flame retardants can also include other organic phosphates (e.g. BDP, RDP), hypophosphite, etc.

[0043] Nitrogen-containing flame retardants: e.g. melamine, melamine cyanurate (MCA), guanidines, etc., which act by releasing non-flammable gases and promoting charring;

[0044] Inorganic hydroxide flame retardants: e.g. aluminum hydroxide (ATH), magnesium hydroxide (MDH), which act by endothermic decomposition to release water and dilute flammable gases.

[0045] The flame retardants employed in the exemplary embodiments of the present application include the following components:

[0046] Melamine: a nitrogen-containing flame retardant which, upon burning, decomposes to release nitrogen gas, which dilutes flammable gases;

[0047] Ammonium polyphosphate: a flame retardant which acts synergistically in both the gas and condensed phases, forming a phosphoric acid expanded char layer upon burning;

[0048] Aluminum hydroxide: which, upon heating, decomposes endothermically and releases water, which dilutes flammable gases;

[0049] Mica powder: which provides a physical barrier due to its platelet structure, hindering the transfer of heat and oxygen.

[0050] These flame retardants collectively impart flame retardant properties to the coating through synergistic flame retardant mechanisms in both the gas and condensed phases, such as endothermic decomposition, release of non-flammable gases to dilute oxygen, formation of an expanded dense char layer to insulate heat and flammable materials, and the physical barrier effect of platelet fillers.

[0051] The A component of the flame retardant coating of the present application can also include various functional fillers and auxiliary components, and in the exemplary embodiments, the A component includes the following pigments, fillers, and dispersants:

[0052] Titanium dioxide: used to provide hiding power and a white base tone;

[0053] Calcium carbonate, talc: used to adjust rheology, enhance mechanical properties, and reduce cost;

[0054] Dispersants: used to improve the dispersion stability of fillers and ensure the uniformity of coating quality, and the dispersants can be dispersants known in the art that are suitable for use in alkyd resin systems, such as high molecular weight polyurethane-based dispersants, modified polyacrylate-based dispersants.

[0055] The mixed solvent in the flame retardant coating of the present application includes xylene, refined methyl ester, 120# solvent, butyl ester, etc., which are used to adjust the application viscosity, optimize the leveling property and drying speed.

[0056] The preparation of the A component in the present application can include the following steps:

[0057] Pre-dispersion stage: The modified alkyd resin, dispersant and part of solvent (e.g. xylene and refined methyl ester) of the present application are sequentially added into a dispersion kettle, and a uniform mixture is formed under low-speed stirring.

[0058] Charging and dispersion stage: The pigments and fillers, such as titanium dioxide, mica powder, calcium carbonate and talc, are sequentially added under continuous stirring, and the stirring speed is increased to fully disperse the pigments and fillers.

[0059] Addition of flame retardant: Melamine, aluminum hydroxide and ammonium polyphosphate are sequentially added, and the dispersion is continued.

[0060] Adjustment stage: The remaining solvent (e.g. 120# solvent) is added, and the mixture is filtered (e.g. using a 200-mesh screen) after stirring to obtain component A.

[0061] The component B of the flame-retardant coating of the present application comprises an isocyanate curing agent. The isocyanate can be an aliphatic or aromatic polyisocyanate curing agent commonly used in the art, such as the biuret or trimer of hexamethylene diisocyanate (HDI), the trimer of isophorone diisocyanate (IPDI), etc. Through the reaction of its -NCO groups with the hydroxyl groups in the modified alkyd resin, a highly cross-linked urethane (polyurethane) network structure is formed, which imparts adhesion, cohesive strength, chemical resistance and mechanical properties to the coating.

[0062] In an exemplary embodiment of the present application, the component B is mixed with solvents (butyl ester, xylene and refined methyl ester) using Covestro N3300 isocyanate curing agent, and low-speed stirring is performed until a uniform transparent state is achieved.

[0063] When the flame-retardant coating of the present application is applied to the surface of a PLA substrate, the ratio of component A to component B depends on the hydroxyl equivalent weight of the modified alkyd resin in component A, the -NCO content of the isocyanate curing agent in component B and the desired cross-linking density. Generally, the -NCO: -OH molar ratio is between 0.8 and 1.5, preferably between 1.0 and 1.2. Components A and B are mixed, and the mixture is used after thorough stirring. The usable time of the mixed coating is about 4 hours (at 25°C).

