JPS5855892B2 - Manufacturing method for heat-shrinkable plastic molded products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a heat-shrinkable plastic molded article.

Conventionally, when manufacturing heat-shrinkable plastic molded products, particularly heat-shrinkable tubes, the tube is expanded in the radial direction of the tube by applying fluid pressure inside the tube at a Ki- temperature above the crystal melting point and below the flow temperature of the material forming the tube. Apply stretching strain to
Next, a method is used in which the stretching strain is fixed by cooling the sheet.

However, with this method, the tube does not necessarily expand uniformly due to uneven heat distribution during tube expansion, and in order to reduce variations in tube wall thickness by making this uniform, it is necessary to Various complicated processes were required.

On the other hand, a method has also been proposed in which the diameter of the tube is stretched in the radial direction by mechanical means by inserting an instrument capable of expanding the diameter into the heated tube. There are unavoidable drawbacks that make the task extremely difficult.

Furthermore, there is also a method of inserting a bag-like article into a tube and applying fluid pressure to it to inflate the tube, and applying internal pressure to the tube to inflate it in a tube of a predetermined diameter in order to regulate the outer diameter. There are also methods.

However, in any case, as mentioned above, when the tube diameter is small, it is difficult to expand the tube, and there is a problem in that the efficiency is significantly reduced.

Further, when the shape of the finished product is not a simple shape such as a cylindrical body, the above method may not be appropriate even if the product has a large diameter.

The inventors completed this invention as a result of intensive studies to solve these problems.

That is, this invention forms a coating layer of crystalline rubber or plastic on a core body that has heat recovery properties that expands in diameter when heated, and then heats the coating layer at a temperature above the crystal melting point and below the flow temperature of the coating material. A method for manufacturing a heat-shrinkable plastic molded article, which comprises expanding the diameter of the core, aligning it with the coating layer to apply a radial stretching strain, and then pulling out the core after fixing the stretching strain. It is.

This invention is used as a diameter expander for a core crystalline rubber or plastic molded product that has heat recovery properties such that its diameter expands when heated, and the covering material on the core expands when the core is heated. By integrally increasing the diameter and applying stretching strain in the radial direction of the covering material, the above-mentioned problem of uneven thickness and operational problems are almost eliminated.

Various methods have already been proposed for obtaining the core body with heat recovery properties that expands in diameter when heated, which is used in this invention.One specific example is the extrusion molding of polyethylene into a string shape with a circular cross section. A product is obtained, crosslinked by irradiation with radiation, and then stretched by a desired amount in the axial direction at a temperature above the crystalline melting point of the polyethylene and below the melting temperature to reduce its diameter and fix it.

This stretched string-like extrusion molded product is heated to the original size &C.
The heat will recover in 4.

The cross-sectional shape of this core body is mainly circular, but depending on the purpose, various other shapes are also used, as well as tapered ones with a diameter that gradually increases in one direction, and ones with a diameter that increases gradually in one direction. Things are also used.

The workpiece materials used in this invention include all plastic materials and molded products made of crystalline rubber, etc., which have the property of being subjected to stretching strain by expanding the diameter in the radial direction. .

The material to be processed is coated on the core, heated at a temperature above the crystal melting point of the material and below the flow temperature, and stretched in the radial direction by expanding the diameter of the core. It is desirable that the crystalline melting point and flow temperature of the material to be processed be as similar as possible, and best if possible, the same.

When the material to be processed is extruded and coated on the core, the extrusion temperature is generally high and heat recovery may occur in the core.In such cases, it is recommended to rapidly cool the material after extrusion. desirable.

However, such a cooling step may not always be necessary if the heat capacity of the sheath is smaller than that of the core.

In addition, by selecting various operations and conditions such as the heat recovery temperature of the core, core diameter, coating layer thickness, extrusion temperature, cooling rate, preheating and precooling of the core, extrusion of the coating layer and expansion of the core can be controlled. It is also possible to perform both in one step.

As described above, the coating layer is stretched in the radial direction by expanding the diameter of the core, and then it is cooled and fixed.

The core is then pulled out, and in order to facilitate this core pull-out, it is desirable to appropriately select the material of the core and perform mold release treatment on the surface of the core.

Although the above description takes as an example the case in which the sheath is continuously extruded, the sheath may be formed by other methods, such as being shredded, pre-formed, cooled, and then placed over the core. Alternatively, a core body may be inserted.

As described above, the present invention uses a core body having heat recovery properties that expands in diameter when heated, forms a coating layer thereon, and applies stretching strain in the radial direction of the coating layer by expanding the diameter of the core body. Therefore, since the stretching is carried out integrally with the diameter expansion of the core, the problem of uneven thickness is solved, and the above-mentioned operational problems when the diameter is small are also significantly reduced. has been completely solved and its industrial value is extremely large.

