Preparation method of heat shrink tubing

Abstract

The present invention relates to a method for preparing a heat shrinkable tube, comprising the following steps: heating a thermoplastic tube to a highly elastic state for expansion, cooling and forming the tube to obtain a heat shrinkable tube; controlling a and b to satisfy the following conditions: ab>1, and controlling the pushing speed v' and pulling speed v of the thermoplastic tube during the expansion to satisfy the following conditions: Δs=v' / v-1>1%, so that the obtained heat shrinkable tube expands radially and contracts axially 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, and Δs is the pulling speed difference rate during expansion. The above-mentioned preparation method provides a new preparation method for heat shrinkable tubes that can be axially extended after being heated during use, and the obtained heat shrinkable tubes have broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of medical devices, and in particular to a method for preparing a heat shrink tube. Background Art

[0002] The thermoplastic material used in heat shrink tubing is in a glassy state at room temperature and becomes highly elastic when heated. It has high-temperature shrinkage, softness, flame retardancy, insulation and corrosion resistance. It is coated on parts that need protection, such as wires and cables, electronic components, assembled medical accessories, etc., and has a wide range of applications in industrial, electronic, medical and other fields.

[0003] During the traditional heat shrink tubing production process, the thermoplastic tubing is heated to a highly elastic state, a load is applied to cause it to expand radially, and while maintaining this radial expansion, it is rapidly cooled to return to a glassy state. During use, the heat shrink tubing is heated, causing the material to return to a highly elastic state. At this point, without the application of a load, the tubing contracts radially, tightly wrapping the tubing around the component to be protected.

[0004] However, during application, heat shrink tubing not only shrinks radially after being heated, but also, in most cases, changes in length in the axial direction, such as shrinking and shortening in the axial direction. Heat shrink tubing that shrinks and shortens after being heated may cause various problems. For example, if wrinkles occur in the heat shrink tubing during the shrinking and shortening process, it will cause surface defects such as undulations and protrusions; the wrinkles of the heat shrink tubing may even cause wrinkles on the surface of the material it is wrapped with, reducing the flatness of the surface of the wrapped material and increasing the difficulty of rework. In addition, the components originally wrapped by the heat shrink tubing may be exposed to the heat source due to the shrinkage of the heat shrink tubing, causing the exposed parts to melt and deform. In order to avoid the defects caused by the shrinkage and shortening of the heat shrink tubing after being heated, the heat shrink tubing is sometimes stretched while being heated to prevent its axial length from shrinking and shortening after being heated. However, this method can easily cause the heat shrink tubing to stretch and deform, and even damage the material of the component wrapped by the heat shrink tubing. Summary of the Invention

[0005] Based on this, it is necessary to provide a method for preparing a heat shrinkable tube that can be axially extended after being heated during use.

[0006] The present invention is achieved through the following technical solutions.

[0007] The present invention provides a method for preparing a heat shrink tube, comprising the following steps:

[0008] Thermoplastic tubing is heated to a high elastic state for expansion, and then cooled and formed to produce a heat shrink tubing;

[0009] Controlling a and b to satisfy the following condition: ab>1, and controlling the pushing speed v' and the pulling speed v of the thermoplastic tube during the expansion to satisfy the following condition: Δs=v' / v-1>1%, so that the obtained heat shrinkable tube expands radially and contracts axially compared to the thermoplastic tube;

[0010] 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, and Δs is the pulling speed difference rate during expansion.

[0011] In some embodiments, controlling a and b satisfies the following conditions:

[0012]

[0013] 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.

[0014] In some embodiments, the expansion is performed in a mold;

[0015] 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;

[0016] Alternatively, the mold is an outer 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.

[0017] In some embodiments, the ratio a of the inner diameter of the heat shrink tube after expansion to the inner diameter of the thermoplastic tube before expansion is ≥ 1.2; and / or,

[0018] When the material of the heat shrinkable tube is selected from aromatic polyether ketone, a≤1.5; when the material of the heat shrinkable tube is selected from fluoroplastic, a≤4.0; when the material of the heat shrinkable tube is selected from polyester, a≤7.5; when the material of the heat shrinkable tube is selected from polyolefin, a≤10.

[0019] In some embodiments, 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.

[0020] In some embodiments, the kinematic viscosity of the fluid at 40°C is ≥17 mm 2 / s.

