Flame-retardant master batch and preparation method thereof

Abstract

The invention provides a flame-retardant master batch and a preparation method thereof. The master batch is composed of 45-70% of matrix resin, 25-40% of a composite flame retardant, 3-12% of a dynamic cross-linking agent and 2-7% of a processing aid, the composite flame retardant provides phosphorus-nitrogen synergistic flame retardant activity through phosphate grafted chitosan, physical protection is achieved by coating a polyurethane packaging layer, and flame retardant migration and interface degradation are effectively prevented. The epoxy prepolymer is used as a dynamic cross-linking agent to regulate and control the rheological behavior of the material: dynamic bond dissociation reduces the melt viscosity during processing, bond recombination enhances the toughness after molding, and meanwhile, the master batch is endowed with self-repairing capability. The preparation method comprises the steps of in-situ packaging, segmented melt blending and dynamic crosslinking extrusion, flame retardant dispersion and control over a crosslinking network are achieved through temperature gradient and mechanical shearing, the contradiction between the mechanical property and the flame retardant property of a traditional flame retardant system is broken through, and the excellent processing stability is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, in particular to the technical field of masterbatch production and processing, and in particular to a flame retardant masterbatch and a preparation method of the flame retardant masterbatch. Background Art

[0002] Flame-retardant materials are widely used in the fields of electronics and electrical engineering, construction and building materials, transportation, etc. Traditional flame-retardant systems usually disperse flame retardants in the matrix resin by physical blending. However, in order to achieve a high flame retardancy level, this method requires a significant increase in the amount of flame retardant added. Excessive flame retardant will destroy the continuity of the matrix resin, resulting in a significant decrease in the mechanical strength of the material, forming a contradiction between flame retardancy and mechanical properties. On the other hand, flame retardants have poor compatibility with the resin interface and are prone to agglomeration or migration, which not only reduces the flame retardant efficiency, but also causes problems such as a surge in melt viscosity and deterioration in fluidity during processing, limiting their application.

[0003] Flame-retardant masterbatch is a functional particle added to polymer materials such as plastics and rubber to enhance their fire resistance. When exposed to high temperatures or open flames, it effectively delays combustion, reduces flame spread, and even prevents spontaneous combustion. It typically consists of a base resin and a flame retardant, which is then mixed evenly with the other resins. The advent of flame-retardant masterbatch has significantly improved the dispersibility and processing of flame retardants.

[0004] However, traditional flame-retardant masterbatches rely on irreversible chemical bonds or static encapsulation structures, and the toughness of the material is severely lost after processing. During long-term use or multiple processing, interface degradation or flame retardant degradation can easily lead to performance degradation, and its reliability is greatly reduced. Summary of the Invention

[0005] The purpose of the present invention is to provide a flame retardant masterbatch to overcome the problem of performance degradation of the flame retardant masterbatch in the prior art during the mixing process with other resins.

[0006] To achieve the above-mentioned purpose, the technical solution provided by the present invention is a flame retardant masterbatch, characterized in that it includes the following components by mass percentage: base resin, 45-70%; composite flame retardant, 25-40%; dynamic cross-linking agent, 3-12%; processing aid, 2-7%; the composite flame retardant is phosphate grafted chitosan, which is provided with a polyurethane encapsulation layer, and the dynamic cross-linking agent is an epoxy prepolymer.

[0007] The grafting rate of phosphate grafted chitosan is preferably in the range of 10%-20%, and the number average molecular weight of the polyurethane prepolymer is preferably controlled in the range of 800-3000.

[0008] Furthermore, the epoxy prepolymer is selected from at least one of bisphenol A epoxy resin, novolac epoxy resin, and alicyclic epoxy resin.

[0009] Epoxy prepolymers refer to oligomers or polymer precursors that contain epoxy groups but have not yet fully cured. They are used as crosslinkers, adhesives, or reactive intermediates. Dynamic crosslinking in this invention involves a reversible ring-opening reaction between epoxy groups and amino or hydroxyl groups in the polyurethane encapsulation layer. This temporarily breaks the crosslink network at temperatures between 160°C and 210°C, reducing the melt viscosity. When the temperature drops below 80°C, the dynamic bonds reform, restoring the crosslink network.

[0010] Furthermore, the mass ratio of the polyurethane encapsulation layer to the phosphate-grafted chitosan is 1:5 to 1:2.

[0011] Furthermore, the matrix resin is at least one of polyethylene, polypropylene, polyamide, and polyester.

