WO2023160440A1

WO2023160440A1 - Preparation method for heat-shrinkable tube

Info

Publication number: WO2023160440A1
Application number: PCT/CN2023/076112
Authority: WO
Inventors: 戴礼浩; 邓智华; 梁驹; 何光彬
Original assignee: 浙江脉通智造科技(集团)有限公司; 创脉医疗科技(上海)有限公司
Priority date: 2022-02-25
Filing date: 2023-02-15
Publication date: 2023-08-31
Also published as: CN116690963A

Abstract

The present application relates to a preparation method for a heat-shrinkable tube. The preparation method comprises the following steps: heating a thermoplastic tube material to a high-elastic state for expansion, and then carrying out cooling molding to obtain a heat-shrinkable tube; and controlling a and b to meet the following condition: ab > 1, and controlling a pushed speed v' and a pulled speed v of the thermoplastic tube material during expansion to meet the following condition: Δs = v'/v - 1 > 1%, such that compared with the thermoplastic tube material, the prepared heat-shrinkable tube is radially expanded and axially contracted, wherein a is the ratio of the inner diameter of the heat-shrinkable tube after expansion to the inner diameter of the thermoplastic tube material before expansion, b is the ratio of the wall thickness of the heat-shrinkable tube after expansion to the wall thickness of the thermoplastic tube material before expansion, and Δs is the difference rate of a pulling speed during expansion.

Description

Preparation method of heat shrinkable tube

This application claims the priority of the Chinese patent application submitted to the China Patent Office on February 25, 2022, with the application number 2022101820604 and the title of the invention "Preparation method of heat-shrinkable tube", the entire content of which is incorporated in this application by reference.

technical field

The present application relates to the technical field of medical devices, in particular to a method for preparing a heat-shrinkable tube.

Background technique

The thermoplastic material used in the heat-shrinkable tube is glassy at room temperature, and becomes highly elastic after heating. It has the functions of high-temperature shrinkage, softness, flame retardancy, insulation and corrosion resistance, and is coated on wires and cables, electronic components, assembled medical accessories, etc. It has a wide range of applications in industrial, electronic, medical and other fields on the parts that need to be protected.

In the production process of the traditional heat shrinkable tube, the thermoplastic tube is heated to a high elastic state, a load is applied to cause it to expand radially, and it is rapidly cooled while maintaining the radially expanded state, so that it enters a glass state. Heat the heat-shrinkable tube during use, and the material of the heat-shrinkable tube becomes highly elastic when heated. At this time, no load is applied, and the heat-shrinkable tube shrinks radially, and it is tightly covered by the radial shrinkage of the heat-shrinkable tube. protected parts.

However, during the application process, the heat-shrinkable tube will not only shrink in the radial direction after being heated, but also change in length in the axial direction in most cases, for example, shrink in the axial direction and become shorter. Heat shrink tubing that shrinks and shortens when exposed to heat can cause various problems. For example, if the heat-shrinkable tube is wrinkled during the process of shrinking and shortening, it will cause defects such as surface undulations and protrusions; the wrinkle of the heat-shrinkable tube may even cause the surface of the material covered by it to wrinkle, reducing the coverage. The flatness of the surface of the covered material increases the difficulty of rework. In addition, parts that are originally covered by heat shrink tubing may be damaged by The shrinkage of the heat-shrinkable tube shortens and exposes to the heat source, resulting in melting and deformation of some exposed parts. In order to avoid the defects caused by the shrinkage and shortening of the heat-shrinkable tube after being heated, sometimes the heat-shrinkable tube is stretched while heating to prevent its axial length from shrinking and shortening after being heated. However, this method is easy to stretch and deform the heat-shrinkable tube, and even damage the material of the component covered by the heat-shrinkable tube.

Contents of the invention

Based on this, the application provides a kind of preparation method of heat-shrinkable tubing, comprises the steps:

Heat the thermoplastic tubing to a high elastic state for expansion, then cool and form it to make a heat-shrinkable tubing;

Control a and b to meet the following conditions: ab>1, and control the pushed speed v' and drawn speed v of the thermoplastic pipe during the expansion to meet the following conditions: Δs=v'/v-1>1%, Compared with the thermoplastic tubing, the prepared heat-shrinkable tube expands radially and shrinks axially;

Wherein, a is the ratio of the inner diameter of the heat-shrinkable tube after expansion to the inner diameter of the thermoplastic tube before expansion, b is the ratio of the wall thickness of the heat-shrinkable tube after expansion to the wall thickness of the thermoplastic tube before expansion, Δs is the traction speed difference rate during expansion.

