A bio-based micro-cross-linked halogen-free intrinsic flame-retardant polyester hot melt adhesive and its preparation method

Abstract

The present invention discloses a bio-based micro-cross-linked halogen-free intrinsic flame-retardant polyester hot melt adhesive and a preparation method thereof, belonging to the technical field of flame-retardant hot melt adhesives. A bio-based micro-cross-linked halogen-free intrinsic flame-retardant polyester hot melt adhesive, the structure of which is shown in Formula 1: #imgabs0# wherein 2≤m≤4, 2≤n≤4. The present invention adopts the above-mentioned bio-based micro-cross-linked halogen-free intrinsic flame-retardant polyester hot melt adhesive and a preparation method thereof, uses bio-based raw materials, and prepares a new flame-retardant polyester hot melt adhesive. By introducing a phosphorus-containing flame-retardant monomer in the +3 oxidation state, the hot melt adhesive is made highly efficient and halogen-free in flame retardancy; at the same time, by introducing unsaturated double bonds and inducing micro-cross-linking, its environmental resistance in long-term use is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of flame-retardant hot-melt adhesives, and in particular to a bio-based slightly cross-linked halogen-free intrinsically flame-retardant polyester hot-melt adhesive and a preparation method thereof. Background Art

[0002] Hot melt adhesives are fast, solvent-free, harmless to the human body, easy to transport and store, can be melted and bonded repeatedly, and can bond a variety of materials. Therefore, they are widely used in various industries. In addition to traditional ethylene-vinyl acetate copolymer (EVA) hot melt adhesives, new varieties such as polyester and polyamide hot melt adhesives are urgently needed in China.

[0003] Polyester hot melt adhesive has excellent electrical insulation and good bonding strength, and has good impact resistance, heat resistance, cold resistance, medium resistance and elasticity.

[0004] In the field of industrial adhesives, hot melt adhesives are commonly used to bond a variety of products together, including wood, building materials, and electronic materials. These raw materials require hot melt adhesives to have good flame retardant properties.

[0005] Traditional methods for flame-retardant modification of hot-melt adhesives fall into two categories: one involves adding organic or inorganic flame retardants to the hot-melt adhesive matrix. Organic flame retardants include aliphatic halides and phosphates, while inorganic flame retardants include antimony trioxide, borax, and alum. The other involves synthesizing polyester using monomers containing flame-retardant elements, primarily halogen-containing monomers such as tetrachlorophthalic anhydride and dibromoneopentyl glycol. In this additive method, a very high dosage of inorganic flame retardants is required to achieve the desired flame retardant effect. Furthermore, inorganic compounds have poor compatibility with polyester, leading to sedimentation and delamination. Furthermore, the use of halogen-containing flame retardants is not environmentally friendly.

[0006] Phosphorus-containing flame retardants are effective non-halogen flame retardants. By preparing phosphorus-containing flame retardant monomers and introducing them into the polyester molecular chain skeleton to prepare intrinsic phosphorus-containing flame retardant hot melt adhesives, the above problems can be effectively avoided. Summary of the Invention

[0007] The purpose of the present invention is to provide a bio-based slightly cross-linked halogen-free intrinsic flame-retardant polyester hot melt adhesive and a preparation method thereof, so as to achieve high-efficiency halogen-free flame retardancy of the hot melt adhesive and enhance its environmental resistance during long-term use.

[0008] To achieve the above objectives, the present invention provides a bio-based slightly cross-linked halogen-free intrinsic flame-retardant polyester hot melt adhesive. The structure of the polyester hot melt adhesive is shown in Formula 1:

[0009] Among them, 2≤m≤4, 2≤n≤4.

[0010] Preferably, the polyester hot melt adhesive is prepared by a micro-crosslinking reaction of the structure shown in Formula 2;

[0011] Among them, 2≤m≤4, 2≤n≤4.

[0012] Preferably, the structure shown in Formula 2 is prepared from 1,2-propylene glycol, itaconic acid, and a bio-based dibasic acid monomer containing a +3 oxidation state phosphorus structure synthesized based on itaconic acid.

