Solid state tackification of semi-aromatic polyamides

Abstract

The application belongs to the technical field of polyamides, and particularly relates to a solid-phase viscosity-increasing method for semi-aromatic polyamides. The method comprises the following steps: (1) mixing dicarboxylic acid monomers, diamine monomers, water, a catalyst and a metal compound to perform a salt formation reaction, and then heating to 200-270 DEG C to perform a polymerization reaction, so as to obtain a polyamide resin melt with a relative viscosity of 1.9-2.55; and (2) adding an ester of dicarboxylic acid to the polyamide resin melt, uniformly mixing, and then heating to 175-235 DEG C to perform a solid-phase viscosity-increasing treatment, until the relative viscosity reaches 2.9-3.8, so as to obtain the semi-aromatic polyamide. According to the method, the ester of dicarboxylic acid and the metal compound are introduced, the occurrence of a gel side reaction is significantly inhibited, the solid-phase viscosity-increasing reaction is ensured to maintain a high efficiency, and thus the semi-aromatic polyamide resin with a high relative viscosity and without gel is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyamides, and particularly relates to a solid-phase viscosity-increasing method for semi-aromatic polyamides. BACKGROUND

[0002] Polyamide (also known as nylon) is an engineering plastic with excellent mechanical strength, chemical corrosion resistance and processing fluidity, and is widely used in the industrial fields of automobile manufacturing, electronics and electrical appliances, aerospace, textile fibers and the like, and is a key material in the modern industrial system. Among them, semi-aromatic polyamides, due to the combination of the flexibility of aliphatic segments and the rigidity of aromatic segments in the molecular structure, not only retain the easy processing characteristics of aliphatic polyamides, but also have excellent heat resistance, dimensional stability and creep resistance of aromatic polyamides, and the market demand in high-end application scenarios (such as high-temperature-resistant electronic connectors, automobile engine peripheral parts) continues to grow.

[0003] In the industrial production of semi-aromatic polyamides, high relative viscosity (usually required to be greater than or equal to 3) resin is the key to meet the application requirements of high strength, high toughness and the like, and solid-phase viscosity-increasing is the mainstream post-processing technology for industrial molecular weight and viscosity improvement. This process uses the condensation reaction of the terminal amino and carboxyl groups of the resin molecular chain to extend the molecular chain at a temperature lower than the melting point of the resin, thereby increasing the relative viscosity. However, the existing solid-phase viscosity-increasing method for semi-aromatic polyamides still has many technical bottlenecks, and it is difficult to balance the viscosity-increasing efficiency, product quality and process stability: the low reactivity of carboxyl and amino groups in traditional processes leads to a long viscosity-increasing reaction time, and the resin is prone to thermal oxidation aging and yellowing under high temperature for a long time, affecting the appearance and performance; although metal compounds are introduced to inhibit gel formation, basic metal compounds can reduce the condensation reaction rate of carboxyl and amino groups, making it difficult to balance gel inhibition and viscosity-increasing rate; and the slow removal rate of condensation reaction byproducts such as water hinders the forward reaction and leads to uneven resin performance, and improper process adjustment during high-viscosity resin preparation can exacerbate yellowing or gel problems, which cannot stably meet the needs of high-end applications.

[0004] Therefore, it is an urgent problem in the field to develop a semi-aromatic polyamide solid-phase viscosity-increasing method that can effectively inhibit gel reaction, reduce thermal yellowing and optimize byproduct removal while ensuring the rate of solid-phase viscosity-increasing. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a solid-phase viscosity-increasing method for semi-aromatic polyamides, which introduces esterification of dicarboxylic acid and gel inhibitors (metal compounds) to effectively inhibit gel reaction while ensuring the rate of solid-phase viscosity-increasing reaction, thereby obtaining high relative viscosity semi-aromatic polyamide resin without gel.

[0006] The technical solutions adopted by the present application are as follows:

[0007] The solid-phase viscosity-increasing method of the semi-aromatic polyamide comprises the following steps:

[0008] (1) mixing dicarboxylic acid monomers, diamine monomers, water, a catalyst and a metal compound to perform a salt reaction, and then heating to 200-270°C to perform a polymerization reaction to obtain a polyamide resin melt with a relative viscosity of 1.9-2.55;

[0009] (2) adding an ester of dicarboxylic acid to the polyamide resin melt, uniformly mixing, heating to 175-235°C to perform a solid-phase viscosity-increasing treatment, until the relative viscosity reaches 2.9-3.8, to obtain the semi-aromatic polyamide.

[0010] The dicarboxylic acid monomers comprise more than 90% by mole of adipic acid.