In some of these embodiments, control a and b meet the following conditions:

Wherein, d is the original inner diameter of the thermoplastic pipe before expansion, and w is the original wall thickness of the thermoplastic pipe before expansion.

In some of these embodiments, the ratio of the inner diameter of the heat-shrinkable tube after expansion to the inner diameter of the thermoplastic tubing before expansion is greater than or equal to 1.2; and/or,

When the material of the heat-shrinkable tube is selected from aromatic polyetherketone, a≤1.5; when the material of the heat-shrinkable tube is selected from fluoroplastics, a≤4.0; when the material of the heat-shrinkable tube is selected from polyether When the material of the heat-shrinkable tube is selected from polyolefin, a≤7.5; when the material of the heat-shrinkable tube is selected from polyolefin, a≤10.

In some of these embodiments, the expanding is performed in a mould;

The mold is an inner support mold, and the material of the thermoplastic pipe, the outer diameter of the inner support mold and the inner diameter of the thermoplastic pipe are controlled to control a and b to meet the conditions;

Alternatively, the mold is an external support mold, and the material of the thermoplastic pipe, the inner diameter of the outer support mold and the outer diameter of the thermoplastic pipe are controlled to control a and b to meet the conditions.

In some of the embodiments, a fluid is filled between the thermoplastic pipe and the mold during the expansion, and the fluid is an inert gas or a lubricating liquid.

In some of the embodiments, the kinematic viscosity of the fluid at 40°C is ≥17 mm ² /s.

In some of these embodiments, the traction speed difference rate Δs>4.5% is controlled during the expansion.

In some of these embodiments, the traction speed difference rate Δs>10% is controlled during the expansion.

In some of these embodiments, the traction speed difference rate Δs≤e/(e+1) received during the expansion is controlled;

in,

d is the inner diameter of the thermoplastic pipe before expansion, w is the wall thickness of the thermoplastic pipe before expansion, and e is the axial length change rate of the heat-shrinkable tube before and after shrinking in use.

In some of these embodiments, the cooling rate of the cooling forming is ≤60°C/s.

In some of these embodiments, the cooling rate of the cooling forming is <3°C/s.

The details of one or more embodiments of the application are set forth in the description below. Other features, objects and advantages of the application will be apparent from the description and claims.

Detailed ways

In order to facilitate the understanding of the present application, the following will describe the present application more fully and give preferred embodiments of the present application. However, the present application can be embodied in many different forms and is not limited to the embodiments described herein. It should be understood that the purpose of providing these examples is to make the disclosure of the application The understanding of open content is more thorough and comprehensive.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used herein in the specification of the application are only for the purpose of describing specific embodiments, and are not intended to limit the application.

Aiming at the above-mentioned technical problems in the application process of the heat-shrinkable tube that shrinks axially and shortens after being heated, the traditional solution is to stretch the heat-shrinkable tube while heating to prevent its axial length from shrinking and shortening after being heated. However, this method is easy to stretch and deform the heat-shrinkable tube, and even damage the material of the component covered by the heat-shrinkable tube. This method can only be performed by operators with high technique skills, which requires extremely high personnel. Based on a large amount of research, the technicians of the present application deeply analyzed the preparation principle of the heat-shrinkable tube, and proposed a preparation method of the heat-shrinkable tube that can be stretched axially after being heated during use.

