Process for the preparation of high cohesive polyamide resins

Abstract

The application belongs to the technical field of polyamides, and particularly relates to a preparation method of high-viscosity polyamide resin. The preparation 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 increasing the temperature to 190-280 DEG C to perform polymerization, so as to obtain low-viscosity polyamide resin; (2) adding the low-viscosity polyamide resin and a dianhydride or a hydrolysis product of the dianhydride into an extruder, and extruding the low-viscosity polyamide resin at 200-310 DEG C to increase the viscosity, so as to obtain high-viscosity polyamide resin; wherein the molar proportion of adipic acid in the dicarboxylic acid monomers is more than 90%, and the molar proportion of m-xylylenediamine in the diamine monomers is more than 90%. By using the extrusion viscosity-increasing mode to replace the traditional solid-phase viscosity-increasing mode, the reaction time is shortened, the high-viscosity polyamide resin prepared has more excellent melt stability, and there is no gel phenomenon.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polyamide, and particularly relates to a preparation method of high-viscosity polyamide resin. BACKGROUND

[0002] Polyamide refers to a kind of polymer with an amide bond (-CONH-) in the main chain. Due to the existence of the amide bond, there is a strong hydrogen bond interaction between the polyamide molecular chains. The existence of the hydrogen bond not only promotes the crystallization of the polyamide resin, but also enhances the interaction between the polyamide molecular chains. Therefore, the polyamide resin has good mechanical properties, wear resistance, and chemical resistance. The polyamide resin is usually applied in various fields in the form of pipes, profiles, parts, films, or fibers, such as the fields of automobiles, electronic appliances, building materials, lighting, aerospace, etc.

[0003] Poly(m-xylylene adipamide), also known as special nylon MXD6, is synthesized by polycondensation reaction with m-xylylenediamine (MXDA) and adipic acid (AA) as raw materials. It is a kind of semi-aromatic nylon material with high barrier property, high strength, high rigidity, low water absorption, and easy processability, which can be applied to cheese, ham sausage, functional beverage, and other food packaging with high barrier property requirements. Special nylon MXD6 has high barrier property to gas molecules such as oxygen and carbon dioxide. Its gas barrier property is more than 10 times that of nylon 6 under normal temperature conditions, which can effectively prevent the oxidation and deterioration of fat and protein when used in food packaging materials.

[0004] Due to the existence of benzyl methyl on the MXDA monomer, the MXD6 resin is prone to gelation reaction in the molten state, which leads to the generation of gel particles in the resin melt, thereby reducing the use value of the MXD6 resin. In order to inhibit the formation of gel in the MXD6 resin, sodium acetate, sodium hydroxide, and other gel inhibitors are often added in the polymerization reaction as described in Chinese patents CN1451678A, CN104892386A, and US7687562B2. Although alkali substances such as sodium acetate, sodium bicarbonate, and sodium hydroxide can inhibit the gelation reaction of MXD6 resin, they also reduce the amide reaction rate of polyamide, which leads to the inability to obtain high-viscosity polyamide resin.

[0005] MXD6 resin applied in the field of packaging and blown film has high requirements for the relative viscosity (RV) of the resin due to the requirements of the blown film processing technology. The relative viscosity of the polyamide resin is usually required to be higher than 3. High-viscosity polyamide resin is generally obtained by solid-phase thickening. The solid-phase thickening reaction usually needs to be carried out at 180-230℃ for 5-20h. Long-time thickening reaction not only leads to low production efficiency and high energy consumption, but also easily causes yellowing of the resin under high temperature conditions, which leads to poor color of the resin and affects the use of the material.

[0006] Therefore, there is an urgent need for a new preparation method to solve the above problems. SUMMARY

[0007] In view of the deficiencies of the prior art, the purpose of the present application is to provide a preparation method of high-viscosity polyamide resin, which replaces the traditional solid-phase tackifying method with an extrusion tackifying method, thereby shortening the reaction time and obtaining high-viscosity polyamide resin with more excellent melt stability and without gel phenomenon.

