A method for preparing modified liquid crystal polyester and a method for preparing modified liquid crystal polyester foam

Abstract

The present invention provides a preparation method of a modified liquid crystal polyester and a preparation method of a modified liquid crystal polyester foam, and belongs to the field of polymer foaming. The preparation method provided by the present invention comprises the following steps: blending a liquid crystal polyester, a nucleating agent, a chain extender and a compatibilizer, causing a chain extension reaction, and obtaining the modified liquid crystal polyester; the melting point of the liquid crystal polyester is within the temperature use range of the chain extender; the blending temperature is 295-340°C, and the time is 5-10 minutes; the mass of the chain extender is 0.05-5wt% of the liquid crystal polyester. An appropriate amount of chain extender enables the liquid crystal polyester to have suitable mechanical rheological properties; the appropriate blending time and temperature enable the chain extension reaction to be sufficient and slow down the oxidative degradation of the liquid crystal polyester, so that the melt has suitable strength to support the growth of the pores; the nucleating agent increases the nucleation sites, optimizes the pore morphology, and improves the uniformity of the pores; the compatibilizer makes the nucleating agent dispersed evenly, and improves the uniformity of the pores.

Description

Technical Field

[0001] The invention relates to the field of polymer foaming, and in particular to a method for preparing a modified liquid crystal polyester and a method for preparing a modified liquid crystal polyester foam. Background Art

[0002] With the expansion of Internet technology applications, wireless communication technology has developed rapidly in recent years. The emergence of 5G technology has met the needs of technologies such as telemedicine, Internet of Things, unmanned driving and augmented reality. But at the same time, higher frequency and high-speed signal transmission has put forward higher requirements for related electronic components. Copper clad laminate (CCL), as the core material for PCB board manufacturing, plays a key role in structural support and connecting various load electronic components. It consists of a dielectric substrate layer (usually a polymer) and copper foil covering one or both sides.

[0003] The signal transmission rate and signal loss in the dielectric material are highly correlated with the dielectric constant and dielectric loss of the material itself, which means that high-frequency and high-speed signal transmission technology places higher requirements on the dielectric properties of CCL substrate materials. At the same time, in order to ensure stability during operation, good heat resistance and low moisture absorption are also necessary properties of substrate materials. At present, finding CCL substrate materials with excellent performance is one of the challenges facing 5G technology.

[0004] Liquid crystal polyester is a type of fully aromatic polymer with a large number of rigid benzene ring structures on the main chain of the anisotropic molecule. The special structure gives it excellent properties including low hygroscopicity, chemical corrosion resistance, good weather resistance, heat resistance, flame retardancy and low dielectric loss, taking into account both high performance and functionality. It is currently widely used in high-tech fields such as electronics, aerospace, national defense, optoelectronic communications, etc. At the same time, the stable dielectric properties of liquid crystal polyester in the full radio frequency range of 110GHz can meet the needs of 5G high-frequency and high-speed networks, and it is one of the most promising low-dielectric polymer materials.

[0005] Although there are patents that have designed the molecular structure of low-dielectric polymer materials (CN107057065A), the low-dielectric polymer designed based on polyimide materials has not gotten rid of the disadvantage of high water absorption of polyimide, and the dielectric constant has not dropped below 2. Introducing pores inside the material is currently the only method that can reduce the dielectric constant to below 2. The patent (CN107793585B) adopts a method without adding a foaming agent, and utilizes the byproduct acetic acid in the polycondensation process to decompose and release CO2 at high temperature to form a microporous structure to prepare a liquid crystal polyester foam with flame retardant properties. However, due to the large number of uncontrollable factors in this method, it is impossible to prepare a liquid crystal polyester foam with uniform pore size, high magnification and excellent mechanical properties. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a modified liquid crystal polyester and a method for preparing a modified liquid crystal polyester foam. The modified liquid crystal polyester foam prepared by the modified liquid crystal polyester prepared by the present invention has uniform pore size and high ratio, and has excellent comprehensive performance.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing a modified liquid crystal polyester, comprising the following steps:

[0009] The liquid crystal polyester, the nucleating agent, the chain extender and the compatibilizer are mixed to cause a chain extension reaction to obtain the modified liquid crystal polyester;

[0010] The melting point of the liquid crystal polyester is within the temperature range of the chain extender;

[0011] The blending temperature is 295-340°C and the blending time is 5-10 minutes;

[0012] The mass of the chain extender is 0.05-5wt% of the liquid crystal polyester.

