Heat-shrinkable tube

Heat shrinkable tube

The present invention relates to a thermoplastic polyester tube provided with heat shrinkability. In particular, it relates to a heat-shrinkable polyester tube suitable for use as an outer layer or coating of an electronic part or assembly including a capacitor such as an aluminum capacitor or a tantalum capacitor.

Currently, heat-shrinkable tubes made from polyvinyl chloride are widely used as outer layers or coatings for electronic parts such as capacitors. However, in the areas where the miniaturization and surface mounting of electronic parts such as capacitors have made great progress, the heat resistance of PVC pipes is not applicable.

For electronic parts such as heat-shrinkable tubes used in the outer layer of capacitors, the following properties are required.

(a) When an electronic component such as a capacitor is shrunk with a heat-shrinkable tube, the two open end portions (nozzle portion) of the tube are bent inward to cover the terminal surface of the electronic component. Each socket part must be evenly and tightly mounted on the terminal surface of the electronic component to present a good appearance. That is, it is undesirable that the inner edge of the nozzle portion of the inner bend of the shrinking tube becomes lumpy or warped like a horn, or the nozzle portion is curled and not tightly mounted on the terminal surface, so that it exhibits a poor appearance.

This state is illustrated by the figure. FIG. 1 illustrates the state in which the capacitor is shrunk with a heat-shrinkable tube, where the reference numeral 1 indicates the capacitor, and the numeral 2 indicates the cross-sectional part of the shrunk tube.

Figure 1 shows the condition of the tube with good finish, and Figures 2 to 4 show the condition of the tube with poor finish. In the case illustrated in Figure 1, the inner elbow portion of the shrinkable tube is uniformly attached to the terminal surface of the capacitor. However, in the situation illustrated in FIG. 2, the front edge of the mouth of the inner bend is raised like a horn. In some cases, not only the front edge, but also the entire nozzle part is tilted up. In the case illustrated in Fig. 3, the leading edge of the curved nozzle portion becomes larger. In the situation illustrated in Fig. 4, the inner curve of the curved nozzle is not close to the surface of the terminal. In conventional processing, such poor retouching is often seen.

(b) After being applied to electronic parts, the shrink tube undergoes heat treatment for thermal curing. It is expected that during this heat treatment, the tube will not crack or the tube will not shrink anymore.

(c) Even if the tube is kept at 125°C for 5000 hours, the color of the tube is only slightly faded.

In order to improve the heat resistance, it has been proposed to use thermoplastic polyester resin as the material of the heat-shrinkable tube (Japanese Laid-open Patent Nos. 32972/1974 and 100118/1980). However, this tube cannot fully meet the requirement (a), although it can meet the requirements (b) and (c) in the above requirements (a), (b) and (c). Therefore, it is desired to develop a thermoplastic polyester heat-shrinkable tube (hereinafter sometimes referred to as a heat-shrinkable tube) with these three necessary properties.

The inventors thoroughly studied to meet this requirement, and as a result, successfully demonstrated the heat-shrinkable polyester tube of the present invention having the necessity described in (a), (b) and (c) above.

Therefore, the present invention proposes a heat-shrinkable polyester tube, which is a tube that imparts heat-shrinkability by performing tubular stretching of an unstretched tube made of thermoplastic polyester resin, and has a heat shrinkability of not more than 20% Crystallinity and MD shrinkage greater than 5% and not greater than 26% and radial shrinkage (TD) at least 25%.

In the drawings; Figures 1 to 4 illustrate the state where the capacitor is covered with a heat-shrinkable tube. Figure 1 illustrates the state of good finish of the coating. However, Figures 2, 3 and 4 illustrate the poor finish of the cladding.

Fig. 5 illustrates the method of measuring the curvature of the heat-shrinkable tube of the present invention heated to a predetermined temperature.

Now, the present invention will be described in detail with reference to preferred examples.

