CN109021541B - TPU elastomer composition based on dialkyldithiohypophosphite composite flame retardant system for wire and cable and preparation method thereof - Google Patents

Abstract

The invention discloses a TPU elastomer composition based on a dialkyldithiohypophosphite composite flame retardant system for wires and cables. The raw material composition comprises: 65-90 wt% of a TPU matrix material; 9-30 wt% of a composite flame-retardant system ; Auxiliary agent 0.1 to 5 wt%; the composite flame retardant system includes dialkyl dithio hypophosphite and carbon-forming components, and the structural formula of dialkyl dithio hypophosphite is shown in the following formula (I), in which , R ₁ , R ₂ are independently selected from straight-chain alkyl or branched-chain alkyl, M is selected from Mg, Ca, Al, Sb, Sn, Ge, Ti, Fe, Zr, Zn, Ce, Bi, Sr, Mn , Li, Na, K, H or NH ₄ , m is 1 to 4; the cable material prepared with the TPU elastomer composition has no melting drop, high flame retardancy, migration resistance, softness and abrasion resistance, oil resistance, etc. Features.

Description

TPU based on dialkyldithiohypophosphite composite flame retardant system for wire and cable Elastomer composition and method of making the same

technical field

The invention relates to the technical field of halogen-free flame retardant TPU, in particular to a TPU elastomer composition based on a dialkyldithiohypophosphite composite flame retardant system for wires and cables and a preparation method thereof.

Background technique

Polyurethane is a type of polymer containing -NHCOO- repeating structural units in the main chain, abbreviated as PU, and is formed by the polymerization of isocyanate (monomer) and hydroxyl compounds. Due to the strong polar urethane group, it is insoluble in non-polar solvents and has good oil resistance, toughness, wear resistance, aging resistance, etc., and has been widely used in many fields. Polyurethane includes two types of materials, one is thermosetting PU, which is usually used in synthetic leather, foaming and other fields; the other is thermoplastic polyurethane, referred to as TPU, which has the processing method of thermoplastic materials and has the performance of thermosetting PU. At present, it is developing rapidly and is mainly used in the fields of shoe soles and cables. Especially in the field of new electric vehicles and charging cables, they have given full play to their soft, wear-resistant, oil-resistant and other characteristics, and have attracted much attention.

For the application of TPU in the field of cables, relevant standards have put forward requirements for flame retardant. Polyurethane is a flammable substance with a low oxygen index, and TPU has serious melting droplets when it is burned at high temperature, and it is difficult to achieve the resistance specified in the standard. Therefore, it is difficult to be flame retardant.

At present, for the flame retardant of TPU elastomer, there are two basic flame retardant systems: halogen flame retardant system and non-halogen flame retardant system. Halogen-based flame retardant systems are usually bromine-containing flame retardants combined with antimony trioxide. A large number of studies have shown that TPU materials added with bromine-based flame retardants will produce heavy smoke and hydrogen bromide and other harmful substances when burning, which can cause damage to the human body. asphyxia. Therefore, the development of safe, environmentally friendly and halogen-free flame retardant systems for TPU elastomer materials has become a research hotspot. In recent years, new types of halogen-free flame retardants for TPU elastomer materials have emerged.

According to literature reports, the halogen-free flame retardants used in TPU elastomer materials mainly include two basic systems: one is inorganic hydroxide system, including magnesium hydroxide and aluminum hydroxide; combustion system. For the inorganic hydroxide system, its flame retardant effect is limited. In order to meet the requirements of various specifications and standards, the addition amount is usually very high, sometimes as high as 80% of the entire formulation system. Incompatibility is dispersed in the matrix resin in the form of a filler. Therefore, high filler content will greatly reduce the mechanical properties of the material. Sometimes in order to reduce the amount of inorganic hydroxide added, red phosphorus is also used synergistically, but the application of red phosphorus will have problems with the appearance and color of the material, and the combustion of red phosphorus is prone to produce toxic gases such as phosphine and a large amount of smoke. So this is not the best solution either.