[0012] Furthermore, the processing aid comprises at least one of an antioxidant, an anti-drip agent, and a flow promoter. The antioxidant can be selected from hindered phenols, phosphites, and the like. Its function is to act as a sacrificial agent, preferentially reacting with oxygen during the flame retardant masterbatch processing, particularly during extrusion granulation, to protect the flame retardant's activity. The anti-drip agent can be selected from polytetrafluoroethylene, and the flow promoter can be selected from polyethylene wax, polypropylene wax, polydimethylsiloxane, and the like to improve compatibility between the composite flame retardant and the matrix resin.

[0013] Furthermore, the epoxy equivalent of the epoxy prepolymer is 180-250 g / eq. As a further explanation, the number average molecular weight of the epoxy prepolymer corresponding to the epoxy equivalent is 800-2000, and the molar ratio of epoxy groups to polyurethane-NCO groups is 1:0.8-1.2.

[0014] The present invention also provides a method for preparing a flame retardant masterbatch having at least one of the above technical features, comprising the following steps: S1: Phosphate grafted chitosan and polyurethane prepolymer are in situ encapsulated at 60-80°C to prepare a composite flame retardant; S2: Premix the base resin, composite flame retardant, dynamic crosslinking agent and processing aid, and melt blend at 160-190°C; S3: Dynamic crosslinking reaction is carried out in a twin-screw extruder with a screw speed of 200-400 rpm and a residence time of 2-5 minutes.

[0015] Furthermore, the in-situ encapsulation reaction in S1 is carried out under nitrogen protection, the reaction time is controlled to be 1-3 hours, the molar ratio of the polyurethane prepolymer to the phosphate-grafted chitosan is 1:0.8-1.2, and the -NCO functional group content of the polyurethane prepolymer is 5-8wt%.

[0016] The in-situ encapsulation reaction specifically includes adding a polyurethane prepolymer and phosphate-grafted chitosan into a reactor, then adding 0.1-0.3 wt% dibutyltin dilaurate, controlling the stirring rate to 300-500 rpm, and maintaining the viscosity of the reaction system at 500-2000 mPa·s for 24 hours. The encapsulation is completed when the flame retardant masterbatch is extracted with an ethanol reagent for 24 hours and the mass loss of the flame retardant is ≤2%.

[0017] Furthermore, the melt blending in S2 is carried out in stages: the first stage: mixing the base resin and the processing aid at 160-170° C. for 5-8 minutes; the second stage: adding the composite flame retardant and the dynamic cross-linking agent at 180-190° C. for 10-15 minutes.

[0018] Furthermore, the dynamic crosslinking reaction in S3 is carried out in a twin-screw extruder, the temperature of the twin-screw extruder is gradually increased from 160-210° C. toward the die head, and the pressure in the extruder is set at 0.5-2.0 MPa.

[0019] The advantages and beneficial effects of the present invention are: The phosphate-grafted chitosan of the present invention forms a phosphorus-nitrogen synergistic system through chemical bonding, which significantly improves the flame retardant efficiency; the polyurethane encapsulation layer physically protects the flame retardant, avoids interface defects caused by direct contact between the flame retardant and the matrix resin, maintains the long-term effectiveness of the flame retardant, and ensures that the flame retardant masterbatch achieves high flame retardancy.

[0020] The dynamic crosslinker epoxy prepolymer reacts with the amino groups in the polyurethane encapsulation layer to form reversible covalent bonds. During high-temperature processing, the dynamic bonds reversibly dissociate, reducing melt viscosity and improving processing fluidity. Upon cooling, the dynamic bonds reform, enhancing material toughness. Furthermore, the responsiveness of the dynamic bonds imparts a degree of self-healing capability to the masterbatch, extending the lifespan of the flame-retardant masterbatch. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of the flame retardant masterbatch of the present invention; Figure 2 This is a flow chart for preparing the flame retardant masterbatch of the present invention. DETAILED DESCRIPTION

[0022] This invention provides a flame-retardant masterbatch. The flame retardant is a phosphorus-nitrogen synergistic system of phosphate-grafted chitosan. Chitosan, a natural polymer, provides a nitrogen source. The phosphate groups generate phosphoric acid / polyphosphoric acid during combustion, promoting the formation of a carbon layer and achieving synergistic flame retardancy in both the gas and condensed phases. The grafting ratio is controlled between 10% and 20%. A lower grafting ratio reduces this synergistic effect, while a higher grafting ratio may damage the chitosan molecular structure. A polyurethane encapsulation layer is placed between the flame retardant and the matrix resin to reduce interfacial defects in the flame retardant and minimize particle agglomeration and migration. The epoxy groups form reversible covalent bonds with the amino / hydroxyl groups in the polyurethane encapsulation layer. During the processing phase (160-210°C), dynamic bonds dissociate, reducing melt viscosity and improving processing fluidity. During the cooling phase (<80°C), dynamic bonds reform, restoring the crosslinked network and enhancing material toughness. The epoxy equivalent weight is controlled between 180 and 250 g / eq to prevent processing difficulties caused by excessive crosslinking density and insufficient toughness improvement due to insufficient dynamic bonds.