[0013] Preferably, the method for preparing a bio-based dibasic acid monomer containing a +3 oxidation state phosphorus structure synthesized based on itaconic acid comprises:

[0014] Diphenyl phosphite containing a +3 phosphorus oxidation state structure and itaconic acid are stirred and mixed at a molar ratio of 1:1 at 50-70° C., and then continuously stirred at 140-160° C. in a nitrogen environment for 3-6 hours to produce an addition reaction;

[0015] The structure of the bio-based dibasic acid monomer containing a +3 oxidation state phosphorus structure synthesized based on itaconic acid is shown in Formula 3:

[0016]

[0017] A method for preparing the above-mentioned bio-based slightly cross-linked halogen-free intrinsic flame-retardant polyester hot melt adhesive comprises the following steps:

[0018] S1. Stir and mix 1,2-propylene glycol, itaconic acid, a dibasic acid monomer of the structure shown in Formula 3, p-benzoquinone, and dibutyltin dilaurate uniformly under a nitrogen atmosphere at 60-80° C.; continue stirring for 3-6 hours under a nitrogen atmosphere at 150-170° C. to carry out a polycondensation reaction, then raise the temperature to 170-190° C. and continue the reaction under vacuum until the acid value is less than 80 mg KOH / g, to obtain a structure of Formula 2;

[0019] S2. Adding an appropriate amount of dibenzoyl peroxide into the reaction system causes a micro-crosslinking reaction in the structure of Formula 2, thereby finally obtaining a bio-based micro-crosslinked water-resistant and flame-retardant polyester hot melt adhesive.

[0020] Preferably, in step S1, the mass of p-benzoquinone is 0.5% of the mass of itaconic acid; the mass of dibutyltin dilaurate is 0.1% of the mass of itaconic acid and the dibasic acid monomer of the structure shown in Formula 3.

[0021] Preferably, in step S2, the mass of dibenzoyl peroxide is 0.5-1.5% of the mass of the structure shown in formula 2.

[0022] Therefore, the present invention adopts the above-mentioned bio-based slightly cross-linked halogen-free intrinsic flame-retardant polyester hot melt adhesive and its preparation method, which has the following technical effects:

[0023] (1) Using bio-based renewable raw materials to prepare hot melt adhesives to reduce dependence on fossil resources;

[0024] (2) Using bio-based dibasic acid monomers containing a +3 oxidation state phosphorus structure, compared to -1 and +1 oxidation state phosphorus structures, the +3 oxidation state phosphorus flame retardant structure takes into account both gas phase and condensed phase flame retardant mechanisms and has better flame retardant effect;

[0025] (3) In order to avoid the problems of poor water resistance and easy hydrolysis of polyester materials, the water resistance and thermal stability of polyester hot melt adhesive can be enhanced by introducing unsaturated double bonds and inducing micro-crosslinking, thereby enhancing its environmental resistance during long-term use. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The bio-based dibasic acid monomer containing a +3 oxidation state phosphorus structure prepared in Example 1 ( Figure 1 (Part A) and bio-based slightly cross-linked halogen-free intrinsic flame retardant polyester hot melt adhesive ( Figure 1 (B) 1 H NMR spectrum;

[0027] Figure 2 The thermal gravimetric behavior of the bio-based slightly cross-linked halogen-free intrinsically flame-retardant polyester hot melt adhesive prepared in Example 1 (part (A) in the figure) and the bio-based non-flame-retardant polyester hot melt adhesive prepared in Comparative Example 1 (part (B) in the figure);

[0028] Figure 3 The heat release rate and total heat release of the bio-based slightly cross-linked halogen-free intrinsically flame-retardant polyester hot melt adhesive prepared in Example 1 (part (A) in the figure) and the bio-based non-flame-retardant polyester hot melt adhesive prepared in Comparative Example 1 (part (B) in the figure). DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0030] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0031] Example 1

[0032] A bio-based slightly cross-linked halogen-free intrinsic flame-retardant polyester hot melt adhesive is prepared by the following method:

[0033] S1. Preparation of a bio-based dibasic acid monomer containing a +3 oxidation state phosphorus structure: 0.05 mol of diphenyl phosphite containing a +3 oxidation state phosphorus structure and 0.05 mol of itaconic acid were stirred and mixed at 60° C., and then stirred under a nitrogen environment at 150° C. for 6 hours to cause an addition reaction, as shown in Formula A:

[0034]

[0035] S2. Stir and mix 0.44 mol of 1,2-propylene glycol, 0.08 mol of itaconic acid, 0.32 mol of the phosphorus-containing dibasic acid monomer obtained in step S1, p-benzoquinone (0.5% by mass of the itaconic acid), and dibutyltin dilaurate (0.1% by mass of the dibasic acid) at 80°C in a nitrogen atmosphere; continue stirring at 160°C in a nitrogen atmosphere for 6 hours to carry out a polycondensation reaction, then raise the temperature to 180°C and continue the reaction under vacuum until the acid value is less than 80 mg KOH / g. The reaction formula is shown in Formula B:

[0036] Among them, 2≤m≤4, 2≤n≤4.