[0013] Preferably, the nucleating agent includes one or more of talc, nano clay, nano calcium carbonate, nano calcium oxide, nano silicon dioxide and nano aluminum oxide.

[0014] Preferably, the nucleating agent is 0.05 to 5 wt % of the liquid crystal polyester.

[0015] Preferably, the chain extender comprises a polyepoxy functional group chain extender and / or a high melting point acid anhydride.

[0016] Preferably, the polyepoxy functional group chain extender includes ADR; and the high melting point acid anhydride includes PMDA.

[0017] Preferably, the compatibilizer comprises PAR.

[0018] Preferably, the compatibilizer is 5-10 wt % of the liquid crystal polyester.

[0019] The present invention also provides a method for preparing the modified liquid crystal polyester foam, comprising the following steps:

[0020] The modified liquid crystal polyester prepared by the preparation method described in the above scheme is subjected to saturated adsorption and pressure release foaming in an environment containing a gas foaming agent to obtain the modified liquid crystal polyester foam;

[0021] The saturated adsorption temperature is T m ~T m +100℃, T m is the melting temperature of the modified liquid crystal polyester.

[0022] Preferably, the saturated adsorption pressure is 4-20 MPa, and the time is 30-120 min.

[0023] Preferably, the pressure relief rate of the pressure relief foaming is 0.1-300 MPa / s.

[0024] The invention provides a preparation method of a modified liquid crystal polyester, comprising the following steps: blending a liquid crystal polyester, a nucleating agent, a chain extender and a compatibilizer to generate a chain extension reaction to obtain the modified liquid crystal polyester; the melting point of the liquid crystal polyester is within the temperature use range of the chain extender; the blending temperature is 295-340°C and the blending time is 5-10 minutes; the mass of the chain extender is 0.05-5wt% of the liquid crystal polyester. The melting point of the liquid crystal polyester is within the temperature range of the chain extender, which can ensure the occurrence of the chain extension reaction; the appropriate amount of chain extender can introduce an appropriate amount of long-chain branching structure into the liquid crystal polyester so that it has suitable mechanical rheological properties; the appropriate blending time and temperature make the chain extension reaction sufficient and slow down the oxidative degradation of the liquid crystal polyester, so that the modified liquid crystal polyester melt has suitable strength to support the growth of the pores, thereby improving the foaming ratio; the nucleating agent can transform the liquid crystal polyester from the original homogeneous nucleation to heterogeneous nucleation, reduce the nucleation resistance of the gas foaming agent, increase the nucleation sites, optimize the pore morphology, and improve the uniformity of the pores; the volume expander makes the nucleating agent dispersed evenly in the liquid crystal polyester and improves the uniformity of the pores; the applicable temperature of the chain extender matches the melting point of the liquid crystal polyester. The results of the embodiment show that the pore uniformity parameter of the modified liquid crystal polyester foam prepared by the modified liquid crystal polyester prepared by the present invention is 1.1-1.64, and the foaming ratio is 5.81-7.36. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a scanning electron microscope image of the modified liquid crystal polyester foam of Example 1;

[0026] Figure 2 This is a scanning electron microscope image of the modified liquid crystal polyester foam of Comparative Example 3;

[0027] Figure 3 This is a scanning electron microscope image of the modified liquid crystal polyester foam of Comparative Example 5;

[0028] Figure 4 This is a scanning electron microscope image of the modified liquid crystal polyester foam of comparative example 8. DETAILED DESCRIPTION

[0029] The present invention provides a method for preparing a modified liquid crystal polyester, comprising the following steps:

[0030] The liquid crystal polyester, the nucleating agent, the chain extender and the compatibilizer are mixed to cause a chain extension reaction to obtain the modified liquid crystal polyester;

[0031] The melting point of the liquid crystal polyester is within the temperature range of the chain extender;

[0032] The blending temperature is 295-340°C and the blending time is 5-10 minutes;

[0033] The mass of the chain extender is 0.05-5wt% of the liquid crystal polyester.

[0034] In the present invention, the brand of the liquid crystal polyester preferably includes KG300.