[0011] The dicarboxylic acid monomers comprise adipic acid, and can further comprise a copolymerization diacid monomer, which comprises one or more of sebacic acid, dodecanedioic acid, tetradecanedioic acid, terephthalic acid or isophthalic acid.

[0012] The diamine monomers comprise more than 90% by mole of m-xylylenediamine.

[0013] The diamine monomers comprise m-xylylenediamine, and can further comprise a copolymerization diamine monomer, which comprises one or more of 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,10-decanediamine, 1,12-dodecanediamine or p-xylylenediamine.

[0014] The catalyst is one of phosphoric acid, phosphorous acid, hypophosphorous acid, phenylphosphoric acid, phenylhypophosphorous acid, or a salt or ester of the above acids.

[0015] The metal compound is one of a metal oxide, a metal hydroxide, a metal carbonate, a metal bicarbonate or a metal carboxylate, and the metal is one of sodium, potassium, lithium, magnesium or calcium. Preferably, the metal compound is sodium acetate or sodium benzoate.

[0016] The molar ratio of the dicarboxylic acid monomers to the diamine monomers is 1:(1-1.05).

[0017] The water is added in an amount of 30-70 wt.% based on the total mass of the dicarboxylic acid monomers, the diamine monomers, water, the catalyst and the metal compound; and the catalyst is added in an amount of 100 ppm-1000 ppm based on the total mass of the dicarboxylic acid monomers and the diamine monomers.

[0018] The molar ratio of the metal compound to the catalyst is (0.6-5):1.

[0019] The amount of the ester of dicarboxylic acid is 0.5-5 wt.% of the total amount of the polyamide resin melt.

[0020] The time of the solid-phase tackifying treatment is 1-5 h.

[0021] The ester of dicarboxylic acid is a methyl ester of dicarboxylic acid or an ethyl ester of dicarboxylic acid.

[0022] The dicarboxylic acid is a dicarboxylic acid monomer containing 4-36 carbon atoms, such as one or more of adipic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, terephthalic acid, or isophthalic acid.

[0023] The ester of dicarboxylic acid can be added into the polymerization kettle at the end of the polymerization reaction, and mixed with the polyamide resin melt by the stirring action of the polymerization kettle; or can be added through a double-screw or single-screw extruder, and mixed with the polyamide resin melt by the blending function of the extruder.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] (1) The ester of dicarboxylic acid used in the present application has higher reactivity with amino groups and faster reaction rate, effectively shortening the solid-phase tackifying reaction time and reducing the heat experienced by the resin, thereby reducing the yellowing phenomenon during the solid-phase tackifying process;

[0026] (2) The reaction rate of the ester of dicarboxylic acid with amino groups used in the present application is not inhibited by the presence of basic metal compounds, ensuring a high solid-phase polymerization rate while inhibiting the gelation reaction rate;

[0027] (3) The by-product of the condensation reaction of the ester of dicarboxylic acid with amino groups used in the present application is methanol or ethanol, which has a faster escape rate than water, the by-product of traditional reactions. DETAILED DESCRIPTION

[0028] The present application is further described below in conjunction with examples, which do not limit the implementation of the present application.

[0029] The raw materials used in the examples and comparative examples are all conventional commercially available raw materials unless otherwise specified, and the process methods used in the examples and comparative examples are all conventional methods in the art unless otherwise specified.

[0030] Some of the raw materials used in the examples and comparative examples are described as follows:

[0031] M-phenylenediamine: purchased from Mitsubishi Chemical Corporation, Japan.

[0032] Adipic acid: purchased from Huafeng Chemical Co., Ltd.

[0033] Isophthalic acid: purchased from Formosa Chemicals & Fibre (Ningbo) Co., Ltd.

[0034] Phosphoric acid: purchased from Shandong Yihong Chemical Co., Ltd.

[0035] Sodium benzoate: purchased from Suzhou Changhong Chemical Co., Ltd.

[0036] Sodium bicarbonate: purchased from Hubei Shuanghuan Technology Co., Ltd.

[0037] Dimethyl terephthalate: purchased from Shandong Xindongneng Chemical Co., Ltd.

[0038] Diethyl terephthalate: purchased from Shandong Xiya Chemical Co., Ltd.

[0039] Dimethyl adipic acid: purchased from Jinan Nuochuang Chemical Co., Ltd.