The traditional method of preparing heat-shrinkable tubing is to heat the thermoplastic tubing to a temperature lower than the melting point of the thermoplastic polymer tubing and higher than its glass transition temperature to form a high elastic state, apply a load to the tubing to radially expand the tubing, and make the The tube cools below its glass transition temperature in the radially expanded state, entering the glassy state. So far, the heat-shrinkable tube has been made. According to the analysis of the skilled person of the present application, the essence of the preparation method of the heat-shrinkable tube is to store the radial expansion stress applied to the tube in its polymer chain. And the pipe shrinks again when it is heated again, because this stress is released when the pipe is heated again, causing the pipe to shrink radially. In fact, the heat-shrinkable tube not only shrinks radially after being heated, but also changes in length in the axial direction in most cases, including axial shrinkage shortening or axial elongation. Compared with the heat-shrinkable tube that shrinks in the axial direction after being heated during use, the heat-shrinkable tube that is stretched in the axial direction after being heated during use is a more economical and convenient choice. The technicians of the present application proposed an innovation of the preparation process. If according to similar principles, the radial expansion and axial shortening of the pipe can be realized through the production process of the heat shrinkable tube, then the stress of radial expansion and the stress of axial extrusion Stress can be simultaneously stored in its polymer chains. These stresses are released when the tube is reheated, causing simultaneous radial contraction and axial elongation of the tube.

In order to realize the axial shortening of the tube in the manufacturing process of the heat-shrinkable tube, it is first necessary to design a suitable tube size. Set the length of the tubing before it is made into a heat-shrinkable tube (that is, before expansion) as L, and the inner diameter as d, The wall thickness is w in the same unit. If the inner diameter expansion ratio in the expansion process is set as a, and the wall thickness thinning ratio is set as b, that is, the pipe with the original inner diameter d, the original wall thickness w, and the original length L becomes the inner diameter ad after expansion. , a heat-shrinkable tube with a wall thickness of bw and a length of L'. In other words, the expansion ratio of the inner diameter is the ratio of the inner diameter of the heat-shrinkable tube to the inner diameter of the thermoplastic tube; the ratio of wall thickness thinning is the ratio of the wall thickness of the heat-shrinkable tube to the wall thickness of the thermoplastic tube.

However, the heat-shrinkable tube shrinks after being heated during use, and returns to the heat-shrinkable tube with a length of L, an inner diameter of d, and a wall thickness of w, which is the same as the state before expansion. The length, inner diameter and wall thickness of the tubing in three states before expansion, after expansion and after contraction are shown in Table 1 below. Among them, the original pipe material before the heat-shrinkable pipe is made before expansion, the pipe formed after the heat-shrinkable pipe is made after expansion, and the heat-shrinkable pipe after shrinkage is used.

Table 1

After expansion, the molecular chain segments of the pipe material move, and the pipe shows a large deformation in a certain dimension, but the whole expansion process does not involve the crosslinking and polymerization of the pipe material, which affects the density of the polymer material of the pipe. , In addition, the length, inner diameter and wall thickness in Table 1 are all parameters at room temperature, and there is no process of temperature affecting the density of polymer materials. Therefore, the change in density of the tubing material before and after expansion is small and negligible in this system. Therefore, according to the conservation of mass, we know that:
[(d+2w) ² -d ² ]·L＝[(ad+2bw) ² -(ad) ² )]·L' (1)

The change rate of the axial length of the heat-shrinkable tube before and after expansion is the ratio of the length L' after expansion to the length L before expansion minus 1. If the manufacturing process of the heat-shrinkable tube realizes the axial shortening of the tube, that is, the rate of change of the axial length of the heat-shrinkable tube before and after expansion is <0. In other words, it is necessary to make: the change rate of the axial length of the heat-shrinkable tube before and after use > 0, where the change rate of the axial length of the heat-shrinkable tube before and after use is the length of the heat-shrinkable tube after shrinkage The ratio of the degree L to the length L' of the heat shrinkable tube before use (that is, after expansion) minus 1. If the change rate of the axial length of the heat shrinkable tube before and after use is e, then
e=L/L'-1 (2)

According to the above formula (1) and formula (2), it can be known that the following formula (3):

To realize that when the heat-shrinkable tube is heated, the tube will elongate in the axial direction, then e>0 is a necessary condition. The condition for making e>0 is the following formula (4):

Since the original inner diameter d and original wall thickness w of the tube before expansion are positive numbers, that is, w/d>0; and because the wall thickness thinning ratio b<1, the axial length change rate e of the heat shrinkable tube before and after use is realized. The necessary condition for >0 is: ab>1. That is, the product of the inner diameter expansion ratio a and the wall thickness thinning ratio b>1 is controlled.