[0035] In the present invention, the nucleating agent is preferably 0.05-5wt% of the liquid crystal polyester, more preferably 1-4wt%, and further preferably 2-3wt%; the nucleating agent preferably includes one or more of talc, nanoclay, nano calcium carbonate, nano calcium oxide, nano silicon dioxide and nano aluminum oxide. When the liquid crystal polyester is in the liquid crystal state, since the nucleating agent is distributed between the oriented liquid crystal structures, the liquid crystal polymer changes from the original homogeneous nucleation to heterogeneous nucleation, thereby reducing the nucleation resistance of CO2 at the nucleating agent and increasing the nucleation sites. Without adding a nucleating agent, the foam obtained by foaming in the liquid crystal state is uneven and large in size. Adding an excessive amount of nucleating agent will cause the pore size to be uneven again due to uneven distribution.

[0036] In the present invention, the chain extender is 0.05-5wt% of the liquid crystal polyester, preferably 1-4wt%, more preferably 2-3wt%; the chain extender includes a polyepoxy functional group chain extender and / or a high melting point anhydride. In the present invention, the polyepoxy functional group chain extender preferably includes ADR; the high melting point anhydride preferably includes PMDA. The role of the chain extender is to introduce an appropriate amount of long-chain branching structure so as to have suitable rheological properties, thereby improving the mechanical rheological properties of the liquid crystal polyester and optimizing the foaming properties.

[0037] In the present invention, the compatibilizer is preferably 5-10wt% of the liquid crystal polyester, more preferably 6-9wt%, and further preferably 7-8wt%; the compatibilizer preferably includes PAR (polyarylate). The role of the compatibilizer is to increase the compatibility of the nucleating agent with the liquid crystal polyester and improve the dispersibility of the nucleating agent therein.

[0038] In the present invention, the blending is preferably carried out in a torque rheometer; the blending temperature is preferably 295-340°C, preferably 300-320°C; the time is 5-10 min, more preferably 6-9 min; the blending torque speed is preferably 50-100 rpm, more preferably 60-90 rpm, and further preferably 70-80 rpm. During the blending process, the liquid crystal polyester and the chain extender undergo a chain extension reaction.

[0039] The present invention also provides a method for preparing the modified liquid crystal polyester foam, comprising the following steps:

[0040] The modified liquid crystal polyester prepared by the preparation method described in the above scheme is subjected to saturated adsorption and pressure release foaming in an environment containing a gas foaming agent to obtain the modified liquid crystal polyester foam;

[0041] The saturated adsorption temperature is T m ~T m +100℃, T m is the melting temperature of the modified liquid crystal polyester.

[0042] Before subjecting the modified liquid crystal polyester to saturated adsorption in an environment containing a gas foaming agent, the present invention preferably heats the high-pressure foaming equipment to a pressure-releasing foaming temperature and then places the modified liquid crystal polyester in the high-pressure foaming equipment, then replaces the air in the high-pressure foaming equipment by purging with an inert gas, and then adds a gas foaming agent to the reactor through a pressurizing device to a pressure of saturated adsorption.

[0043] In the present invention, the length, width and height of the modified liquid crystal polyester are preferably 80×10×4 mm.

[0044] In the present invention, the gas foaming agent preferably includes one or more of CO2, N2, methanol and butane.

[0045] In the present invention, the saturation adsorption pressure is preferably 4-20MPa, more preferably 5-15MPa, and further preferably 8-12MPa; the time is preferably 30-120min, more preferably 50-100min, and further preferably 60-80min. Too long saturation time will reduce processing efficiency, and the foaming effect will not be much different. Too short saturation adsorption time will result in the gas foaming agent not being completely dissolved in the modified liquid crystal polyester, which is insufficient to support the nucleation and growth of the foam cells during the foaming process.

[0046] In the present invention, the pressure relief rate of the pressure relief foaming is preferably 0.1-300 MPa / s, more preferably 50-250 MPa / s, and further preferably 100-150 MPa / s. The pressure relief rate in the above range is conducive to the foaming agent in the gas saturated state inside the liquid crystal polyester for the nucleation and growth of the cells.

[0047] After the pressure is released and foamed, the obtained foam is preferably quickly placed in ice water to cool until the pores are shaped to obtain the modified liquid crystal polyester foam.

[0048] The following is a detailed description of the preparation method of the modified liquid crystal polyester and the preparation method of the modified liquid crystal polyester foam provided by the present invention in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0049] Example 1

[0050] (a) Start the torque rheometer and heat it to 300 °C.