For phosphorus-nitrogen flame retardant system, this is a kind of high-efficiency flame retardant system, which has high flame retardant efficiency, and can achieve high flame retardant with greatly reduced dosage, which is a hot research topic at present. At present, the most commonly used flame retardant systems are high polymerized ammonium polyphosphate (APP) and organic phosphate esters, and high polymerized ammonium polyphosphate (APP) flame retardant system. Compared with the inorganic hydroxide system, its addition amount is greatly reduced, but APP is still incompatible with the matrix material due to its surface hydrophilic properties and certain water solubility. Therefore, the flame retardant TPU elasticity of the APP system The mechanical strength of the bulk material is still low, and it is easy to migrate and precipitate. The whitening phenomenon of the precipitation on the surface of the cable not only affects the appearance, but also causes the flame retardant performance of the cable to gradually decrease with the precipitation. In addition, due to the existence of ammonium ions, APP is easy to absorb moisture. After a period of time, there are water droplets on the surface of the TPU cable, which reduces the insulation performance of the material and poses a major safety hazard; while some organic phosphates are still water-soluble, and some are still water-soluble. Although the water solubility is small, which overcomes the problem of moisture absorption, its flame retardant mechanism belongs to condensed phase flame retardant, which belongs to non-intumescent type. For TPU elastomer material, it is easy to form dripping and ignite. Other combustibles and molten droplets will affect the flame retardant effect, and it is difficult to meet the standard requirements.

In general, the main defects of the flame retardant system currently used in cable TPU materials are: poor flame retardancy, easy to melt droplets, easy moisture absorption and migration and whitening. Therefore, it is necessary to develop a new type of halogen-free flame retardant system for TPU elastomer materials.

SUMMARY OF THE INVENTION

The invention develops a TPU elastomer composition based on a dialkyldithiohypophosphite composite flame retardant system for wires and cables, and the prepared cable material has no melting drop, high flame retardancy, migration resistance, softness and resistance Wear, oil resistance and other characteristics. It can be used in the field of cables with high flame retardant, oil resistance, soft and wear resistance requirements such as new energy vehicles.

The specific technical solutions are as follows:

A TPU elastomer composition based on a dialkyldithiohypophosphite composite flame retardant system for wires and cables, by weight percentage, the raw material composition comprises:

TPU matrix material 65～90%;

Composite flame retardant system 9 to 30%;

Other additives 0.1～5%;

The composite flame retardant system includes a dialkyldithiohypophosphite and a carbon-forming component;

Described dialkyl dithio hypophosphite, structural formula is shown in following formula (I):

In the formula, R ₁ and R ₂ are independently selected from a straight-chain alkyl group or a branched-chain alkyl group, and the carbon number of the straight-chain alkyl group or branched-chain alkyl group is 1-6;

M is selected from Mg, Ca, Al, Sb, Sn, Ge, Ti, Fe, Zr, Zn, Ce, Bi, Sr, Mn, Li, Na, K, H or NH ₄ , and m is 1-4;

The carbon-forming component is an insoluble and infusible cross-linked polymer, and the cross-linking point structure is shown in the following formula (II):

The present invention relates to the development of halogen-free flame retardant TPU elastomer. The novel low water-solubility dialkyldithiohypophosphite is applied to form an intumescent flame-retardant mechanism for TPU elastomer through the synergy of special low-water-solubility carbon-forming compounds. , to solve the defects of the existing flame retardant system with a large amount of addition, poor compatibility with the TPU substrate, easy moisture absorption to form water droplets, easy migration, precipitation and molten droplets. The new flame retardant system can be well adapted to the TPU elastomer material, resulting in a halogen-free flame retardant, migration-resistant, and droplet-free TPU cable material with excellent performance.

The present invention will be described in detail below.

The present invention aims to solve various defects existing in the existing halogen-free flame retardant TPU elastomer cable material, and the inventor has conducted extensive and in-depth research. Aiming at the problem of existing flame retardant systems in flame retardant TPU elastomer materials, a new flame retardant system was investigated, and it was found that dialkyldithiohypophosphite combined with special carbon-forming components can solve this problem well.

The structural formula of the dialkyldithiophosphinate is shown in the above formula (I); preferably, in the dialkyldithiophosphinate, R ₁ and R ₂ are independently selected from methyl, ethyl , n-propyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, n-hexyl or isohexyl; M is selected from Mg, Ca, Al, Sn, Ti or Zn.