The thermoplastic polyester resin constituting the tube of the present invention may be, in addition to polyethylene terephthalate containing terephthalic acid as an acid component and ethylene glycol as a glycol component, with a mixture in the main amount Dicarboxylic acids in terephthalic acid such as isophthalic acid are copolymers with acid components, or copolymers with polyethylene glycol mixed with ethylene glycol as glycol components, or blends of such polyesters And composition. An example of a preferable polyester resin that can be described is (1) 30 to 80% by weight of polyester copolymer, which includes 65 to 95% by weight of terephthalic acid and 5 to 35% by weight of isophthalic acid Formic acid is an acid component, ethylene glycol is a glycol component, and (2) a blended composition of 20 to 70% by weight of polyethylene terephthalate. The heat-shrinkable tube made from this polyester blend composition preferably has a crystallinity not higher than 12%. When the heat shrinkable tube contains (1) a mixture of polyethylene glycol and ethylene glycol as the glycol component, and terephthalic acid, or terephthalic acid and a small amount of isophthalic acid, as the acid component, (2) Polyester containing polyethylene terephthalate as the main component, such as terephthalic acid, or terephthalic acid and a small amount of isophthalic acid, which are acid components and ethylene When the diol is a glycol component polyester blending material, it is better to adjust the crystallinity to not higher than 20%.

In addition, when extremely high intrinsic viscosity (η), such as (η)>1 polyethylene terephthalate is used as the main component, the dimensional stability of the undrawn tube after extrusion can be improved. The advantage is that it can be easily manufactured.

In the resin material used in the tube of the present invention, organic lubricants or inorganic lubricants can be added to improve the sliding properties of the tube, and if necessary, additives such as stabilizers, colorants and antioxidants can be mixed.

Now, the method of making the tube of the present invention will be described. The above-mentioned polyester resin material is dried in a conventional method and subjected to tube extrusion to obtain an unstretched tube having a thickness of usually at most 300 μm. The unstretched tube is then stretched in the longitudinal direction (hereinafter referred to as MD) and radial direction (hereinafter referred to as TD). The stretching ratio is 1.01 to 1.4 times in MD, preferably 1.05 to 1.25 times, and TD is 1.3 to 2.2 times, preferably 1.4 to 2.0 times.

The stretching temperature is preferably low as long as thickness unevenness does not occur, and is usually preferably selected from 72 to 98°C.

The stretching method can be conventional tubular stretching, and the stretched tube can be wound to obtain a finished product.

The thickness of the resulting stretched tube is not particularly limited. However, as for the shrinkable tube used for electronic parts such as capacitors, a tube with a thickness of 30 to 200 µm, preferably 50 to 150 µm is generally used.

The shrinkage rate of the obtained shrinkable tube (measured at 98±2°C) is preferably more than 5% and not more than 26% in MD and at least 25% in TD.

If the shrinkage rate of MD is 5% or less, when the capacitor is covered with a heat-shrinkable tube, a gap will also be formed between the nozzle part of the shrinkable tube and the surface of the capacitor terminal. On the other hand, if it exceeds 26%, the longitudinal thermal shrinkage is so large that the coating is displaced or deformed. On the other hand, if the TD shrinkage rate is less than 25%, it is difficult to achieve the closeness of the heat shrinkable tube when the capacitor is thermally coated, and the coating is easy to loosen. Preferably, the MD shrinkage rate is not higher than 20%, and the TD shrinkage rate is at least 28%. The TD shrinkage rate is preferably set to be at least 15% larger than the MD shrinkage rate.

By performing tubular stretching under the above conditions and keeping the crystallinity of the stretched tube in the range of not more than 20%, the external finishing of electronic parts such as capacitors can be significantly improved (to obtain a defect-free finishing of the nozzle part after shrinking , As described in the necessity (a) of the heat-shrinkable tube), it cannot be achieved with the conventional heat-shrinkable tube.