The present invention will be specifically explained below with reference to Examples.

Example 1 A string-like extruded product with a diameter of 1.61n71L was made from low-density polyethylene, and crosslinked by irradiating it with an electron beam of 40 Mrad.

This string-like extruded product is heated to 140°C and stretched,
The diameter was reduced to 1.1 degrees and the core material was cooled and fixed.

Separately, a cross-linked polyethylene tube was prepared by irradiating a low-density polyethylene tube with an inner diameter of 1.1 mm and a wall thickness of 0.118 mm with an electron beam of 40 Mrad.

The core material was cut to a length of 300 mm, and silicone grease was applied thinly to the surface to perform mold release and lubrication treatment.

Approximately 100 pieces of the above cross-linked polyethylene tube is placed on top of it.
It was cut into a length of mm, inserted and coated, and placed approximately in the middle of the entire length of the core material.

Hot air of 135 to 140'C is blown from approximately the center one by one so that both the covering material and the core material reach the heat distortion temperature or higher, and the heating position is sequentially moved from the middle part to both ends to move the core body in the radial direction. Inflated.

At this time, the core gradually reduces its length and is drawn into the covering.
I'm going to go.

After the diameter expansion of the core was almost completed, the entire core was transferred to a constant temperature air bath at 135° C. and heated for 10 minutes to complete the diameter expansion.

After cooling, the core was pulled out to obtain a heat-shrinkable cross-linked polyethylene tube with an inner diameter of 1.6 mm.

This heat-shrinkable tube has a very high roundness in cross-section, especially on the inner surface, and the thickness distribution of the residual wall is almost similar to the distribution before expansion, meaning that specific parts are concentrated in diameter and become thinner. There was no.

A copper wire with a diameter of L4 mm was passed through this tube and heated and shrunk with a burner, resulting in good adhesion and a coated wire was obtained.

Example 2 A cross-linked low-density polyethylene rod with a diameter of 20 mm was placed in a sleeve with a length of 20 cm, an inner diameter of 11 mm, and an outer diameter of 15 mm, at a temperature of 140°C to have a diameter of 12 mm. A cross-linked polyethylene rod-shaped body with a length of 80 cm obtained by stretching it to
The core was heat-recovered by being kept in a constant temperature bath kept at 5°C.

Through this heat treatment, the diameter of the core was expanded to approximately 18 mm, and the sleeve was expanded to have an inner diameter of 18 mm.The sleeve was made of heat-shrinkable EPR rubber.
Steel pipe between R rubber sleeve diameter 12 and outer diameter 16m7I
After it was inserted onto each L steel pipe for the purpose of connecting it, it was heated and shrunk with a burner, and was able to be attached extremely firmly to both pipes.

Example 3 Cross-linked polyethylene was used to form main bodies 1 to 3 as shown in Figure 1.
A core material 3 having a shape in which the book technique 2 was protruded was obtained.

This core material 3 was heated to about 140'C and stretched to about three times the length of Technique 2, and the main body 1 was rolled with a roll to reduce its outer diameter by 30%, and then cooled and solidified.

Next, after applying mold release grease to the entire surface of this core body 3, a thin-walled cross-linked polyethylene molded product with a wall thickness of 1.2 mm and made equal to the shape of this core body is covered, and an electric current of 135°C is applied. The core body 3 is heated in a constant temperature bath to recover the heat, and the thin-walled molded product is subjected to stretching strain.After cooling and solidifying the thin-walled molded product by 1 inch, the core body 3 is extracted and the technique 6 is removed from the large diameter main body 5 in FIG. The present protruded cable terminal cap 4 was obtained.

When this cable end cap 4 was used to insulate the end of a three-core cable 7 as shown in the figure, the cable 7 and core 8 were easily inserted and the adhesion was good due to heating, which was very good.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a core used as a button in one embodiment of the present invention, and FIG. 2 is a perspective view of a cable terminal portion insulated with a cable end cap formed using the concentric body. 3... Core body, 4... Cable terminal cap.

Claims (1)

[Claims] 1. A coating layer made of crystalline rubber or plastic is formed on a core body that has a heat recovery property that expands in diameter when heated, and then the core body is expanded by heating at a temperature above the crystalline melting point and below the flow temperature of the coating material. A method for producing a heat-shrinkable plastic molded article, which comprises applying stretching strain in the radial direction to the coating layer, fixing the stretching strain, and then pulling out the core.