JPH03224723A - Heat-shrinkable tube - Google Patents

Abstract

PURPOSE:To provide superior transparency and gloss by tubularly orienting a non-oriented tube of thermoplastic polyester resin to manufacture a heat- shrinkable tube and specifying the range of its crystallization. CONSTITUTION:A non-oriented tube manufactured by drying a thermoplastic polyester resin material, and then tubularly extruding the same is tubularly oriented in the longitudinal direction (MD direction) and the radial direction (TD direction). The orientation ratio at that time is 1.01-1.4 times in the MD direction and 1.3-2.2 times in the TD direction. In that case, the crystallization degree of an oriented tube can be made in the range of 4-20% by quenching (for example, 20 deg.C) the non-oriented tube which is melt extruded out of a ring die, and bringing the same into contact with, for example, a metal cylinder cooled down to 15-30 deg.C after orientation.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a thermoplastic polyester tube with heat shrinkability, which is particularly suitable for use as an exterior for capacitors such as electronic components such as aluminum electrolytic capacitors and tantalum capacitors. It concerns a suitable heat-shrinkable polyester tube.

(Prior art and problems to be solved by the invention) Conventionally,
Heat-shrinkable tubes mainly made of polyvinyl chloride have been widely used for the exterior of electronic components such as capacitors. However, in the field where electronic components such as capacitors are becoming lighter, thinner, shorter, smaller, and more surface-mounted, polyvinyl chloride tubes do not have sufficient heat resistance.

Heat-shrinkable tubes for the exterior of electronic components such as capacitors are required to have the following characteristics.

(b) When a heat-shrinkable tube is used to shrink and fit an electronic component such as a capacitor, both open ends of the tube are bent at different angles to cover the end face of the electronic component. adheres uniformly to the end surface of the object to be sheathed,
It must have a good appearance, i.e. the innermost end of the shrink tube should not be lumpy, stand up like a horn, or curl inward instead of sticking tightly. However, such inconveniences must not occur.

To show these in drawings, Figures 1 to 4 are explanatory diagrams showing the state when a capacitor is shrink-covered with a heat-shrinkable tube. It is a part.

Figure 1 shows an example of a well-finished tube, and Figures 2 to 4 show examples of poorly finished tubes. However, in the one shown in Figure 2, the leading edge, which curves inward, rises upward in the shape of a corner. Note that the leading edge may not only partially rise in an angular shape, but also the entire end may rise. In the case of the one shown in Fig. 3, the bent end is lumpy, and in the case of Fig. 4, the bent part does not fit tightly and is curled.In the past, such poor finishing was often observed.

(b) After being fitted into electronic parts, etc., the shrinkable tube is heat-treated to heat-fix it, but at this time, the tube should not crack or shrink again.

(c) There is little discoloration of the tube even if it is kept under the conditions of 125°C for 5000 hours.

In order to improve heat resistance, it has been proposed to use thermoplastic polyester resin as a material for heat-shrinkable tubes (Japanese Patent Application Laid-open Nos. 49-32972, 1973-
100118 Publication), although such a tube also satisfies (B) and (C) among the above-mentioned necessary characteristics (A), (B), and (C), (I) ), but it is hoped that a thermoplastic polyester heat-shrinkable tube (hereinafter sometimes simply referred to as heat-shrinkable tube) that has all three necessary properties will be produced. There is.

(Means for Solving the Problems) As a result of intensive research in order to meet the above requirements, the present inventors have
We have succeeded in providing the heat-shrinkable polyester tube of the present invention, which has the necessary characteristics (a), (b), and (c) above.