Further preferably, the dialkyldithiohypophosphite is selected from diethylaluminum dithiohypophosphite or diisobutylaluminum dithiohypophosphite.

The invention also discloses a preparation process of the dialkyldithiohypophosphite, taking the preparation of aluminum dialkyldithiohypophosphite as an example, specifically:

(1) reacting the sodium dialkyldithiophosphite solution and the aluminum sulfate solution under acidic conditions to obtain the suspension of the aluminum dialkyldithiophosphite precipitate;

(2) The suspension is filtered, washed, dried at 120° C., and pulverized to a certain particle size to obtain a dialkyldithioaluminum hypophosphite flame retardant.

Wherein, the sodium dialkyldithiophosphite as raw material can be obtained by commercially available, or be prepared by the following method:

(a) In the presence of initiator and under certain temperature and pressure, linear olefin and phosphine can undergo radical addition reaction to generate dialkyl phosphine;

(b) reacting dialkyl phosphine with sulfur to generate dialkyl dithio hypophosphorous acid;

(c) reacting the dialkyldithiophosphinic acid with sodium hydroxide to generate a water-soluble sodium dialkyldithiophosphite.

Dialkyldithiohypophosphites are characterized by high phosphorus content, synergy of sulfur elements, good flame retardancy, high initial decomposition temperature, extremely low water solubility, migration resistance and no moisture absorption. A new type of engineering plastics such as nylon and polyester, especially glass fiber reinforced engineering plastics. Applied to polyurethane materials, due to the extremely low water solubility, there will be no problems of moisture absorption and water stains, but due to the condensed phase flame retardant mechanism, the polyurethane materials are easy to drip during combustion, reducing the flame retardant performance, and cannot be Through the flame retardant requirements specified in the standard, if the flame retardant requirements are achieved by increasing the addition amount, the material properties will be reduced.

The inventor found through research that in the presence of dialkyldithiohypophosphite, adding a suitable carbon-forming component, the flame retardant mechanism of the TPU elastomer material becomes an intumescent flame retardant, while in the Under the action of the expanded carbon layer, the droplets of the material are also controlled, showing good flame retardancy, which can meet the flame retardancy requirements of VW-1.

As a carbon-forming component, it is generally a polyhydroxy compound, such as pentaerythritol and other compounds, but these compounds have a good carbon-forming effect due to the presence of hydroxyl groups, but the water solubility is high, and they will be applied to TPU elastomer cable materials. Problems with moisture absorption occur, causing problems with sticky surfaces and water droplets.

Through the research of the inventor, it is found that two compounds of methylphosphonic acid and trihydroxyethyl isocyanurate are subjected to a polycondensation reaction under equivalent conditions to obtain a thermosetting ester product, and the ester product is pulverized to a certain particle size during application. The powder in the diameter range is the carbon-forming component. The carbon-forming component has a good carbon-forming effect, and has good synergy with dialkyldithiohypophosphite. The presence of phosphorus and nitrogen elements in the molecular structure can reduce the addition of dialkyldithiohypophosphite. At the same time, due to the absence of water-absorbing groups in the molecular structure, it does not absorb moisture, does not form water spots, and does not cause the surface to be sticky.

The preparation method of the carbon-forming component is specifically:

(1) Equivalent trihydroxyethyl isocyanurate and methylphosphonic acid are reacted at 150-220° C. for 4-8 hours under the action of a phase transfer catalyst to obtain an esterified prepolymer;

(2) Vacuuming and heating to 260-280° C., the esterified prepolymer is obtained by polycondensation and solidification, and then pulverized.

During the preparation of the prepolymer in step (1), in order to speed up the reaction, a phase transfer catalyst needs to be used. Preferably, the phase transfer catalyst is selected from quaternary ammonium salts, such as tetrabutylammonium bromide.

In step (2), the high-temperature polycondensation and curing of the prepolymer requires high vacuum and high temperature conditions. Preferably, the vacuum is evacuated to a degree of vacuum not higher than 50KPa. The reaction can be carried out in an oven, or a high-power kneader with stirring function can be used.

The flame retardant obtained by polycondensation and curing is a block. In order to be added to the matrix material, it needs to be pulverized. Use mechanical pulverizing equipment to control the average particle size of the flame retardant D50<5μm.