In order to ensure that the heat shrinkable tube can be easily sleeved outside other objects, usually a≥1.2. On this basis, according to the above analysis, the larger the inner diameter or outer diameter of the mold used for expansion, the larger a is. However, according to the mechanical properties of the thermoplastic material of the pipe, the value of a has an upper limit: for example, a of aromatic polyetherketone heat shrinkable tube is usually ≤1.5, a of fluoroplastic heat shrinkable tube is usually ≤4.0, and a of polyester heat shrinkable tube Usually ≤7.5, a of polyolefin heat shrink tube is usually ≤10.

On the basis of determining the material of the thermoplastic pipe, the upper limit of the inner diameter expansion ratio a is determined. Within this upper limit, select a mold of appropriate size. When the inner diameter and outer diameter of the thermoplastic tubing are determined, the inner diameter expansion ratio a can be determined by the mold size control of the heat-shrinkable tubing manufacturing process, because the manufacturing process of the heat-shrinkable tubing usually uses an inner support mold with a fixed outer diameter to move the tubing from the inside Stretch to fix the inner diameter of the tube after expansion; or use an outer support mold with a fixed inner diameter to wrap the outside of the tube to fix the outer diameter of the tube after expansion.

For the inner support mold, the outer diameter of the inner support mold is larger than the inner diameter of the thermoplastic pipe, the outer diameter of the inner support mold is the inner diameter of the expanded thermoplastic pipe, and the ratio of the outer diameter of the inner support mold to the inner diameter of the thermoplastic pipe is the inner diameter. Support the preset inner diameter expansion ratio of the mold.

For the outer support mold, the inner diameter of the outer support mold is larger than the outer diameter of the thermoplastic pipe, and the outer support mold The inner diameter of the support mold is the expanded outer diameter of the thermoplastic pipe, and the preset inner diameter expansion ratio of the outer support mold can be more accurately estimated through the inner diameter of the outer support mold and the inner diameter and wall thickness of the thermoplastic pipe.

In summary, the inner diameter expansion ratio a is determined by the outer diameter of the inner support mold and the inner diameter of the thermoplastic pipe, or by the inner diameter of the outer support mold and the inner diameter and wall thickness of the thermoplastic pipe.

The wall thickness thinning ratio b can usually be controlled and determined by the internal diameter expansion ratio a and the material of the thermoplastic pipe. Generally, the larger the upper limit value of a of the heat-shrinkable tube material, or the larger a obtained during expansion, the smaller b is. For example, the upper limit of a for fluoroplastic heat shrinkable tubes is 4.0, while b is usually in the range of 0.25 to 0.85; while the upper limit of a for polyester heat shrinkable tubes is 7.5, and b is usually in the range of 0.02 to 0.2 . Therefore, by adopting a suitable size mold and selecting the material of the thermoplastic pipe, the production process of the heat shrinkable pipe can theoretically shorten the axial direction of the pipe, and produce a heat shrinkable pipe with an axial length change rate of more than 0% after complete shrinkage. shrink tube.

When the material of the thermoplastic pipe is determined, the mold is an inner support mold, and the material of the thermoplastic pipe, the outer diameter of the inner support mold and the inner diameter of the thermoplastic pipe can be controlled to control a and b to meet the above conditions.

When the material of the thermoplastic pipe is determined, the mold is an external support mold, and the material of the thermoplastic pipe, the inner diameter of the outer support mold, and the inner diameter and wall thickness of the thermoplastic pipe are controlled to control a and b to meet the above conditions.

Furthermore, in order to realize the axial shortening of the pipe in the manufacturing process of the heat-shrinkable tube, in addition to promoting the axial shortening of the pipe itself in the manufacturing process through the above-mentioned suitable size mold and the selection of thermoplastic tubing materials, it is also necessary to carry out the production process. The control is mainly to prevent the axial stretch introduced by the process from offsetting the axial shortening of the pipe itself.

On this basis, combined with the actual situation, in order to mass-produce heat-shrinkable tubes in a limited space, relative movement between the tube and the mold is inevitable during expansion. During this movement, the axial traction force on the pipe will cause the pipe to be stretched in the axial direction, offsetting its own tendency to shorten in the axial direction. In order to avoid such process-induced axial stretching, the pushing speed v' of the thermoplastic pipe can be controlled to be greater than the pulling speed v. If the traction speed difference rate Δs is used to quantify the axial The degree of stretching, where the traction speed difference rate Δs=v'/v-1, has been verified by experiments, and it is necessary to control the pushed speed v' and the drawn speed v of the thermoplastic pipe during expansion to meet the following conditions: Δs=v'/ v-1>1%.