The reason for this improvement is not fully understood. However, when comparing the degree of crystallinity or crystal distribution on the same peripheral plane, the shrinkage rate and degree of shrinkage in the heat shrinkage of the tube of the present invention are quite balanced. Therefore, it is believed that the reason for this improvement is that the shrinkage of the two nozzle parts of the tube is extremely uniform on the same peripheral plane.

In order to adjust the crystallinity of the stretched tube to not higher than 20%, the unstretched tube extruded from the ring die is preferably quickly quenched (for example, to 20°C) to control the crystallinity to a low level. At the same time, The stretching ratio of MD is reduced to no more than 1.4 times. After stretching, the stretching tube contacts the metal cylinder cooled to 15 to 30°C for rapid cooling. Moreover, the crystal growth is better controlled.

The rapid cooling after stretching is used to prevent the crystallinity from reducing the shrinkage rate, so the MD shrinkage rate can be made not 5% or less. In addition, the shrinkage rate of the stretched tube can be adjusted to a level greater than 5% and not greater than 26% to control the MD shrinkage rate of the quenched unstretched tube in the range of 0 to 5%.

If the crystallinity of the tube of the present invention exceeds 20%, the uniformity of the shrinkage will be undesirably damaged (that is, the tube opening is likely to bend in the terminal surface of the covered product).

The stretch ratio is minimized as in the above method, and a thinner unstretched tube can be used to obtain a stretched tube of the same size, which facilitates the rapid cooling after extrusion and reduces the crystallinity.

In addition, when the tube is heated from the outside to the proper stretching temperature, the heating can be carried out evenly to the inside, so that the surface roughness caused by the improper temperature rise inside the tube during stretching can be avoided, and as a result, transparency and gloss can be obtained. The stretched tube with superior degree of strength.

It is desirable to minimize the change in crystallinity of the tube on the same peripheral plane (for example, no more than 30%). According to the present invention, a stretched tube with crystallinity fluctuations as small as not more than 3% (ie, the difference between the maximum and minimum crystallinity values on the same peripheral plane) can be obtained, which has not yet been achieved. It is believed that this is due to the use of a thinner stretched tube, the quenching after extrusion can be uniformly performed, so no crystallinity change occurs. In addition, the crystal growth caused by the stretching orientation is the smallest, so the crystallinity of the undrawn tube hardly changes.

As for another property required for the heat-shrinkable tube used in the outer layer of the capacitor, the tube needs to be clearly printed. As far as polyester heat-shrinkable tubes are concerned, some people propose to increase the wettability of the surface (outer peripheral surface) (that is, increase the affinity with the printing ink for clear printing, and the printed ink can hardly be removed). a) Apply corona discharge treatment to the surface of the heat-shrinkable polyethylene terephthalate tube, or (b) add polyalkylene glycol to form the glycol component of the polyester.

However, according to the method (a), the surface wettability deteriorates with the passage of time, and according to the method (b), if the polyalkylene glycol component is added to meet the actual amount of surface wettability, the formed tube is easy to It turns yellow, the color is damaged, and the mechanical strength is low, so it is easy to damage the properties of the polyester tube.

The inventor found that the surface wettability can be improved by improving the printability of the heat-shrinkable polyester tube, which includes polyesters containing polyethylene terephthalate as the main component and polyethylene terephthalate containing Corona discharge treatment is applied to the surface of the heat-shrinkable polyester tube made of the blend of the polyester copolymer of the glycol component, and the polyethylene glycol content of the polyester component in the tube is 0.1 to In the 4% weight range (polyethylene glycol content is represented by a), apply 100 to 800W on the surface of the tube. min/m²The discharge energy is treated as a corona discharge (the applied discharge energy value is represented by b), and the relationship between the polyethylene glycol content a and the discharge energy value b is shown in the following formula: (1.2-5×10^{<u style="single">3</u>}a) be where e is the base of natural logarithm.