[0023] The following embodiments are further described in conjunction with the accompanying drawings and examples. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0024] Example 1 A flame-retardant masterbatch comprising, by weight, 60% polypropylene matrix resin, 30% composite flame retardant, 8% dynamic crosslinking agent, and 2% processing aid. The composite flame retardant comprises phosphate-grafted chitosan and a polyurethane encapsulation layer in a 1:5 weight ratio. The dynamic crosslinking agent is a bisphenol A epoxy resin with an epoxy equivalent weight of 200 g / eq. The processing aid comprises 10101% antioxidant, 0.5% polytetrafluoroethylene anti-drip agent, and 0.5% polyethylene wax.

[0025] The preparation method is as follows: S1. Preparation of composite flame retardant: Phosphate-grafted chitosan with a grafting rate of 15% and a polyurethane prepolymer with an -NCO content of 6 wt% were added to a reactor in a molar ratio of 1:1. 0.2% dibutyltin dilaurate was added. Under a nitrogen atmosphere, the reactor was heated to 70°C. The electric stirrer equipped with the reactor was started, and the reaction was stirred at 400 rpm for 2 hours. The viscosity of the reaction system was controlled at 1500 mPa·s. After encapsulation, the mass loss of the flame retardant was ≤1.5% after ethanol extraction for 24 hours.

[0026] S2, segmented melt blending: The base resin and the processing aid were mixed in a reactor at 165°C for 7 minutes, then the temperature was raised to 185°C, the composite flame retardant and the dynamic crosslinking agent were added, and the mixture was mixed for 12 minutes. The reactor was then opened to obtain the composite flame retardant resin.

[0027] S3, dynamic cross-linking extrusion, transfer the reviewed flame retardant resin into a twin-screw extruder, set the screw speed to 300 rpm, the flame retardant resin stays in the twin-screw extruder for 3 minutes, the temperature of each zone of the twin-screw extruder to the die is 160℃→190℃→210℃, the die pressure is 1.5MPa, after extrusion water cooling, shear granulation is carried out according to actual needs to obtain flame retardant masterbatch.

[0028] Example 2 A flame-retardant masterbatch comprising, by weight, 55% polyamide 6 matrix resin, 35% composite flame retardant, 7% dynamic crosslinker, and 3% processing aid. The composite flame retardant comprises a phosphate-grafted chitosan and polyurethane encapsulation layer in a 1:3 ratio by weight, the dynamic crosslinker is a phenolic epoxy resin with an epoxy equivalent weight of 230 g / eq, and the processing aid comprises 1681.5% phosphite antioxidant and 1.5% polydimethylsiloxane flow promoter. The preparation method is as follows: S1, Preparation of the Composite Flame Retardant: A phosphate-grafted chitosan with a grafting rate of 12% and a polyurethane prepolymer with a -NCO content of 7wt% were added to a reactor at a molar ratio of 1:0.9. 0.2% dibutyltin dilaurate was added. Under a nitrogen atmosphere, the reactor was heated to 75°C. The electric stirrer on board the reactor was activated and stirred at 450 rpm for 2.5 hours. The viscosity of the reaction system was controlled at 800 mPa·s. After packaging, the flame retardant mass loss was ≤1.8% after ethanol extraction for 24 hours. S2, Staged Melt Blending: The base resin and processing aid were mixed in a reactor at 170°C for 6 minutes. The temperature was then raised to 180°C. The composite flame retardant and dynamic crosslinker were added and mixed for 15 minutes. The reactor was then opened to obtain the completed flame-retardant resin. S3, dynamic cross-linking extrusion, transfer the reviewed flame retardant resin into a twin-screw extruder, set the screw speed to 250rpm, and let the flame retardant resin stay in the twin-screw extruder for 4 minutes. The temperature of each zone of the twin-screw extruder to the die is 170℃→200℃→210℃, and the die pressure is 0.8MPa. After extrusion water cooling, shearing and granulation are carried out according to actual needs to obtain flame retardant masterbatch.

