1. A halogen-free flame retardant is characterized by having a structural formula shown as a formula (1):

。

2. the method for preparing the halogen-free flame retardant according to claim 1, comprising: in the presence of an organic solvent and alkali, bis (4-hydroxyphenyl) phenylphosphine oxide and epichlorohydrin are subjected to substitution reaction to obtain the compound.

3. The process for preparing halogen-free flame retardant according to claim 2, wherein the molar ratio of bis (4-hydroxyphenyl) phenylphosphine oxide to epichlorohydrin is 1: (2.5-3.5); preferably, the molar ratio of bis (4-hydroxyphenyl) phenylphosphine oxide to base is 1: (1-2); preferably, the reaction temperature of the substitution reaction is 80-100 ℃, and the reaction time is 6-8 h; preferably, the base is sodium hydroxide, potassium hydroxide, or a combination thereof; preferably, the organic solvent is tetrahydrofuran, N-dimethylformamide, or a combination thereof.

4. The method for preparing halogen-free flame retardant according to claim 2 or 3, comprising: dissolving bis (4-hydroxyphenyl) phenylphosphine oxide and alkali in an organic solvent, adding epoxy chloropropane, and carrying out substitution reaction under an alkaline condition to obtain the compound; preferably, the dissolving temperature is 50-80 ℃, and the dissolving time is 1-3 h.

5. The use of the halogen-free flame retardant of claim 1 in the preparation of flame retardant polyester materials, wherein the raw materials of the flame retardant polyester materials comprise polyester resins containing terminal carboxyl groups.

6. The application of claim 5, wherein the halogen-free flame retardant accounts for 0.4-1.6% of the total mass of the polyester material; preferably, the preparation method of the flame-retardant polyester material comprises the following steps: and (3) blending the halogen-free flame retardant and the polyester resin containing the terminal carboxyl groups, melting and extruding.

7. The use of the halogen-free flame retardant of claim 1 in the preparation of a flame retardant polyester film, wherein the flame retardant polyester film comprises a flame retardant layer, and the raw materials of the flame retardant layer comprise a carboxyl-terminated polyester resin and the halogen-free flame retardant; preferably, the mass of the halogen-free flame retardant accounts for 0.5-2% of the total mass of the raw materials of the flame-retardant layer; preferably, the thickness of the flame-retardant layer accounts for 40-100% of the thickness of the film, and preferably 60-90%.

8. The flame-retardant biaxially oriented polyester film is characterized by sequentially comprising an upper surface layer, a middle layer and a lower surface layer, wherein the middle layer is a flame-retardant layer and comprises the following raw materials in percentage by mass: 97.5-99.5% of film-grade polyester chip, 0.5-2% of the halogen-free flame retardant of claim 1 and 0-0.5% of antioxidant.

9. The flame-retardant biaxially oriented polyester film according to claim 8, wherein the thickness of the intermediate layer is 40 to 100%, preferably 60 to 90% of the thickness of the polyester film; preferably, the thickness of the polyester film is 9-23 μm; preferably, the upper surface layer and the lower surface layer are anti-blocking layers, and the raw materials comprise the following components in percentage by mass: 30-40% of film-grade polyester chips and 60-70% of anti-sticking master batch; preferably, the anti-sticking master batch contains 3000-3300 ppm of smooth particles; preferably, the smooth particles are at least one of silicon dioxide, kaolin, calcium carbonate, barium sulfate and PMMA, and the particle size of the smooth particles is 2.0-3.5 μm.