The polyester used as the material for this example is a mixture, which includes (a) a polyester containing polyethylene terephthalate as the main component, for example, including terephthalic acid or terephthalic acid Formic acid and a small amount of isophthalic acid are the acid component, and ethylene glycol is the polyester of the glycol component, and (b) the polyester copolymer containing polyethylene glycol as the glycol component (that is, including poly Ethylene glycol and ethylene glycol are glycol components, and terephthalic acid, or terephthalic acid and a small amount of isophthalic acid, are polyester copolymers of acid components). An example of the composition of this mixture is a blend comprising 20 to 99.5% by weight of polyester (a) and 0.5 to 80% by weight of polyester copolymer (b), which contains 5 to 20% by weight of polyethylene The glycol is selected to blend the ratio so that the polyethylene glycol content in the composition is from 0.1 to 4% by weight.

Therefore, for the polyester mixture containing (a) and (b) to be used as the material of this example, the polyethylene glycol content in the polyester component needs to be 0.1 to 4% by weight. In the polyester, additives such as antioxidants, ultraviolet absorbers, stabilizers, etc. can be blended as required. However, the content of the above polyethanol is determined by the amount of the polyester mixture other than such additives. If the amount of polyethylene glycol is less than 0.1% by weight, the improvement of surface wettability is improper. On the other hand, if the amount of polyethylene glycol exceeds 4% by weight, the yellowing of the tube will be obvious, and the mechanical strength and thermal stability will be damaged.

Using the polyester mixture with the above composition as the material, the heat-shrinkable tube can be made by the above method.

On the obtained heat-shrinkable tube, corona discharge treatment was applied to the entire peripheral surface. This treatment can be carried out in accordance with a customary method used to treat the surface of plastic products. In the present invention, corona discharge treatment is applied to apply 100 to 800W on the surface of the tube. min/m²The discharge energy. If the discharge energy in this treatment is less than 100W. min/m², The pipe surface wettability is poor. If the content of polyethylene glycol is increased to improve the wettability, the yellowing of the tube will become obvious, and the mechanical strength and thermal stability will be damaged. On the other hand, if the discharge can exceed 800W. min/m², Then the excessive discharge energy is applied to the tube, so the surface is melted. As a result, the tube becomes wavy or deformed, which is undesirable.

In addition, the relationship between the polyethylene glycol content wt% (a) and the discharge energy value (b) used for corona discharge treatment must be shown in the following formula: (1.2-5×10^<i>-3</i>a) be where e is the base of the natural logarithm.

(1.2-5×10^<i>-3</i>a)

When b&lt;e part, the wettability is improper.

This method is not only effective for the outer layer of the capacitor, but also for other purposes, for printing on it, or for polyester heat-shrinkable tubes with crystallinity and shrinkage outside the above-mentioned range.

Now, the present invention will be described in more detail with reference to examples and comparative examples. However, it should be understood that the present invention is by no means limited to this specific example.

In the following examples and comparative examples, various properties are measured as follows:

(1) Shrinkage rate: The sample is immersed in 98±2°C hot water for 10 seconds, and then the shrinkage rate is calculated according to the following formula:<maths><img file="TW201718B_D0001.tif" /></maths>In the formula, L0 is the length before contraction, and L1 is the length after contraction.

(2) Crystallinity: According to the density gradient tube method. The crystallinity Xc is calculated according to the following formula:<maths><img file="TW201718B_D0002.tif" /></maths>In the formula, 1.335 is the density of amorphous polyethylene terephthalate, 1.455 is the density of crystalline polyethylene terephthalate, and d is the density of the measured tube.

(3) Crystallinity on the same peripheral surface: Collect samples from 8 to 10 on the same peripheral surface, and measure the crystallinity of each sample. For tubes with large diameters, the number of samples collected increases. However, for tubes with a small diameter, the number of samples collected is reduced.

In the table showing the measured crystallization of the example, for example, 4-6% shows that among the samples collected on the same peripheral surface, the lowest crystallinity is 4% and the highest crystallinity is 6%.

(4) Tensile strength: According to JIS C-2132.