Among them, Δs is the traction speed difference rate.

The preparation method of the above-mentioned heat-shrinkable tube satisfies specific conditions by controlling the ratio a of the inner diameter of the heat-shrinkable tube to the inner diameter of the thermoplastic tube, and the ratio b of the wall thickness of the heat-shrinkable tube to the wall thickness of the thermoplastic tube, and at the same time controls the expansion time The traction speed difference rate Δs satisfies certain conditions, which can make the heat shrinkable tube radially expand and axially shrink compared with the thermoplastic tube. In this way, the heat-shrinkable tube can achieve axial elongation while shrinking radially after being heated and completely shrunk again. The above preparation method provides a brand-new preparation method for the heat-shrinkable tube that can be extended axially after being heated during use, and the prepared heat-shrinkable tube has broad application prospects.

In order to avoid the deviation between theory and practice, as far as possible to ensure the axial length change rate of the heat-shrinkable tube after it is completely shrunk, that is, the axial length change rate of the heat-shrinkable tube before and after shrinking in the use state is e>0, and the theoretical value of e> can be specified> 5%. According to the above formula (1), the pipe size design of the heat shrinkable tube needs to control a and b to meet the following conditions:

Among them, the original inner diameter d and the original wall thickness w of the pipe can be determined by the previous process before the production of the heat-shrinkable tube starts. Therefore, in one embodiment, combining the original internal diameter d of the pipe material, the original wall thickness w, and adopting a suitable size mold and the material selection of the thermoplastic pipe material, so that controlling a and b satisfy the above formula (5), can help improve the obtained The change rate e of the axial length of the heat-shrinkable tube before and after shrinking in the state of use. Specifically, before the finished heat-shrinkable tube is produced, the values of a, b, d, and w are obtained through the design of the size and material of the thermoplastic tube, and the selection of the expansion die, and the e is calculated in advance according to formula (3). theoretical value. Considering that there may be a deviation between the theoretical value and the actual value, a margin must be left for the value of e, so the combination selection of the values of a, b, d, and w must satisfy the formula (5). In the actual production process, the actual value of e is as close as possible to the theoretical value through the regulation of process parameters.

It can be understood that the tube needs to be heated during the preparation process of the heat-shrinkable tube, so the selected mold is a mold with a heating function, which is called a heating mold. During the expansion process, the tube and mold will not Relative motion inevitably occurs. During this movement, the friction between the tube and the heated die also causes the tube to be stretched axially, counteracting its own tendency to axially shorten. In order to avoid this kind of axial stretching introduced by the process, the method of filling fluid between the pipe and the heating mold can be used to lubricate to reduce the above-mentioned frictional force. Further, the above fluid is an inert gas or a lubricating liquid; further, the lubricating liquid is preferably a high temperature resistant lubricating liquid.

At present, there is no direct way to quantify the friction force, but the kinematic viscosity of the fluid (fluid refers to the general term for gas and liquid) between the pipe and the mold can be used to indirectly quantify the friction force. In one embodiment, the range of controlling the kinematic viscosity of the fluid between the pipe and the mold is ≥17 mm ² /s (40° C.).

In some of these embodiments, the traction speed difference rate Δs>4.5% is controlled, and in one embodiment, when the traction speed difference rate is controlled to be >10%, the manufacturing process of the heat-shrinkable tube can better realize the expansion of the tube. Axial shortening, and a heat-shrinkable tube with an axial length change rate of more than 0% after complete shrinkage is produced.

Furthermore, there is an upper limit for Δs, otherwise, when the pipe is pushed at a speed v' too fast but pulled at a speed v too slow, the pipe will accumulate at the mold and easily disrupt the continuity of production. This phenomenon is called " stack pipe". In order to avoid "pipe stacking", it is required that during the entire expansion process of the pipe, the amount of accumulation caused by the difference between the pushing and pulling speeds cannot exceed the shortening of the pipe itself, that is, the following conditions are met:
v't-vt≤L-L' (6)

Among them, t is the total time of the tube expansion process, that is, L/v. Substituting the relationship of t=L/v into the above formula (6) can get: v'L/v-L≤L-L';

Namely: v'/v-1≤1-L'/L.

