A forming method for widening the stable processing window of PPS plate

Abstract

The present application relates to a kind of forming methods for widening the stable processing window of PPS plate, first PPS raw material is laid into mould, put into moulding press, under the condition of pressurization, temperature is raised to 330~350 ℃ at a rate of 10 ℃ / min or more, so that PPS is completely melted, then temperature is reduced, so that the PPS after melting is fully crystallized solidification, then the mould is heated again under the condition of pressurization, so that PPS is melted, then temperature is reduced again, so that the PPS after melting in mould is fully crystallized solidification, when being heated again to melt, PPS melt can form metastable state region in the melting temperature range of 295~320 ℃, so that the fluctuation value of crystallization temperature is not more than 0.2 ℃ when temperature is reduced again.The method of the present application widens the range of PPS plate processing window, so that in a wider melting temperature range, the crystallization temperature is unchanged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polymer material processing, and relates to a forming method for widening a stable processing window of PPS plate material. BACKGROUND

[0002] Polyphenylene sulfide (PPS) is a high-temperature engineering plastic, which is composed of benzene rings and sulfur atoms alternately. It has excellent mechanical properties, chemical resistance and friction performance. Therefore, it has a wide range of applications in many fields such as electronic devices, automobile industry and chemical industry. In addition, it also has excellent mechanical properties, so it is also one of the important matrices of advanced thermoplastic composite materials. As a semi-crystalline polymer, people often use injection molding, compression molding, 3D printing and other processes to form it. These processes involve the process of heating, melting and then cooling and solidifying PPS.

[0003] However, due to its unique molecular structure, PPS has a large melt viscosity and is prone to complex reactions such as chain scission and crosslinking at high temperatures. CN103547618B discloses a thermoplastic molding composition with improved processing stability made of polyarylether and polyphenylene sulfide, which proposes to add other polymers during use to improve its processing performance. In addition, in order to improve the crystallization ability of PPS, document 1 (Isotermal Crystallization Kinetics of Carbon Nanotubes Modified Polyphenylene Sulfide Composites [J]. Journal of Beijing University of Chemical Technology (Natural Science Edition), 2011, 38(01): 68-71.) proposes to add some inorganic hybrid particles as nucleating agents to promote the nucleation and crystallization growth of PPS. However, the above methods cannot effectively regulate the unique correspondence between the melting temperature and the crystallization temperature, so that in the actual production process, there is a temperature difference in different positions in the equipment, and different temperatures will cause the starting and ending time of the internal crystallization of the material to be inconsistent. The larger the material, the more serious the impact. This seriously affects the consistency of the material's internal crystallization behavior, and ultimately affects the instability of the material's internal performance. SUMMARY

[0004] The purpose of the present application is to solve the problem that the correspondence between the crystallization temperature and the melting temperature cannot be regulated in the prior art, which seriously affects the crystallization behavior of the material in the actual production process, and ultimately leads to the instability of the internal performance of the final product. The present application provides a forming method for widening the stable processing window of PPS plate material.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] The forming method for widening the stable processing window of PPS plate material comprises the following steps: firstly, laying PPS raw material into a mold, and then putting the mold into a mold pressing machine, and then heating the mold to 330-350 DEG C at a rate of 10 DEG C / min or more under pressure, and then cooling the mold to make the molten PPS fully crystallize and solidify, and then heating the mold again to melt the PPS under pressure, and then cooling the mold again to make the molten PPS in the mold fully crystallize and solidify.

[0007] When the mold is heated again to melt, the PPS melt can form a metastable state region in the melting temperature range of 295-320 DEG C, so that the crystallization temperature fluctuation is not more than 0.2 DEG C when the mold is cooled again.