At the same time, the water generated by the esterification reaction should be drained away in time. To prevent discoloration of the prepolymer, the reaction can be carried out in a nitrogen atmosphere.

In order to further improve the synergistic flame retardant effect, the composite flame retardant system, by weight percentage, consists of raw materials:

Dialkyldithiohypophosphite 50～90wt%;

The carbon-forming component is 10 to 50 wt%.

The average particle size of the dialkyldithiohypophosphite is D50<5μm, and the carbon-forming component is also pulverized to an average particle size D50<5μm.

The TPU base material is thermoplastic polyurethane, which can be processed by similar processing methods of thermoplastic polymer materials, such as extrusion, injection molding, etc., and has polyurethane elastomer properties. At least one of ether-type polyurethane, polycarbonate-type polyurethane, polycaprolactone-type polyurethane and aliphatic anti-yellowing polyurethane.

In the halogen-free flame retardant TPU elastomer material of the present invention, other additives, such as antifungal agents, antistatic agents, lubricants, anti-UV agents, Antioxidants etc.

Further preferably, by weight percentage, the raw material composition of the TPU elastomer composition based on the dialkyldithiohypophosphite composite flame retardant system includes:

TPU matrix material 75～85%;

Composite flame retardant system 14-22%;

Auxiliary 1～5%;

The composite flame retardant system, by weight percentage, the raw material composition includes:

Dialkyldithiohypophosphite 55～78wt%;

Carbon-forming component 22-45wt%.

Still further preferably, the mass ratio of the dialkyldithiohypophosphite to the carbon-forming component is 1.25-3.5:1, and the dialkyldithiohypophosphite is selected from diisobutyldithiohypophosphite aluminum.

The invention also discloses the preparation method of the TPU elastomer composition based on the dialkyldithiohypophosphite composite flame retardant system, including:

After the components are mixed uniformly, extrusion granulation is carried out.

The TPU elastomer composition is extruded and pelletized in a twin-screw extruder. Since the flame retardant is a heat-sensitive substance, the processing temperature must be controlled. The maximum temperature of the twin-screw does not exceed 230°C, preferably below 220°C. The composition is extruded and pelletized in a twin-screw extruder, which has certain requirements for extrusion equipment. The aspect ratio of the twin-screw extruder is not less than 44, preferably not less than 48, more preferably 52. The composition is extruded and pelletized in a twin-screw extruder, and can be pelletized by water-cooling, water-ring pelletizing or underwater pelletizing.

The TPU elastomer composition prepared according to the above method can be used as the sheath material or insulating material of the cable, and the cable can be prepared on the existing cable equipment through the extrusion molding process.

Compared with the prior art, the present invention has the following advantages:

The invention provides a TPU elastomer composition based on a dialkyldithiohypophosphite composite flame retardant system for wires and cables, which comprises a novel compound composed of dialkyldithiohypophosphite and special carbon-forming components. Flame retardant system, the prepared cable material has the characteristics of no droplet, high flame retardant, migration resistance, softness and wear resistance, oil resistance, etc., and can reach the flame retardant standard of VW-1.

Detailed ways

Example 1

(1) Compounding of halogen-free flame retardant TPU system

Pre-dry the TPU, add the pre-weighed TPU, compound flame retardant system and other additives in the high-speed mixer according to the proportion (if there is no special statement, the proportion in the present invention is weight percentage), start high-speed stirring, Stir for 10 minutes to complete the compounding of the halogen-free flame retardant TPU system and discharge.

(2) Extrusion granulation of material

Set the temperature of each zone of the twin-screw extruder at a predetermined temperature (the maximum temperature of the plasticizing section of the screw is 210°C). After the temperature is stable for 20 minutes, add the uniformly mixed halogen-free flame retardant TPU system from the hopper, and start the host and feeder. , to complete the extrusion granulation of the material. The granulated material is sent to the silo through the air conveying system and dried.

(3) Application and testing of materials

The dried materials are injected into the injection molding machine to produce standard samples specified by various test standards, and the relevant material properties are tested. Prepare qualified cables on the wire and cable pulling equipment, take samples and conduct relevant wire and cable tests. The main focus is on the following performance metrics:

1. Flame retardant and droplet properties

Tested according to the VW-1 test standard for cable material, with attention to droplets.