[0029] Example 3 A flame-retardant masterbatch comprising, by weight, 50% polyethylene terephthalate (PET) matrix resin, 40% composite flame retardant, 8% dynamic crosslinker, and 2% processing aid. The composite flame retardant comprises a phosphate-grafted chitosan and polyurethane encapsulation layer in a 1:4 weight ratio. The dynamic crosslinker is an alicyclic epoxy resin with an epoxy equivalent weight of 180 g / eq. The processing aid comprises 10761% hindered phenol antioxidant and 1% polypropylene wax.

[0030] The preparation method is as follows: S1. Preparation of composite flame retardant: Phosphate-grafted chitosan with a grafting rate of 18% and a polyurethane prepolymer with an -NCO content of 7 wt% were added to a reactor in a molar ratio of 1:1.1. 0.3% dibutyltin dilaurate was added. Under a nitrogen atmosphere, the reactor was heated to 65°C and the electric stirrer equipped in the reactor was started. The mixture was stirred at 380 rpm for 3 hours. The viscosity of the reaction system was controlled at 1200 mPa·s. After encapsulation, the mass loss of the flame retardant was ≤1.2% after ethanol extraction for 24 hours.

[0031] S2, segmented melt blending: The base resin and the processing aid are mixed in a reactor at 160°C for 8 minutes, then the temperature is raised to 190°C, the composite flame retardant and the dynamic crosslinking agent are added, and the mixture is mixed for 10 minutes. The reactor is then opened to obtain the composite flame retardant resin.

[0032] S3, dynamic cross-linking extrusion, transfer the reviewed flame retardant resin into a twin-screw extruder, set the screw speed to 400 rpm, and let the flame retardant resin stay in the twin-screw extruder for 2.5 minutes. The temperature of each zone of the twin-screw extruder to the die is 160℃→185℃→200℃, and the die pressure is 2.0 MPa. After extrusion and water cooling, shearing and granulation are carried out according to actual needs to obtain flame retardant masterbatch.

[0033] Example 4 A flame-retardant masterbatch comprising, by weight, 70% high-density polyethylene (HDPE) matrix resin, 25% composite flame retardant, 3% dynamic crosslinking agent, and 2% processing aid. The composite flame retardant is a phosphate-grafted chitosan and polyurethane encapsulation layer in a 1:2 weight ratio. The dynamic crosslinker is a bisphenol A epoxy resin with an epoxy equivalent weight of 250 g / eq. The processing aid contains 1% polytetrafluoroethylene anti-drip agent, 0.5% phosphite antioxidant, and 0.5% silicone flow agent.

[0034] The preparation method is as follows: S1. Preparation of composite flame retardant: Phosphate-grafted chitosan with a grafting rate of 10% and a polyurethane prepolymer with an -NCO content of 5 wt% were added to a reactor in a molar ratio of 1:0.8. 0.1% dibutyltin dilaurate was added. Under a nitrogen atmosphere, the reactor was heated to 80°C. The electric stirrer equipped with the reactor was started, and the reaction was stirred at 300 rpm for 1 hour. The viscosity of the reaction system was controlled at 2000 mPa·s. After encapsulation, the mass loss of the flame retardant was ≤2.0% after ethanol extraction for 24 hours.

[0035] S2, segmented melt blending: The base resin and the processing aid were mixed in a reactor at 165°C for 5 minutes, then the temperature was raised to 185°C, the composite flame retardant and the dynamic crosslinking agent were added, and the mixture was mixed for 12 minutes. The reactor was then opened to obtain the composite flame retardant resin.

[0036] S3, dynamic cross-linking extrusion, transfer the reviewed flame retardant resin into a twin-screw extruder, set the screw speed to 350rpm, and let the flame retardant resin stay in the twin-screw extruder for 4 minutes. The temperature of each zone of the twin-screw extruder to the die is 165℃→190℃→205℃, and the die pressure is 1.2MPa. After extrusion water cooling, shearing and granulation are carried out according to actual needs to obtain flame retardant masterbatch.

[0037] Example 5 A flame-retardant masterbatch comprising, by weight, 65% polypropylene / polyamide 6 blended matrix resin (PP / PA6 = 3:1), 30% composite flame retardant, 4% dynamic crosslinker, and 1% processing aid. The composite flame retardant comprises a phosphate-grafted chitosan and polyurethane encapsulation layer in a 1:4 ratio by weight, the dynamic crosslinker is a bisphenol A epoxy resin with an epoxy equivalent weight of 220 g / eq, and the processing aid contains 0.6% polyethylene wax and 0.4% antioxidant 1010-0.4%.