[0008] The first heating rate is greater than or equal to 10 DEG C / min, and if the heating rate is less than 10 DEG C, the resin will undergo cold crystallization during the heating process and have sufficient time to perfect, such as undergoing recrystallization, annealing and other processes, so that the PPS cannot be fully melted in the set melting temperature range, and a small amount of ordered structure is still contained in the melt, which affects the size and perfection of the crystallization. Small crystalline size and low perfection degree will cause the number of defects in the amorphous region of PPS to increase, ultimately affecting the second metastable state region and causing the performance of the final product to decrease; large crystalline size and high perfection degree will result in fewer defects in the amorphous region of PPS, and the metastable state region formed in the second melting and cooling process will be more stable and have fewer defects, and the stability of the final product performance will be improved.

[0009] The second heating is to the temperature range of 295-320 DEG C, at which the spherulites are melted, but the melt still contains a region of local order of molecular chains, which exhibits molecular chain relaxation, but is limited by the surrounding amorphous entangled molecular chains and cannot diffuse with each other to form a kind of metastable conformation. This region has a low entropy value, which can promote the nucleation process of the next crystallization. If the temperature is greater than 320 DEG C, the spherulites will be completely melted, the melt metastable region will be destroyed by the thermal motion of the molecular chains and become disordered, and the nucleation process of the next crystallization will be affected. If the temperature is less than 295 DEG C, the spherulites will be partially melted or form a melt containing residual grains, and the melt metastable region cannot be formed.

[0010] The PPS raw material is initially amorphous, and cold crystallization and recrystallization occur during the first heating process, which is greatly affected by the heating rate, so the heating rate is set to be greater than or equal to 10 DEG C / min. After the first crystallization is completed, the second heating rate of the material has less effect on the structure of the crystal than the first heating, so it is not necessary to deliberately set the second heating rate to be greater than or equal to 10 DEG C / min.

[0011] As a preferred technical solution:

[0012] The forming method for widening the stable processing window of PPS plate material as described above, wherein the PPS raw material is PPS film or PPS powder.

[0013] The forming method for widening the stable processing window of PPS plate material as described above, and the specific steps are as follows:

[0014] (1) The PPS raw material is laid into the mold and placed into the molding machine, and then the temperature is initially raised to 330-350℃ under pressure, and the PPS raw material is completely melted after a certain period of holding and pressure maintaining; if the hot-pressing temperature is less than 330℃, the thermal history of PPS may not be eliminated, which affects the subsequent crystalline structure; if the hot-pressing temperature is greater than 350℃, PPS may undergo thermal oxidative degradation, resulting in a decrease in material performance;

[0015] (2) The mold is cooled to 150-200℃ and held for a period of time, so that the melted PPS in the mold is fully crystallized and solidified; if the cooling temperature is lower than 150℃, the forming efficiency will be affected; if the cooling temperature is higher than 200℃, the crystallization may not be sufficient;

[0016] (3) The mold is again heated under pressure and held for a period of time, so that the crystallized and solidified PPS is melted;

[0017] (4) The mold is again cooled to room temperature, so that the melted PPS in the mold is again crystallized and solidified, and the formed PPS plate material is taken out.

[0018] The forming method for widening the stable processing window of PPS plate material as described above, wherein the initial heating rate in step (1) is 10-40℃ / min, and the holding and pressure maintaining time is 30-40min.

[0019] The forming method for widening the stable processing window of PPS plate material as described above, wherein the pressure in step (1) is 0.6-1.5MPa.

[0020] The forming method for widening the stable processing window of PPS plate material as described above, wherein the cooling rate in step (2) is 5-20℃ / min, and the holding time after cooling is 5-10min. The moderate cooling rate is to form a perfect initial crystalline structure. If the cooling rate is lower than 5℃, the forming efficiency will be affected; if the cooling rate is higher than 20℃, the perfection of the crystal during the cooling process will be affected.

[0021] The forming method for widening the stable processing window of PPS plate material as described above, wherein the re-heating rate in step (3) is 10-40℃ / min, and the holding and pressure maintaining time is 30-40min.

[0022] The forming method for widening the stable processing window of PPS plate material as described above, the pressure in the step (3) is 0.6-1.5 MPa.