[0051] Weigh 50g of liquid crystal polyester, add 1% of the mass of liquid crystal polyester nano-silicon dioxide (specific surface area of ​​80-140m 2 / g), 2% ADR 4368C chain extender by weight of liquid crystal polyester and 10% PAR by weight of liquid crystal polyester, add them into the feeding barrel and start the screw, blending for 7 minutes to allow the chain extension reaction to proceed fully;

[0052] (b) The blended liquid crystal polyester is formed into a spline using an injection molding machine. The temperature of the injection zone of the injection molding machine is set to 300° C., the temperature of the molding zone is set to 70° C., and the size of the spline is 80 mm×10 mm×4 mm. A portion of the spline is used for bending performance testing using the standard GB / T9341-2008, and the other portion is used for the subsequent foaming process.

[0053] (c) After the high-pressure foaming device is heated to the foaming temperature, the sample strip to be foamed is placed in the high-pressure foaming device, and the air therein is replaced by CO2 purging in the high-pressure foaming device. CO2 is added to the reactor by a pressurizing device to a pressure of 15 MPa, and the liquid crystal polyester is saturatedly adsorbed in the CO2 atmosphere at a temperature of 310° C. for 1 hour.

[0054] (d) the pressure is rapidly released at a rate of 200 MPa / s, and the obtained foam is rapidly cooled in ice water until the pores are fixed.

[0055] Embodiments 2 to 8

[0056] The differences from Example 1 are shown in Table 1, and the rest are the same as Example 1.

[0057] Table 1 Differences between Examples 2 to 8 and Example 1

[0058] Chain extender dosage / wt.% Saturated adsorption temperature / ℃ Example 2 2 300 Example 3 2 320 Example 4 2 330 Example 5 1 300 Example 6 1 310 Example 7 1 320 Example 8 1 330

[0059] Comparative Example 1

[0060] (a) Start the torque rheometer and heat it to 300 °C.

[0061] Weigh 50g of liquid crystal polyester, add 1% nano-silicon dioxide by weight of liquid crystal polyester, 2% ADR4368C chain extender by weight of liquid crystal polyester and 10% compatibilizer PAR by weight of liquid crystal polyester, add to the feeding barrel and start the screw, blend for 7 minutes to allow the chain extension reaction to proceed fully;

[0062] (b) The blended liquid crystal polyester is formed into a spline using an injection molding machine. The temperature of the injection zone of the injection molding machine is set to 300° C., the temperature of the molding zone is set to 70° C., and the size of the spline is 80 mm×10 mm×4 mm. A portion of the spline is used for bending performance testing using the standard GB / T9341-2008, and the other portion is used for the subsequent foaming process.

[0063] (c) After the high-pressure foaming device is heated to the foaming temperature, the sample strip to be foamed is placed in the high-pressure foaming device, and the air therein is replaced by CO2 purging in the high-pressure foaming device. CO2 is added to the reactor by a pressurizing device to a pressure of 15 MPa, and the liquid crystal polyester is saturatedly adsorbed in the CO2 atmosphere at a temperature of 270° C. for 1 hour.

[0064] (d) the pressure is rapidly released at a rate of 200 MPa / s, and the obtained foam is rapidly cooled in ice water until the pores are fixed.

[0065] Comparative Examples 2 to 12

[0066] The differences from Comparative Example 1 are shown in Table 2, and the rest are the same as Comparative Example 1.

[0067] Table 2 The difference between Comparative Examples 2 to 12 and Comparative Example 1

[0068]

[0069] Effect Example

[0070] The unfoamed liquid crystal polyester strips of Examples 1 to 8 and Comparative Examples 1 to 12 were subjected to mechanical testing, and the bending modulus was determined using a universal testing machine with a bending rate of 2 mm / min. An analytical balance with an attached density component was used to determine the apparent density of the liquid crystal polyester foamed product, and the foaming ratio was calculated. The resulting foamed product was quenched with liquid nitrogen, gold was sprayed on the cross section, and the pore structure was determined and analyzed using a scanning electron microscope. The thermal expansion coefficient of the liquid crystal polyester foam was determined using a thermal expansion instrument to characterize the dimensional stability of the foam. The dielectric constant and dielectric loss of the liquid crystal polyester before and after foaming were detected using a dielectric constant meter and a precision digital bridge, and the results are recorded in Table 3.