[0021] In some embodiments, the pulling speed difference rate Δs during the expansion is controlled to be greater than 4.5%.

[0022] In some embodiments, the pulling speed difference rate Δs during the expansion is controlled to be greater than 10%.

[0023] In some embodiments, the pulling speed difference rate Δs during the expansion is controlled to be ≤ e / (e+1); wherein,

[0024]

[0025] d is the inner diameter of the thermoplastic tube before expansion, w is the wall thickness of the thermoplastic tube before expansion, and e is the rate of change of the axial length of the heat shrinkable tube before and after shrinkage in use.

[0026] In some embodiments, the cooling rate of the cooling forming is ≤60°C / s.

[0027] In some embodiments, the cooling rate of the cooling forming is less than 3°C / s.

[0028] The above-mentioned method for preparing heat-shrink tubing, by controlling the ratio a of the inner diameter of the heat-shrink tubing to the inner diameter of the thermoplastic tubing, and the ratio b of the wall thickness of the heat-shrink tubing to the wall thickness of the thermoplastic tubing to meet specific conditions, and simultaneously controlling the pulling speed difference rate Δs during expansion to meet specific conditions, can ensure that the resulting heat-shrink tubing expands radially and contracts axially, compared to the thermoplastic tubing. In this way, after the heat-shrink tubing is heated again and fully contracted, it can simultaneously expand axially while contracting radially. This preparation method provides a novel method for preparing heat-shrink tubing that can expand axially upon heating during use, and the resulting heat-shrink tubing has broad application prospects. DETAILED DESCRIPTION

[0029] To facilitate understanding of the present invention, the present invention will be described more fully below, along with preferred embodiments thereof. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. It should be understood that these embodiments are provided for the purpose of providing a more thorough and comprehensive understanding of the disclosure of the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0032] In response to the above-mentioned technical problem of heat shrink tubing shrinking axially and shortening after being heated, the traditional solution is to stretch the heat shrink tubing while heating to prevent its axial length from shrinking and shortening after being heated. However, this method can easily cause the heat shrink tubing to stretch and deform, and even damage the material of the component covered by the heat shrink tubing. This method can only be performed by operators with high technical skills, and the requirements for personnel are extremely high. Based on extensive research and in-depth analysis of the preparation principle of heat shrink tubing, the technical personnel of the present invention have proposed a method for preparing a heat shrink tubing that can be axially extended after being heated during use.

[0033] The traditional method for producing heat-shrink tubing involves heating a thermoplastic tubing to a temperature below the melting point of the thermoplastic polymer and above its glass transition temperature, forming a highly elastic state. A load is then applied to the tubing, causing it to expand radially. The tubing, while still in the radially expanded state, is then cooled to below its glass transition temperature, returning to a glassy state. The heat-shrink tubing is now complete. The inventors of this invention have analyzed that the essence of this method is to store the stress caused by the radial expansion of the tubing within its polymer chains. The tubing shrinks and shortens upon further heating because this stress is released upon further heating, causing the tubing to contract radially. In fact, heat-shrink tubing not only shrinks radially upon heating, but also, in most cases, changes in length axially, either shrinking or elongating. Compared to heat-shrink tubing that shrinks axially upon heating, heat-shrink tubing that elongates axially upon heating is a more economical and convenient option. The inventors of this invention have proposed an innovative manufacturing process. Based on a similar principle, if the manufacturing process of heat shrink tubing can achieve radial expansion and axial contraction of the tubing, the stress from radial expansion and axial compression can be stored simultaneously within the polymer chains. These stresses are released when the tubing is heated again, causing the tubing to simultaneously contract radially and extend axially.

[0034] In order to achieve axial shortening of the heat shrink tubing during its manufacturing process, it is first necessary to design the appropriate tubing dimensions. The length of the tubing before it is made into a heat shrink tubing (i.e., before expansion) is set to L, the inner diameter to d, and the wall thickness to w, all in the same units. If the inner diameter expansion ratio during the expansion process is set to a, and the wall thickness thinning ratio is set to b, then a tubing with an original inner diameter of d, an original wall thickness of w, and an original length of L, after expansion, becomes a heat shrink tubing with an inner diameter of ad, a wall thickness of bw, and a length of L'. In other words, the inner diameter expansion ratio is the ratio of the inner diameter of the heat shrink tubing to the inner diameter of the thermoplastic tubing; the wall thickness thinning ratio is the ratio of the wall thickness of the heat shrink tubing to the wall thickness of the thermoplastic tubing.