[0023] The forming method for widening the stable processing window of PPS plate material as described above, the rate of the second time of cooling in the step (4) is 5-40 ℃ / min (if the cooling rate is lower than 5 ℃, the forming efficiency will be affected; if the cooling rate is higher than 40 ℃, the perfection degree of the crystal in the cooling process will be affected).

[0024] The maximum of the first time of cooling rate is lower than that of the second time of cooling rate, because the first time of cooling rate needs to be slow, because the material needs to form perfect spherulites in the first time of cooling process, if the cooling rate is too fast, the spherulite growth will be affected and become imperfect; after the second time of heating, the melt forms a metastable state region, in which the molecular chains are in a relaxed but not diffused state, this metastable structure promotes the nucleation process of spherulites, and the promoting effect is very obvious, which makes the second time of cooling rate faster than the first time of cooling rate.

[0025] Invention principle:

[0026] The forming method for widening the stable processing window of PPS plate material, the first time of heating for heat pressing has a heating rate higher than 10 ℃ / min, the PPS resin can be fully melted in the heating process, the crystal size is large, the number of defects in the amorphous region of PPS is small, the metastable state region formed in the second time of melting and cooling is stable, and the number of defects is small, and the stability of the final performance of the product is increased.

[0027] When the crystallized PPS is melted for the second time, different melting temperatures will lead to different structures of PPS molecular chains in the melt. When the melting temperature is between Tm-Tm+15 ℃ (280-295 ℃), the PPS crystal is not fully melted, and there are residual grains in the melt. When the melting temperature increases, these structures will disappear with the increase of temperature, leading to the decrease of the ability to promote nucleation, and thus the crystallization temperature decreases. When the melting temperature is Tm+15 ℃-Tm+40 ℃ (295-320 ℃), the ordered structure of PPS relaxes, but the rigid molecular chain structure of PPS and the topological network structure formed by the complex molecular chain reaction at high temperature hinder the mutual diffusion of molecular chains, so that the molecular chains cannot diffuse back to the random coil state. Thus, a metastable state is formed at Tm+15 ℃-Tm+40 ℃, and PPS remains in this relaxed but not diffused state in this temperature range. Therefore, the crystallization temperature remains unchanged in this melting range, greatly widening the stable processing window of PPS plate material.

[0028] Metastable state is a necessary condition for forming a stable process window. If metastable state is affected, the final stability of the product is reduced, and the performance will be reduced. The formation of metastable state requires PPS to form regular spherulites in the first cooling process. The formation of spherulites requires that the first heating rate cannot be too slow, because the raw material is amorphous, and cold crystallization will occur during the first heating process and gradually improve. Slow heating rate will cause the molten blank (some residual grains are still present in the melt) after the first melting, resulting in irregular crystallization during the first cooling, which affects the formation of metastable state.

[0029] Advantages:

[0030] The forming method of the present application for widening the stable processing window of PPS plate can regulate the corresponding relationship between the crystallization temperature and the melting temperature, so that even if there is a temperature difference in different positions in the equipment during actual production, the crystallization behavior of the material will not be affected, and the internal performance of the final product is stable. This forming method provides a stable processing window for PPS, and significantly widens the temperature range of the stable processing window of PPS plate. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 Figure 1 is a graph of the change of the crystallization peak temperature Tc of Example 1 with heat treatment temperature Ts; wherein the dashed box is the processing window;

[0032] Figure 2 Figure 3 is a comparison of the tensile strength of the PPS plate after forming of Example 1 and Comparative Example 1;

[0033] Figure 3 Figure 4 is a comparison of the tensile modulus of the PPS plate after forming of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0034] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. In addition, it should be understood that after reading the content taught by the present application, those skilled in the art can make various modifications or modifications to the present application, and these equivalent forms also fall within the scope of the claims attached to the present application.

[0035] The test method used in the present application is as follows:

[0036] Tensile strength, tensile modulus: PPS samples are prepared according to ASTM D638 standard, and tensile performance test is carried out at room temperature with a crosshead speed of 1 mm / min using a universal tensile testing machine. Tensile stress is determined by dividing the tensile load by the initial cross-sectional area, and tensile strain is calculated by the ratio of the length increment between the clamps to the initial gauge length; the maximum value of stress is the tensile strength, and the tensile modulus is obtained by the stress-strain slope.