[0008] The technical solutions adopted by the present application are as follows:

[0009] The preparation method of high-viscosity polyamide resin comprises the following steps:

[0010] (1) mixing dicarboxylic acid monomers, diamine monomers, water, a catalyst and a metal compound to perform a salt formation reaction, and then heating to 190-280℃ to perform polymerization, thereby obtaining low-viscosity polyamide resin;

[0011] (2) adding the low-viscosity polyamide resin and dianhydride or a hydrolysis product of dianhydride into an extruder, and extruding at 200-310℃ to increase the viscosity, thereby obtaining high-viscosity polyamide resin;

[0012] Among them, the molar proportion of adipic acid in the dicarboxylic acid monomers is more than 90%; the molar proportion of m-xylylenediamine in the diamine monomers is more than 90%.

[0013] The catalyst is one of phosphoric acid, phosphorous acid, hypophosphorous acid, phenylphosphoric acid and phenylhypophosphorous acid, or a borate salt of the above acids, or an ester of the above acids. For example, triphenyl phosphate, triphenyl phosphite or tris(nonylphenyl) phosphite, preferably hypophosphite.

[0014] The metal compound is one of metal oxides, metal hydroxides, metal carbonates, metal bicarbonates or metal carboxylates, and the metal is one of sodium, potassium, lithium, magnesium or calcium. The metal compound is preferably sodium or potassium acetate, or sodium or potassium bicarbonate.

[0015] The molar ratio of the dicarboxylic acid monomers to the diamine monomers is 1:(1-1.05).

[0016] The amount of water added is between 30-70wt.% of the total mass of the dicarboxylic acid monomers, the diamine monomers, water, the catalyst and the metal compound.

[0017] The amount of catalyst added is between 100ppm-800ppm of the total mass of the dicarboxylic acid monomers and the diamine monomers.

[0018] The molar ratio of the metal compound to the catalyst is (0.6-6):1.

[0019] The dianhydride is an aliphatic dianhydride or an aromatic dianhydride, preferably an aromatic dianhydride, more preferably a phthalic dianhydride or a biphenyl tetracarboxylic dianhydride.

[0020] The dicarboxylic acid monomer includes adipic acid, and can further include a copolymerization diacid monomer, which includes one or more of sebacic acid, dodecanedioic acid, tetradecanedioic acid, terephthalic acid or isophthalic acid.

[0021] The diamine monomer includes m-xylylenediamine, and can further include a copolymerization diamine monomer, which includes one or more of 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,10-decanediamine or p-xylylenediamine.

[0022] The amount of the dianhydride or the hydrolysis product of the dianhydride is 0.1-5 wt.% of the total amount of the low-viscosity polyamide resin.

[0023] The relative viscosity of the low-viscosity polyamide resin is 1.85-2.85, and the relative viscosity of the high-viscosity polyamide resin is 2.9-3.8.

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

[0025] (1) The preparation method of the high-viscosity polyamide resin can significantly inhibit the reaction activity of the gel reaction by adding a metal compound, and the prepared polyamide resin has higher melt stability in the molten state;

[0026] (2) The reactivity of the acid anhydride group with the amino group is higher than that of the carboxylic acid with the amino group, so the reaction can occur rapidly without the presence of a catalyst in the extrusion tackification process;

[0027] (3) In the preparation method of the high-viscosity polyamide resin, the residence time of the extrusion tackification reaction is only 1-5 min, which greatly shortens the tackification time, improves the production efficiency, and reduces the energy consumption in the tackification process. DETAILED DESCRIPTION

[0028] The present application is further described below in conjunction with examples, but it does 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-xylylenediamine: purchased from Mitsubishi Chemical Corporation, Japan.

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

[0033] Isophthalic acid: purchased from Taizheng Industry (Ningbo) Co., Ltd.

[0034] Sodium hypophosphite: purchased from Shandong Yihong Chemical Co., Ltd.

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

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

[0037] Pyromellitic dianhydride: purchased from Jinan Mingsheng Chemical Co., Ltd.