[0035] During use, the heat-shrink tubing shrinks after being heated, returning to its original length L, inner diameter d, and wall thickness w, the same as before expansion. The length, inner diameter, and wall thickness of the tubing before, after, and after contraction are shown in Table 1. "Before expansion" refers to the original tubing before production, "after expansion" refers to the tubing formed after production, and "after contraction" refers to the tubing after contraction.

[0036] Table 1

[0037] state length inner diameter wall thickness Before expansion L d w After expansion L’ ad bw After contraction L d w

[0038] After expansion, the molecular chains of the tubing material shift, and the tubing exhibits significant deformation in a certain dimension. However, the entire expansion process does not involve crosslinking or polymerization, which would affect the density of the tubing's polymer material. Furthermore, the length, inner diameter, and wall thickness listed in Table 1 are all room temperature parameters, and there is no temperature-dependent effect on polymer density. Therefore, the change in the tubing's density before and after expansion is minimal and can be ignored in this system. Therefore, according to the law of conservation of mass, we can conclude that:

[0039] [(d+2w) 2 -d 2 ]·L=[(ad+2bw) 2 -(ad) 2 )]·L' (1)

[0040] The axial length change rate of the heat shrink 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 shrink tube is to achieve axial shortening of the tube, that is: the axial length change rate of the heat shrink tube before and after expansion is less than 0. In other words, it is necessary to make the axial length change rate of the heat shrink tube before and after use greater than 0, wherein the axial length change rate of the heat shrink tube before and after use is the ratio of the length L of the heat shrink tube after shrinkage to the length L' of the heat shrink tube before use (i.e. after expansion) minus 1. If the axial length change rate of the heat shrink tube before and after use is e, then

[0041] e=L / L'-1 (2)

[0042] According to the above formula (1) and formula (2), we can get the following formula (3):

[0043]

[0044] If the heat shrink tubing is to be heated and the tubing is to undergo axial elongation, then e>0 is a necessary condition. The condition for e>0 is as follows (4):

[0045]

[0046] Because the original inner diameter d and wall thickness w of the tubing before expansion are both positive numbers, i.e., w / d > 0, and the wall thickness thinning ratio b < 1, the necessary condition for achieving a heat shrink tubing axial length change rate e > 0 before and after use is: ab > 1. In other words, the product of the inner diameter expansion ratio a and the wall thickness thinning ratio b must be greater than 1.

[0047] To ensure that heat shrink tubing can be easily slipped over other objects during use, a is typically ≥ 1.2. Based on this analysis, the larger the inner or outer diameter of the mold used for expansion, the larger a becomes. However, due to the mechanical properties of the thermoplastic material used for the tubing, a has an upper limit: for example, a for aromatic polyetherketone heat shrink tubing is typically ≤ 1.5, for fluoroplastic heat shrink tubing is typically ≤ 4.0, for polyester heat shrink tubing is typically ≤ 7.5, and for polyolefin heat shrink tubing is typically ≤ 10.

[0048] Based on the material of the thermoplastic tubing, the upper limit of the inner diameter expansion ratio a is determined. Within this upper limit, a mold of appropriate size is selected. Given the inner and outer diameters of the thermoplastic tubing, the inner diameter expansion ratio a can be determined by controlling the mold dimensions during the heat shrink tubing manufacturing process. Heat shrink tubing manufacturing typically uses an inner support mold with a fixed outer diameter to expand the tubing from the inside, thereby fixing the expanded inner diameter; or an outer support mold with a fixed inner diameter is used to wrap around the tubing to fix the expanded outer diameter.

[0049] For the inner support mold, the outer diameter of the inner support mold is larger than the inner diameter of the thermoplastic tube. The outer diameter of the inner support mold is the inner diameter of the thermoplastic tube after expansion. The ratio of the outer diameter of the inner support mold to the inner diameter of the thermoplastic tube is the preset inner diameter expansion ratio of the inner support mold.

[0050] For the outer support mold, the inner diameter of the outer support mold is larger than the outer diameter of the thermoplastic pipe. The inner diameter of the outer support mold is the outer diameter of the thermoplastic pipe after expansion. The preset inner diameter expansion ratio of the outer support mold can be estimated more accurately by comparing the inner diameter of the outer support mold with the inner diameter and wall thickness of the thermoplastic pipe.