[0037] The PPS film used in the example is from Zhejiang Xinhengcheng Co., Ltd., and the trade name is 3518.

[0038] Example 1

[0039] A molding method for widening the stable processing window of PPS plates, the specific steps are as follows:

[0040] (1) The PPS film is laid into the mold and placed into the mold pressing machine. Under the pressure of 0.9 MPa, the temperature is initially raised from 23℃ to 330℃ at a rate of 10℃ / min, and the temperature and pressure are maintained for 30 min;

[0041] (2) The mold is cooled at a rate of 5℃ / min, and the temperature is lowered to 150℃, and the temperature is maintained for 10 min;

[0042] (3) The mold is again heated at a rate of 10℃ / min under the pressure of 0.9 MPa, and the temperature and pressure are maintained for 40 min;

[0043] (4) The mold is again cooled at a rate of 5℃ / min, and the temperature is lowered to 23℃, so that the molten PPS in the mold is again crystallized and solidified, and the mold is opened to take out the molded PPS plate.

[0044] Through changing the end point temperature of heating in step (3) above, a plurality of experiments were conducted, and it was found that heating to a temperature range of 295-320℃ can form a metastable state region of PPS melt, so that the crystallization temperature is maintained at 252.1±0.2℃ (as shown in Figure 1 ) when cooled again in step (4).

[0045] When the end point temperature of heating in step (3) is 295℃, as shown in Figure 2 、 3 , the tensile strength of the molded PPS plate is 91.1 MPa, and the tensile modulus is 3.2 GPa.

[0046] Comparative Example 1

[0047] A molding method for PPS plates, which is basically the same as Example 1, except that steps (3) and (4) are omitted, and after step (2), the temperature is continuously lowered to room temperature at a rate of 5℃ / min, the mold is opened, and the molded PPS plate is taken out.

[0048] By changing the endpoint temperature of the heating in step (1) above, multiple sets of experiments were conducted. It was found that the PPS melt could not form a metastable region when heated to a temperature range of 295 to 320°C. As a result, the crystallization temperature could not remain stable after cooling down in step (2). In the temperature range of 295 to 320°C, the crystallization temperature decreased from 249.1°C to 244.3°C as the melt temperature increased.

[0049] like Figure 2 , 3 As shown, the tensile strength of the molded PPS sheet is 80.7 MPa, and the tensile modulus is 2.4 GPa. Comparing Comparative Example 1 with Example 1, it can be seen that the tensile strength of Example 1 is increased by 12.9% compared to Comparative Example 1, and the tensile modulus of Example 1 is increased by 33.3% compared to Comparative Example 1.

[0050] Comparative Example 2

[0051] A method for forming PPS sheets is basically the same as in Example 1, except that the heating rate in step (1) is 5℃ / min.

[0052] By changing the endpoint temperature of the heating in step (3) above, multiple sets of experiments were conducted. It was found that heating to a temperature range of 300-315℃ could form a metastable region in the PPS melt, thereby maintaining the crystallization temperature at 245.5±0.6℃.

[0053] When the final temperature of step (3) is 295℃, the tensile strength of the formed PPS sheet is 85.2MPa and the tensile modulus is 2.7GPa.

[0054] Compared with Example 1, the processing temperature range for forming the metastable melt in Comparative Example 2 is narrower and the degree of stability is reduced. In addition, the tensile strength and tensile modulus of the formed PPS sheet are reduced. This is because the first heating rate is too slow, and the recrystallization time of PPS during the first heating process is long, which makes it impossible to eliminate the thermal history in PPS. As a result, the crystal size is small and the degree of perfection is low during the first cooling, which affects the metastable region in the second process and ultimately leads to a decrease in product performance.

