Method for forming large size tpu balloon

Abstract

The application is a forming method of large-size TPU balloon with uniform wall thickness and simple process, which solves the problem of difficulty in forming balloon of semi-compliant material; the non-forming part of the hollow material pipe with large diameter is axially drawn to form a small-diameter hollow blank, the diameter and thickness of the hollow blank have reached the diameter and thickness of the end part of the balloon, so that the subsequent end stretching and setting process is not needed; the size of the mold is used to ensure the accuracy of the size of the non-forming part after drawing, and the heating mold is beneficial to the rearrangement of the material pipe molecules at the joint of the non-forming part and the forming part, so that the balloon can form a shoulder with complete outer size, and even the secondary stretching and setting process of the shoulder is not needed; the balloon can be blown and expanded under a smaller pressure, so that the balloon is slowly and uniformly expanded; the material pipe is repeatedly relaxed between the pre-blowing step and the forming step, so that the plasticity of the material is enhanced.

Description

Technical Field

[0001] This invention relates to the field of medical device technology, specifically to a method for molding a large-size TPU balloon. Background Technology

[0002] Intra-aortic balloon pump (IABP) is a treatment method that involves inserting a balloon between the descending aorta and renal artery via femoral artery puncture. Driven and controlled by an intra-aortic balloon pump, the balloon inflates during diastole and deflates at the end of diastole, thereby increasing coronary perfusion and reducing cardiac workload. As a crucial component of the IABP catheter, the balloon's performance directly determines the overall performance of the IABP catheter. The balloon requires extremely high burst resistance, as well as thin and uniform walls, and flexibility and foldability. Meeting these requirements necessitates not only polymer materials with exceptional mechanical and physical properties but also demanding high standards in the molding process.

[0003] Different manufacturers use different methods for balloon molding, broadly categorized into dip molding and thermoforming, with thermoforming currently being more widely used. Traditional thermoforming involves: placing the tube into the mold of the balloon molding machine, introducing nitrogen gas, and stretching and shaping the tube once when the mold reaches a specified temperature to form the main body of the balloon; then stretching and shaping the tube a second time to form the shoulder (conical part); and finally stretching and shaping the tube a third time to form the end of the balloon. This method can achieve a relatively uniform wall thickness in the cone and shoulder sections of the balloon, but it requires three stretching and shaping processes, making the process complex. Summary of the Invention

[0004] The purpose of this invention is to provide a molding method for large-size TPU balloons with uniform wall thickness and simple process.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for molding large-size TPU balloons, characterized by comprising the following steps: S1) Clamping: Provide hollow blanks for clamping onto the balloon forming machine to ensure that the forming section is located in the center of the balloon forming mold; S2) Pre-blowing: Seal one end of the hollow material blank and introduce compressed gas with a pressure of p1 into its inner cavity from the other end of the hollow material blank. At the same time, heat the hollow material blank to a temperature T1 so that the hollow material blank slowly and uniformly expands into a spherical blank. The outer diameter of the spherical blank is only slightly larger than the outer diameter of the hollow material tube. At this time, the diameter of the material tube has increased, but no yielding has occurred. It can continue to expand in subsequent steps.

[0006] S3) Relaxation: Maintaining the balloon embryo at temperature T1, the balloon embryo is repeatedly pressurized and depressurized. The repeated application of tension enhances the plasticity of the material, providing conditions for the subsequent expansion of the blow-molded part. During the pressurization process, the balloon embryo is slightly stretched axially to ensure that the balloon embryo does not soften and sag, and also to prevent the shoulder and end from being blown up due to the heating of the end mold.

[0007] S4) Molding: Compressed gas at a pressure of p2 is introduced into the inner cavity of the relaxed balloon preform to maintain the temperature of the balloon preform at T1, and the balloon preform is axially stretched until it is completely attached to the inner wall of the balloon molding mold to obtain the balloon. The axial stretching speed is greater than the natural inflation speed of the balloon. In this process, the material forming the shoulder and end of the balloon is redistributed to both sides from the material of the tube part that has been blown and expanded in step S2), rather than being formed by the expansion of other tube parts that have not been blown. Therefore, the required thickness of the shoulder and end can be achieved in a short time, which not only improves the uniformity of the overall balloon wall thickness, but also shortens the balloon molding time.