[0051] 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.

[0052] The wall thickness thinning ratio b is usually determined by the inner diameter expansion ratio a and the material of the thermoplastic tubing. Generally, the larger the upper limit of a for the heat shrink tubing material, or the larger the a achieved during expansion, the smaller b. For example, the upper limit of a for fluoroplastic heat shrink tubing 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 shrink tubing is 7.5, and b is usually in the range of 0.02 to 0.2. Therefore, by using a mold of appropriate size and selecting the material of the thermoplastic tubing, the manufacturing process of heat shrink tubing can theoretically achieve axial shortening of the tubing, producing a heat shrink tubing with an axial length change rate of more than 0% after complete shrinkage.

[0053] 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.

[0054] 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 external 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.

[0055] Furthermore, in order to achieve axial shortening of the tube in the manufacturing process of the heat shrink tubing, in addition to promoting the axial shortening of the tube itself during the manufacturing process through the above-mentioned selection of the appropriate size mold and the material of the thermoplastic tube, it is also necessary to control the manufacturing process, mainly to prevent the axial stretching introduced by the process from offsetting the axial shortening of the tube itself.

[0056] On this basis, and in light of practical circumstances, in order to mass-produce heat-shrink tubing within a limited space, relative movement between the tubing and the mold is unavoidable during expansion. During this movement, the axial pulling forces acting on the tubing, among other things, will cause the tubing to stretch axially, counteracting its inherent tendency to shorten axially. To avoid this process-induced axial stretching, the push velocity v' of the thermoplastic tubing can be controlled to be greater than the pull velocity v. If the pull velocity difference ratio Δs is used to quantify the degree of axial stretch experienced by the tubing, where the pull velocity difference ratio Δs = v' / v-1, experimental verification has shown that the push velocity v' and the pull velocity v of the thermoplastic tubing during expansion must satisfy the following condition: Δs = v' / v-1 > 1%.

[0057] Wherein, Δs is the traction speed difference rate.

[0058] The above-mentioned method for preparing heat-shrink tubing, by controlling the ratio a of the inner diameter of the heat-shrink tubing to the inner diameter of the thermoplastic tubing, and the ratio b of the wall thickness of the heat-shrink tubing to the wall thickness of the thermoplastic tubing to meet specific conditions, and simultaneously controlling the pulling speed difference rate Δs during expansion to meet specific conditions, can ensure that the resulting heat-shrink tubing expands radially and contracts axially, compared to the thermoplastic tubing. In this way, after the heat-shrink tubing is heated again and fully contracted, it can simultaneously expand axially while contracting radially. This method provides a novel method for preparing heat-shrink tubing that can expand axially upon heating during use, and the resulting heat-shrink tubing has broad application prospects.

[0059] To avoid deviations between theory and practice, the axial length change rate of the heat shrink tubing after complete shrinkage should be maintained as much as possible, that is, the axial length change rate of the heat shrink tubing before and after shrinkage in use should be greater than 0. The theoretical value of e can be set to be greater than 5%. According to the above formula (1), the design of the heat shrink tubing material size needs to control a and b to meet the following conditions:

[0060]

[0061] Among them, the original inner diameter d and the original wall thickness w of the tube can be determined by the previous process before the heat shrink tube is produced. Therefore, preferably, the original inner diameter d and the original wall thickness w of the tube are combined, and a mold of appropriate size and the material selection of the thermoplastic tube are used, so that a and b are controlled to meet the above formula (5), which can help improve the axial length change rate e of the heat shrink tube before and after shrinkage in the use state. Specifically, before the finished heat shrink tube is produced, the values ​​of a, b, d, and w are known through the design of the size and material of the thermoplastic tube and the selection of the expansion mold, and the theoretical value of e is calculated in advance according to formula (3). Considering that there may be deviations between the theoretical value and the actual value, the value of e needs to have a margin, so the combination of a, b, d, and w values ​​must meet formula (5). In the actual production process, the actual value of e is made as close to the theoretical value as possible through the regulation of process parameters.