10. A method for preparing a flame-retardant biaxially oriented polyester film according to claim 8 or 9, which comprises the steps of:

s1, respectively blending the raw materials of the upper surface layer, the middle layer and the lower surface layer, performing melt extrusion in different extruders, and filtering to obtain an upper surface layer melt, a middle layer melt and a lower surface layer melt, wherein the melt extrusion temperature of the raw material of the middle layer is 275-280 ℃, and the melt extrusion temperature of the raw material of the upper surface layer and the raw material of the lower surface layer is 270-275 ℃;

s2, co-extruding the upper-layer melt, the middle-layer melt and the lower-layer melt through a die head, and casting the upper-layer melt, the middle-layer melt and the lower-layer melt onto a chill roll to form a cast sheet, wherein the die head temperature is 270-280 ℃, and the chill roll temperature is 25-30 ℃;

s3, longitudinally stretching the cast sheet to obtain a longitudinal pull sheet, wherein the longitudinal stretching temperature is 108-115 ℃, and the longitudinal stretching ratio is 4.0-4.5;

s4, transversely stretching the longitudinal pull sheet, annealing, shaping and cooling to obtain the aluminum alloy sheet, wherein the transverse stretching temperature is 110-130 ℃, the transverse stretching ratio is 3.5-4.0, the shaping temperature is 235-245 ℃, and the cooling temperature is 80-100 ℃.

Background

The biaxially oriented polyester film (BOPET) is a film material which is prepared by using polyethylene glycol terephthalate as a raw material, preparing a thick sheet by adopting a multilayer coextrusion method and then carrying out biaxial orientation. BOPET has excellent mechanical properties, high rigidity and toughness, good thermal stability and gas barrier properties, high light transmittance, light weight, low price and other excellent characteristics, and thus is widely used in various fields such as various packaging materials, electrical insulating materials, printed circuit boards and the like.

In the prior art, the common polyester flame retardant technology is a copolymerization method and a blending method. The copolymerization method adopts copolymerization type flame retardant to copolymerize with terephthalic acid and ethylene glycol to prepare flame-retardant polyester chips, and then the chips are subjected to film drawing; however, the method has the defects of high copolymerization cost, complex process, large equipment investment and the like, and simultaneously, the introduction of flame retardant molecules on a molecular chain can change the glass transition temperature and the melting point of a polyester matrix. The blending method comprises the steps of blending and extruding a flame retardant and polyester slices to obtain flame-retardant master batches, then carrying out melt extrusion on the flame-retardant master batches and the polyester slices to cast slices, and finally drawing a film; although the flame retardant performance can be improved to a certain extent by blending flame retardant, the mechanical properties of the polyester material are unstable due to the large addition amount of the flame retardant of the small molecular compounds and poor compatibility with resin base materials, and the appearance of the polyester product and the durability of the flame retardant effect are influenced due to the migration and precipitation of the flame retardant after long-term use.

Therefore, the development of a flame retardant which not only can enable the polyester material to have flame retardant performance, but also can avoid adverse effects on the mechanical performance and stability of the polyester material has very important value.

Disclosure of Invention

Based on the technical problems in the background art, the invention provides a halogen-free flame retardant and a preparation method and application thereof.

The invention provides a halogen-free flame retardant, which has a structural formula shown as a formula (1):

preferably, the preparation method of the halogen-free flame retardant comprises the following steps: in the presence of an organic solvent and alkali, bis (4-hydroxyphenyl) phenylphosphine oxide and epichlorohydrin are subjected to substitution reaction to obtain the compound.

Preferably, the molar ratio of the bis (4-hydroxyphenyl) phenylphosphine oxide to epichlorohydrin is 1: (2.5-3.5); preferably, the molar ratio of bis (4-hydroxyphenyl) phenylphosphine oxide to base is 1: (1-2); preferably, the reaction temperature of the substitution reaction is 80-100 ℃, and the reaction time is 6-8 h; preferably, the base is sodium hydroxide, potassium hydroxide, or a combination thereof; preferably, the organic solvent is tetrahydrofuran, N-dimethylformamide, or a combination thereof.

Preferably, the preparation method of the halogen-free flame retardant comprises the following steps: dissolving bis (4-hydroxyphenyl) phenylphosphine oxide and alkali in an organic solvent, adding epoxy chloropropane, and carrying out substitution reaction under an alkaline condition to obtain the compound; preferably, the dissolving temperature is 50-80 ℃, and the dissolving time is 1-3 h.

The reaction route of the halogen-free flame retardant is as follows:

the halogen-free flame retardant is applied to the preparation of the flame-retardant polyester material, and the raw material of the flame-retardant polyester material comprises polyester resin containing terminal carboxyl.

