JPS6241860B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for manufacturing a heat-shrinkable tube made of polyester resin. Due to its excellent heat resistance, corrosion resistance, and mechanical properties, demand for heat-shrinkable tubes made of polyester resin (hereinafter simply referred to as heat-shrinkable tubes) has gradually increased in recent years, mainly for coating purposes such as the exterior of capacitors. I've been doing it. In order to closely coat the article, the shrinkage rate in the tube radial direction (100℃
(hereinafter simply referred to as the shrinkage rate) is required, and for example, a shrinkage rate of 40% or more is normally required to coat a capacitor without failure. Such polyester shrink tubes are usually produced by simultaneously stretching an unstretched tube extruded from an annular die in the axial and radial directions in a heating zone (stretching zone) in which a fluid such as air is forced into the tube and heated in that state. However, it has been extremely difficult to stably produce seamless tubes with a high degree of shrinkage from crystalline resins such as polyester resins.
In addition, in tubular stretching of such polyester resin, the stretching speed is extremely high;
Due to reasons such as a temperature difference occurring between the front and back sides of the tube when heated to the stretching temperature, and unstretched tubes extruded from an annular die having poor thickness accuracy, heat-shrinkable tubes after stretching have a high degree of orientation and crystallinity. The coating becomes non-uniform and local distortion occurs, resulting in a curved or meandering state, which is particularly difficult to coat continuously using an automatic machine. The present invention provides a method for stably manufacturing a polyester shrink tube that maintains a high degree of shrinkage, particularly in the radial direction, and also improves appearance defects such as curving and waving as described above. The purpose is to: (A) The acid component consists of 95 to 65% by weight of terphthalic acid and 5 to 35% by weight of isophthalic acid, and the alcohol component consists of ethylene glycol. 10-80% by weight of polyester copolymer resin,
(B) An unstretched tube made of a mixture with 90 to 20% by weight of polyethylene terephthalate, the tube temperature at the starting point of stretching is kept at 80 to 95°C, and the tube temperature at the end of stretching is 5 to 20°C higher than the stretching starting point. Pressurize gas into the tube while keeping it low and radially
A polyester heat-shrinkable tube that is stretched 2.5 times or more, then relaxed by 0.5 to 15% in the axial direction while being maintained at 70 to 85°C, and simultaneously re-stretched by 1 to 20% in the radial direction. It consists in the manufacturing method. The present invention will be explained in detail below. The polyester of the material constituting the tube of the present invention is a polyester copolymer resin (hereinafter referred to as A resin ) and polyethylene terephthalate resin (hereinafter referred to as B resin). The relationship between the two types of acid components in the above resin A is that if the amount of terephthalic acid is too large, the physical strength will be high, but the shrinkage rate at low temperatures will be poor, and conversely, if the amount of terephthalic acid is too small, the physical strength will be low. It is important that it is within the above range, since not only will the drawability become poor, but continuous and stable production will not be possible. In addition, the above B resin has an intrinsic viscosity of 0.63~
0.72 solution haze of 35-75% is well used. Resin A and resin B are mixed at a ratio of 10 to 80% by weight of the former and 90 to 20% by weight of the latter. If the mixing ratio deviates from this, it is not possible to stably and continuously produce seamless tubes with a high degree of shrinkage. A more preferable mixing ratio is A resin ratio of 20
The amount of shrinkage is at least 30% by weight, preferably at least 30% by weight, and a particularly high shrinkage rate can be obtained within this range. Further, it is preferable that the proportion of resin A is about 60% by weight or less, and even if it is mixed in more than that, the shrinkage rate will not increase so much, and there is a disadvantage that the cost of the film will increase. The raw material resin is obtained by uniformly mixing both resins using a blender, or by adding appropriate lubricants, colorants, and other additives. The raw resin is dried with a hopper dryer, etc., then kneaded in an extruder at a temperature of 270 to 290°C, extruded into a cylindrical shape with an annular die, and rapidly cooled to obtain a raw cube. Next, the unstretched tube thus obtained is heated and stretched while gas is pressurized into the tube, but at this time, the temperature of the tube at the starting point of stretching is 80