According to the previous formula (2) e=L/L'-1, the following formula is obtained:
Δs=v'/v-1≤e/(e+1) (7)

According to the previous formula (3), where:

In some of these embodiments, the cooling rate of cooling molding is ≤60°C/s, such as 60°C/s, 59°C/s, 58°C/s, 57°C/s, 56°C/s, 55°C/s, 50°C/s, 40°C/s, 30°C/s, 20°C/s, 18°C/s, 16°C/s, 14°C/s, 12°C/s, 10°C/s, 8°C/s, 6°C/s, 5°C/s, 4.5°C/s, 4°C/s, 3°C/s, 2°C/s, 1°C/s. Further, as an optional condition to promote the heat-shrinkable tube to store the axial extrusion stress, so that the preparation process of the heat-shrinkable tube can achieve a better axial shrinkage effect, after the heat-shrinkable tube is formed, the cooling rate dT can be set to <3 Slowly cool at a rate of ℃/s to prevent excessive cooling, resulting in the stress of axial extrusion not being well stored by the heat-shrinkable tube, and avoiding that the axial length change rate of the heat-shrinkable tube is lower than the expected level after the heat-shrinkable tube is completely shrunk.

In order to make the purpose, technical solutions and advantages of the present application more concise and clear, the present application is described with the following specific examples, but the present application is by no means limited to these examples. The embodiments described below are only preferred embodiments of the present application, which can be used to describe the present application, and should not be construed as limiting the scope of the present application. It should be noted that any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included within the protection scope of the present application.

In order to better illustrate the present application, the content of the present application will be further described below in conjunction with the embodiments. The following are specific examples.

It should be noted that the preparation of the heat-shrinkable tubes of the following comparative examples and embodiments are all carried out in the external support mold, and the expected value of the external support mold can be estimated more accurately by the inner diameter of the outer support mold and the inner diameter and wall thickness of the thermoplastic pipe. Set the inner diameter expansion ratio a.

Comparative example 1:

Using an external support mold with an inner diameter of 8.5 mm, a polyester pipe with an original inner diameter of 5.08 mm and an original wall thickness of 0.32 mm was expanded to a hot tubing with an inner diameter of 8.35 mm (a=1.64) and a wall thickness of 0.05 mm (b=0.16). shrink tube.

Among them, the expansion temperature used is 130°C, the traction speed difference rate Δs is 0.0%, and the cooling rate dT for cooling and forming after expansion is 2.4°C/s.

After the prepared heat-shrinkable tube was heated at a temperature of 240° C., the average axial length change rate ē after complete shrinkage was -82.6%.

Example 1:

Using an external support mold with an inner diameter of 8.5mm, expand the fluororesin tubing with an original inner diameter of 5.08mm and an original wall thickness of 0.32mm to a heat pipe with an inner diameter of 7.95mm (a=1.56) and a wall thickness of 0.23mm (b=0.72). shrink tube.

Among them, the expansion temperature used in the process is 180°C, the traction speed difference rate Δs is 1.2%, and the cooling rate dT for cooling and forming after expansion is 2.4°C/s.

After the prepared heat-shrinkable tube was heated at a temperature of 240°C, the average axial length change rate ē was 2.3% after complete shrinkage.

Example 2:

Embodiment 2 is basically the same as Embodiment 1, except that the cooling rate dT used in the process of Embodiment 2 is 56.7° C./s.

After the prepared heat-shrinkable tube was heated at a temperature of 240° C., the average axial length change rate ē was 0.7% after complete shrinkage.

Example 3:

Using an external support mold with an inner diameter of 5.9mm, expand a fluororesin pipe with an original inner diameter of 3.20mm and an original wall thickness of 0.38mm to a heat pipe with an inner diameter of 5.28mm (a=1.65) and a wall thickness of 0.29mm (b=0.76). shrink tube.

Among them, the expansion temperature used in the process is 180°C, and the traction speed difference rate Δs is 6.4%; the cooling rate dT for cooling and forming after expansion is 56.7°C/s.