Preferably, the halogen-free flame retardant accounts for 0.4-1.6% of the total mass of the polyester material; preferably, the preparation method of the flame-retardant polyester material comprises the following steps: blending, melting and extruding the halogen-free flame retardant and polyester resin containing terminal carboxyl to enable epoxy groups in the halogen-free flame retardant to generate coupling reaction with the terminal carboxyl of the polyester resin; preferably, the temperature of the melt extrusion is 270-285 ℃.

The application of the halogen-free flame retardant in the preparation of the flame-retardant polyester film comprises a flame-retardant layer, wherein the raw materials of the flame-retardant layer comprise polyester resin containing terminal carboxyl and the halogen-free flame retardant; preferably, the mass of the halogen-free flame retardant accounts for 0.5-2% of the total mass of the raw materials of the flame-retardant layer; preferably, the thickness of the flame-retardant layer accounts for 40-100% of the thickness of the film, and preferably 60-90%.

The preparation method of the flame-retardant polyester film comprises the step of carrying out blending melt extrusion treatment on raw materials of a flame-retardant layer.

Polyester resins used in industry are generally synthesized from polyhydric alcohols and polybasic acids by polyesterification reaction, and many polyester resin products contain unreacted terminal carboxyl groups due to the selection of raw materials for the reaction, process conditions, and the like; particularly, for film grade polyester chips used for film preparation, in the actual production, due to the production process and parameter control, the generation of terminal carboxyl groups in the chips is caused by residual carboxyl groups of unesterified terephthalic acid and side reactions such as thermal degradation and thermal oxidation degradation in the reaction process, so the terminal carboxyl groups are an important quality index for the production of the film grade polyester chips, and the size of the terminal carboxyl groups directly influences the thermal stability, hue and film forming quality of the chips. Based on the above, the applied flame retardant action mechanism of the halogen-free flame retardant in the preparation of the flame retardant polyester material, especially the flame retardant polyester film is as follows: when the polyester resin contains unreacted terminal carboxyl, the terminal carboxyl is easy to react with an epoxy group in the halogen-free flame retardant during melt extrusion, so that the content of the terminal carboxyl is reduced, the molecular weight of the polyester is improved, and phosphorus is introduced to a macromolecular chain to achieve the flame retardant effect. The method specifically comprises the following steps:

when the terminal carboxyl of two-molecule PET reacts with one-molecule diepoxide, two-molecule PET coupling reaction occurs, chain extension and tackifying are carried out, so that the content of the terminal carboxyl is reduced, and the reaction formula is as follows:

the reaction of one PET end carboxyl group with one molecular diepoxide compound to obtain epoxy group terminated PET molecule has the following reaction formula:

the flame-retardant biaxially oriented polyester film sequentially comprises an upper surface layer, a middle layer and a lower surface layer, wherein the middle layer is a flame-retardant layer and comprises the following raw materials in percentage by mass: 97.5-99.5% of film-grade polyester chip, 0.5-2% of halogen-free flame retardant and 0-0.5% of antioxidant.

Wherein the film grade polyester chip contains terminal carboxyl.

Preferably, the antioxidant is 1010, antioxidant 168, or a combination thereof; preferably, the antioxidant consists of an antioxidant 1010 and an antioxidant 168, wherein the mass ratio of the antioxidant 1010 to the antioxidant 168 is 1: 1.

Preferably, the thickness of the middle layer accounts for 40-100% of the thickness of the polyester film, and preferably 60-90%; preferably, the thickness of the polyester film is 9-23 μm; preferably, the upper surface layer and the lower surface layer are anti-blocking layers, and the raw materials comprise the following components in percentage by mass: 30-40% of film-grade polyester chips and 60-70% of anti-sticking master batch; preferably, the anti-sticking master batch contains 3000-3300 ppm of smooth particles; preferably, the smooth particles are at least one of silicon dioxide, kaolin, calcium carbonate, barium sulfate and PMMA, and the particle size of the smooth particles is 2.0-3.5 μm.