2. Migration resistance test

Put a certain length of flame-retardant TPU cable sample into a constant temperature and humidity box, set the temperature to 85°C and the relative humidity to 85%, and visually observe the state of the surface of the sample after 168 hours.

In the present embodiment, with diisobutyl dithio aluminum hypophosphite as raw material, the preparation technique is as follows:

Prepare 1392 g of sodium diisobutyl dithiohypophosphite aqueous solution with a concentration of 20 wt % and 228 g of aluminum sulfate solution with a concentration of 30 wt % respectively, add 1500 g of desalinated water to the reactor, and add 75 g of sulfuric acid solution with a concentration of 25 wt %, and the temperature is increased to 80 ℃, start to drip the sodium diisobutyl dithiohypophosphite aqueous solution and aluminum sulfate solution synchronously in proportion to the reaction kettle to obtain the diisobutyl dithio hypophosphite aluminum precipitate, complete the dropwise addition in 2 hours, and keep the temperature for 1 hour, then filtered, washed and dried to obtain 254 g of diisobutyl dithioaluminum hypophosphite flame retardant (yield 97%).

After testing, the initial decomposition temperature of the product is 350°C, and its solubility in water is 0.02%;

The preparation process of the carbon-forming component in the present embodiment is as follows:

In a 1L flask, add 522 g (2 moles) of trihydroxyethyl isocyanurate, under nitrogen protection, heat to 150°C to melt tris hydroxyethyl isocyanurate, and then add 2.7 g of tetrabutyl Ammonium bromide and 288g (3 moles) methylphosphonic acid, vigorously stir the mixture, heat from 150°C to 210°C within 6 hours, discharge the water in the reaction process, and condense and measure, keep at 210°C for 1 hour, cool down At 150°C, the melt was discharged to a metal tray. After the melt was cooled, a pale yellow brittle solid was obtained, the melting point ranged from 100 to 120°C, and the residual acid value was 7 mg KOH/g.

Put the prepolymer together with the tray into a vacuum oven, vacuumize, keep the vacuum degree at 50KPa, heat up to 270°C, hold for 2 hours, complete curing, cool down and discharge. Pulverize the material to an average particle size D50<5 microns for use.

After analysis:

The carbon-forming components prepared in this example have a phosphorus content of 10.5% and a nitrogen content of 10.1% (the phosphorus and nitrogen contents are the actual measured values, which are slightly lower than the theoretical calculated values), the solubility is less than 0.1%, and the weight loss is 1%. The decomposition temperature is 320°C.

Unless otherwise specified, the diisobutylaluminum diisobutyldithiophosphite and carbon-forming components in the following examples all use the products prepared in this example.

In the embodiment, each material and proportion are shown in Table 1, and the performance test result of the obtained material is shown in Table 1.

Example 2

The implementation process is the same as in Example 1, except that the ratio of aluminum diisobutyl dithiophosphite and carbon-forming components is adjusted, the ratio of aluminum diisobutyl dithio hypophosphite is increased, and the total amount of the flame retardant system is kept constant. Change. Other materials and proportions are shown in Table 1, and the obtained material results are shown in Table 1.

Example 3

The implementation process is the same as in Example 1, except that the ratio of aluminum diisobutyl dithiohypophosphite and carbon-forming components is adjusted, the proportion of carbon-forming components is increased, and the total amount of the flame retardant system is kept unchanged. Other materials and proportions are shown in Table 1, and the obtained material results are shown in Table 1.

Example 4

The implementation process is the same as in Example 1, except that the proportion of the formula is adjusted, and the proportion of the total amount of the flame retardant system is reduced. Other materials and proportions are shown in Table 1, and the obtained material results are shown in Table 1.

Example 5

The implementation process is the same as in Example 1, except that the proportion of the formula is adjusted, and the total proportion of the flame retardant system is increased. Other materials and proportions are shown in Table 1, and the obtained material results are shown in Table 1.

Comparative Example 1

The implementation is the same as in Example 1, except that no carbon-forming component is used. Other materials and proportions are shown in Table 1, and the obtained material results are shown in Table 1.