[0064] The coating operation uses a spraying device (such as a pneumatic spray gun) to spray the surface of a PLA substrate that has been cleaned. The spraying pressure can be set to 0.3-0.4 MPa. After spraying, the coating is naturally dried at room temperature (25°C) for a certain period of time to achieve complete curing. Alternatively, the coating can be baked at 50°C to accelerate curing and form a flame-retardant coating.

[0065] The present application will be further described in detail below in conjunction with exemplary embodiments of the present application.

[0066] Example 1

[0067] The fire-retardant coating of the present embodiment comprises A component and B component, wherein the film-forming resin in the A component adopts modified alkyd resin 1.

[0068] I. Preparation of modified alkyd resin 1

[0069] The base raw material components of the modified alkyd resin 1 include pentaerythritol, glycerol, phthalic anhydride, and soybean oil fatty acid. During the polyesterification reaction, hydroxyl-terminated polycaprolactone diol (PCL-diol, number average molecular weight Mn=800 g / mol) with a mass fraction of 7% of the total solid mass of the alkyd resin is introduced as a copolymerization modification monomer, and the ratio of polyols (molar ratio of pentaerythritol to glycerol) and anhydride is adjusted, so that the hydroxyl value of the finally synthesized modified alkyd resin 1 is controlled at 100 mg KOH / g, and the acid value reaches 8.5 mg KOH / g. The modified alkyd resin is dissolved in a mixed solvent of xylene and refined methyl ester to a solid content of 60%. The preparation raw material components of the modified alkyd resin 1, their amounts, and their function explanations are shown in Table 1.

[0070] Table 1. Preparation raw material components of modified alkyd resin 1, their amounts, and their function explanations

[0071]

[0072] The preparation steps of the modified alkyd resin 1 are as follows:

[0073] 1. Dehydration pretreatment: In the reaction kettle, pentaerythritol 13 parts by weight and glycerol 8 parts by weight are sequentially added, the temperature is raised to 110-120°C, and vacuum dehydration (-0.08 MPa) is performed for 30 minutes.

[0074] 2. Esterification reaction: phthalic anhydride 23.1 parts by weight, soybean oil fatty acid 38.8 parts by weight, and esterification catalyst 0.1 part by weight are sequentially added; nitrogen protection (flow rate 1 L / min) is performed, and the temperature is gradually raised to 200-220°C; the reaction is kept for 2-3 hours, and the acid value is monitored in real time; when the acid value is reduced to 20-25 mg KOH / g, the next step is entered.

[0075] 3. PCL-diol copolymerization modification: the temperature is lowered to 160-170°C, and PCL-diol (7 parts by weight) dissolved in xylene (10 parts by weight) is slowly added; the temperature is controlled at 165±5°C, and the reaction is performed for 1.5-2 hours; during the reaction, the acid value is detected by sampling, and the reaction is continued until the acid value is ≤15 mg KOH / g.

[0076] 4. Regulation and end control: temperature is raised to 190-200°C, vacuum (-0.09 MPa) dehydration polycondensation for 1 hour; when the acid value is 8.0-9.0 mg KOH / g (measured value 8.5±0.5 mg KOH / g), the hydroxyl value reaches 98-102 mg KOH / g (measured value 100±2 mg KOH / g), the reaction is terminated.

[0077] 5. Dilution and post-treatment: temperature is lowered to 80°C, xylene / methyl ester mixed solvent (7:3) is added, and the solid content is adjusted to 60±1%; filtration (200 mesh screen) is performed to obtain a transparent viscous resin solution, which is the solution of modified alkyd resin 1, which is stored in a sealed container.

[0078] II. Formulation and preparation of A component

[0079] The A component of this example uses modified alkyd resin 1 as the film-forming resin, and the formulation and function of the A component are shown in Table 2.

[0080] Table 2. Formulation and amount and function of A component of Example 1

[0081]

[0082] The preparation steps of the A component are as follows:

[0083] 1. Preparation of base liquid: in a dispersion kettle, 25 parts by weight of modified alkyd resin 1 (solid content 60%), 0.5 parts by weight of dispersant and part of solvent (7.0 parts by weight of xylene, 4.0 parts by weight of methyl ester) are added in sequence, and low-speed stirring is performed for 5 minutes to form a uniform base mixture.