That is, the gist of the present invention is a tube obtained by tubular stretching an unstretched tube made of a thermoplastic polyester resin to impart heat shrinkability, and the crystallinity of the tube is 4 to 20%. A heat-shrinkable polyester tube characterized by:

The thermoplastic polyester resin constituting the tube of the present invention includes polyethylene terephthalate, in which the acid component is terephthalic acid and the glycol component is ethylene glycol, as well as a mixture of a predominant amount of terephthalic acid and a dicarboxylic acid such as isophthalic acid as the acid component. A copolymer formed by mixing polyethylene glycol with a glycol component or ethylene glycol, or a blend of these polyesters can be used. Among them, one example of a preferable polyester resin is (1) the acid component is 95 to 65% by weight of terephthalic acid and 5 to 65% by weight of isophthalic acid.
35% by weight, 30-80% by weight of a polyester copolymer which is an alcohol component or ethylene glycol, and (
2) Those consisting of a mixture with 70 to 20% by weight of polyethylene terephthalate can be mentioned. The heat-shrinkable tube manufactured from this polyester blend product preferably has a degree of crystallinity in the range of 4 to 12%, and also uses a mixture of polyethylene glycol and ethylene glycol as the glycol component, and terephthalic acid as the acidic component. When a heat-shrinkable tube is made from a mixture of polyester and polyethylene terephthalate, the degree of crystallinity is preferably in the range of 8 to 20%.

In addition, for example, when [η] has a relatively large intrinsic viscosity [η]
By using polyethylene terephthalate (1) as the main component, the dimensional stability of the raw tube immediately after extrusion is improved and there are advantages in that it is easy to manufacture.

Organic or inorganic lubricants are added to the resin material of the tube of the present invention to improve the slipperiness of the tube, and auxiliary agents such as stabilizers, colorants, and antioxidants are added as necessary. be able to.

Next, a method for manufacturing the tube of the present invention will be illustrated.

After drying the polyester resin material as described above in a normal dryer, tube extrusion is performed to obtain an unstretched tube. Tubular stretching is performed in the TD direction (hereinafter referred to as the TD direction). The stretching ratio at this time is MD
The left direction is 1.01 to 1.4 times, preferably 1.05 to 1
．． 25 times, and 1.3 to 2.2 times in the TD direction, preferably 1.4 to 2.0 times.

As long as thickness unevenness is not worsened, a lower temperature is better for the stretching temperature, and it is generally preferable to select a temperature in the range of about 72 to 98°C.

The drawing method may be the commonly used tubular drawing, and the drawn tube thus obtained can be made into a wound product.

The thickness of the tube obtained as described above is not particularly limited, but for shrink tubes for electronic components such as capacitors, it is usually 30 to 200all, preferably 50 to 200all.
One example is one having a thickness of 150 μf.

Shrinkage rate of the resulting shrinkable tube (measured at 98±2°C)
It is recommended that the MD force direction should be more than 5% and 26% or less, and the TD force direction should be more than 25%. If the MD force direction shrinkage is 5% or less, it will be difficult to cover capacitors etc. with heat shrink coating. A gap is likely to occur between the end face of the shrink tube and the end face of the capacitor, etc., and on the other hand, 26%
If it is larger than this, there is a risk that it will shrink greatly in the vertical direction due to thermal contraction, causing the covering position to shift and deform. Also, if the TD force direction shrinkage is less than 25%, the adhesion of the shrink tube when heat-shrinking a capacitor etc. is poor and there is a risk of loosening. Preferably, the MD force direction shrinkage is 20% or less. , the TD force direction contraction rate is 28% or more, and the TD force direction contraction rate is 15% higher than the MD force direction contraction rate.
Increase by at least %.

By carrying out tubular drawing under the above conditions and making the crystallinity of the drawn tube fall within the range of 4 to 20%, capacitors that cannot be obtained with conventional heat-shrinkable polyester tubes can be produced. We were able to significantly improve the exterior finish of electronic components such as [a finish that does not cause any inconvenience at the end of the tube after shrinkage, as listed in item (a) of the required characteristics for heat-shrinkable tubes above]. .

The exact reason is not known, but the level of crystallinity,
Comparing the crystallinity distribution on the same circumferential surface, the tube of the present invention has a well-balanced shrinkage speed and amount of shrinkage during heat shrinkage, so the shrinkage at both ends of the same circumference is extremely uniform. It is thought that this is because it is carried out.