[0037] S3. Add 1.5 g of dibenzoyl peroxide to the reaction system to cause a micro-crosslinking reaction of the product of formula B, and finally obtain a bio-based micro-crosslinked water-resistant flame-retardant polyester hot melt adhesive. The reaction formula is shown in formula C:

[0038] Among them, 2≤m≤4, 2≤n≤4.

[0039] Comparative Example 1

[0040] A bio-based non-flame retardant polyester hot melt adhesive is prepared by the same method as in Example 1, except that the bio-based dibasic acid monomer containing a +3 oxidation state phosphorus structure is replaced by succinic acid.

[0041] The specific reaction formula is shown in Formula D:

[0042] Among them, 2≤m≤4, 2≤n≤4.

[0043] Comparative Example 2

[0044] A flame-retardant hot melt adhesive without a micro-crosslinking structure is prepared using the same method as in Example 1, except that no dibenzoyl peroxide is added.

[0045] Experimental testing

[0046] (1) The structure of the bio-based dibasic acid monomer containing a +3 oxidation state phosphorus structure and its hot melt adhesive prepared in Example 1 was determined. 1 H NMR spectrum Figure 1 shown.

[0047] Figure 1 Part (A) is a bio-based dibasic acid monomer containing a +3 oxidation state phosphorus structure. 1H NMR spectrum; wherein 11.94 ppm is the characteristic peak position of the proton in the phosphorus-containing dibasic acid; 6.76-7.90 ppm are the characteristic peaks of the aromatic hydrogen atoms in the phosphorus-containing dibasic acid; 3.79 ppm is the characteristic peak of the methylene hydrogen connected to the carboxyl group; 3.24 ppm is the characteristic peak of the methine hydrogen connected to the carboxyl group; 2.07 ppm is the characteristic peak of the methylene hydrogen connected to the phosphorus atom.

[0048] Figure 1 Part (B) is a bio-based slightly cross-linked halogen-free intrinsic flame retardant polyester hot melt adhesive 1 H NMR spectrum; the characteristic peaks in the range of 7.17-8.25 ppm come from the phosphorus-containing diphenyl ester structure in the hot melt adhesive molecular chain; the peaks at 5.83 and 6.21 ppm are the incompletely reacted carbon-carbon double bond structures in itaconic acid, indicating that the degree of crosslinking in the hot melt adhesive can be controlled; the peaks at 4.84 and 1.05 ppm are the methine hydrogen and methyl hydrogen after the reaction of 1,2-propylene glycol in the molecular chain, respectively; the peak at 2.72 ppm is the methylene hydrogen after the condensation reaction of the phosphorus-containing dibasic acid; the peaks in the range of 3.25-3.69 are the methylene hydrogen after the condensation reaction of itaconic acid and 1,2-propylene glycol in the molecular chain.

[0049] (2) Comparison of the thermogravimetric behavior of Example 1 and Comparative Example 1.

[0050] like Figure 2 As shown, the flame-retardant hot melt adhesive exhibits higher high-temperature charring properties than the non-flame-retardant hot melt adhesive. The flame-retardant hot melt adhesive in Example 1 has a charring rate of 11.4 wt% at 800°C in air, while the non-flame-retardant hot melt adhesive in Comparative Example 1 has a charring rate of only 0.3 wt% under the same conditions.

[0051] (3) Comparison of heat release rate and total heat release between Example 1 and Comparative Example 1.

[0052] like Figure 3 As shown in the figure, the heat release rate (HRR) and total heat release (THR) of flame retardant hot melt adhesive are significantly reduced compared with non-flame retardant hot melt adhesive. In the HRR curve, the peak heat release rate is 820kW / m 2 Down to 540kW / m 2 In the THR curve, the THR value is 54MJ / m for non-flame retardant hot melt adhesive. 2 Down to 37MJ / m 2 .

[0053] (4) Comparison of vertical combustion, oxygen index, and 180° peel strength between Example 1 and Comparative Example 1.

[0054] As shown in Table 1, compared with the non-flame retardant hot melt adhesive which had no level in the vertical burning test and an oxygen index value of 22.5%, the flame retardant hot melt adhesive reached the vertical burning V0 level and had an oxygen index value as high as 28.5%. At the same time, in the peel strength test, there was no obvious difference in strength between the two.