[0008] S5) Shaping: The balloon is heated to T3 and held to shape the balloon. The balloon is shaped at a higher temperature.

[0009] S6) Cooling: Cool the balloon to temperature T4 while maintaining pressure, then evacuate and remove the balloon after cooling; Among them, temperature T3>T1≥T2>T4, and pressure p1>p2.

[0010] In step S2), the air pressure p1 injected into the hollow preform is 3 bar to 4 bar. First, the temperature is rapidly increased to T5 and maintained for t1 time. Then, the temperature is decreased by 0.5 bar and increased by 10°C each time and maintained for t1 time until the temperature reaches T1. The step-type heating and depressurization pre-blowing method can further ensure that the material tube expands slowly and uniformly, and prevent the problem of low balloon forming rate caused by excessively rapid changes in radial dimensions and uneven wall thickness.

[0011] Among them, T1 > T5 > T4.

[0012] Preferably, T5 is 80℃~150℃, t1 is 25s~35s, and T2 is 120℃~160℃.

[0013] Through numerous experiments, it was found that in step S4), axial stretching is performed at a stretching speed of 2 mm / s to 8 mm / s under an air pressure of 1.6 bar to 2 bar at p2.

[0014] As a preferred embodiment of the present invention, before step S1), a stretching machine is used to axially stretch the non-shaped sections at both ends of a large-diameter hollow tube into hollow blanks. After stretching, the diameter of the non-shaped sections is equal to the diameter of the end of the finished balloon, and the middle stretching section forms the shaping section of the balloon. The length of the hollow blank is 50-60mm. In the stretching step, only the non-shaped sections at both ends of the shaping section are axially stretched into small-diameter tubes, while the middle shaping section retains its original size, that is, the diameter of the middle shaping section is equal to the diameter of the large-diameter hollow tube. If a large-diameter hollow tube is directly stretched into shape, the wall thickness of the shoulder (conical part) of the formed balloon will be relatively thick, and the diameter of the shoulder (the tube section that will be connected to the guide tube and TIP head later) will also be relatively large. Therefore, the shoulder and end need to be post-processed—secondary stretching and shaping, and tertiary stretching and shaping. In this application, the non-formed sections at both ends of the large-diameter hollow tube are first axially drawn to form a small-diameter hollow blank. The diameter of the small-diameter section is already the size of the end used for welding on the finished balloon. Therefore, the end stretching and shaping process is not required in the post-processing. As for the tube at the junction of the non-formed section and the formed section, the material in this part is also stretched to a certain extent when it is thinned, and the material molecules are rearranged. In this way, the balloon can form a shoulder with a complete outer size, and even the secondary stretching and shaping process of the shoulder is not required.

[0015] The stretching of large-diameter hollow tubes adopts a heated mold and unidirectional stretching method. This method can ensure the accuracy of the non-formed section size after thinning and is conducive to the rearrangement of tube material molecules at the junction of the non-formed section and the formed section.

[0016] Furthermore, in step S3), the spherical embryo is repeatedly pressurized and depressurized 2 to 5 times while maintaining a temperature T1 of 120°C to 160°C to enhance the plasticity of the material.

[0017] In step S5), the balloon is heated to 140℃~165℃ or higher for shaping, resulting in excellent high-temperature shaping effect.

[0018] In step S6), the balloon is cooled to 20°C to 30°C under a constant pressure of 3 bar to 4 bar.

[0019] This application does not limit the type of compressed gas, which can be any one or more of inert and / or non-inert gases, such as nitrogen, helium, argon and xenon, with nitrogen being preferred.

[0020] The balloon forming mold is located inside a water jacket. A chiller provides constant-temperature cold water into the water jacket, and a heating unit is installed on the inner wall of the water jacket to heat the balloon forming mold. The response to heating and cooling of the balloon is relatively rapid and timely, while simplifying the overall structure of the balloon forming machine.