The preparation method of the flame-retardant biaxially oriented polyester film comprises the following steps:

s1, respectively blending the raw materials of the upper surface layer, the middle layer and the lower surface layer, performing melt extrusion in different extruders, and filtering to obtain an upper surface layer melt, a middle layer melt and a lower surface layer melt, wherein the melt extrusion temperature of the raw material of the middle layer is 275-280 ℃, and the melt extrusion temperature of the raw material of the upper surface layer and the raw material of the lower surface layer is 270-275 ℃;

s2, co-extruding the upper-layer melt, the middle-layer melt and the lower-layer melt through a die head, and casting the upper-layer melt, the middle-layer melt and the lower-layer melt onto a chill roll to form a cast sheet, wherein the die head temperature is 270-280 ℃, and the chill roll temperature is 25-30 ℃;

s3, longitudinally stretching the cast sheet to obtain a longitudinal pull sheet, wherein the longitudinal stretching temperature is 108-115 ℃, and the longitudinal stretching ratio is 4.0-4.5;

s4, transversely stretching the longitudinal pull sheet, annealing, shaping and cooling to obtain the aluminum alloy sheet, wherein the transverse stretching temperature is 110-130 ℃, the transverse stretching ratio is 3.5-4.0, the shaping temperature is 235-245 ℃, and the cooling temperature is 80-100 ℃.

The flame retardant provided by the invention is introduced into a macromolecular chain through a polyester carboxyl-terminated reaction, so that the film has flame retardant property, and the content of the polyester carboxyl-terminated groups is reduced. The problem of large addition amount of the small molecular flame retardant is solved, and the stability of the mechanical property of the polyester film is prevented from being influenced. The preparation method of the flame retardant and the flame-retardant polyester film is simple in process and easy to operate.

The invention has the following beneficial effects:

the halogen-free flame retardant can introduce a flame-retardant component phosphorus element into a polyester structure in a coupling mode through the reaction between an epoxy group in the flame retardant and a terminal carboxyl group of a PET molecule, on one hand, the phosphorus element is used as the flame-retardant component and mainly forms a phosphoric acid and polyphosphoric acid adhesive film layer on the surface of a polymer through thermal decomposition, so that the purpose of flame retardancy of the polymer can be achieved, and the halogen-free flame retardant is halogen-free, non-toxic, low-smoke, free of corrosive gas and resistant to ultraviolet irradiation, and accords with the development direction of environmental protection; on the other hand, phosphorus is introduced into the polyester structure in a coupling mode through the reaction between the epoxy group in the flame retardant and the terminal carboxyl group of the PET molecule, so that the condition that the flame-retardant component migrates and even separates out after long-term use in the polyester material can be effectively avoided, the compatibility of the flame-retardant component and the polyester is improved, the terminal carboxyl group content of the polyester is reduced, the molecular weight of the polyester is improved, the durability and the appearance effect of the flame-retardant effect of the polyester material can be improved, and the polyester has good mechanical properties.

Drawings

FIG. 1 shows the NMR spectra of the halogen-free flame retardant prepared in example 1.

Detailed Description

The technical solution of the present invention will be described in detail below with reference to specific examples.

In the following examples and comparative examples, film grade polyester chips were produced from certified chemical fiber, type FG 620.

Example 1

A halogen-free flame retardant having a structural formula as shown in formula (1):

the preparation method comprises the following steps: adding 1mol of bis (4-hydroxyphenyl) phenylphosphine oxide into 500mL of tetrahydrofuran, stirring, adding 1mol of sodium hydroxide, stirring for 2h at 60 ℃, adding 2.5mol of epoxy chloropropane, slowly heating to 90 ℃, reacting for 7h, cooling to room temperature, filtering, washing and drying to obtain the halogen-free flame retardant shown in the formula (1), wherein the name is 4, 4-bis (4- (epoxypropyl) phenyl) phenylphosphonate; the nuclear magnetic resonance spectrum is shown in figure 1.

Example 2

The flame-retardant biaxially oriented polyester film sequentially comprises an upper surface layer, a middle layer and a lower surface layer, wherein the middle layer is a flame-retardant layer and comprises the following raw materials in percentage by mass: 99% of film-grade polyester chip, 0.5% of halogen-free flame retardant and 0.5% of antioxidant.