[0084] 2. Pigment and filler addition and dispersion: under continuous stirring, 13 parts by weight of titanium dioxide, 12 parts by weight of mica powder, 4 parts by weight of calcium carbonate and 5 parts by weight of talc are added in sequence, the stirring speed is increased to medium speed, and stirring is performed for 15 minutes; then, the stirring speed is increased to high speed (about 1000 rpm), and dispersion is performed for 30 minutes to fully wet and disperse the pigments and fillers.

[0085] 3. Addition of flame retardant: the stirring speed is reduced to medium speed, 3 parts by weight of melamine, 4 parts by weight of aluminum hydroxide and 5 parts by weight of ammonium polyphosphate are added in sequence, and dispersion is continued for 15 minutes.

[0086] 4. Adjustment stage: the remaining solvent (7.1 parts by weight of xylene, 4.3 parts by weight of methyl ester, 6.1 parts by weight of 120# solvent) is added, low-speed stirring is performed for 10 minutes, and filtration (200 mesh screen) is performed to obtain the A component.

[0087] III. Formulation and preparation of B component

[0088] The formulation and function of the B component of this example are shown in Table 3.

[0089] Table 3. Formulation of B component of Example 1 and its function description

[0090]

[0091] According to the formulation shown in Table 3, the Covestro Desmodur® N3300A isocyanate curing agent was slowly added into the mixed solvent consisting of butyl ester, xylene and refined methyl ester, and stirred at low speed for 10 minutes until uniform and transparent, to obtain the B component.

[0092] Application Example 1

[0093] In application example 1, the flame-retardant coating prepared in example 1 was applied to the surface of polylactic acid substrate to form a flame-retardant coating, and the specific steps were as follows:

[0094] 1. Proportioning calculation of A component and B component

[0095] According to the molar ratio of -NCO in B component to -OH in A component being 1.05, the mass ratio of A component to B component was calculated to be about 100:67.5.

[0096] 2. Coating

[0097] The specific operation steps of coating the coating on the surface of PLA substrate were as follows:

[0098] (1) Pretreatment of PLA substrate: The surface of PLA substrate was first wiped with a dust-free cloth soaked with 95% anhydrous ethanol to remove oil stains and dust; then the surface was lightly sanded with 400-600 mesh sandpaper to increase the surface roughness and improve the adhesion of the coating; the cleaned substrate was placed in a 50°C oven for drying for 10 minutes to ensure that the surface was free of residual solvent and moisture.

[0099] (2) Coating mixing and preparation: A component and B component were weighed according to the mass ratio calculated above, and stirred with a mechanical stirrer at a speed of 300-500 rpm for 3-5 minutes to ensure uniform mixing. The viscosity of the mixed coating was controlled to be 20-25 seconds (T-4 cup, 25°C) to meet the requirements of spraying. The mixed coating should be used up within 4 hours at 25°C to avoid gelation.

[0100] (3) Coating construction: A pneumatic spray gun with a caliber of 1.2-1.5 mm was selected, the spraying pressure was set to 0.3-0.4 MPa, the spray gun was placed at a distance of 20-30 cm from the substrate surface, and moved at a uniform speed (about 0.5-1 m / s) to control the wet film thickness to be 80-100 pm.

[0101] (4) Curing: the sprayed workpiece is baked at 50°C for 4 h to promote the crosslinking and curing of components A and B, forming a cured coating layer with a dry film thickness of about 45 μm.

[0102] 3. Adhesion and flame retardant performance test of coating

[0103] (1) Adhesion test

[0104] According to the national standard GB / T9286-2021 “Colour Coatings and Clear Coatings Cross-cut Test”, a cross-cut test is performed. Specifically, a six-blade cutting knife (knife spacing 1 mm) is used to cut 6x6 squares on the surface of the coating layer coated on the surface of the PLA substrate, and the cut must completely penetrate to the substrate. Then, the debris is gently swept away with a soft brush at an angle of 45°, and the coating surface is observed as shown in Figure 1 . It is found that there is no peeling in the grid. According to the above standard, the adhesion level is 0 level, indicating that the bonding performance of the coating and the PLA substrate is optimal.