[0055] Example 2

[0056] A molding method for broadening the stable processing window of PPS sheets, the specific steps of which are as follows:

[0057] (1) Lay the PPS film into the mold, put it into the molding machine, and heat it from 24°C to 335°C at a heating rate of 15°C / min under a pressure of 1.0MPa, and keep it at the temperature and pressure for 32min.

[0058] (2) cooling the mold at a cooling rate of 7℃ / min to 160℃ and keeping the temperature for 9min;

[0059] (3) re-heating the mold at a heating rate of 15℃ / min under a pressure of 1.0MPa and keeping the temperature and pressure for 38min;

[0060] (4) re-cooling the mold at a cooling rate of 10℃ / min to 24℃, making the molten PPS in the mold crystallize and solidify again, and taking out the formed PPS plate.

[0061] Through changing the end temperature of heating in step (3) above, it is found that the temperature range of 295-320℃ can make the PPS melt form a metastable state region, so that the crystallization temperature is kept at 252.2±0.2℃.

[0062] When the end temperature of heating in step (3) is 300℃, the tensile strength of the formed PPS plate is 91.0MPa, and the tensile modulus is 3.2GPa.

[0063] Example 3

[0064] A forming method for widening the stable processing window of PPS plate, the specific steps are as follows:

[0065] (1) PPS film is laid in the mold and put into the mold pressing machine, heated from 25℃ to 340℃ at a heating rate of 20℃ / min under a pressure of 1.0MPa, and kept for 34min;

[0066] (2) cooling the mold at a cooling rate of 9℃ / min to 170℃ and keeping the temperature for 8min;

[0067] (3) re-heating the mold at a heating rate of 20℃ / min under a pressure of 1.0MPa and keeping the temperature and pressure for 36min;

[0068] (4) re-cooling the mold at a cooling rate of 15℃ / min to 25℃, making the molten PPS in the mold crystallize and solidify again, and taking out the formed PPS plate.

[0069] Through changing the end temperature of heating in step (3) above, it is found that the temperature range of 295-320℃ can make the PPS melt form a metastable state region, so that the crystallization temperature is kept at 253.0±0.2℃.

[0070] When the end temperature of the temperature rising in step (3) is 305℃, the tensile strength of the formed PPS plate is 90.6MPa, and the tensile modulus is 3.1GPa.

[0071] Example 4

[0072] A forming method for widening the stable processing window of PPS plate, the specific steps are as follows:

[0073] (1) PPS film is laid into the mold, and is put into the mold pressing machine, under the pressure of 1.1MPa, the temperature is initially raised from 25℃ to 345℃ at the temperature rising rate of 30℃ / min, and is kept for 38min;

[0074] (2) The mold is cooled at the cooling rate of 13℃ / min, and is cooled to 190℃, and is kept for 6min;

[0075] (3) The mold is raised in temperature again under the pressure of 1.1MPa, and is raised in temperature to 310℃ at the temperature rising rate of 25℃ / min, and is kept for 35min;

[0076] (4) The mold is cooled again at the cooling rate of 20℃ / min, and is cooled to 25℃, so that the molten PPS in the mold is crystallized and solidified again, and the formed PPS plate is taken out.

[0077] Through changing the end temperature of the temperature rising in the above step (3), a plurality of experiments are carried out, it is found that the temperature rising to the temperature range of 295-320℃ can make the PPS melt form a metastable state region, so that the crystallization temperature is kept at 250.3±0.2℃.

[0078] When the end temperature of the temperature rising in step (3) is 310℃, the tensile strength of the formed PPS plate is 90.5MPa, and the tensile modulus is 3.1GPa.