After the prepared heat-shrinkable tube was heated at a temperature of 240°C, the average axial length change rate ē was 5.2% after complete shrinkage.

Comparative example 2:

Comparative Example 2 is basically the same as Example 3, the only difference being that the traction speed difference rate Δs used in the process is 0.2%.

After the prepared heat-shrinkable tube is heated at a temperature of 240° C., the average value of the axial length change rate ē after complete shrinkage is -1.4%.

Example 4:

Using an external support mold with an inner diameter of 1.3mm, expand a fluororesin tube with an original inner diameter of 0.39mm and an original wall thickness of 0.32mm to a heat pipe with an inner diameter of 0.79mm (a=2.03) and a wall thickness of 0.25mm (b=0.78). shrink tube.

Among them, the expansion temperature used in the process is 180°C, the traction speed difference rate Δs is 11.1%, and the cooling rate dT for cooling and forming after expansion is 0.4°C/s.

After the prepared heat-shrinkable tube was heated at a temperature of 240° C., the average axial length change rate ē was 10.4% after complete shrinkage.

Example 5:

Embodiment 5 is basically the same as Embodiment 4, the only difference is that the traction speed difference rate Δs used in the process is 4.5%.

After the prepared heat-shrinkable tube was heated at a temperature of 240°C, the average axial length change rate ē was 3.8% after complete shrinkage.

Embodiment 6:

Using an external support mold with an inner diameter of 10.4mm, expand a fluororesin pipe with an original inner diameter of 5.50mm and an original wall thickness of 0.50mm to a heat pipe with an inner diameter of 9.73mm (a=1.77) and a wall thickness of 0.31mm (b=0.62). shrink tube.

Among them, the expansion temperature used in the process is 180°C, the traction speed difference rate Δs is 1.7%, and the cooling rate dT for cooling and forming after expansion is 6.0°C/s.

After the prepared heat-shrinkable tube is heated at a temperature of 240°C, the average axial length change rate ē after complete shrinkage is 0.1%, the maximum value in the test data is 0.4%, and the minimum value is -0.8%.

Partial parameters of each embodiment are as shown in table 2:

Wherein, the theoretical value of e refers to (abd+b ² w)/(d+w)-1.

Δs=Pushing speed of the pipe/pulling speed of the pipe-1.

The mean value of the axial length change rate ē refers to the average value of the length change rates measured by taking 10 parallel samples. The theoretical value of e and the mean ē are positive, indicating that the length change is an elongation trend; negative, indicating that A change in length is a contraction trend.

Table 2

It can be known from the above examples that, using the above preparation process, a heat-shrinkable tube that can be stretched in the axial direction after complete shrinkage can be produced, and the axial length change rate of the prepared heat-shrinkable tube after complete contraction The length change rate e is as high as 10.4%.

Comparative example 1 controls ab<1, the theoretical value of e is negative, and the average value ē of the actual heat-shrinkable tube is also negative, indicating that the heat-shrinkable tube is shortened axially after reheating and shrinking completely. . The reason is that the relationship of ab>1 is not satisfied, resulting in the shrinkage of the heat shrinkable tube product in the axial direction after complete shrinkage.

Comparative Example 2 is basically the same as Example 3. Although the controlled ab > 1, the traction speed difference rate Δs controlled in Comparative Example 2 is < 1%, and the theoretical value of e is positive. However, the actual heat shrinkable tube has a The mean value ē is a negative value, and the heat-shrinkable tube is shortened axially after reheating and shrinking completely.

From the comparison of Example 1 and Example 2, it can be seen that in Example 1, controlling the cooling rate of the cooling forming to be <3°C/s is beneficial to improve the axial length change rate of the obtained heat-shrinkable tube after complete shrinkage.

It can be seen from Examples 4 and 5 that, compared with Example 5, Example 4 controls the traction speed difference rate Δs>4.5%, which is beneficial to improve the axial length change rate of the prepared heat shrinkable tube after complete shrinkage.

The ab>1 controlled by embodiment 6, its e theoretical value is a positive value, and the average value of the heat-shrinkable tube actually made ē is also positive, but close to 0. The average value ē of the axial length change rate of the heat-shrinkable tube prepared in Example 6 before and after use is smaller than that of other examples. The reason is that because the relationship described in the previous formula (5) (ie the theoretical value of e > 5%) is not satisfied, the theoretical value of e in Example 6 is ≤ 5%, and the dimensional tolerances and processes of molds and pipes Parameter fluctuations and other reasons make the actual value of e deviate from the theoretical value.