If it is lower than ℃, it will not be possible to stably stretch it to the specified diameter, and if it is higher than 95℃, the stretching start point will tend to move and stable stretching will not be possible, so keep it at 80 to 95℃, preferably 85 to 95℃. It is necessary. In order to maintain the above temperature, various heating means such as a hot water bath, hot air, and infrared radiation can be used, but in order to rapidly and uniformly heat the tube, hot water bath heating is preferable, and heated steam may also be used in combination with this. Also, if you preheat the tube to a temperature lower than 80°C, it will be easier to heat it more quickly and uniformly. Note that it is preferable to maintain approximately the same temperature from the stretching start point to the point at which the tube is stretched to 1.5 times the diameter of the unstretched tube. Furthermore, it is necessary to lower the temperature to create a temperature difference from the stretching start point to the stretching end point. In other words, if the temperature difference between the two points is less than 5°C, the stretching end point will move too much and stable stretching will not be possible.Also, when using an outer diameter regulating ring (described later), friction will occur between the inner surface of the outer diameter regulating ring and the tube surface. This will hinder the collection of the item. On the other hand, if this temperature difference is greater than 20°C, it is impossible to stretch to a predetermined outer diameter. The temperature at the end of stretching is preferably within the above range and at least 75°C. In order to create this temperature difference, the stretching end point can be kept at a predetermined temperature by using an outer diameter regulating ring.The outer diameter regulating ring is equipped with a water-cooling jacket, and cooling water at a predetermined temperature is supplied to the outer diameter regulating ring. You can pass it through. This method is particularly useful for manufacturing small-diameter (outer diameter 20 mm or less) heat-shrinkable tubes that are often used for condenser exteriors because they can easily maintain a temperature difference. Furthermore, the radial stretching ratio of the tube is 2.5.
If it is smaller than 40%, the radial shrinkage rate of the final product will be less than 40%.
2.5 times or more, preferably 2.5 to 4.0 times, is required. Further, the stretching ratio in the axial direction is not particularly limited, but it is usually 2.0 to 4.0 in order to perform stable stretching.
times, preferably 3.0 to 4.0 times. The biaxially stretched tube obtained by the above stretching operation is passed through a hot water bath with internal pressure applied, or through a heating zone (heat treatment zone) heated by an electric or infrared heater, and then heated for 70 minutes. Keep within the range of ~85°C. And at the same time 0.5% or more 15% in the axial direction
Relaxation of 1% or more in the radial direction20
% or less. To continue these operations from the previous drawing process, the tube exiting the drawing zone is cooled, passed through a Nippro roll, passed through the heat treatment zone maintained at 70 to 85°C, and then passed through a Nippro roll. . The desired degree of axial relaxation is then achieved by varying the rotational speeds of the first and subsequent nip rolls, and at the same time the compressed gas in the drawing zone is introduced by adjusting the gap between the first nip rolls. The inner pressure of the tube may be adjusted to keep the re-stretching ratio in the tube radial direction within a desired range. In the above heat treatment, if the treatment temperature is less than 70°C, there will be no heat treatment effect, and the curvature and waviness of the biaxially stretched tube will not be improved. Also, the heat treatment temperature is 85
If the temperature exceeds .degree. C., the shrinkage rate in the axial and radial directions of the tube will decrease significantly, and the shrinkage rate cannot be maintained by re-stretching, making it unsuitable for practical use. Therefore, it is essential to maintain the temperature within the above-mentioned range of 70 to 85°C, preferably 75 to 80°C. In the above heat treatment, the axial direction of the tube is
Relax by 0.5% or more and 15% or less. The preferred relaxation range is 1-10%, more preferably 1-5%. This operation relieves the strain that exists in the axial direction,
This is to prevent new distortion from occurring in the heat-treated area and reduce curvature and waving.The reason for setting it below 15% is that if the relaxation exceeds this, the processing temperature will increase to 85%.