In order to make the crystallinity of the stretched tube 4 to 20%,
The unstretched tube melted and extruded from the annular die is rapidly cooled (
For example, at 20°C), the degree of crystallinity is kept low, and MD
It is preferable to reduce the stretching ratio in the force direction to 1.4 times or less, and to rapidly cool the film after stretching by, for example, contacting it with a metal cylinder cooled to 15 to 30°C, in order to suppress the growth of crystals.

This rapid cooling after stretching can prevent crystallization that lowers the shrinkage rate, so it is also effective in preventing the MD force direction shrinkage rate from becoming 5% or less. In addition, it is also possible to keep the MD force direction contraction rate of the unstretched tube in the range of 0 to 5% after cooling the unstretched tube.
It is effective in reducing the amount to 26% or less.

When the degree of crystallinity exceeds 20% in the tube of the present invention, the uniformity of shrinkage is inhibited (the end of the tube tends to curl inward on the end surface of the heat-shrinkable material). ) Therefore, if the crystallinity level of the old invention tube is less than 4%, it is necessary to thin the unstretched tube and suppress crystallization by rapid cooling, and also to suppress oriented crystals by stretching, so the stretching ratio must be lowered, resulting in a lower shrinkage rate of the drawn tube.

Decreasing the stretching ratio as in the above-mentioned manufacturing method means that a thinner unstretched tube can be used to obtain a stretched tube of the same diameter, making it easier to rapidly cool the tube after extrusion and keeping the degree of crystallinity low. There is also.

In addition, this makes it possible to uniformly heat the inner surface when heating from the outer surface to the appropriate temperature for stretching, which prevents roughening of the surface during stretching due to insufficient inner temperature, resulting in a stretched tube with excellent transparency and gloss. can get.

Further, it is preferable that the variation in the degree of crystallinity on the same circumferential surface of the tube is small (for example, within 3%), but according to the present invention, for example, within 3% (the maximum value of the degree of crystallinity on the same circumference) It is possible to obtain a stretched tube with small variation in crystallinity, which was not previously possible. The reason for this is thought to be that by using a thinner stretched tube, the extrusion after extrusion is uniformly carried out, and variations in crystallinity do not occur. It is also thought that since there is little crystal growth due to stretching orientation, it is difficult to increase the variation in crystallinity of the original tube.

(Example) In the following Examples and Comparative Examples, various characteristics were measured as follows.

(1) Shrinkage rate = Calculated using the following formula after immersion in hot water at 98°C±2'C for 10 seconds.

Dimensions before shrinkage - Dimensions after shrinkage Shrinkage rate (%) = ×100 Dimensions before shrinkage (2) Crystallinity: by density gradient tube method.

(3) Crystallinity of the same circumferential surface: Samples are taken from 8 to 10 locations on the same circumferential surface, and the crystallinity of each sample is measured. If the diameter of the tube is extremely large, the number of samples to be collected is increased; on the other hand, if the diameter of the tube is not extremely small, the number of samples to be collected is reduced.

For example, in the table showing the measurement results of Examples, 4 to 6% means that among the samples collected on the same circumferential surface, 4% showed the lowest crystallinity, and 4% showed the highest crystallinity. This means that it was 6%.

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

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

(6) Resistance to heat cracking: After covering the capacitor with a tube, use a No. 8 dressmaker's needle to touch the body of the capacitor with a force of 0.94 kgf to see if it is enlarged. In Table 2, for example, it says 0/30, but the denominator is the number of samples tested and the numerator is the number of enlarged holes.

(7) Finishing quality: After coating the applied capacitor, there may be problems such as lumps, horn-like rising parts, or curling at both ends of the tube. When observed with the naked eye, an X mark indicates that these disadvantages are clearly recognized, an O nose mark indicates that these disadvantages are extremely slight, and a c mark indicates that these disadvantages are not observed at all.

Examples 1 to 6 are ethylene glycol, and the intrinsic viscosity [η] is 0.8
60% by weight of a polyester copolymer of 5 and [η] of 0
．． A mixture of No. 66 and 40% by weight of polyethylene terephthalate was dried using a drier and then extruded into a tubular tube to obtain an unstretched tube having the original tube thickness (μm) shown in Table 1.