[0038] Pyromellitic acid: purchased from Jinan Mingsheng Chemical Co., Ltd.

[0039] 3,3',4,4'-diphenyl tetracarboxylic dianhydride: purchased from Wuhan Smaker Biological Technology Co., Ltd.

[0040] Example 1

[0041] The method for preparing the high-viscosity polyamide resin comprises the following steps:

[0042] (1) A 200 L stainless steel salt formation reactor was selected, the reactor was heated by internal coil, and was equipped with a mechanical stirring device and a glass sight window. 27.783 kg (204 mol) of m-xylylenediamine, 29.228 kg (200 mol) of adipic acid, 11.4 g of sodium hypophosphite, 21.26 g of sodium acetate and 60 kg of deionized water were added to the salt formation reactor through the feeding port. After the feeding was completed, nitrogen was introduced into the salt formation reactor through the nitrogen gas pipeline, and the air in the salt formation reactor was exhausted by nitrogen purging. The temperature was raised to 97.5±2.5℃, and the salt formation reaction was completed under the action of mechanical stirring. The salt solution obtained by the salt formation reaction was pumped into a 200 L high-pressure polymerization kettle through a pump, and the high-pressure polymerization kettle was equipped with an exhaust valve, mechanical stirring, kettle wall jacket heating, temperature sensor, bursting disc and other devices. Nitrogen was filled and discharged three times to exhaust the air in the high-pressure reactor. The mechanical stirring and heating were turned on, and the mechanical stirring speed was set to 35 rpm. The temperature was raised to 220℃ in the high-pressure polymerization kettle under stirring. The pressure in the high-pressure polymerization kettle was controlled to be 1.5 MPa by the exhaust valve, and the temperature in the high-pressure polymerization kettle was gradually increased. When the temperature in the high-pressure polymerization kettle reached 250℃, the exhaust valve was opened, and the pressure in the high-pressure polymerization kettle was gradually reduced to normal pressure. Then, under the condition of normal pressure, the temperature in the high-pressure polymerization kettle was maintained at 260℃, and the stirring polymerization reaction was carried out for 45 min. The exhaust valve was closed, the discharge bottom valve was opened, nitrogen was filled into the high-pressure polymerization kettle through the nitrogen inlet pipe, and the nitrogen pressure was maintained at 0.5 MPa. Under the nitrogen pressure, the resin melt was extruded through the kettle bottom die, cooled in a cooling water tank, and the resin strand was cut into particles to obtain a low-viscosity polyamide resin; the low-viscosity polyamide resin was placed in a 200 L double-cone vacuum dryer and vacuum dried at 85℃ for 12 h;

[0043] (2) The dried low-viscosity polyamide resin was mixed with pyromellitic dianhydride in a mixer until uniform, and the amount of pyromellitic dianhydride was 1.5 wt.% of the total amount of low-viscosity polyamide resin. After mixing, it was added to a twin-screw extruder for extrusion and tackification to obtain a high-viscosity polyamide resin. The mixture was added through the main feeding port, the screw speed was 100 r / min, the temperatures of the first to sixth zones of the twin-screw extruder were set to 200℃ / 230℃ / 250℃ / 260℃ / 260℃ / 260℃, and the total residence time of the material in the twin-screw extruder was 90 s.

[0044] Example 2

[0045] The difference from Example 1 is that in step (2), the amount of pyromellitic dianhydride is 1.8 wt.% of the total amount of low-viscosity polyamide resin, and the others are the same as in Example 1.

[0046] Example 3

[0047] The difference from Example 1 is that in step (2), the amount of pyromellitic dianhydride is 2.0 wt.% of the total amount of low viscosity polyamide resin, and the others are the same as Example 1.

[0048] Example 4

[0049] The difference from Example 1 is that in step (2), pyromellitic dianhydride is replaced by 3,3',4,4'-diphenyl tetracarboxylic dianhydride of the same mass, and the others are the same as Example 1.

[0050] Example 5

[0051] The difference from Example 1 is that in step (1), 21.26 g of sodium acetate is replaced by 21.78 g of sodium bicarbonate, and the others are the same as Example 1.