[0105] (2) Flame retardant performance test

[0106] According to the national standard GB / T 20641-2014, the test is performed. Specifically, the coated PLA substrate is cut into 100 mm x 100 mm x 3 mm PLA substrate samples and pretreated for 24 hours under the conditions of 20.1°C and relative humidity of 39.9%. Then, the hot wire is preheated to 750±15°C, the actual temperature at the top of the hot wire is 653.4°C, and the coating layer of the sample is vertically contacted with a pressure of 1.0 N for 30 seconds. During the test, the sample did not produce obvious flame or continuous bright light, and within 30 seconds after the hot wire was removed, any fire source was completely extinguished. At the same time, the underlying tissue paper did not ignite, and the pine board did not burn. The surface of the coating layer after the hot wire top contact test is shown in Figure 2 . As can be seen from Figure 2 , except for the local burning marks at the puncture site directly contacted by the top of the hot wire, there is no burning expansion phenomenon in the surrounding area, which proves the effective flame retardant protection effect of the coating on the PLA substrate. The comprehensive results show that the sample does not ignite under the test conditions, and exhibits good flame retardant performance.

[0107] Example 2

[0108] The flame retardant coating of this example includes component A and component B, wherein component B remains the same as that of Example 1. The film-forming resin in component A uses the modified alkyd resin 1 described in Example 1, and the difference from the component A of Example 1 is that the amount of modified alkyd resin 1 is adjusted from 25 parts by weight in Example 1 to 15 parts by weight. In addition, the amount of solvent in component A is adjusted to maintain a suitable solid content and application viscosity.

[0109] The formulation of the A component of Example 2 and the description of its functions are shown in Table 4.

[0110] Table 4. Formulation of the A component of Example 2 and the description of its functions and the amount used

[0111]

[0112] Application Example 2

[0113] In Application Example 2, the flame-retardant coating prepared in Example 2 was applied to the surface of a polylactic acid substrate to form a flame-retardant coating.

[0114] According to the calculated ratio of -NCO:-OH = 1.05:1, the mass ratio of the A component to the B component was 100:40.5. The A component and the B component were weighed according to this mass ratio, and the two were mixed uniformly using the same method as in Application Example 1 to obtain the coating. The viscosity of the coating was 18-20 seconds (T-4 cup, 25°C).

[0115] The coating was applied to the PLA substrate, and the specific operation steps of the application were the same as in Application Example 1.

[0116] The adhesion and flame-retardant properties of the coating obtained in Application Example 2 were tested using the test standards described in Application Example 1, and the test results were as follows:

[0117] The grid test was performed on the coating of Application Example 2. After observation, it was found that the grid had coating peeling at the intersection of the cuts, and the affected intersection cutting area was greater than 5% but less than 15% without peeling, indicating that the grid test reached level 2, and the adhesion performance was good.

[0118] The flame-retardant performance test was performed on the coating of Application Example 2, and the test results showed that the test sample did not ignite under the test conditions.

[0119] Example 3

[0120] The flame-retardant coating of this example includes an A component and a B component. The B component remains the same as in Example 1. The film-forming resin in the A component uses the modified alkyd resin 1 described in Example 1. The difference from the A component of Example 1 is that the amount of modified alkyd resin 1 is adjusted from 25 parts by weight in Example 1 to 35 parts by weight. In addition, only the amount of solvent in the A component is adjusted to maintain a suitable solid content and application viscosity.

[0121] The formulation of the A component of Example 3 and the description of its functions are shown in Table 5.

[0122] Table 5. Formulation of the A component of Example 3 and the description of its functions and the amount used

[0123]

[0124] Application Example 3

[0125] In application example 3, the flame retardant coating prepared in example 3 was applied to the surface of polylactic acid substrate to form a flame retardant coating.

[0126] The mass ratio of A component to B component was calculated to be 100:94.7 according to the ratio of -NCO:-OH=1.05:1, and A component and B component were weighed according to the mass ratio, and then mixed uniformly by the same method as application example 1 to obtain the coating, and the viscosity of the coating was 35-37 seconds (T-4 cup, 25°C).

[0127] The coating was applied to the PLA substrate, and the specific operation steps of coating were the same as application example 1.

[0128] The adhesion and flame retardant properties of the coating obtained in application example 3 were tested by the test standards described in application example 1, and the test results were as follows:

[0129] The grid test was carried out on the coating of application example 3, and after observation, it was found that there was slight stringing in the grid but the paint did not fall off, indicating that the grid test reached level 0, reaching the best level.

[0130] The flame retardant performance test was carried out on the coating of application example 3, and the test results showed that the test sample did not ignite under the test conditions.

[0131] Example 4

[0132] The flame retardant coating of this example includes A component and B component, wherein the film-forming resin in the A component uses modified alkyd resin 2.