Wherein the antioxidant consists of an antioxidant 1010 and an antioxidant 168, and the mass ratio of the antioxidant 1010 to the antioxidant 168 is 1: 1.

The upper surface layer and the lower surface layer are anti-adhesion layers, and the anti-adhesion layers comprise the following raw materials in percentage by mass: 35% of film grade polyester chips and 65% of anti-sticking master batch, wherein the anti-sticking master batch contains 3300ppm of smooth particles, and the smooth particles are silicon dioxide with the particle size of 3.0 mu m.

The thickness of the intermediate layer was 10 μm, the thickness of the upper surface layer was 2.5 μm, and the thickness of the lower surface layer was 2.5 μm.

Preparing a flame-retardant biaxially oriented polyester film:

s1, respectively blending the raw materials of the upper surface layer, the middle layer and the lower surface layer, performing melt extrusion in different extruders, and filtering to obtain an upper surface layer melt, a middle layer melt and a lower surface layer melt, wherein the melt extrusion temperature of the raw material of the middle layer is 275-280 ℃, and the melt extrusion temperature of the raw material of the upper surface layer and the raw material of the lower surface layer is 270-275 ℃;

s2, co-extruding the upper-layer melt, the middle-layer melt and the lower-layer melt through a die head, and casting the upper-layer melt, the middle-layer melt and the lower-layer melt onto a chill roll to form a cast sheet, wherein the die head temperature is 270-280 ℃, and the chill roll temperature is 25-30 ℃;

s3, longitudinally stretching the cast sheet to obtain a longitudinal pull sheet, wherein the longitudinal stretching temperature is 108-115 ℃, and the longitudinal stretching ratio is 4.0-4.5;

s4, transversely stretching the longitudinal pull sheet, annealing, shaping and cooling to obtain the aluminum alloy sheet, wherein the transverse stretching temperature is 110-130 ℃, the transverse stretching ratio is 3.5-4.0, the shaping temperature is 235-245 ℃, and the cooling temperature is 80-100 ℃.

Example 3

Example 3 differs from example 2 only in that: the intermediate layer is made of different raw materials, and specifically comprises the following raw materials:

the middle layer is a flame-retardant layer and comprises the following raw materials in percentage by mass: 98.5 percent of film-grade polyester chip, 1.0 percent of halogen-free flame retardant and 0.5 percent of antioxidant.

Example 4

Example 4 differs from example 2 only in that: the intermediate layer is made of different raw materials, and specifically comprises the following raw materials:

the middle layer is a flame-retardant layer and comprises the following raw materials in percentage by mass: 98 percent of film-grade polyester chip, 1.5 percent of halogen-free flame retardant and 0.5 percent of antioxidant.

Example 5

Example 4 differs from example 2 only in that: the intermediate layer is made of different raw materials, and specifically comprises the following raw materials:

the middle layer is a flame-retardant layer and comprises the following raw materials in percentage by mass: 97.5 percent of film-grade polyester chip, 2 percent of halogen-free flame retardant and 0.5 percent of antioxidant.

Comparative example 1

Comparative example 1 differs from example 2 only in that: the intermediate layer is made of different raw materials, and specifically comprises the following raw materials:

the middle layer comprises the following raw materials in percentage by mass: 99.5 percent of film grade polyester chip and 0.5 percent of antioxidant.

Comparative example 2

Comparative example 1 differs from example 2 only in that: the intermediate layer is made of different raw materials, and specifically comprises the following raw materials:

the middle layer comprises the following raw materials in percentage by mass: 99% of film-grade polyester chip, 0.5% of flame retardant and 0.5% of antioxidant, wherein the flame retardant is bis (4-hydroxyphenyl) phenylphosphine oxide.

The biaxially oriented polyester films obtained in examples 2 to 5 and comparative examples 1 to 2 were subjected to the performance test, and the test results are shown in Table 1.

TABLE 1 results of Performance test of biaxially oriented polyester film

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.