[0055] Table 1 Comparison of vertical combustion, oxygen index and 180° peel strength of samples prepared in Example 1 and Comparative Example 1

[0056] sample Vertical combustion Oxygen index (%) Peel strength (kN / m) Example 1 V0 28.5 1.5 Comparative Example 1 No rating 22.5 1.6

[0057] (5) The flame retardant hot melt adhesive prepared in Example 1 and the flame retardant hot melt adhesive without cross-linking structure prepared in Comparative Example 2 were immersed in 35° C. water for 24 h to conduct a water resistance test.

[0058] The test results, shown in Table 2, show that the water content of the minimally cross-linked hot melt adhesive in Example 1 was lower, and the vertical flammability rating, oxygen index, and glass strength results remained unchanged before and after the immersion treatment. The water content of the non-minimal cross-linked hot melt adhesive in Comparative Example 2 increased significantly, and the vertical flammability rating, oxygen index, and peel strength decreased after the immersion treatment.

[0059] Table 2 Water resistance test of samples of Example 1 and Comparative Example 2

[0060] sample Water content (%) Vertical combustion Oxygen index (%) Peel strength (kN / m) Example 1 0.20 V0 29.0 1.5 Example 1 (immersion treatment) / V0 29.0 1.5 Comparative Example 2 0.45 V0 28.5 1.5 Comparative Example 2 (immersion treatment) / V1 28.0 1.3

[0061] Therefore, the present invention adopts the above-mentioned bio-based micro-cross-linked halogen-free intrinsic flame-retardant polyester hot melt adhesive and its preparation method, uses bio-based raw materials to prepare a new flame-retardant polyester hot melt adhesive, and achieves high-efficiency halogen-free flame retardancy of the hot melt adhesive by introducing a phosphorus-containing flame retardant monomer in the +3 oxidation state; at the same time, by introducing unsaturated double bonds and inducing micro-cross-linking, its environmental resistance in long-term use is enhanced.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A bio-based slightly cross-linked halogen-free intrinsically flame-retardant polyester hot melt adhesive, characterized by: The structure of polyester hot melt adhesive is shown in formula 1: Where 2≤m≤4, 2≤n≤4; The polyester hot melt adhesive is prepared by micro-crosslinking reaction of the structure shown in formula 2; Where 2≤m≤4, 2≤n≤4; The structure shown in Formula 2 is prepared from 1,2-propylene glycol, itaconic acid, and a bio-based dibasic acid monomer containing a +3 oxidation state phosphorus structure synthesized based on itaconic acid; The preparation method of a bio-based dibasic acid monomer containing a +3 oxidation state phosphorus structure synthesized based on itaconic acid includes: Diphenyl phosphite containing a +3 phosphorus oxidation state structure and itaconic acid are stirred and mixed at a molar ratio of 1:1 at 50-70° C., and then continuously stirred at 140-160° C. in a nitrogen environment for 3-6 hours to produce an addition reaction; The structure of the bio-based dibasic acid monomer containing a +3 oxidation state phosphorus structure synthesized based on itaconic acid is shown in Formula 3: A method for preparing a bio-based slightly cross-linked halogen-free intrinsic flame-retardant polyester hot melt adhesive comprises the following steps: S1. Stir and mix 1,2-propylene glycol, itaconic acid, a dibasic acid monomer of the structure shown in Formula 3, p-benzoquinone, and dibutyltin dilaurate uniformly under a nitrogen atmosphere at 60-80° C.; continue stirring for 3-6 hours under a nitrogen atmosphere at 150-170° C. to carry out a polycondensation reaction, then raise the temperature to 170-190° C. and continue the reaction under vacuum until the acid value is less than 80 mg KOH / g, to obtain a structure of Formula 2; S2. Adding an appropriate amount of dibenzoyl peroxide to the reaction system causes a micro-crosslinking reaction of the structure of Formula 2, thereby obtaining a bio-based micro-crosslinked water-resistant and flame-retardant polyester hot melt adhesive; In step S1, the mass of p-benzoquinone is 0.5% of the mass of itaconic acid; the mass of dibutyltin dilaurate is 0.1% of the mass of itaconic acid and the dibasic acid monomer of the structure shown in Formula 3; In step S2, the mass of dibenzoyl peroxide is 0.5-1.5% of the mass of the structure shown in formula 2.

Images