[0079] Example 5

[0080] A forming method for widening the stable processing window of PPS plate, the specific steps are as follows:

[0081] (1) PPS film is laid into the mold, and is put into the mold pressing machine, under the pressure of 1.1MPa, the temperature is initially raised from 25℃ to 345℃ at the temperature rising rate of 30℃ / min, and is kept for 38min;

[0082] (2) The mold is cooled at the cooling rate of 13℃ / min, and is cooled to 190℃, and is kept for 6min;

[0083] (3) The mold is reheated to 315°C at a heating rate of 30°C / min under a pressure of 1.1 MPa, and the temperature is kept for 34 min;

[0084] (4) The mold is reheated to 315°C at a heating rate of 30°C / min under a pressure of 1.1 MPa, and the temperature is kept for 34 min;

[0085] A plurality of experiments are performed by changing the end temperature of heating in step (3) above, and it is found that the PPS melt forms a metastable state region when heated to a temperature in the range of 295-320°C, so that the crystallization temperature is kept at 249.1±0.2°C.

[0086] When the end temperature of heating in step (3) is 315°C, the tensile strength of the formed PPS plate is 90.3 MPa, and the tensile modulus is 3.0 GPa.

[0087] Example 6

[0088] A molding method for widening the stable processing window of PPS plate is provided, and the specific steps are as follows:

[0089] (1) The PPS film is placed in the mold, and is placed in the mold press. The temperature is initially raised from 27°C to 350°C at a heating rate of 40°C / min under a pressure of 1.2 MPa, and the temperature is kept for 40 min;

[0090] (2) The mold is cooled to 200°C at a cooling rate of 20°C / min, and the temperature is kept for 5 min;

[0091] (3) The mold is reheated to 320°C at a heating rate of 40°C / min under a pressure of 1.2 MPa, and the temperature is kept for 30 min;

[0092] (4) The mold is reheated to 320°C at a heating rate of 40°C / min under a pressure of 1.2 MPa, and the temperature is kept for 30 min;

[0093] A plurality of experiments are performed by changing the end temperature of heating in step (3) above, and it is found that the PPS melt forms a metastable state region when heated to a temperature in the range of 295-320°C, so that the crystallization temperature is kept at 248.2±0.2°C.

[0094] When the end temperature of heating in step (3) is 320°C, the tensile strength of the formed PPS plate is 88.7 MPa, and the tensile modulus is 2.9 GPa.

Claims

1. A method of forming a PPS sheet material with a broadened processing window, characterized by: Firstly, the PPS raw material is laid into the mold, and is put into a mold pressing machine, and is initially heated to 330-350℃ at a rate of 10℃ / min or more under pressure, and is kept warm and pressurized for a period of time, so that the PPS raw material is completely melted; then the mold is cooled to 150-200℃ at a rate of 5-20℃ / min, and is kept warm for 5-10min, so that the melted PPS in the mold is fully crystallized and solidified; then the mold is heated again to 295-320℃ under pressure, and is kept warm and pressurized for a period of time, so that the crystallized and solidified PPS is melted; then the mold is cooled again to room temperature at a rate of 5-40℃ / min, so that the melted PPS in the mold is fully crystallized and solidified, the mold is opened, and the formed PPS plate is taken out; When the PPS is melted again, the PPS melt can form a metastable state region in the melting temperature range, so that the crystallization temperature fluctuation is not more than 0.2℃ when cooled again.

2. The forming method for widening the stable processing window of PPS sheets according to claim 1, characterized in that, The PPS raw material is a PPS film or a PPS powder.

3. The forming method for widening the stable processing window of PPS sheets according to claim 1, characterized in that, The initial heating rate is 10-40℃ / min, and the warm and pressurized time is 30-40min.

4. The forming method for widening the stable processing window of PPS sheets according to claim 1, characterized in that, When the PPS is melted again, the PPS melt can form a metastable state region in the melting temperature range, so that the crystallization temperature fluctuation is not more than 0.2℃ when cooled again.

5. The forming method for widening the stable processing window of PPS sheets according to claim 1, characterized in that, The initial heating rate is 10-40℃ / min, and the warm and pressurized time is 30-40min.

6. The method of claim 1, wherein the PPS sheet is formed by a method comprising: When the PPS is melted again, the PPS melt can form a metastable state region in the melting temperature range, so that the crystallization temperature fluctuation is not more than 0.2℃ when cooled again.

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