(5) Elongation: According to JIS C-2132.

(6) Thermal crack resistance: Place the tube on the capacitor. Then place the No. 8 needle into the capacitor body with a force of 0.94 kg f to form a hole in the tube. This capacitor is placed in a 150°C air furnace for 10 minutes to detect the magnification of the hole. In Table 2, for example, 0/30 is shown, where the denominator shows the number of samples tested, and the numerator shows the number of samples with enlarged holes.

(7) Retouching: After the tube is placed on the capacitor, the defects at both ends of the tube (tube mouth part) such as block edges, raised horns or involution due to curling are visually determined, and the symbol × indicates The defect is clearly observed, the symbol indicates that the defect is very slight, and the symbol indicates that the defect is not observed.

Examples 1 to 6

Including 60% heavy polyester copolymer with intrinsic viscosity (η) of 0.85, which contains 75% by weight terephthalic acid and 25% by weight isophthalic acid as the acid component and ethylene glycol as the alcohol component, and 40% The polyethylene terephthalate mixture with a heavy intrinsic viscosity (η) of 0:66 was dried in a dryer, and then subjected to tubular extrusion to obtain an undrawn tube with a thickness (μm) shown in Table 1.

This unstretched tube was tubular stretched at a temperature of 85° C. and the MD and TD stretch ratios (multiples) shown in Table 1 to obtain stretched tubes each having a thickness of 90 μm in Examples 1 to 6. The MD and TD shrinkage (%) of the stretched tube in each case and the crystallinity on the same peripheral surface are shown in Table 1. In addition, the tensile strength of the tube obtained in each case (kg/cm²) And elongation (%), as well as retouch evaluation and thermal crack resistance when the capacitor is covered with this tube are shown in Table 2.

<tables><img file="TW201718B_D0003.tif" /></tables>

<tables><img file="TW201718B_D0004.tif" /></tables>

Examples 7 to 11

The polyester mixture having the same composition as in Example 1 was dried in a dryer, and then subjected to tubular extrusion to obtain an undrawn tube having a thickness as shown in Table 3. This unstretched tube was subjected to tubular drawing at a temperature of 95° C. and a draw ratio of 1.1 times MD and 1.5 times TD to obtain a stretched tube having a thickness as shown in Table 3. Use this stretched tube to cover the capacitor by heat shrinkage. The finishing of the covered product is shown in Table 3.

<tables><img file="TW201718B_D0005.tif" /></tables>

Examples 12 to 17

In this example, the following polyester blend composition was used as the tube material. That is, using polyethylene terephthalate with an intrinsic viscosity (η) of 1.2 by weight of 67%, polyethylene terephthalate with an intrinsic viscosity (η) of 28% by weight of 0.66 and 5% by weight A polyester copolymer with a viscosity (η) of 0.74, which contains ethylene glycol and polyethylene glycol as the alcohol component and terephthalic acid as the acid component (ie 10% heavy polyethylene glycol, the rest being other components) The blending composition of part) is a material.

The polyester blend composition was dried by a dryer, and then tubular extruded to obtain an unstretched tube having a thickness shown in Table 4.

The unstretched tube was subjected to tubular drawing at a temperature of 90° C. and the draw ratio (multiple) shown in Table 4 below for MD and TD to obtain a stretched tube with a thickness (μm) shown in Table 4 below. The shrinkage rate (%) of MD and TD in each stretched tube and the crystallinity on the same peripheral surface are shown in Table 4. In addition, the tensile strength (kg/cm²) And elongation (10%), as well as the evaluation of retouching and thermal crack resistance when covering capacitors are shown in Table 5.

Comparative examples 1 and 2

Using the polyester blend composition of Example 12, a heat-shrinkable tube was prepared in the same manner as in Example 12, except for the thickness of the unstretched tube, the MD and TD stretch ratio and the warp stretch of the tube during the stretching operation The thickness change of the stretched tube is shown in Table 4. The MD and TD shrinkage rates and crystallinity of each heat-shrinkable tube obtained, as well as the elongation, finishing and thermal crack resistance of each tube coated on the capacitor are shown in Table 5.