[0040] Example 1

[0041] The solid-phase thickening method for semi-aromatic polyamides includes the following steps:

[0042] (1) A 200L stainless steel salt-forming reactor was selected. 47.667 kg (350 mol) m-phenylenediamine, 51.150 kg (350 mol) adipic acid, 19.76 g phosphoric acid, 49.4 g sodium benzoate, and 70 kg deionized water were added to the reactor through the feeding port. After the addition was completed, the valve was closed, and a vacuum was drawn to remove air from the reactor. The temperature was raised to 97.5 ± 2.5℃, and the salt-forming reaction was completed under mechanical stirring. The salt solution obtained from the salt-forming reaction was pumped into a 300L high-pressure polymerization reactor, and a vacuum was drawn to remove air from the reactor. Mechanical stirring and heating were turned on, and the stirring speed was set to 35 rpm. The temperature inside the high-pressure polymerization reactor was raised to 220℃ under stirring. The pressure inside the reactor was controlled at 1.45 MPa through the exhaust valve, and the temperature inside the high-pressure polymerization reactor was gradually increased. When the pressure inside the high-pressure polymerization reactor drops to atmospheric pressure, the reaction is carried out at a temperature of 255°C for 30 minutes under atmospheric pressure conditions to obtain polyamide resin melt.

[0043] (2) adding dimethyl adipate into the high-pressure polymerization kettle through the solid feeding port, the amount of which is 0.5wt.% of the total amount of the polyamide resin melt. The temperature in the high-pressure polymerization kettle is maintained at 255°C, and after 15 minutes of mixing and stirring, the discharge bottom valve is opened, nitrogen is filled into the high-pressure polymerization kettle, and the discharge is carried out under the condition of a pressure of 0.3 MPa, and then the polyamide resin particles are obtained after cooling in a cooling water tank, drawing and cutting. The polyamide resin particles are placed in a 200L double-cone vacuum dryer, vacuum dried at 80°C for 12 hours, and then the relative viscosity is tested. Subsequently, the temperature is increased to 205°C, and the solid-phase tackifying reaction is carried out under vacuum for 2 hours, and then the reaction is stopped, and the semi-aromatic polyamide is obtained after cooling to 65°C.

[0044] Example 2

[0045] The difference from Example 1 is that in step (2), the amount of dimethyl adipate is 1wt.% of the total amount of the polyamide resin melt, and the others are the same as in Example 1.

[0046] Example 3

[0047] The difference from Example 1 is that in step (2), dimethyl adipate is replaced by an equal amount of dimethyl terephthalate, and the others are the same as in Example 1.

[0048] Example 4

[0049] The difference from Example 1 is that in step (2), dimethyl adipate is replaced by diethyl terephthalate, and the amount of diethyl terephthalate is 1wt.% of the total amount of the polyamide resin melt, and the others are the same as in Example 1.

[0050] Example 5

[0051] The difference from Example 1 is that in step (1), 49.4g of sodium benzoate is replaced by 49.4g of sodium bicarbonate, and the others are the same as in Example 1.

[0052] Example 6

[0053] The difference from Example 1 is that in step (1), 51.150kg (350mol) of adipic acid is replaced by 332.5mol (48.593kg) of adipic acid and 17.5mol (2.907kg) of isophthalic acid, and the others are the same as in Example 1.

[0054] Comparative Example 1

[0055] The solid-phase tackifying method of the semi-aromatic polyamide comprises the following steps:

[0056] (1) A 200 L stainless steel salt formation reactor was selected, 47.667 kg (350 mol) of m-xylylenediamine, 51.150 kg (350 mol) of adipic acid, 19.76 g of phosphoric acid, 49.4 g of sodium benzoate and 70 kg of deionized water were added into the salt formation reactor through the feeding port. After the feeding was completed, the valve was closed, vacuum was applied, and the air in the salt formation reactor was removed. The temperature was raised to 97.5±2.5℃, and the salt formation reaction was completed under mechanical stirring. The salt solution obtained by the salt formation reaction was pumped into a 300 L high-pressure polymerization kettle through a pump, and the air in the high-pressure polymerization kettle was removed by vacuum. The mechanical stirring and heating were turned on, and the stirring speed was set to 35 rpm. The temperature was raised to 220℃ under stirring until the temperature in the high-pressure polymerization kettle reached 220℃. The pressure in the kettle was controlled to 1.45 MPa by an exhaust valve, and the temperature in the high-pressure polymerization kettle was gradually increased. When the pressure in the high-pressure polymerization kettle decreased to normal pressure, the temperature in the high-pressure polymerization kettle was maintained at 255℃ under normal pressure for 45 min. After the reaction was completed, the discharge bottom valve was opened, nitrogen was filled into the polymerization kettle, and the discharge was carried out under a pressure of 0.3 MPa. After cooling in a cooling water tank, the resin particles were obtained by strand cutting;

[0057] (2) The resin particles were placed in a 200 L double-cone vacuum dryer and vacuum dried at 80℃ for 12 h. After drying, the relative viscosity was tested. Then the temperature was raised to 205℃, and the solid-phase tackifying reaction was carried out under vacuum for 2 h. The reaction was stopped, and the product was obtained after cooling to 65℃.