This is because such high-temperature treatment lowers the shrinkage rate in the radial direction as well as in the axial direction of the tube, making it impractical. Particularly, it is preferable to perform this relaxation in a range of 1 to 5% because low temperature treatment is possible so that the shrinkage rate does not decrease, the film can be fed with high film tension, and the stability of the heat treatment process is high. Furthermore, the effects of improving curvature, waving, etc. reach the best condition at around 5%. The reason why the tube is re-stretched in the radial direction by 1% or more and 20% or less is to keep the radial direction under tension so as to prevent a decrease in the shrinkage rate in the radial direction and also to prevent the diameter from wobbling in the axial direction. The degree of re-stretching is determined by the processing temperature and internal pressure, but the limit is 20%, preferably in the range of 1 to 15%. If heat treatment is performed without this re-stretching, it will be difficult to regulate the diameter and cause deviation in the diameter, which is not preferable. As detailed above, according to the method for manufacturing a heat-shrinkable tube of the present invention, the shrinkage rate of the tube in the axial direction and radial direction is at a practically satisfactory level, and there is little appearance disadvantage such as curving or waving. That is, a polyester shrink tube with an excellent product appearance can be obtained. Therefore, the heat-shrinkable tube obtained by the method of the present invention has excellent chemical resistance, heat resistance, and mechanical properties, as well as excellent shrinkage characteristics and product appearance. For example, the tube of the present invention can be used in the capacitor manufacturing process. When implementing integrated production of capacitors by incorporating the exterior packaging process using
The incidence of rejected products due to poor appearance, etc. can be significantly reduced, and this has great industrial significance. Examples of the present invention will be described below. Example 1 Resin A (intrinsic viscosity 0.8) whose acid components are 90% by weight of terephthalic acid and 10% by weight of isophthalic acid and whose alcohol component is ethylene glycol, and resin B which is polyethylene terephthalate (intrinsic viscosity
0.7) in the proportions shown in Table 1 No. 1 to No. 5 (invention) or Nos. 6 and 7, each alone (comparative example), are used as the material resin, and these are mixed at the cylinder temperature. It was extruded from an annular die (die temperature: 270°C) using an extruder at 280 to 270°C, and immediately quenched in water at 20°C to obtain a raw polyester resin tube with an outer diameter of 4.0 mm and a thickness of 0.6 mm. After preheating this in a hot water bath at 78°C, air was injected under pressure while maintaining the stretching start point at 85°C and the stretching end point at 80°C in the hot water bath, and then inside the outer diameter regulating ring, the temperature was increased by 2.6 times in the radial direction, and in the axial direction. The film was stretched 3.8 times and immediately cooled to 40°C. Next, this tube was heated to 78°C, and
% relaxation and heat treatment while simultaneously re-stretching in the radial direction by 2%. Table 1 shows the shrinkage rate of the obtained tube in boiling water at 100°C for 10 seconds. In addition, we cut each shrinkable polyester tube to a length of 21 mm, placed it over a condenser with a diameter of 10φmm and a length of 14 mm, and heated it in hot air at 180°C for 10 seconds to shrink the tube and tightly cover the condenser. did. Each tube was equipped with 100 capacitors, and their pass/fail was judged visually.
The results are shown in Table 1. In addition, stretchability was evaluated as follows. If a heat-shrinkable tube of a predetermined diameter can be stably and continuously obtained, it is indicated as good stretchability and marked with a mark of ◯. If the diameter fluctuates and is not constant, it is indicated as poor stretchability and is marked with an x.

[Table] As is clear from Table 1 above, the shrinkage rate at 100°C in the radial direction of the heat-shrinkable tube of the present invention is 45
%, but that of the comparative example is 39%.