[0062] It is understandable that the tube needs to be heated during the preparation of the heat shrink tubing, so the mold selected is a mold with a heating function, called a heating mold. During the expansion process, the tube and the mold will inevitably move relative to each other. During this movement, the friction between the tube and the heating mold will also cause the tube to be axially stretched, offsetting its own tendency to shorten axially. In order to avoid this type of axial stretching introduced by the process, a method of filling a fluid between the tube and the heating mold can be used to lubricate and reduce the above-mentioned friction. Furthermore, the above-mentioned fluid is an inert gas or a lubricating liquid; further, the lubricating liquid is preferably a high-temperature resistant lubricating liquid.

[0063] There is no direct way to quantify friction, but the kinematic viscosity of the fluid (fluid is a general term for gas and liquid) between the pipe and the mold can be used to indirectly quantify friction. Preferably, the kinematic viscosity of the fluid between the pipe and the mold is controlled to be ≥17mm 2 / s(40℃).

[0064] In some embodiments, when the pulling speed difference rate Δs is controlled to be greater than 4.5%, and more preferably greater than 10%, the manufacturing process of the heat shrinkable tube can better achieve axial shortening after the tube is expanded, and a heat shrinkable tube with an axial length change rate of more than 0% after complete contraction can be obtained.

[0065] Furthermore, there is an upper limit to Δs. Otherwise, if the pushing speed v' of the tube is too fast but the pulling speed v is too slow, the tube will accumulate at the die, easily disrupting the continuity of production. This phenomenon is called "tube pile-up." To avoid "tube pile-up," the amount of tube accumulation caused by the difference in pushing and pulling speeds must not exceed the amount of tube shortening during the entire expansion process. This means that the following conditions must be met:

[0066] v't-vt≤L-L' (6)

[0067] Where t is the total time of the tube expansion process, that is, L / v. Substituting the relationship t=L / v into the above formula (6), we can obtain: v'L / vL≤L-L';

[0068] That is: v' / v-1≤1-L' / L.

[0069] According to the above formula (2) e = L / L'-1, the following formula is obtained:

[0070] Δs=v' / v-1≤e / (e+1) (7)

[0071] According to the above formula (3), where:

[0072]

[0073] In some embodiments, the cooling rate of the cooling molding is ≤60℃ / s, for example, 60℃ / s, 59℃ / s, 58℃ / s, 57℃ / s, 56℃ / s, 55℃ / s, 50℃ / s, 40℃ / s, 30℃ / s, 20℃ / s, 18℃ / s, 16℃ / s, 14℃ / s, 12℃ / s, 10℃ / s, 8℃ / s, 6℃ / s, 5℃ / s, 4.5℃ / s, 4℃ / s, 3℃ / s, 2℃ / s, and 1℃ / s. Furthermore, as an optional condition for promoting the heat shrinkable tube to store 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 slowly cooled at a rate of <3℃ / s to prevent excessive cooling, which results in the axial extrusion stress not being well stored by the heat shrinkable tube, and avoids the axial length change rate of the heat shrinkable tube being lower than the expected level after it is fully shrunk.

[0074] In order to make the purpose, technical solutions and advantages of the present invention more concise and clear, the present invention is illustrated by the following specific embodiments, but the present invention is by no means limited to these embodiments. The embodiments described below are only preferred embodiments of the present invention and can be used to describe the present invention. They should not be understood as limiting the scope of the present invention. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0075] In order to better illustrate the present invention, the present invention is further described below with reference to the following embodiments.

[0076] It should be noted that the preparation of the heat shrinkable tubes in the following comparative examples and embodiments is carried out in an external support mold. The preset inner diameter expansion ratio a of the external support mold can be estimated more accurately by the inner diameter of the external support mold and the inner diameter and wall thickness of the thermoplastic tube.

[0077] Comparative Example 1:

[0078] Using an outer support die with an inner diameter of 8.5 mm, the polyester tube with an original inner diameter of 5.08 mm and an original wall thickness of 0.32 mm was expanded to a heat shrink tube with an inner diameter of 8.35 mm (a=1.64) and a wall thickness of 0.05 mm (b=0.16).

[0079] The expansion temperature used was 130° C., the pulling speed difference rate Δs was 0.0%, and the cooling rate dT of the cooling molding after expansion was 2.4° C. / s.

[0080] After the prepared heat shrinkable tube is heated at a temperature of 240° C. and then fully shrunk, the average axial length change rate ē is -82.6%.