This unstretched tube was tubular stretched in the MD force direction and TD force direction at a temperature of 85°C at the stretching ratio (times) shown in Table 1, and the thickness was 90μ in any of Examples 1 to 6.
A stretched tube of T was obtained. Table 1 shows the shrinkage percentage (%) in the MD force direction and TD force direction of the stretched tube in each example, and the degree of crystallinity on the same circumferential surface, and the tensile strength of the tube obtained in each example. (kg/aA
) and elongation (%), as well as the evaluation of finish quality and heat cracking resistance obtained by coating a capacitor using each tube, are shown in Table 2.

Table 2 Examples 7 to 11 A polyester blend having the same composition as used in Example 1 above was dried using a drier, then tubular extruded, and unstretched to the thickness shown in Table 3. Got the tube. This unstretched tube was heated at a temperature of 95°C in the MD force direction 1.
Tubular stretching was performed at a magnification of 1x and 1.5x in the TD hole direction to obtain a stretched tube with the wall thickness shown in Table 3. This stretched tube was used to cover a capacitor with heat shrinkage. Table 3 shows the coating finish of the obtained product.

Examples 12-17 In these examples, the following polyester blends were used as tube materials. That is, it contains 67% by weight of polyethylene terephthalate with an intrinsic viscosity [η] of 1.2, 28% by weight of polyethylene terephthalate with an [η] of 0.66, ethylene glycol and polyethylene glycol as alcohol components, and terephthalic acid as an acid component. (contains 10% by weight polyethylene glycol, the rest is other ingredients)
A blend consisting of 5% by weight of a polyester copolymer with [η] of 0.74 was used as the material.

After drying this polyester using a dryer, it is extruded into a tubular tube, and the raw tube thickness (μ) shown in Table 4 is obtained.
An unstretched tube was obtained.

This unstretched tube was tubular stretched in the MD force direction and TD force direction at a temperature of 90'C at the stretching ratio (times) shown in Table 4 below to obtain a stretched tube with the thickness (μ) shown in Table 4. Ta. Table 4 shows the shrinkage percentage (%) in the MD force direction and TD force direction of the stretched tube in each example, and the degree of crystallinity on the same circumferential surface.

In addition, the tensile strength (kg/d) and elongation rate (%) of the tubes obtained in each of Examples 12 to 17, and the evaluation of the finish and heat resistance of capacitors coated with each tube. The cracking properties are shown in Table 5.

Comparative Examples 1 and 2 Polyester having the same composition as used in Example 12 was used, and the thickness of the unstretched tube, the stretching ratio in the MD force direction and TD force direction of the tube during stretching, and the thickness of the resulting stretched tube were determined. As shown in Table 4, other details are as in Example 1.
A heat-shrinkable tube was manufactured in the same manner as in 2. Table 4 shows the shrinkage rate and crystallinity in the MD force direction and TD force direction of the obtained heat-shrinkable tube, as well as the tensile strength, elongation rate, finish quality and heat cracking resistance of a capacitor coated with the obtained tube. The properties are shown in Table 5.

The heat-shrinkable tube of the present invention as explained above in Table 1 further exhibits the following unique physical properties. It exhibits a bending phenomenon, but when left in a high temperature atmosphere, the bending becomes noticeable. The polyester film forming the heat-shrinkable tube of the present invention bends when exposed to an atmosphere of 100°C ± 2°C (for example, in an air oven) for 5 minutes, but its curvature is 0.
．． 2 or less, in other words, the degree of curvature is small.

100°C ± 2°C for the film forming the heat-shrinkable tube obtained in Example 14 and Comparative Example 2 above.
The curvatures were measured after being placed in an air oven for 5 minutes and taken out, and found to be 0.0461 and 0.452, respectively.

Note that this curvature is measured as follows.

FIG. 5 is an explanatory diagram showing how to obtain the curvature.