[0052] Example 6

[0053] The difference from Example 1 is that in step (1), 29.228 kg (200 mol) of adipic acid is replaced by 190 mol (27.767 kg) of adipic acid and 10 mol (1.661 kg) of isophthalic acid, and the others are the same as Example 1.

[0054] Example 7

[0055] The difference from Example 1 is that in step (1), the amount of sodium hypophosphite is adjusted to 22.8 g, and the amount of sodium acetate is adjusted to 42.52 g, and the others are the same as Example 1.

[0056] Example 8

[0057] The difference from Example 1 is that in step (2), pyromellitic dianhydride is replaced by pyromellitic acid of the same mass, and the others are the same as Example 1.

[0058] Comparative Example 1

[0059] The preparation method of the polyamide resin comprises the following steps:

[0060] (1) The difference from step (1) of Example 1 is that no sodium acetate is added;

[0061] (2) The dried low viscosity polyamide resin is placed in a 200L double-cone vacuum dryer, and solid-phase tackifying reaction is carried out at 215°C under vacuum for 12h, and then cooled to 65°C and taken out to obtain the polyamide resin.

[0062] Comparative Example 2

[0063] The difference from Comparative Example 1 is that no sodium hypophosphite is added in step (1), and the others are the same as Comparative Example 1.

[0064] Comparative Example 3

[0065] The method for preparing the polyamide resin comprises the following steps:

[0066] (1) Same as step (1) in Example 1;

[0067] (2) Same as step (2) in Comparative Example 1.

[0068] Comparative Example 4

[0069] The difference from Example 1 is that no sodium acetate is added in step (1), and the others are the same as Example 1.

[0070] The relative viscosity (denoted as low viscosity) of the low viscosity polyamide resin prepared in step (1) and the yellowness value, gel condition, melt stability and relative viscosity (denoted as high viscosity) of the polyamide resin prepared in step (2) in Examples 1-8 and Comparative Examples 1-4 are tested respectively, and the test results are shown in Tables 1-2.

[0071] The test method is as follows:

[0072] Relative viscosity: tested according to GB / T 12006.1-2009.

[0073] Yellowness value: tested using a spectrophotometer.

[0074] Gel condition: 1 g of polyamide resin is weighed and added to 100 mL of hexafluoroisopropanol, and stirred and dissolved for 12 h. After complete dissolution, the polyamide solution is filtered through a G5 type glass sand core funnel, and the gel residue on the funnel sand core is observed and recorded (A represents no gel, B represents a small amount of gel, and C represents a large amount of gel).

[0075] Melt stability: 10 g of polyamide resin is weighed and added to a melt flow rate instrument, and after being kept at 270℃ for 30 min, the resin melt is extruded through a die. 1 g of the extruded resin strip is cut into short strips, placed in 100 mL of hexafluoroisopropanol, and stirred and dissolved for 12 h. After complete dissolution, the polyamide solution is filtered through a G5 type glass sand core funnel, and the gel residue on the funnel sand core is observed and recorded (A represents no gel, B represents a small amount of gel, and C represents a large amount of gel).

[0076] Table 1 Test results of properties of examples

[0077]

[0078] As can be seen from the results of Examples 1-3, with the increase of the amount of dianhydride added, the relative viscosity of the polyamide resin prepared after extrusion tackification gradually increases, and is greater than 3, which can meet the requirements of the film blowing process. In addition, the high-tack polyamide resin prepared by the method of the present application has high relative viscosity, no gel exists in the resin, and the melt stability is good, and no gel particles are formed in the molten state for 30 min.

[0079] As can be seen from the comparison of Example 1 and Example 4, the tackifying efficiency of 3,3',4,4'-biphenyl tetracarboxylic dianhydride is lower than that of phthalic dianhydride, which may be due to the higher reactivity and lower molecular weight of phthalic dianhydride.