[0133] I. Preparation of modified alkyd resin 2

[0134] The base component of modified alkyd resin 2 is similar to modified alkyd resin 1, but the modification method is different. The modification method of the alkyd resin of this example is: in the polyesterification reaction process, itaconic acid is used to replace part of the dibasic acid (phthalic anhydride) in example 1, and the amount of itaconic acid is 10 mol% of the total acid component, and a diol containing amide groups (such as N,N-bis(2-hydroxyethyl)acetamide) with a mass fraction of 5% of the total solid mass of the alkyd resin is introduced as a copolymerization modifier monomer, and the reaction conditions are adjusted to control the hydroxyl value of the finally synthesized modified alkyd resin 2 to be 85 mg KOH / g, and the acid value is 8 mg KOH / g. The resin is dissolved with a solvent to a solid content of 60%. The raw material components, their amounts and functional explanations of the preparation of modified alkyd resin 2 are shown in Table 6.

[0135] Table 6. Raw material components, their amounts and functional explanations of the preparation of modified alkyd resin 2

[0136]

[0137] The preparation steps of the modified alkyd resin 2 are as follows:

[0138] 1. Dehydration of polyols: In a reaction kettle, pentaerythritol 13.6 parts by weight and glycerol 8.3 parts by weight were added in sequence, heated to 120±2℃, vacuumized (-0.08 MPa) for dehydration for 40 minutes.

[0139] 2. First-stage esterification: Phthalic anhydride 18 parts by weight and soybean oil fatty acid 36 parts by weight were added in sequence; nitrogen protection (1.5 L / min) was conducted, and programmed temperature rising was performed: 150℃ for 30 minutes, 180℃ for 1 hour, and 200-210℃ for 2 hours; termination was performed when the acid value was reduced to 22-25 mg KOH / g.

[0140] 3. Low-temperature addition of itaconic acid and amide monomers: The temperature was reduced to 140-145℃, itaconic acid 7 parts by weight and anti-gelling agent 0.1 parts by weight were added; the temperature was controlled at 145±2℃, and reaction was performed for 1 hour (the acid value was reduced to 18-20 mg KOH / g); N,N-bis(2-hydroxyethyl)acetamide 5 parts by weight was added, and reaction was continued at 145℃ for 1.5 hours (the acid value was ≤15 mg KOH / g).

[0141] 4. High-temperature polycondensation and end-point control: The temperature was raised to 190-195℃, and vacuumization (-0.095 MPa) was performed for 1.5 hours; the acid value / hydroxyl value was measured every 30 minutes, and the end-point requirements were: the acid value was 7.5-8.5 mg KOH / g (the measured value was 8.0±0.5 mg KOH / g), and the hydroxyl value was 85±2 mg KOH / g.

[0142] 5. Dilution and filtration: The temperature was reduced to 85℃, dimethylbenzene / ethyl methyl ester (6:4) mixed solvent was added to adjust the solid content to 60±1%, and the yellowish transparent resin, i.e., the solution of the modified alkyd resin 2, was obtained after filtration through a 5 μm filter bag.

[0143] II. Formulation and preparation of A component

[0144] The A component of the present example uses the modified alkyd resin 2 as the film-forming resin, and the formulation and function of the A component are shown in Table 7. Compared with the A component of Example 1, the modified alkyd resin 1 in the A component of the present example is replaced by the modified alkyd resin 2, and the amount remains 25 parts by weight. Except that the total amount of the solvent is adjusted accordingly to maintain a suitable solid content and application viscosity, the proportions of other components remain unchanged.

[0145] Table 7. Formulation, amount and function of the A component of Example 4

[0146]

[0147] The preparation procedure of the A component is the same as that of the A component in Example 1.

[0148] The B component in this example is the same as that in Example 1.

[0149] Application Example 4

[0150] In Application Example 4, the flame-retardant coating prepared in Example 4 is applied to the surface of a polylactic acid substrate to form a flame-retardant coating.

[0151] The mass ratio of the A component to the B component is calculated to be 100:57 according to the ratio of -NCO:-OH = 1.05:1, and the A component and the B component are weighed according to the mass ratio, and the two are mixed uniformly by the same method as in Application Example 1 to obtain the coating, and the viscosity of the coating is 18-22 seconds (T-4 cup, 25°C).

[0152] The coating is applied to the PLA substrate, and the specific operation steps of the coating are the same as those in Application Example 1.