[0071] Table 3 Experimental results

[0072]

[0073]

[0074] The modified liquid crystal polyester foams prepared in Example 1, Comparative Example 3, Comparative Example 5 and Comparative Example 8 were subjected to SEM analysis. The results are as follows: Figures 1 to 4 shown.

[0075] The present invention is composed of Table 3 and Figures 1 to 4 It can be seen that the modified liquid crystal polyester foam prepared by using Examples 1 to 8 has a controllable foaming ratio and a uniform cell structure, and also has excellent mechanical properties, dimensional stability and dielectric properties. Example 1 adjusts the optimal modification formula ratio and modification process, determines the optimal foaming conditions, and the obtained liquid crystal polyester and the corresponding modified liquid crystal polyester foam have the best comprehensive performance;

[0076] The modified formula and process of Comparative Example 1 are the same as those of Example 1, but the foaming temperature is too low and foaming cannot be performed;

[0077] In comparative examples 2 to 4, no chain extender was added for modification. The overall foaming ratio was compared. The foaming ratio of the modified liquid crystal polyester foam did not change with the temperature. The ratio was uncontrollable and low, and the mechanical properties were poor.

[0078] Comparative Example 5, which was not modified by a chain extender and a nucleating agent, had poor mechanical properties, non-uniform pores, and poor dimensional stability;

[0079] Comparative Example 6, using a polyol chain extender, the melting point of the liquid crystal polyester is not within the operating temperature range of DEG, the ratio and mechanical properties do not change significantly, and the dielectric constant, dielectric loss and thermal expansion coefficient are relatively high;

[0080] Comparative Example 7: The chain extension and blending time is too long, the liquid crystal polyester is oxidatively degraded, and the foaming ratio is affected;

[0081] Comparative Example 8, no nucleating agent was added, the cells were uneven and large in size, and the thermal expansion coefficient was high;

[0082] In comparative example 9, the chain extension blending time was too short, the branching chain extension reaction was not completely carried out, and the mechanical properties and foaming ratio were not significantly improved;

[0083] In comparative example 10, the amount of chain extender added was too much, the dielectric properties increased, and foaming could not be performed;

[0084] In comparative example 11, no compatibilizer was added, the nucleating agent was unevenly dispersed, the optimization of the cell size and density was not obvious, the cell size was uneven, and the comprehensive performance of the foam was poor;

[0085] In Comparative Example 12, the foaming temperature is relatively low and the foaming ratio is not high.

[0086] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a modified liquid crystal polyester, characterized in that: The following steps are involved: The liquid crystal polyester, the nucleating agent, the chain extender and the compatibilizer are mixed to cause a chain extension reaction to obtain the modified liquid crystal polyester; The melting point of the liquid crystal polyester is within the temperature range of the chain extender; The blending temperature is 295-340°C and the blending time is 5-10 minutes; The mass of the chain extender is 1-2wt% of the liquid crystal polyester; The compatibilizer is PAR.

2. The preparation method according to claim 1, characterized in that: The nucleating agent includes one or more of talc, nano clay, nano calcium carbonate, nano calcium oxide, nano silicon dioxide and nano aluminum oxide.

3. The preparation method according to claim 1 or 2, characterized in that: The nucleating agent is 0.05-5wt% of the liquid crystal polyester.

4. The preparation method according to claim 1, characterized in that: The chain extender includes a polyepoxy functional group chain extender and / or a high melting point acid anhydride.

5. The preparation method according to claim 4, characterized in that: The polyepoxy functional group chain extender includes ADR; and the high melting point acid anhydride includes PMDA.

6. The preparation method according to claim 1, characterized in that: The compatibilizer is 5-10wt% of the liquid crystal polyester.

7. A method for preparing a modified liquid crystal polyester foam, characterized in that: The following steps are involved: The modified liquid crystal polyester prepared by the preparation method according to any one of claims 1 to 6 is subjected to saturated adsorption and pressure release foaming in an environment containing a gas foaming agent to obtain the modified liquid crystal polyester foam; The saturated adsorption temperature is Tm~Tm+100°C, Tm is the melting temperature of the modified liquid crystal polyester.

8. The preparation method according to claim 7, characterized in that: The saturated adsorption pressure is 4-20 MPa, and the time is 30-120 min.

9. The preparation method according to claim 7, characterized in that: The pressure relief rate of the pressure relief foaming is 0.1-300 MPa / s.

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