[0021] The above solution has at least the following beneficial effects: 1. One-time molding of large-size TPU balloons solves the problem of difficult balloon molding using semi-compliant materials; 2. First, the non-forming parts at both ends of the large-diameter hollow tube are axially drawn to form a small-diameter hollow blank. The diameter and thickness of the hollow blank already meet the diameter and thickness of the balloon end. Therefore, there is no need to perform end stretching and shaping processes in the subsequent process, which further simplifies the forming operation. 3. The size of the mold ensures the accuracy of the non-shaped section size after thinning, and heating the mold helps the material molecules at the junction of the non-shaped section and the shaped section to rearrange, so that the balloon can form a shoulder with complete outer dimensions, and even the secondary stretching and secondary shaping process of the shoulder is not required. 4. The balloon can be blow-molded and expanded under relatively low pressure, ensuring that the balloon expands slowly and evenly, thus guaranteeing the safety of the molding process; 5. The main body and shoulder of the balloon are formed by re-blowing of the pre-blown hollow preform, which improves the uniformity and consistency of the balloon wall thickness. 6. The material tube is repeatedly relaxed between the pre-blowing and molding steps to enhance the plasticity of the material. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the balloon structure; Figure 2 This is a schematic diagram of the structural changes during the balloon formation process; Figure 3 This is a flowchart of balloon prototyping. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Example 1

[0024] (1) Take a hollow tube 1 and use a stretching machine to stretch the large-diameter hollow tube 1 axially to form a small-diameter hollow blank 2; (2) Clamp the hollow blank 2 onto the balloon forming machine, ensuring that the forming section is located in the center of the balloon forming mold; (3) Inject 3 bar of nitrogen into the hollow material blank 2, raise the temperature to 90°C and maintain it for 20 seconds, then lower the temperature by 0.5 bar each time and raise the temperature by 10°C and maintain it for 20 seconds until it reaches 140°C to obtain the balloon blank 3. The diameter of the balloon blank 3 is slightly larger than that of the balloon material tube. (4) At a temperature of 140°C, the balloon embryo 3 is subjected to pressure and depressurization three times. During the pressure process, slight stretching is performed to ensure that the tube does not soften and fall or the end is blown up due to the heating of the end mold. (5) While increasing the pressure to 1.6 bar, stretch it and stretch it axially at a speed of 3 mm / s until the balloon embryo 3 is completely attached to the inner wall of the balloon forming mold to obtain the balloon 4; (6) The temperature was then further increased to 150°C to fix the shape of the balloon 4; (7) Cool to 25°C while maintaining a pressure of 3 bar. After cooling, evacuate the vacuum and remove the balloon 4. Example 2

[0025] (1) Take a hollow tube 1 and use a stretching machine to stretch the large-diameter hollow tube 1 axially to form a small-diameter hollow blank 2; (2) Clamp the hollow blank 2 onto the balloon forming machine, ensuring that the forming section is located in the center of the balloon forming mold; (3) Inject 3.5 bar of nitrogen into the hollow material blank 2, raise the temperature to 110°C and maintain it for 25 seconds, then lower the temperature by 0.5 bar each time and raise the temperature by 10°C and maintain it for 25 seconds until it reaches 150°C to obtain the balloon blank 3. The diameter of the balloon blank 3 is slightly larger than that of the balloon material tube. (4) At a temperature of 150°C, the balloon embryo 3 was repeatedly pressurized and depressurized 5 times. During the pressurization process, slight stretching was performed to ensure that the tube would not soften and fall or the end would not be blown up due to the heating of the end mold. (5) While increasing the pressure to 1.8 bar, stretch it and stretch it axially at a speed of 2 mm / s until the balloon embryo 3 is completely attached to the inner wall of the balloon forming mold to obtain the balloon 4; (6) The temperature was then further increased to 155°C to fix the shape of the balloon 4; (7) Cool to 20°C while maintaining a pressure of 3.5 bar. After cooling, evacuate the vacuum and remove the balloon 4. Example 3

[0026] (1) Take a hollow tube 1 and use a stretching machine to stretch the large-diameter hollow tube 1 axially to form a hollow blank 2 with small diameters at both ends; (2) Clamp the hollow blank 2 onto the balloon forming machine, ensuring that the forming section is located in the center of the balloon forming mold; (3) Inject 4 bar of nitrogen into the hollow material blank 2, raise the temperature to 120°C and maintain it for 20 seconds, then lower the temperature by 0.5 bar and raise it by 10°C each time and maintain it for 20 seconds until it reaches 140°C to obtain the balloon blank 3. The diameter of the balloon blank 3 is equal to the outer diameter of the middle main body of the finished balloon. (4) At a temperature of 140°C, the balloon embryo 3 was repeatedly pressurized and depressurized 4 times. During the pressurization process, slight stretching was performed to ensure that the tube would not soften and fall or the end would not be blown up due to the heating of the end mold. (5) While increasing the pressure to 2 bar, stretch it and stretch it axially at a speed of 2.5 mm / s until the balloon embryo 3 is completely attached to the inner wall of the balloon forming mold to obtain the balloon 4; (6) The temperature was then further increased to 150°C to fix the shape of the balloon 4; (7) Cool to 30°C while maintaining a pressure of 3.5 bar. After cooling, evacuate the vacuum and remove the balloon 4. Example 4