The technical features of the above-mentioned embodiments can be combined arbitrarily. To make the description concise, all possible combinations of the technical features in the above-mentioned embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, should be considered as within the scope of this specification.

The above-mentioned embodiments only express several implementation modes of the present application, and the description thereof is relatively specific and detailed, but it should not be construed as limiting the scope of the patent for the invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the scope of protection of the patent application shall be based on the appended claims, and the description may be used to interpret the content of the claims.

Claims

A method for preparing a heat-shrinkable tube, comprising the steps of:

Heat the thermoplastic tubing to a high elastic state for expansion, then cool and form it to make a heat-shrinkable tubing;

Control a and b to meet the following conditions: ab>1, and control the pushed speed v' and drawn speed v of the thermoplastic pipe during the expansion to meet the following conditions: Δs=v'/v-1>1% , so that the prepared heat-shrinkable tube is radially expanded and axially contracted compared to the thermoplastic tube;

Wherein, a is the ratio of the inner diameter of the heat-shrinkable tube after expansion to the inner diameter of the thermoplastic tube before expansion, b is the ratio of the wall thickness of the heat-shrinkable tube after expansion to the wall thickness of the thermoplastic tube before expansion, Δs is the traction speed difference rate during expansion.
The preparation method of heat-shrinkable tube as claimed in claim 1, is characterized in that, control a and b meet the following conditions:

Wherein, d is the inner diameter of the thermoplastic pipe before expansion, and w is the wall thickness of the thermoplastic pipe before expansion.
The method for preparing a heat-shrinkable tube according to any one of claims 1 to 2, characterized in that the ratio of the inner diameter of the heat-shrinkable tube after expansion to the inner diameter of the thermoplastic tube before expansion is greater than or equal to 1.2; and/or ,

When the material of the heat-shrinkable tube is selected from aromatic polyetherketone, a≤1.5; when the material of the heat-shrinkable tube is selected from fluoroplastics, a≤4.0; when the material of the heat-shrinkable tube is selected from polyether When the material of the heat-shrinkable tube is selected from polyolefin, a≤7.5; when the material of the heat-shrinkable tube is selected from polyolefin, a≤10.
The method for preparing a heat-shrinkable tube according to any one of claims 1 to 3, wherein the expansion is performed in a mould;

The mold is an inner support mold, and the material of the thermoplastic pipe, the outer diameter of the inner support mold and the inner diameter of the thermoplastic pipe are controlled to control a and b to meet the conditions;

Alternatively, the mold is an external support mold, and the material of the thermoplastic pipe, the external branch The inner diameter of the mold and the outer diameter of the thermoplastic pipe are controlled to satisfy the conditions of a and b.
The method for preparing a heat-shrinkable tube according to claim 4, wherein a fluid is filled between the thermoplastic tube and the mold during the expansion, and the fluid is an inert gas or a lubricating liquid.
The method for preparing a heat-shrinkable tube according to claim 5, wherein the kinematic viscosity of the fluid at 40° C. is ≥17 mm 2 /s.
The method for preparing the heat-shrinkable tube according to any one of claims 1 to 6, characterized in that the traction speed difference rate Δs>4.5% is controlled during the expansion.
The manufacturing method of the heat-shrinkable tube according to claim 7, characterized in that the traction speed difference rate Δs>10% is controlled during the expansion.
The method for preparing a heat-shrinkable tube according to any one of claims 1 to 8, characterized in that the traction speed difference rate Δs≤e/(e+1) received during the expansion is controlled;

in,

d is the inner diameter of the thermoplastic pipe before expansion, w is the wall thickness of the thermoplastic pipe before expansion, and e is the axial length change rate of the heat-shrinkable tube before and after shrinking in use.
The method for preparing a heat-shrinkable tube according to any one of claims 1 to 9, characterized in that, the cooling rate of the cooling forming is ≤60°C/s.
The method for preparing the heat-shrinkable tube according to claim 10, characterized in that, the cooling rate of the cooling molding is <3°C/s.