[0081] Example 1:

[0082] Using an outer support die with an inner diameter of 8.5 mm, the fluororesin tube with an original inner diameter of 5.08 mm and an original wall thickness of 0.32 mm was expanded to a heat shrink tube with an inner diameter of 7.95 mm (a=1.56) and a wall thickness of 0.23 mm (b=0.72).

[0083] The expansion temperature used in the process is 180°C, the pulling speed difference rate Δs is 1.2%, and the cooling rate dT of the cooling molding after expansion is 2.4°C / s.

[0084] After the prepared heat shrinkable tube is heated at a temperature of 240° C. and then fully shrunk, the average axial length change rate ē is 2.3%.

[0085] Example 2:

[0086] Example 2 is substantially the same as Example 1, except that the cooling rate dT used in the process of Example 2 is 56.7° C. / s.

[0087] After the prepared heat shrinkable tube is heated at a temperature of 240° C. and then fully shrunk, the average axial length change rate ē is 0.7%.

[0088] Example 3:

[0089] Using an outer support die with an inner diameter of 5.9 mm, the fluororesin tube with an original inner diameter of 3.20 mm and an original wall thickness of 0.38 mm was expanded to a heat shrink tube with an inner diameter of 5.28 mm (a=1.65) and a wall thickness of 0.29 mm (b=0.76).

[0090] The expansion temperature used in the process is 180°C, the pulling speed difference rate Δs is 6.4%, and the cooling rate dT of the cooling molding after expansion is 56.7°C / s.

[0091] After the prepared heat shrinkable tube is heated at a temperature of 240° C. and then fully shrunk, the average axial length change rate ē is 5.2%.

[0092] Comparative Example 2:

[0093] Comparative Example 2 is substantially the same as Example 3, except that the pulling speed difference rate Δs used in the process is 0.2%.

[0094] After the prepared heat shrink tubing is heated at a temperature of 240° C. and then fully shrunk, the average axial length change rate ē is -1.4%.

[0095] Example 4:

[0096] Using an outer support die with an inner diameter of 1.3 mm, the fluororesin tube with an original inner diameter of 0.39 mm and an original wall thickness of 0.32 mm was expanded to a heat shrink tube with an inner diameter of 0.79 mm (a=2.03) and a wall thickness of 0.25 mm (b=0.78).

[0097] The expansion temperature used in the process is 180°C, the pulling speed difference rate Δs is 11.1%, and the cooling rate dT of the cooling molding after expansion is 0.4°C / s.

[0098] After the prepared heat shrinkable tube is heated at a temperature of 240° C. and then fully shrunk, the average axial length change rate ē is 10.4%.

[0099] Example 5:

[0100] Example 5 is basically the same as Example 4, with the only difference being that the pulling speed difference rate Δs used in the process is 4.5%.

[0101] After the prepared heat shrinkable tube is heated at a temperature of 240° C. and then fully shrunk, the average axial length change rate ē is 3.8%.

[0102] Example 6:

[0103] Using an outer support die with an inner diameter of 10.4 mm, the fluororesin tube with an original inner diameter of 5.50 mm and an original wall thickness of 0.50 mm was expanded to a heat shrink tube with an inner diameter of 9.73 mm (a=1.77) and a wall thickness of 0.31 mm (b=0.62).

[0104] The expansion temperature used in the process is 180° C., the pulling speed difference rate Δs is 1.7%, and the cooling rate dT of the cooling molding after expansion is 6.0° C. / s.

[0105] After the prepared heat shrink tubing is heated at 240°C and then fully shrunk, the average axial length change rate ē is 0.1%, the maximum value in the test data is 0.4%, and the minimum value is -0.8%.

[0106] Some parameters of each embodiment are shown in Table 2:

[0107] Among them, the theoretical value of e is (abd+b 2 w) / (d+w)-1.

[0108] Δs = pipe pushing speed / pipe pulling speed - 1.

[0109] The mean axial length change rate, ē, is the average of the length change rates measured for 10 parallel samples. Positive values ​​for the theoretical value of e and the mean ē indicate an elongational length change; negative values ​​indicate a contractional length change.

[0110] Table 2

[0111]

[0112] From the above embodiments, it can be seen that the above preparation process can be used to produce a heat shrinkable tube that is axially extended after complete shrinkage. The axial length change rate of the heat shrinkable tube after complete shrinkage, that is, the axial length change rate e of the heat shrinkable tube before and after use, is as high as 10.4%.