[0027] (1) Take a hollow tube 1 and use a stretching machine to stretch the large-diameter hollow tube 1 axially to form a small-diameter hollow blank 2; (2) Clamp the hollow blank 2 onto the balloon forming machine, ensuring that the forming section is located in the center of the balloon forming mold; (3) Inject 4 bar of nitrogen into the hollow material blank 2, raise the temperature to 130°C and maintain it for 20 seconds, then lower the temperature by 0.5 bar and raise it by 10°C each time and maintain it for 20 seconds until it reaches 150°C to obtain the balloon blank 3. The diameter of the balloon blank 3 is equal to the outer diameter of the middle main body of the finished balloon. (4) At a temperature of 150°C, the balloon embryo 3 was repeatedly pressurized and depressurized 4 times. During the pressurization process, slight stretching was performed to ensure that the tube would not soften and fall or the end would be blown up due to the heating of the end mold. (5) While increasing the pressure to 2 bar, stretch it and stretch it axially at a speed of 2 mm / s until the balloon embryo 3 is completely attached to the inner wall of the balloon forming mold to obtain the balloon 4; (6) The temperature was then further increased to 160°C to fix the shape of the balloon 4; (7) Cool to 30°C while maintaining a pressure of 3.5 bar. After cooling, evacuate the vacuum and remove the balloon 4. Example 5

[0028] (1) Clamp the hollow tube 1 onto the balloon forming machine, ensuring that the forming section is located in the center of the balloon forming mold; (2) Inject 4 bar of nitrogen into the hollow tube 1, raise the temperature to 120°C and maintain it for 30 seconds, then lower the temperature by 0.5 bar each time and raise the temperature by 10°C and maintain it for 30 seconds until it reaches 140°C to obtain the balloon embryo 3. The diameter of the balloon embryo 3 is equal to the outer diameter of the middle main body of the finished balloon. (3) At a temperature of 140°C, the balloon embryo 3 was repeatedly pressurized and depressurized 4 times. During the pressurization process, slight stretching was performed to ensure that the tube would not soften and fall or the end would be blown up due to the heating of the end mold. (4) While increasing the pressure to 2 bar, stretch it and stretch it axially at a speed of 3 mm / s until the balloon embryo 3 is completely attached to the inner wall of the balloon forming mold to obtain the balloon 4; (5) The temperature was then further increased to 150°C to fix the shape of the balloon 4; (6) Cool to 30°C while maintaining a pressure of 3.5 bar. After cooling, evacuate the vacuum and remove the balloon 4.

[0029] Comparative Examples

[0030] (1) Clamp the tubing onto the balloon forming machine, ensuring that the forming section is located in the center of the balloon forming mold; (2) Seal one end of the tube and fill the other end with high-pressure gas of 30 bar. Heat the entire balloon molding mold to 150°C. The tube softens under high temperature and adheres to the inner wall of the balloon molding mold under high pressure to form a cone shape. (3) After the temperature stabilizes, the pipe is stretched for the first time at a speed of 10 mm / s at both ends of the pipe to make the main body of the pipe reach the pre-designed thickness. After stretching, hold for 20 seconds. (4) Cool the intermediate heating mold to room temperature, and while the intermediate heating mold is cooling down, heat the shoulder heating mold and the end heating mold to 200°C; (5) After the temperature stabilizes, the pipe is stretched for the second time. Both ends of the pipe are stretched at a speed of 10 mm / s to make the shoulder of the pipe reach the pre-designed thickness. After stretching, hold for 20 seconds to allow the shoulder heating mold to cool to room temperature. While the shoulder heating mold is cooling, the end heating mold is heated to 200°C. (6) After the temperature stabilizes, the tube is stretched for the third time at a speed of 10 mm / s at both ends of the tube so that the ends of the tube reach the pre-designed thickness. After stretching, hold for 20 seconds, then cool the end heating mold to room temperature, open the mold, and obtain the balloon.

