JP2555693B2 - Method for manufacturing heat-shrinkable tube - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for producing a heat shrinkable tube having a low axial shrinkage rate, which is suitable for coating a capacitor.

(Prior Art) Heat-shrinkable tubes are widely used for coating various articles, and polyvinyl chloride resin (PVC) tubes are mainly used for capacitors for purposes such as rating display.
With the recent miniaturization of capacitors, the demand for coating tubes has become strict.

(Problems to be solved by the invention) A problem with capacitor tubes is that they undergo various heat treatments after coating the capacitors or the tubes undergo "secondary shrinkage" due to the high temperatures during use, causing "shoulder dislocation" and appearance. It is defective and the printed display becomes unreadable.

That is, as shown in the vertical cross-sectional view in FIG. 1, the condenser 1 is heat-shrinked to cover the tube 2 from the upper shoulder to the bottom, but when exposed to high temperature in this state, the tube 2 shrinks, There is a problem that the diameter D of the exposed portion becomes large, and finally it comes off the shoulder.

In the secondary shrinkage, when a heat-shrinkable tube is obtained, it is subjected to a considerable axial (longitudinal) tension during extrusion of the unstretched tube, so that the tube has an axial strain, and this strain is 150- This is because it appears as shrinkage in a high temperature range of 180 ° C.

In order to reduce this axial shrinkage, PVC is extruded at a high temperature, and the pull-down ratio (ratio between the slit spacing of the extrusion die and the thickness of the extruded tube) during extrusion is reduced so that axial distortion does not occur. It is possible to do so, but PV
There are problems such as thermal decomposition of C and a decrease in extrusion amount due to an increase in back pressure during extrusion, which is not practical.

Another problem is that the heat resistance of the tube is insufficient,
The heat treatment causes the tube to crack. This is because shrinkage stress remains in the shrink-coated tube, and when the tube softens at high temperature, the residual shrinkage stress relatively exceeds the strength of the tube.

(Means for Solving the Problem) The present invention is to solve the above problems all at once, by stretching an extruded unstretched PVC tube substantially only in the radial direction, and irradiating it with γ-rays to a suitable degree. By cross-linking the PVC tube, only the shrinkage at high temperature in the axial direction is reduced without lowering the radial shrinkage of the PVC tube, and the heat resistance of the tube is improved.

Irradiation of a tube made of polyethylene or the like is usually performed before stretching, which is to impart a contracting function.
On the other hand, irradiation of the PVC tube is performed solely for improving heat resistance because the material itself already has a heat shrink function, and irradiation is performed before stretching so as not to impair the shrink function imparted by stretching. ing.

However, surprisingly, as described above, it has been found that a tube stretched only in the radial direction can be irradiated with radiation after stretching and appropriately crosslinked to obtain the above-mentioned properties suitable for coating a capacitor. It is a thing.

 Hereinafter, the present invention will be described specifically.

The material of the tube in the method of the present invention is 100 parts by weight of PVC to which 1 to 30 parts by weight of a polyfunctional monomer or oligomer having two or more functional groups in the molecule is added.

As the PVC, either a normal homopolymer or a copolymer containing a small amount of a copolymer component can be used.

The polyfunctional monomer or / and oligomer added to PVC as a cross-linking agent is a compound having two or more functional groups such as acryl group, methacryl group, allyl group and vinyl group in the molecule. Known per se can be used as disclosed in Japanese Patent No. 17694.

Specifically, diallyl isocyanurate, triallyl isocyanurate, di (meth) acrylic isocyanurate, tri (meth) acrylic isocyanurate, 1,4-butanediol di (meth) acrylate, polyethylene glycol di (meth) acrylate, Examples thereof include pentaerythritol di (meth) acrylate, dipentaerythritol hexaacrylate, trimethylolpropane tri (meth) acrylate, and divinylbenzene.

The amount of polyfunctional monomer added is 1 to 100 parts by weight of PVC.
It is in the range of 30 parts by weight, preferably 3 to 15 parts by weight. If the amount is less than 1 part, the effects of the present invention cannot be obtained because crosslinking does not occur sufficiently even when irradiated with γ-rays, and if it exceeds 30 parts, the crosslinking efficiency becomes too large and the radial shrinkage is greatly suppressed. , A tube with good shrinkage coverage cannot be obtained.

To PVC, usual additives such as heat stabilizers, coloring agents and small amounts of plasticizers can be added.

In the method of the present invention, the PVC composition is extruded into a tubular shape, and a usual annular die can be used for it. In this case, if the ratio of the slit spacing of the annular die and the resulting tube thickness (drawing-down ratio) is too large, the extruded tube will have a large axial strain (longitudinal direction), and the γ-ray Since it is not possible to suppress the shrinkage in the axial direction by irradiating and crosslinking the resin, the extrusion temperature and the draw-down ratio of PVC are adjusted so that the shrinkage in the axial direction at 180 ° C is 30% or less, preferably 25 % Or less.

Within this range, it is possible to adjust without impairing productivity.

Then, the extruded tube is cooled to an appropriate drawing temperature, or is once cooled and then reheated to an appropriate drawing temperature to be drawn in the radial direction.

The stretching temperature is 80 to 100 ° C., and the stretching ratio is preferably 1.5 times or more in the radial direction, particularly preferably 1.8 to 2.2 times.