<tables><img file="TW201718B_D0006.tif" /></tables>

<tables><img file="TW201718B_D0007.tif" /></tables>

The heat-shrinkable tube of the present invention also has the following specific physical properties.

The polyester film that composes the heat-shrinkable tube shows the following phenomena, bending due to the difference in stress between the inside and outside of the tube, and the bending becomes more obvious when placed in a high-temperature atmosphere. The polyester film constituting the heat-shrinkable tube of the present invention was bent at 100°C±2°C (for example, a gas furnace) for 5 minutes, but it was found that the curvature was not higher than 0.2. In other words, the curvature is small.

The films of the heat-shrinkable tube obtained in Composition Example 14 and Comparative Example 12 were placed in an air furnace at 100°C±5°C for 5 minutes, and then the curvatures were measured. The invention is 0.046 and 0.452, respectively.

The curvature is measured as follows. Figure 5 illustrates the method of obtaining the curvature. In the figure, reference numeral 11 indicates the heat-shrinkable tube to be measured, and a square sample 12 is cut from the tube while avoiding overlapping lines. The sample size can be selected at will, because the size does not affect the curvature measurement. Usually, the sample is a square with each side length corresponding to 50 to 90% of the folded diameter of the tube. Sample 12 was bent when placed in an atmosphere of 100°C ± 2°C for 5 minutes. As a result, under a rough classification, there is a kind of moving toward arrow A to form a spiral 13 and a kind of moving toward arrow B to form an arc 14 only. For the spiral specimen 13, the circle that constitutes the innermost cylinder is measured and is called 2R. For arc 14, the random position of this arc is connected by a straight line C-C, and the measurement is shown in the figure<img file="TW201718B_D0008.tif" />Value and X value, the R value is obtained by the following formula:<maths><img file="TW201718B_D0009.tif" /></maths>

The curvature is 1/R.

As mentioned above, the heat-shrinkable tube of the present invention has a smaller curvature value than the tube of the comparative example. Therefore, when the capacitor is covered with this tube, the finishing of each terminal surface will not be adversely affected by bending. As shown in Table 4 above, good finishing will be obtained.

Examples 18 to 23 and Comparative Example 3

Composition of tube material:

Use polyethylene terephthalate (component A in the following table 6) and polyester copolymer (component B in the following table 6) in the weight ratio shown in Table 6, which contains ethylene glycol and Polyethylene glycol is a glycol component (including 90% by weight of ethylene glycol and 10% by weight of polyethylene glycol) and terephthalic acid is an acid component, and the mixture is a pipe-making material. The content of polyethylene glycol in the polyester mixture constituting the tube is also shown in Table 6.

<tables><img file="TW201718B_D0010.tif" /></tables>

Preparation of heat shrinkable tube:

The seven materials shown in Table 6 were each dried by a dryer, and then tubular extruded to obtain an unstretched tube with a folded diameter of 8.2 mm and a thickness of 190 μm. This unstretched tube was stretched at a stretching temperature of 90° C., MD 1.15 times and TD 1.7 times stretching ratio to obtain a stretched tube with a folded diameter of 13.8 mm and a thickness of 100 μm.

Corona discharge treatment:

The seven kinds of tubes made as above are each flattened and placed in a corona discharge treatment device, so that discharge treatment is applied to the entire peripheral surface of the tube. This treatment can adjust the discharge capacity to 100, 200, 400, 600 and 800W. min/m²(0 indicates the case of no discharge treatment), as shown in Table 7. For each tube obtained, the surface wettability and color of each tube were tested.

The surface wettability is measured as follows.