[0031] Table 1 shows an overview of the balloons in Examples 1-5 and the comparative examples: Table 1 Example 1 75 0.14 2.96 Example 2 78 0.13 3.05 Example 3 80 0.14 3.15 Example 4 79 0.14 3.10 Example 5 66 0.15 2.80 Comparative Examples 40 0.12 1.90 As shown in Table 1, the large-size balloons prepared using the process of this invention have a significantly improved formation rate, provided that the nominal diameter filling pressure and burst pressure meet the requirements.

[0032] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method for molding a large-size TPU balloon, characterized in that, Includes the following steps: S1) Clamping: Provide hollow blank (2) and clamp it onto the balloon forming machine to ensure that the forming section is located in the center of the balloon forming mold; S2) Pre-blowing: Seal one end of the hollow material blank (2) and introduce compressed gas with a pressure of p1 into its inner cavity from the other end of the hollow material blank (2). At the same time, heat the hollow material blank (2) to a temperature of T1 so that the hollow material blank (2) slowly and evenly expands into a spherical embryo (3). S3) Relaxation: Maintain the blastocyst (3) at temperature T1 and repeatedly pressurize and depressurize the blastocyst (3), and slightly stretch the blastocyst (3) axially during the pressurization process. S4) Molding: Compressed gas with a pressure of p2 is introduced into the cavity of the relaxed balloon embryo (3) to maintain the temperature of the balloon embryo (3) at T2, and axially stretched until the balloon embryo (3) is completely attached to the inner wall of the balloon molding mold to obtain the balloon (4), wherein the axial stretching speed is greater than the natural inflation speed of the balloon. S5) Shaping: The balloon (4) is heated to T3 and held so that the balloon (4) is shaped; S6) Cooling: Cool the balloon (4) under pressure to temperature T4, then evacuate and remove the balloon (4) after cooling. Where temperature T3>T1≥T2>T4, pressure p1>p2; Before step S1), the non-forming sections at both ends of the large-diameter hollow tube (1) are axially drawn using a stretching machine to form a small-diameter hollow blank (2). After thinning, the diameter of the non-forming section is equal to the diameter of the end of the finished balloon, and the middle section is the stretching section that forms the forming section of the balloon.

2. The molding method for large-size TPU balloons according to claim 1, characterized in that: In step S2), the air pressure p1 injected into the hollow blank (2) is 3 bar to 4 bar. First, the temperature is rapidly increased to T5 and maintained for t1 time. Then, the pressure is reduced by 0.5 bar and the temperature is increased by 10°C and maintained for t1 time until the temperature reaches T1. Among them, T1 > T5 > T4.

3. The molding method for large-size TPU balloons according to claim 2, characterized in that: T5 is 80℃~150℃, t1 is 25s~35s, and T2 is 120℃~160℃.

4. The molding method for large-size TPU balloons according to claim 1, characterized in that: In step S4), axial stretching is performed at a stretching speed of 2 mm / s to 8 mm / s under an air pressure of 1.6 bar to 2 bar p2.

5. The molding method for large-size TPU balloons according to claim 1, characterized in that: The large-diameter hollow tube (1) is stretched using a heated mold and unidirectional stretching method.

6. The method for molding large-size TPU balloons according to claim 1, characterized in that: In step S3), the blastocyst (3) is repeatedly pressurized and depressurized 2 to 5 times while maintaining a temperature T1 of 120℃~160℃.

7. The method for molding large-size TPU balloons according to claim 1, characterized in that: In step S5), the balloon (4) is heated to 140℃~165℃ or higher for shaping.

8. The method for molding large-size TPU balloons according to claim 1, characterized in that: In step S6), the balloon (4) is cooled to 20°C to 30°C under a constant pressure of 3 bar to 4 bar.

9. The method for molding large-size TPU balloons according to claim 1, characterized in that: The balloon forming mold is located inside a water jacket. A chiller provides constant-temperature cold water into the water jacket, and a heating unit is installed on the inner wall of the water jacket to heat the balloon forming mold.

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