[0153] The adhesion and flame-retardant properties of the coating obtained in Application Example 4 are tested by the test standards described in Application Example 1, and the test results are as follows:

[0154] The cross-cut test is performed on the coating of Application Example 4, and after observation, it is found that there is a little coating peeling at the intersection of the cuts, but the affected cross-cut area is less than 5%, indicating that the cross-cut test reaches level 1, and the adhesion performance is excellent.

[0155] The flame-retardant performance test is performed on the coating of Application Example 4, and the test results show that the test sample does not ignite under the test conditions.

[0156] Example 5

[0157] The flame-retardant coating of this example includes an A component and a B component, and the B component is the same as that in Example 4, and the film-forming resin in the A component uses the modified alkyd resin 2 in Example 4. The difference between the A component of this example and that of Example 4 is that the amount of modified alkyd resin 2 is adjusted from 25 parts by weight in Example 4 to 15 parts by weight; in addition, except for adjusting the amount of solvent to maintain a suitable solid content and application viscosity, the amounts of other components remain unchanged.

[0158] The formulation of the A component of Example 5 and its function are shown in Table 8.

[0159] Table 8. Formulation of the A component of Example 5 and its amount and function

[0160]

[0161] Application Example 5

[0162] In application example 5, the flame-retardant coating prepared in example 5 was applied to the surface of a polylactic acid substrate to form a flame-retardant coating.

[0163] The mass ratio of the A component to the B component was calculated to be 100:34.5 according to the ratio of -NCO:-OH=1.05:1, and the A component and the B component were weighed according to the mass ratio, and the two were mixed uniformly by the same method as in application example 1 to obtain a coating, and the viscosity of the coating was 18-20 seconds (T-4 cup, 25°C).

[0164] The coating was applied to a PLA substrate, and the specific operation steps of the application were the same as in application example 1.

[0165] The adhesion and flame-retardant properties of the coating obtained in application example 5 were tested by the test standards described in application example 1, and the test results were as follows:

[0166] The cross-cut test was performed on the coating of application example 5, and after observation, it was found that there was a little coating falling off at the intersection of the cuts, but the affected cross-cut area was less than 5%, indicating that the cross-cut test reached level 1, and the adhesion performance was excellent.

[0167] The flame-retardant performance test was performed on the coating of application example 5, and the test results showed that the test sample did not ignite under the test conditions.

[0168] Example 6

[0169] The flame-retardant coating of this example includes an A component and a B component, wherein the B component remains the same as in example 4. The film-forming resin in the A component uses the modified alkyd resin 2 in example 4. Compared with example 4, the difference of the A component is that the amount of modified alkyd resin 2 is adjusted from 25 parts by weight in example 4 to 35 parts by weight; in addition, except for adjusting the amount of solvent to maintain a suitable solid content and application viscosity, the amounts of other components remain unchanged.

[0170] The formulation of the A component of example 6 and its function are shown in table 9.

[0171] Table 9. Formulation of the A component of example 6 and its amount and function

[0172]

[0173] Application example 6

[0174] The mass ratio of the A component to the B component was calculated to be 100:80 according to the ratio of -NCO:-OH=1.05:1, and the A component and the B component were weighed according to the mass ratio, and the two were mixed uniformly by the same method as in application example 1 to obtain a coating, and the viscosity of the coating was 35-37 seconds (T-4 cup, 25°C).

[0175] The coating was applied to the PLA substrate, and the specific operation steps of the coating were the same as those of application example 1.

[0176] The adhesion and flame retardant properties of the coating obtained in application example 6 were tested using the test standards described in application example 1, and the test results are as follows:

[0177] The grid test was performed on the coating of application example 6, and after observation, it was found that there was slight wire drawing in the grid but the paint did not fall off, indicating that the grid test reached level 0 (the best level).

[0178] The flame retardant performance test was performed on the coating of application example 6, and the test results showed that the test sample did not ignite under the test conditions.

[0179] Example 7

[0180] The flame-retardant coating of this example includes component A and component B, wherein component B is the component B in example 1, and the film-forming resin in component A is modified alkyd resin 3.