On the surface of the flattened tube, apply a wettability index standard liquid of 52 dyne/cm in a square area corresponding to the length of the flattened tube on each side. As for this coating liquid, "Wettability Index Standard Solution f-or Wattability Test", a trademark, manufactured by Wako Junyaku Kog-yo KK (components: ethylene glycol and monoethyl ether) was used. Two minutes after the application of the liquid, the area on the pipe surface with the wettability index standard liquid was confirmed, and the wettability was evaluated by the following grades according to the extent of the area.

<tables><img file="TW201718B_D0011.tif" /></tables>

The color of the tube was visually inspected and evaluated according to the following grades. : Good, : slightly yellow, ×: substantially yellowed.

Table 7 shows the evaluation results of surface wettability and tube color.

<tables><img file="TW201718B_D0012.tif" /></tables>

In Table 7, the polyethylene glycol content in the tube is 0.1 to 4.0% by weight and the discharge energy in the corona discharge treatment is 100 to 800W. min/m²Among them, the relationship between polyethylene glycol content% weight and discharge energy value b satisfies the following formula: (1.2-5×10^<i>-3</i>a) be is an example of the present invention, in which the evaluation of both wettability and tube color is .

On the other hand, if the discharge treatment (0) is not applied, when the polyethylene glycol content is 0.1 to 4.0% by weight, the wettability is × or , and when it is 8.0% by weight, the wettability is , but The tube color is ×. In addition, even if corona discharge treatment is applied, if the above formula is not satisfied, that is, if b is 100W. min/m²When a is 0.1 to 1.0% by weight, if b is 200W. min/m²When a is 0.1 to 0.5% by weight, if b is 400W. min/m²When a is 0.1 to 0.2% by weight, or if b is 600W. min/m²When a is 0.1% by weight, the wettability is uncomfortable as shown by .

As mentioned above, the heat-shrinkable tube of the present invention has an extremely low crystallinity of 4 to 20%. Generally speaking, when the crystallinity of the polyester is high (for example, at least 30%), the solvent resistance is good, and when the crystallinity is low, the solvent resistance is poor. When the capacitor is covered with a heat-shrinkable tube, solvent washing (such as acetone) is sometimes performed after the covering. When washing with such a solvent, those covered with the heat-shrinkable tube of the present invention may crack the tube, or form irregularities on the surface to impair the appearance. In order to avoid the formation of this defect, the finished product covered with the heat-shrinkable tube of the present invention (such as a capacitor, the capacitor coating is used here as an example) is placed in a high temperature atmosphere of 100 to 400°C for 10 seconds to 1 hour to remove the tube The crystallinity is increased to at least 30%.

And in the description of the situation where this processing is indeed carried out.

The capacitor is covered with the heat-shrinkable tube of crystallinity 11 to 13 (average value: 12) obtained in Example 14, heat-treated in a high-temperature atmosphere at 200°C for 30 to 120 seconds and heat-treated in a high-temperature atmosphere at 300°C for 10 to 70 seconds. The crystallinity (average value) and solvent resistance of the tube. The measurement results are shown in Table 8. In terms of solvent resistance, the sample is completely immersed in acetone at 20 to 25°C for 30 seconds in a static state, and the state of the tube surface is checked. The results are evaluated according to the following criteria.

It shows that there is no cracking or irregularity on the surface. shows that among 100 finished products, the number of good products without defects except those with cracks or irregular surface defects is at least 30%. × indicates that cracks and surface irregularities are observed on the entire surface of the finished product.

<tables><img file="TW201718B_D0013.tif" /></tables>

As mentioned above, for the finished product covered with the heat-shrinkable tube of the present invention, the solvent resistance can be improved by increasing the crystallinity of the tube. In addition, the shape stability after retouching can also be increased by increasing the crystallinity.

As mentioned above, for heat-shrinkable tubes using thermoplastic polyester resin, when heat-shrinkable coating is applied, the leading edge is warped like a horn or the leading edge is rolled inward and does not fit closely. Part of the mouth was detected. The heat-shrinkable tube of the present invention does not form this defect, and can obtain superior covering and finishing.