Moreover, when actually used for the exterior of a capacitor, the pass rate for the present invention was 90 to 98%, while that for the comparative example was 60% or less. Example 2 A mixture of 40% by weight of resin A and 60% by weight of resin B, as in Example 1, was extruded in the same manner as in Example 1 to obtain an unstretched tube with a diameter of 4φmm and a wall thickness of 0.6mm. After preheating this in a hot water bath at 75°C, air was pressurized while maintaining the stretching start point and stretching end point at each temperature shown in Table 2 in the hot water bath, and the outer diameter regulating ring was expanded 3.0 times in the radial direction. After stretching 3.5 times in the axial direction, heat treatment was performed under the same conditions as in Example 1. The stretchability and shrinkage rate of the obtained tube were measured in the same manner as in Example 1, and the results are shown in Table 2. As shown in the table, experiments No. 1, 2, 5 of the present invention,
In experiments No. 6 and 7, tubes with a radial shrinkage rate of 40% could be stably produced, but in Experiment No. 3, where the temperature difference between the stretching start point and the stretching end point was less than 5°C, the radial shrinkage rate was 40%. %, and the stretching was also unstable. In Experiment No. 4, where the temperature difference was greater than 20°C, although the shrinkage rate was high, the tube diameter fluctuated so much that stable stretching was not possible.

[Table] Example 3 A mixture of 30% by weight of A resin similar to Example 1 and 70% by weight B resin similar to Example 1 was extruded in the same manner as Example 1 to form an unstretched product with an outer diameter of 3.7φmm and an inner thickness of 0.6mm. Got tube. After preheating this in a 75℃ hot water bath, air was pressurized while maintaining the stretching start point at 90℃ and the stretching end point at 80℃ in the hot water bath, and the outer diameter ratio was adjusted in the radial direction in the outer diameter regulating ring.
Stretch 2.5 times and 4 times in the axial direction and immediately at 40℃.
It was cooled to Next, in a heat treatment zone connected to the stretching zone, compressed air is supplied to the stretching zone by adjusting the nip pressure of the second nip roll (a third nip roll is provided at the end of the heat treatment zone, The heat treatment was carried out under the conditions listed in Table 3 below. In this case, the internal pressure in the heat treatment zone was the same as the internal pressure in the stretching zone. The heat treatment time was 3 seconds. Note that the curvature and waviness in Table 1 were measured as follows. Curvature: Place a flattened (folded) contraction tube 500mm long on a horizontal table and measure the width of the curvature when viewed from above. Waving: Place a flattened shrink tube with a length of 500 mm on a horizontal table and measure the waving height in the axial direction when viewed from the side. The measured value is the height of the largest wave within the 500mm length.

[Table] In Table 3 above, experiment numbers 1 to 12 are examples according to the method of the present invention, and experiment numbers 13 to 15 are comparative examples. As is clear from this table, in the examples according to the method of the present invention, the shrinkage rates in the radial and axial directions are maintained at a high level, and the curvature and waviness of the products are improved. On the other hand, in experiment number 13, in which no heat treatment was performed, and in experiment number 14, in which heat treatment was performed but the treatment temperature was too low, and in which axial relaxation and radial re-stretching were not performed, both curvature and waviness were significant. In Experiment No. 15, in which the heat treatment temperature was too high beyond the range of the present invention, both the axial and radial shrinkage rates were significantly reduced. The above explanation and examples are merely illustrative to aid understanding of the present invention, and the present invention is not limited to these examples, and other changes and modifications may be made within the gist of the invention. It is something that can be done.

Claims (1)

[Claims] 1 (A) Terephthalic acid with an acid component of 95 to 65% by weight and 5
An unstretched tube made of a mixture of 10-80% by weight of a polyester copolymer resin consisting of ~35% by weight of isophthalic acid and whose alcohol component is ethylene glycol, and (B) 90-20% by weight of polyethylene terephthalate. , while keeping the tube temperature at the stretching start point at 80 to 95°C and the tube temperature at the stretching end point 5 to 20°C lower than the stretching start point, pressurize gas into the tube and stretch it 2.5 times or more in the radial direction. , and then axially while maintaining the temperature at 70~85℃.
A method for producing a heat-shrinkable polyester tube, characterized by relaxing the tube by 0.5 to 15% and simultaneously re-stretching it in the radial direction by 1 to 20%.