In the figure, 11 is a heat-shrinkable tube to be measured, and a square sample 12 is cut out avoiding the folds of the tube. Since the size of this sample does not affect the measurement of curvature, it may be selected appropriately, and is usually a square with a side having a length of 50 to 90% of the tube fold diameter. When the sample 12 is left in an atmosphere of 100° C.±0.2 for 5 minutes, the sample bends. As a result, the results are roughly divided into those 13 in the direction of arrow A in Figure 5, with a thinly wound shape.
There are two types: one that moves in the direction of arrow B and one that simply becomes a curved arc 14. Thinly rolled one 1
For No. 3, measure the diameter of the circle forming the innermost cylinder and define it as 2R. For the arc-shaped object 14, connect appropriate positions of this arc with a straight line C--C, measure the value of j shown in the figure J2+x2 and the value of X, and obtain the value of R according to the formula R= x.

The curvature is determined by 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, but when covering a capacitor, for example, the finish of the end face is not adversely affected by bending and the curvature value is as shown in Table 4 above. As shown, the result is a good finish.

The heat-shrinkable tube of the present invention described above has a relatively low crystallinity of 4 to 20%, and generally, when the crystallinity of Boester is high (for example, 30% or more), the solvent resistance is poor. However, when the degree of crystallinity is low, the solvent resistance is poor.When covering a capacitor with a heat-shrinkable tube, cleaning is sometimes performed with a solvent (e.g. acetone) after covering the capacitor. When cleaning with a solvent is carried out, the tube coated with the heat-shrinkable tube of the present invention has problems such as cracks in the tube and unevenness on the surface, which impairs the appearance.

In order to avoid the above-mentioned inconvenience, after covering the object to be coated (for example, a capacitor, hereinafter explained in the case of covering a capacitor) with the heat shrinkable tube of the present invention, By leaving the tube in a high temperature atmosphere of 400° C. for 10 seconds to 1 hour, the crystallinity of the tube is increased to 30% or more.

An example of actually performing this process will be described next.

An experiment in which a capacitor was covered with the heat-shrinkable tube with a crystallinity of 11 to 13 (average value 12) obtained in Example 14 above and heat treated in a high temperature atmosphere of 200°C for 30 to 120 seconds, and a high temperature of 300°C. An experiment was conducted in which heat treatment was performed for 10 to 70 seconds in an atmosphere, and the resulting crystallinity of the tube (
average value) and solvent resistance were investigated. The measurement results are shown in Table 6 below.

Solvent resistance was determined by completely immersing the tube in acetone at 20 to 25° C. for 30 seconds, then gently taking it out, observing the condition of the tube surface, and evaluating the results according to the following criteria.

The ○ mark indicates that there are no cracks or surface irregularities, and the Δ mark indicates that out of 100 products, if there is a product with even a portion of the product having cracks or surface irregularities, it will be rejected as a defective product, and it will be considered a non-defective product with no problems. indicates a case where the number is 30% or more, and an X mark indicates a case where the entire surface is cracked or the surface is uneven.

As described above, the tube coated with the heat-shrinkable tube of the present invention can improve solvent resistance by increasing the crystallinity of the tube, and furthermore, by increasing the crystallinity, Dimensional stability after finishing can also be improved.

(Effect of the invention) When a heat-shrinkable tube made of thermoplastic polyester resin is coated with a heat-shrinkable coating, the leading edge of the tube may become lumpy or have corners (horns) at the locations where both open ends of the tube touch. However, the heat-shrinkable tube of the present invention does not have such disadvantages and exhibits an extremely excellent coating finish.

[Brief explanation of drawings]

1 to 4 are explanatory diagrams showing the covering state when a capacitor is covered with a heat-shrinkable tube. 3 and 4 show examples of poor finishing, and FIG. 5 is an explanatory diagram of the method of heating the heat-shrinkable tube of the present invention to a constant temperature and measuring the curvature. In the figure, 1 is a capacitor, and 2 is a longitudinal section of a shrink-coated tube. Figure Figure Figure Figure

Claims (1)

[Claims] (1) A heat-shrinkable tube obtained by tubular stretching an unstretched tube made of thermoplastic polyester resin to impart heat-shrinkability, the tube having a degree of crystallinity of 4 to 20%. polyester tube.