[0181] I. Preparation of modified alkyd resin 3

[0182] The base components of modified alkyd resin 3 are similar to those of example 1, but the modification method is different. In this example, the modification method is to introduce 12% by mass of hydroxyl-terminated oligomeric lactic acid (PLA-OH, number average molecular weight Mn = 1200 g / mol) as a copolymerization modifier after the pre-polymerization of the alkyd resin, in order to produce stronger physical entanglement and interfacial affinity with the PLA substrate, and to adjust the polyol ratio so that the hydroxyl value of the finally synthesized modified alkyd resin 3 is controlled at 110 mg KOH / g, and the acid value is 7.0 mg KOH / g. The resin is dissolved with a solvent to a solid content of 60%. The raw material components, their amounts and functional explanations of modified alkyd resin 5 are shown in Table 10.

[0183] Table 10. Raw material components, their amounts and functional explanations of modified alkyd resin 3

[0184]

[0185] The preparation steps of modified alkyd resin 3 are as follows:

[0186] 1. Prepolymer preparation: In a reaction kettle, add pentaerythritol 13.8 parts by weight, glycerol 10 parts by weight, dehydrate at 115±2℃, -0.09 MPa for 45 minutes; add phthalic anhydride 22 parts by weight, soybean oil fatty acid 30 parts by weight, DBTL 0.1 parts by weight; nitrogen protection (2 L / min), stepwise temperature rise: 150℃ / 30 min → 180℃ / 1 h → 200℃ / 2h, to acid value 18-20 mg KOH / g.

[0187] 2. PLA-OH low-temperature access: cool to 150-155℃, add PLA-OH 12 parts by weight; control temperature 152±2℃, low vacuum (-0.05 MPa) reaction for 2 hours; real-time monitoring of acid value, when the acid value ≤12 mg KOH / g, enter the final polycondensation (acid value drop speed <0.5 mg / h is judged as the end point).

[0188] 3. High-temperature final polycondensation and accurate end point: warm up to 185-190℃ (≤190℃ to prevent PLA degradation), vacuum (-0.095 MPa); reaction for 1.5-2 hours, sample every 20 minutes, end point requirement: 6.5-7.5 mg KOH / g (actual value 7.0±0.5 mg KOH / g), hydroxyl value = 110±2 mg KOH / g.

[0189] 4. Stabilization treatment: cool to 75℃, add antioxidant 0.1 parts by weight; cool to about 60℃, add a mixed solvent of xylene and methyl acetate (ratio 6:4), adjust the solid content to 60%; filter with a 10μm filter core to obtain a solution of modified alkyd resin 3, store under nitrogen.

[0190] II. Formulation and preparation of A component

[0191] The A component of this example uses modified alkyd resin 3 as the film-forming resin, and the formulation and function of the A component are shown in Table 11. Compared with the A component of Example 1, the difference of this example is that the modified alkyd resin 1 is replaced by modified alkyd resin 3, and the amount is 30 parts by weight; in addition, except that the total amount of solvent is adjusted to maintain appropriate solid content and construction viscosity, the proportion of other components remains unchanged.

[0192] Table 11. Formulation of A component of Example 7 and its amount and function

[0193]

[0194] The preparation steps of A component are as follows:

[0195] 1. Base liquid preparation: add the modified alkyd resin 3 prepared by the above method, dispersant and part of solvent (xylene and refined methyl ester) into a dispersing kettle in sequence, and stir at low speed for 5 minutes to form a uniform base mixture;

[0196] 2. Pigment and filler addition and dispersion: under continuous stirring, add titanium dioxide, mica powder, calcium carbonate and talc in sequence, and increase the stirring speed to medium speed and stir for 15 minutes; then, increase the stirring speed to high speed (about 1000 rpm) and disperse for 30 minutes to fully wet and disperse the pigments and fillers;

[0197] 3. Flame retardant addition: reduce the stirring speed to medium speed, and add melamine, aluminum hydroxide and ammonium polyphosphate in sequence, and continue to disperse for 15 minutes;

[0198] 4. Adjustment stage: add the remaining solvent (120# solvent), stir at low speed for 10 minutes, and filter (200 mesh screen) to obtain component A.

[0199] Application Example 7

[0200] In application example 7, the flame-retardant coating prepared in example 7 is applied to the surface of a polylactic acid substrate to form a flame-retardant coating.

[0201] According to the mass ratio of component A to component B calculated according to the ratio of -NCO:-OH=1.05:1, the mass ratio of component A to component B is 100:89.4, and component A and component B are weighed according to the mass ratio and uniformly mixed by the same method as in application example 1 to form a coating with a viscosity of 20-25 seconds (T-4 cup, 25°C).

[0202] The coating is applied to the PLA substrate, and the specific operation steps of the coating are the same as in application example 1.