[0080] Example 5 shows that sodium bicarbonate and sodium acetate have the same gel inhibition effect, but when sodium bicarbonate is used as a gel inhibitor, the yellowness value of the obtained resin is slightly higher, and the comprehensive effect is not as good as sodium acetate.

[0081] The test results of Example 6 show that the introduction of co-monomer isophthalic acid does not affect the extrusion tackification effect.

[0082] The test results of Example 7 show that when the catalyst concentration is increased, as long as the molar ratio of metal compound to catalyst is appropriate, the final obtained resin can still effectively inhibit the generation of gel, and the color performance is better.

[0083] The test results of Example 8 show that phthalic acid and phthalic dianhydride have the same tackifying effect.

[0084] Table 2, comparative example performance test results

[0085]

[0086] As can be seen from the data of Comparative Example 1, in the absence of metal compounds, the polyamide resin prepared by solid-phase tackification will have gel. As can be seen from the comparison of Comparative Example 2 and Comparative Example 1, in the absence of both metal compounds and catalyst, high relative viscosity polyamide resin cannot be obtained by solid-phase tackification, and gel exists in the obtained polyamide resin. As can be seen from the comparison of Comparative Example 3 and Comparative Example 1, after the addition of metal compounds, the polymerization rate of polyamide is inhibited, and under the same solid-phase tackification conditions, the relative viscosity of the low-tack polyamide resin in Comparative Example 3 can only reach 2.65 after 12 h of solid-phase tackification at 215℃. As can be seen from the comparison of Comparative Example 4 and Example 1, in the absence of metal compounds, although extrusion reaction can be used for tackification, gel cannot be avoided in the obtained polyamide resin.

Claims

1. A method for preparing a high-viscosity polyamide resin, characterized in that, Includes the following steps: (1) A dicarboxylic acid monomer, a diamine monomer, water, a catalyst and a metal compound are mixed and subjected to a salt-forming reaction, and then the mixture is heated to 190~280℃ for polymerization to obtain a low-viscosity polyamide resin; the molar ratio of the metal compound to the catalyst is (0.6~6):

1. (2) Add low-viscosity polyamide resin and dianhydride or dianhydride hydrolysis products into an extruder, and extrude at 200~310℃ to thicken. The residence time for extrusion thickening is 1~5min, and high-viscosity polyamide resin is obtained. Wherein, the molar percentage of adipic acid in the dicarboxylic acid monomer is more than 90%; the molar percentage of the diamine monomer intermediate-phenylenediamine is more than 90%; and the dianhydride is pyromellitic dianhydride or biphenyltetracarboxylic dianhydride. The catalyst is one of phosphoric acid, phosphorous acid, hypophosphoric acid, phenylphosphoric acid, phenyl hypophosphoric acid, or a salt of the above acids, or an ester of the above acids; The metal compound is one of the following: metal oxide, metal hydroxide, metal carbonate, metal bicarbonate, or metal carboxylate, and the metal is one of sodium, potassium, lithium, magnesium, or calcium.

2. The method for preparing the high-viscosity polyamide resin according to claim 1, characterized in that, The molar ratio of the dicarboxylic acid monomer to the diamine monomer is 1:(1~1.05).

3. The method for preparing the high-viscosity polyamide resin according to claim 1, characterized in that, The amount of water added is between 30 and 70 wt.% of the total mass of the dicarboxylic acid monomer, diamine monomer, water, catalyst, and metal compound.

4. The method for preparing the high-viscosity polyamide resin according to claim 1, characterized in that, The catalyst is added in an amount of 100 ppm to 800 ppm of the total mass of the dicarboxylic acid monomer and the diamine monomer.

5. The method for preparing the high-viscosity polyamide resin according to claim 1, characterized in that, The amount of the dianhydride or dianhydride hydrolysis product used is 0.1~5 wt. of the total amount of low-viscosity polyamide resin.

6. The method for preparing the high-viscosity polyamide resin according to claim 1, characterized in that, The relative viscosity of the low-viscosity polyamide resin is 1.85~2.85, and the relative viscosity of the high-viscosity polyamide resin is 2.9~3.8.

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