By stretching in this manner, a stretched tube having a shrinkage ratio of 100 to 50 ° C in the radial direction of 30 to 55% and a shrinkage ratio necessary for shrinkage coating processing can be obtained. The strain remains due to the influence of the tension when extruding and taking out.

After the drawn tube is cooled, it is irradiated with γ-rays of 1 to 20 Mrad to crosslink it so that the gel fraction is 5 to 80% by weight, preferably 10 to 60% by weight.

If the irradiation dose is less than 1 Mrad, sufficient cross-linking does not occur, and even if it exceeds 20 Mrad, the cross-linking does not proceed and the decomposition of PVC begins to occur. Particularly preferred is the range of 3-10 Mrad.

Since γ-rays have a high penetrating power, it is preferable that a large number of wound roll-shaped stretched tubes be wound and the γ-ray irradiation treatment be performed at one time.

The gel fraction of the tube is determined depending on the number of functional groups of the cross-linking agent, the addition amount, the irradiation amount, the type of other additives in PVC, etc., but the range of 5 to 80% is preferable. If it is less than 5%, the effect of reducing the longitudinal shrinkage and improving the heat resistance is insufficient, and if it exceeds 80%, the shrinkage in the radial direction required for shrinkage coating is greatly suppressed.

Here, the gel fraction is the weight ratio of the insoluble matter when the tube is immersed in tetrahydrofuran at 20 ° C. for 48 hours.

According to the present invention, by performing γ-ray irradiation after stretching the tube, the radial shrinkage ratio (100
It is possible to significantly reduce only the high-temperature (for example, 180 ° C.) shrinkage ratio in the longitudinal direction that causes shoulder dislocation and the like, with almost no decrease in (° C.).

According to the experiment, by appropriately crosslinking by γ-ray irradiation after stretching, the shrinkage in the radial direction at 100 ° C is reduced only by about 1 to 2%, whereas the shrinkage in the axial direction at 180 ° C is 5 to 15%. To some extent. Therefore, without sacrificing productivity in particular, it is possible to easily obtain a stretched tube having an axial shrinkage at 180 ° C. of 20% or less, preferably 15% or less, which is extremely effective in preventing shoulder dislocation. .

Further, by irradiating the tube after stretching, there is an advantage that the waste raw material generated in the stretching step can be reused because it is not yet cross-linked.

The shrinkable tube obtained by the method of the present invention is particularly suitable for coating a capacitor because it has a small vertical shrinkage at high temperature and high heat resistance.

(Example) The following formulations were uniformly stirred and mixed with a blender, and extruded into a tube shape having a thickness of 0.18 mm and an outer diameter of 3.25 mm with an extruder at a die temperature of 195 ° C, a stretching temperature of 100 ° C, and a radial stretching ratio. It was stretched 1.8 times in the radial direction, cooled, folded and wound into a roll. The tube had a diameter of 5.85 mm and a thickness of 100 μm.

Then, for tube A, gamma
It was irradiated with 5 Mrad to obtain a crosslinked tube.

A ... PVC 100 parts by weight Plasticizer 10 Stabilizer 15 Impact modifier 3 Polyfunctional monomer 5 B ... A excluding polyfunctional monomer Dipentaerythritol hexaacrylate is used as the polyfunctional monomer. used.

 The characteristics of this tube are shown in Table 1.

 Then, the A and B tubes were coated on the condenser.

As the capacitor, a cylindrical aluminum capacitor having a diameter of 5 mm and a height of 7 mm was used, and the tube having a length of 9.1 mm was covered therewith and heated at 250 ° C. for 5 seconds to shrink-coat the tube. The diameter D of the exposed portion of the upper surface of the capacitor was 3.2 mm.

 The following performance was evaluated for the coated capacitors.

(1) Off-shoulder acceleration test 50 capacitors each in 150 ℃ atmosphere for 30 minutes and 200 ℃
Was allowed to stand in the atmosphere for 10 minutes, and the degree of shoulder dislocation (diameter D) of the capacitor was measured.

(2) Crack acceleration test Each side of 30 capacitors was needle-inserted with a needle pressure of 1 kgf / cm ² , and left standing in an atmosphere of 150 ° C for 10 minutes, and the tubes were cracked.

As is clear from the above results, the tube A produced by the method of the present invention has a small axial shrinkage at 180 ° C., and as a result, the reduction in the coating width on the shoulder portion of the capacitor is small. Regarding the state of cracks, in tube B, cracks run to the end of the tube, whereas in tube A, many cracks have stopped halfway, and heat resistance has improved significantly. I understand.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a state in which a heat-shrinkable tube is coated on a capacitor. 1 ... Capacitor, 2 ... Heat-shrinked tube D ... Diameter of exposed part

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location B29L 23:00

Claims (1)

(57) [Claims] 1. A composition obtained by adding 1 to 30 parts by weight of a polyfunctional monomer or oligomer having two or more functional groups in the molecule to 100 parts by weight of a polyvinyl chloride resin is extruded into a tubular shape, Direction, the shrinkage at 100 ° C in the radial direction is 30-55%, and the shrinkage at 180 ° C in the axial direction is 30%.
% Or less, and then 1-20 Mrad γ
Irradiate with a ray to set the gel fraction to 5-80%, and
A method for producing a heat-shrinkable tube, which has a shrinkage rate at 20 ° C. of 20% or less.