[0038] The preparation method is as follows: S1. Preparation of composite flame retardant: Phosphate-grafted chitosan with a grafting rate of 16% and a polyurethane prepolymer with an -NCO content of 8 wt% were added to a reactor in a molar ratio of 1:1.2. 0.2% dibutyltin dilaurate was added. Under a nitrogen atmosphere, the reactor was heated to 60°C and the electric stirrer equipped in the reactor was started. The reaction was stirred at 500 rpm for 3 hours. The viscosity of the reaction system was controlled at 1000 mPa·s. After encapsulation, the mass loss of the flame retardant was ≤1.6% after ethanol extraction for 24 hours.

[0039] S2, segmented melt blending: The base resin and the processing aid were mixed in a reactor at 168°C for 7 minutes, then the temperature was raised to 182°C, the composite flame retardant and the dynamic crosslinking agent were added, and the mixture was mixed for 13 minutes. The reactor was then opened to obtain the composite flame retardant resin.

[0040] S3, dynamic cross-linking extrusion, transfer the reviewed flame retardant resin into a twin-screw extruder, set the screw speed to 280rpm, the flame retardant resin stays in the twin-screw extruder for 3.5min, the temperature of each zone of the twin-screw extruder to the die is 168℃→195℃→210℃, the die pressure is 1.0MPa, after extrusion water cooling, shearing and granulation are carried out according to actual needs to obtain flame retardant masterbatch.

[0041] Each of the above examples was mixed with 80% matrix resin at a 20% weight ratio and injection molded into standard cone specimens measuring 125 mm x 13 mm x 3 mm. Vertical flame tests were conducted according to UL94 and the limiting oxygen index (LOI) was determined according to ASTM D2863. After aging the standard specimens for 500 hours in an 85°C / 85% RH environment, flame retardancy testing was repeated to compare changes in flame retardancy rating and LOI. The specimens were then subjected to the same mechanical property tests as pure matrix resin for comparison. The test results are shown in the following table. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A flame retardant masterbatch, characterized in that: The invention comprises the following components by mass percentage: base resin, 45-70%; composite flame retardant, 25-40%; dynamic cross-linking agent, 3-12%; processing aid, 2-7%; the composite flame retardant is phosphate grafted chitosan, which is provided with a polyurethane encapsulation layer, and the dynamic cross-linking agent is an epoxy prepolymer.

2. The flame retardant masterbatch according to claim 1, characterized in that The epoxy prepolymer is selected from at least one of bisphenol A epoxy resin, novolac epoxy resin and alicyclic epoxy resin.

3. The flame retardant masterbatch according to claim 2, characterized in that The mass ratio of the polyurethane encapsulation layer to the phosphate grafted chitosan is 1:5 to 1:

2.

4. The flame retardant masterbatch according to claim 1, characterized in that The matrix resin is at least one of polyethylene, polypropylene, polyamide and polyester.

5. The flame retardant masterbatch according to claim 1, characterized in that The processing aid comprises at least one of an antioxidant, an anti-drip agent, and a flow promoter.

6. The flame retardant masterbatch according to claim 1, characterized in that The epoxy equivalent weight of the epoxy prepolymer is 180-250 g / eq.

7. A method for preparing the flame retardant masterbatch according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1: Phosphate grafted chitosan and polyurethane prepolymer are in situ encapsulated at 60-80°C to prepare a composite flame retardant; S2: Premix the base resin, composite flame retardant, dynamic crosslinking agent and processing aid, and melt blend at 160-190°C; S3: Dynamic crosslinking reaction is carried out in a twin-screw extruder with a screw speed of 200-400 rpm and a residence time of 2-5 minutes.

8. The preparation method according to claim 7, characterized in that In S1, the in-situ encapsulation reaction is carried out under nitrogen protection, the reaction time is controlled to be 1-3 hours, the molar ratio of the polyurethane prepolymer to the phosphate-grafted chitosan is 1:0.8-1.2, and the -NCO functional group content of the polyurethane prepolymer is 5-8wt%.

9. The preparation method according to claim 7, characterized in that Melt blending in S2 is carried out in stages: Stage 1: Mixing the base resin and processing aid at 160-170°C for 5-8 minutes; The second stage: adding composite flame retardant and dynamic cross-linking agent at 180-190℃ for 10-15 minutes.

10. The preparation method according to claim 7, characterized in that The dynamic crosslinking reaction in S3 is carried out in a twin-screw extruder. The temperature of the twin-screw extruder increases gradually from 160-210° C. toward the die head, and the pressure in the extruder is set at 0.5-2.0 MPa.

Images