JPH0798359B2 - 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 (PVC) tubes are mainly used for capacitors as well for purposes such as rating indication. With the miniaturization of, the demand for coating tubes has become stricter.

(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. Bad,
There is a point that 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 of the slit interval of the extrusion die and the thickness of the extruded tube) at the time of extrusion is made small so that axial distortion does not occur. PVC can be
It is not practical because there are problems such as thermal decomposition of and the decrease of extrusion amount due to the increase of back pressure during extrusion.

Another problem is that the heat resistance of the tube is insufficient and the tube is cracked by heat treatment. 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 appropriately irradiating it with an electron beam. 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.

Surprisingly, however, as described above, it was found that a tube stretched substantially only in the radial direction can be irradiated with radiation after stretching and appropriately cross-linked to obtain the above-mentioned properties suitable for capacitor coating. It is a thing.

The present invention will be specifically described below.

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 isocyanate, triallyl isocyanate, di (meth) acrylic isocyanate, tri (meth) acrylic isocyanurate, 1,4-butanediol di (meth) acrylate, polyethylene glycol di (meth) acrylate, pentaerythritol diisocyanate. Examples thereof include methacrylate, dipentaerythritol hexaacrylate, trimethylolpropane methacrylate, divinylbenzene and the like.

The amount of polyfunctional monomer added is 1 to 30 per 100 parts by weight of PVC.
Parts by weight, preferably in the range of 3 to 15 parts by weight. If the amount is less than 1 part, the effect of the present invention cannot be obtained due to insufficient crosslinking even when irradiated with an electron beam, 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 gap between the slits of the annular die and the thickness of the resulting tube (drawing ratio) is too large,
The extruded tube will have a large strain in the axial direction (longitudinal direction), and it will not be possible to suppress the axial shrinkage even if it is cross-linked by irradiation with an electron beam later. The ratio is adjusted so that the axial shrinkage at 180 ° C. is 30% or less, preferably 25% or less.

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

Then, cool the extruded tube to an appropriate temperature for stretching, or
Alternatively, it is once cooled and then reheated to an appropriate temperature for stretching and stretched in the radial direction.

Stretching temperature is 80 ~ 100 ℃, stretching ratio is 1.5 times or more in the radial direction,
Particularly, the range of 1.8 to 2.2 times is preferable.

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 cooling the stretch tube, fold it preferably flat.
Irradiation with an electron beam of 1 to 20 Mrad is carried out 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.

The electron beam irradiation is 5M from both sides of the folded stretched tube.
It is preferable to perform the treatment in several doses at a dose of rad or less.

The gel fraction of the tube is determined by the number and amount of functional groups in the cross-linking agent,
The range is 5 to 80%, although it depends on the irradiation dose and the types of other additives in PVC. 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 calculated by using a tube in tetrahydrofuran.
It is the weight ratio of the insoluble matter when immersed at 20 ° C for 48 hours.

According to the present invention, by performing electron beam 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 electron beam irradiation after stretching, the shrinkage in the radial direction at 100 ° C is reduced by only 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 thinned tube after stretching, it is possible to cause cross-linking at a relatively low accelerating voltage, so that the irradiation device may be small, and uniform treatment is performed in the thickness direction of the tube. It has the advantage that it can be reused because the waste material generated in the stretching process is not yet crosslinked.

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

(Example) The following compounds were uniformly mixed with a blender by stirring, 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, with respect to the A tube, 2.5Mra electron beam from both sides
A total of 5 Mrad was irradiated for each d 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 Each of 50 capacitors was allowed to stand in an atmosphere of 150 ° C. for 30 minutes and in an atmosphere of 200 ° C. for 10 minutes to measure the degree of shoulder off (diameter D).

(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 observed to crack.

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 decrease in the coating width of the capacitor shoulder 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

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Claims (1)

[Claims] 1. A composition in which 1 to 30 parts by weight of a polyfunctional monomer or oligomer having two or more functional groups in a molecule is added to 100 parts by weight of a polyvinyl chloride resin is extruded into a tube shape to have a diameter of 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 the drawn tube is irradiated with an electron beam of 1 to 20 Mrad to adjust the gel fraction to 5 to 80%, and
A method for producing a heat-shrinkable tube, wherein the shrinkage rate at 0 ° C. is 20% or less.