[0058] Comparative Example 2

[0059] The difference between Comparative Example 1 and the present application is that no sodium benzoate is added in step (1) of Comparative Example 1, and the other steps are the same as those of Comparative Example 1.

[0060] The relative viscosity (denoted as low viscosity) of the resin particles prepared in step (1) and the yellowness value, gel condition and relative viscosity (denoted as high viscosity) of the semi-aromatic polyamide prepared in step (2) in Examples 1-6 and Comparative Examples 1-2 were tested, and the test results are shown in Table 1.

[0061] The test methods are as follows:

[0062] Relative viscosity: tested according to GB / T 12006.1-2009.

[0063] Yellowness value: tested using a spectrophotometer.

[0064] Gel condition: 1 g of polyamide resin was weighed and added to 100 mL of hexafluoroisopropanol, and stirred and dissolved for 12 h. After the dissolution was completed, the polyamide solution was filtered through a G5 type glass sand core funnel, and the gel residue on the sand core of the funnel was observed and recorded (A represents no gel, B represents a small amount of gel, and C represents a large amount of gel).

[0065] Table 1 Performance test results

[0066]

[0067] From the results of the examples, it can be seen that the addition of the ester of the dicarboxylic acid can effectively shorten the time required for solid-phase tackification, and only 2 h of solid-phase tackification is required to produce a semi-aromatic polyamide with a relative viscosity greater than 3.

[0068] As can be seen from the comparison of Comparative Example 1 and Example 1, the addition of the ester of the dicarboxylic acid greatly accelerates the solid-phase tackification reaction rate. Without the addition of the ester of the dicarboxylic acid, the relative viscosity of the semi-aromatic polyamide produced under the same solid-phase tackification conditions in Comparative Example 1 can only reach 2.56.

[0069] As can be seen from the comparison of Comparative Example 2 and Comparative Example 1, in the absence of the addition of a metal compound, the solid-phase tackification reaction rate is improved, and the relative viscosity after 2 h of solid-phase tackification can reach 2.76; however, at the same time, the gelation reaction rate is also accelerated, resulting in a large amount of gel in the resin after solid-phase tackification.

Claims

1. A method for solid state tackification of semi-aromatic polyamides, characterized in that, The method comprises the following steps: (1) mixing dicarboxylic acid monomers, diamine monomers, water, a catalyst and a metal compound to perform a salt reaction, and then heating to 200-270 DEG C to perform a polymerization reaction, to obtain a polyamide resin melt with a relative viscosity of 1.9-2.55; (2) adding an ester of dicarboxylic acid to the polyamide resin melt, uniformly mixing, heating to 175-235 DEG C to perform a solid-phase tackifying treatment, until the relative viscosity reaches 2.9-3.8, to obtain a semi-aromatic polyamide; The catalyst is one of phosphoric acid, phosphorous acid, hypophosphorous acid, phenylphosphoric acid and phenylhypophosphorous acid, or a salt or an ester of the above acids; The metal compound is one of metal oxides, metal hydroxides, metal carbonates, metal bicarbonates and metal carboxylates, and the metal is one of sodium, potassium, lithium, magnesium and calcium; The ester of dicarboxylic acid is methyl ester or ethyl ester of dicarboxylic acid.

2. The process for solid state tackification of semi-aromatic polyamides according to claim 1, characterized in that, The molar proportion of adipic acid in the dicarboxylic acid monomers is more than 90%.

3. The process for solid state tackification of semi-aromatic polyamide according to claim 1, characterized in that, The molar proportion of m-xylylenediamine in the diamine monomers is more than 90%.

4. The process for solid state tackification of semi-aromatic polyamides according to claim 1, characterized in that, The molar ratio of the dicarboxylic acid monomers to the diamine monomers is 1:(1-1.05), and the molar ratio of the metal compound to the catalyst is (0.6-5):

1.

5. The process for solid state tackification of semi-aromatic polyamide according to claim 1, characterized in that, The water is added in an amount of 30-70 wt.% of the total mass of the dicarboxylic acid monomers, the diamine monomers, water, the catalyst and the metal compound, and the catalyst is added in an amount of 100 ppm-1000 ppm of the total mass of the dicarboxylic acid monomers and the diamine monomers.

6. The process for solid state tackification of semi-aromatic polyamides according to claim 1, characterized in that, The ester of dicarboxylic acid is used in an amount of 0.5-5 wt.% of the total amount of the polyamide resin melt.

7. The process for solid state tackification of semi-aromatic polyamide according to claim 1, characterized in that, The solid-phase tackifying treatment is performed for 1-5 h.

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