[0113] In Example 1, where ab<1, the theoretical value of e is negative, and the mean value ē of the heat shrink tubing produced is also negative, indicating that the heat shrink tubing is axially shortened after reheating and complete shrinkage. This is because the ab>1 relationship is not satisfied, resulting in axial shortening of the heat shrink tubing after complete shrinkage.

[0114] 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 less than 1%, and its theoretical value of e is positive. However, the average value ē of the heat shrinkable tube actually obtained is negative. After the heat shrinkable tube is heated again and completely shrunk, it is axially shortened.

[0115] From the comparison between Example 1 and Example 2, it can be seen that in Example 1, the cooling rate of the cooling molding is controlled to be less than 3° C. / s, which is beneficial to improving the axial length change rate of the obtained heat shrinkable tube after complete shrinkage.

[0116] It can be seen from Examples 4 and 5 that, compared with Example 5, Example 4 controls the pulling speed difference rate Δs>4.5%, which is beneficial to improving the axial length change rate of the heat shrinkable tube after it is fully shrunk.

[0117] In Example 6, ab>1 is controlled, and its theoretical value of e is positive. The mean value ē of the heat shrink tubing actually produced is also positive (but close to 0). The axial length change rate e of the heat shrink tubing produced in Example 6 before and after use is smaller than that of the other examples. The reason for this is that the relationship described in the above formula (5) (i.e., the theoretical value of e>5%) is not satisfied, and the theoretical value of e in Example 6 is ≤5%. The dimensional tolerances of the mold and the tubing, the fluctuations in the process parameters, and other reasons cause the actual value of e to deviate from the theoretical value.

[0118] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0119] The above-described embodiments merely represent several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the spirit of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be based on the appended claims, and the description may be used to interpret the content of the claims.

Claims

1. A method for preparing a heat shrink tube, characterized in that: The steps include: Thermoplastic tubing is heated to a high elastic state for expansion, and then cooled and formed to produce a heat shrink tubing; Controlling a and b to satisfy the following condition: ab>1, and controlling the pushing speed v' and the pulling speed v of the thermoplastic tube during the expansion to satisfy the following condition: Δs=v' / v-1>1%, so that the obtained heat shrinkable tube expands radially and contracts axially 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, and Δs is the pulling speed difference rate during expansion.

2. The method for preparing a heat shrinkable tube according to claim 1, wherein: Control a and b to 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.

3. The method for preparing a heat shrinkable tube according to any one of claims 1 to 2, wherein: The expansion is carried out in a mold; 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 outer 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.

4. The method for preparing a heat shrinkable tube according to any one of claims 1 to 2, wherein: The ratio a of the inner diameter of the heat shrink tube after expansion to the inner diameter of the thermoplastic tube before expansion is ≥ 1.2; and / or, When the material of the heat shrinkable tube is selected from aromatic polyether ketone, a≤1.5; when the material of the heat shrinkable tube is selected from fluoroplastic, a≤4.0; when the material of the heat shrinkable tube is selected from polyester, a≤7.5; when the material of the heat shrinkable tube is selected from polyolefin, a≤10.

5. The method for preparing a heat shrinkable tube according to claim 3, wherein: During the expansion, a fluid is filled between the thermoplastic tube and the mold, and the fluid is an inert gas or a lubricating liquid.

6. 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.

7. The method for preparing a heat shrinkable tube according to claim 1, wherein: The pulling speed difference rate Δs during the expansion is controlled to be greater than 4.5%.

8. The method for preparing a heat shrinkable tube according to claim 7, wherein: The pulling speed difference rate Δs during the expansion is controlled to be greater than 10%.

9. The method for preparing a heat shrinkable tube according to any one of claims 1 to 2 and 5 to 8, wherein: Controlling the pulling speed difference rate Δs during the expansion to be ≤ e / (e+1); in, d is the inner diameter of the thermoplastic tube before expansion, w is the wall thickness of the thermoplastic tube before expansion, and e is the rate of change of the axial length of the heat shrinkable tube before and after shrinkage in use.

10. The method for preparing a heat shrinkable tube according to any one of claims 1 to 2 and 5 to 8, wherein: The cooling rate of the cooling forming is ≤60°C / s.

11. The method for preparing a heat shrinkable tube according to claim 10, wherein: The cooling rate of the cooling molding is less than 3°C / s.

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