[0203] The adhesion and flame-retardant properties of the coating obtained in application example 7 are tested according to the test standards described in application example 1, and the test results are as follows:

[0204] The grid test is performed on the coating of application example 7, and after observation, it is found that there is no falling off in the grid, indicating that the grid test reaches level 0, reaching the best level.

[0205] The flame-retardant properties of the coating of application example 7 are tested, and the test results show that the test sample does not ignite under the test conditions.

[0206] The adhesion test results and flame-retardant property test results of the coatings formed by the flame-retardant coatings of examples 1 to 7 described above are summarized in tables 12 and 13, respectively.

[0207] Table 12. Adhesion test results

[0208]

[0209] Table 13. Results of flame retardant performance test

[0210]

[0211] As can be seen from the results of the adhesion and flame retardant performance tests of the coating layer formed on the surface of the PLA substrate by the flame retardant coating of the present application shown in Table 12 and Table 13, the flame retardant coating of the present application, which uses modified alkyd resins 1, 2 and 3 as the film-forming resin, forms a coating layer on the surface of the PLA substrate with excellent adhesion and flame retardant performance.

[0212] It should be noted that, in this document, the terms "comprise", "comprising", or any other variant thereof are intended to cover non-exclusive inclusions, so that processes, methods, articles or apparatuses that comprise a list of elements are not limited to those elements, but can also include other elements not expressly listed, or inherent to such processes, methods, articles or apparatuses. Without more limitations, the elements defined by the term "comprise" do not exclude the presence of other identical elements in the processes, methods, articles or apparatuses that include the elements.

[0213] The above examples are only used to illustrate the technical solutions of the present application, and cannot limit the protection scope of the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can still be modified, or some technical features can be replaced equivalently without departing from the essence and scope of the present application; and these modifications or equivalent replacements still belong to the scope covered by the present application.

Claims

1. A fire-retardant coating comprising a component A and a component B, characterized in that: the component A comprises a film-forming resin and at least one fire-retardant agent, wherein the film-forming resin comprises a modified alkyd resin, and the modified alkyd resin is formed by one of the following modification methods: (1) the modified alkyd resin is copolymerized by introducing a hydroxyl-terminated polycaprolactone diol PCL-diol during the polyesterification reaction for forming an alkyd resin; (2) the modified alkyd resin is copolymerized by introducing an amide group-containing diol during the polyesterification reaction for forming an alkyd resin; (3) the modified alkyd resin is copolymerized by introducing a hydroxyl-terminated oligomeric lactic acid after the prepolymerization of an alkyd resin; the modified alkyd resin has a hydroxyl value of 50-150 mg KOH / g and an acid value of 3-10 mg KOH / g; the solid content of the modified alkyd resin is 15-35 parts by weight based on 100 parts by weight of the total weight of the component A; the component B comprises a curing agent, and the curing agent is an isocyanate curing agent.

2. The fire retardant coating of claim 1, wherein, In the modification method (1), the raw materials for preparing the modified alkyd resin comprise pentaerythritol, glycerol, phthalic anhydride, and soybean oil fatty acid, and the number average molecular weight Mn of the hydroxyl-terminated polycaprolactone diol PCL-diol is 500-1000 g / mol.

3. The fire retardant coating of claim 1, wherein, In the modification method (2), the raw materials for preparing the modified alkyd resin comprise pentaerythritol, glycerol, phthalic anhydride, itaconic acid, and soybean oil fatty acid.

4. The fire retardant coating of claim 3, wherein, The amide group-containing diol comprises N,N-bis(2-hydroxyethyl)acetamide.

5. The fire retardant coating of claim 1, wherein, In the modification method (3), the number average molecular weight Mn of the hydroxyl-terminated oligomeric lactic acid is 1000-1500 g / mol.

6. The fire retardant coating of claim 1, wherein, The modified alkyd resin has a hydroxyl value of 80-120 mg KOH / g and an acid value of 3-8.5 mg KOH / g.

7. Use of the fire-retardant coating according to any one of claims 1 to 6 for preparing a fire-retardant coating layer on a polylactic acid substrate.

8. A flame retardant coating characterized by, The fire-retardant coating layer is formed on a polylactic acid substrate using the fire-retardant coating according to any one of claims 1 to 6.

9. A method for forming a fire-retardant coating layer on a polylactic acid substrate, using the fire-retardant coating according to any one of claims 1 to 6.

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