Comparative Example 2

The procedure was the same as in Example 1, except that aluminum diisobutyldithiophosphite was not used. Other materials and proportions are shown in Table 1, and the obtained material results are shown in Table 1.

Comparative Example 3

The implementation process is the same as that of Example 1, except that only ammonium polyphosphate is used, and no diisobutyl dithioaluminum hypophosphite and carbon-forming components are used. Other materials and proportions are shown in Table 1, and the obtained material results are shown in Table 1.

Comparative Example 4

The implementation procedure was the same as Example 1, except that the aluminum diisobutyl dithiophosphite was replaced by diethyl aluminum hypophosphite. Other materials and proportions are shown in Table 1, and the obtained material results are shown in Table 1.

Table 1

Claims (11)

1. The TPU elastomer composition based on the dialkyl dithiophosphate composite flame-retardant system for the electric wires and cables is characterized by comprising the following raw materials in percentage by weight:

65-90% of TPU base material;

10-30% of a composite flame-retardant system;

0-5% of other auxiliary agents;

the composite flame-retardant system comprises dialkyl dithiophosphate and a carbon forming component;

the dialkyl dithiophosphate has a structural formula shown as the following formula (I):

in the formula, R₁、R₂Independently selected from linear alkyl or branched alkyl, wherein the carbon number of the linear alkyl or branched alkyl is 1-6;

the carbon-forming component is insoluble and infusible cross-linked polymer, and the structure of a cross-linking point is shown as the following formula (II):

2. the TPU elastomer composition for electric wires and cables based on dialkyl dithiophosphate composite flame retardant system according to claim 1, wherein the composite flame retardant system comprises the following raw materials in percentage by weight:

50-90 wt% of dialkyl dithiophosphate;

10-50 wt% of carbon forming component.

3. The TPU elastomer composition for wire and cable of claim 1 based on a dialkyldithiophosphate composite flame retardant system, wherein the dialkyldithiophosphate, R₁、R₂Independently selected from methylEthyl, n-propyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, n-hexyl or isohexyl.

4. The TPU elastomer composition for wire and cable based on dialkyldithiophosphate composite flame retardant system of claim 1, wherein the dialkyldithiophosphate has an average particle size D50<5 μm.

5. The TPU elastomer composition for electric wires and cables based on the dialkyldithiophosphate composite flame retardant system according to claim 1, wherein the preparation process of the carbon forming component specifically comprises the following steps:

(1) enabling equivalent trihydroxyethyl isocyanurate and methyl phosphonic acid to react for 4-8 hours at 150-220 ℃ under the action of a phase transfer catalyst to prepare an esterified prepolymer;

(2) vacuumizing and heating to 260-280 ℃, and carrying out polycondensation curing on the esterified prepolymer and then crushing to obtain the esterified prepolymer.

6. The TPU elastomer composition for wire and cable based on dialkyldithiophosphate composite flame retardant system according to claim 5,

the phase transfer catalyst is selected from quaternary ammonium salts;

vacuumizing until the vacuum degree is not higher than 50 KPa;

the pulverization is carried out until the average particle diameter D50 is less than 5 μm.

7. The TPU elastomer composition for wire and cable based on dialkyl dithiophosphate composite flame retardant system of claim 1, wherein the TPU base material is at least one selected from polyester type polyurethane, polyether type polyurethane and aliphatic yellowing resistant polyurethane.

8. The TPU elastomer composition for wire and cable based on dialkyl dithiophosphate composite flame retardant system of claim 7, wherein the polyester polyurethane is a polycarbonate polyurethane and/or a polycaprolactone polyurethane.

9. The TPU elastomer composition for wire and cable based on dialkyldithiophosphate composite flame retardant system of claim 1, wherein the other auxiliary agent comprises at least one of lubricant, antioxidant, pigment.

10. A preparation method of the TPU elastomer composition based on the dialkyl dithiophosphate composite flame retardant system for the electric wires and cables according to any one of claims 1 to 9 is characterized by comprising the following steps: the components are uniformly mixed and then extruded and granulated.

11. The method for preparing the TPU elastomer composition based on the dialkyldithiophosphate composite flame retardant system for the electric wire and cable according to claim 10, wherein the extrusion granulation is performed in a twin screw extruder at an extrusion temperature of not higher than 230 ℃.