FI76020C - Process and apparatus for producing heat shrinkable polymeric hollow articles mainly of polyvinyl chloride plastics - Google Patents

Description

1 76020

The present invention relates to plastics molding technology and is based on the treatment of preformed, structured, hollow blanks. In particular, the invention relates to a method and an apparatus for manufacturing heat-shrinkable, hollow plastic products from polyvinyl chloride plastics. The heat-shrinkable hollow plastic products thus obtained, which are made of polyvinyl chloride plastics, have a wide range of applications in the electrical and radio industries, electronics and telecommunications for electrical insulation purposes, and in the chemical, petrochemical and gas industries for sealing and packaging purposes.

15 These products are made of (physicochemically or physically) structured plastic to prevent the plastic from leaking during orientation. Heat-shrinkable, hollow plastic products have the property of shrinking when subsequently heated.

A method for making heat-shrinkable articles from polyvinyl chloride plastics is known in the art, which comprises structuring extruded articles by irradiation, subsequent thermal orientation and cooling to obtain a new shape (EE Finkel et 25 RP Braginsky, "Heat-resistant conductors with ", Moscow," Energija ", 1975, pp. 120-125, in Russian). In this method, the amount of crosslinking of the article-specific article material is limited by more than 50% of the gel portion, and thermal orientation of the material 30 is accomplished at temperatures in excess of the temperature of the viscous flow of plastic. The method is forced to achieve a high degree of crosslinking, which causes a lot of work in the manufacture of plastic products and results in their lower heat resistance. In addition, with the thermal orientation of the crosslinked 35 products, a large number of scrap products, more than 10%, occur due to the large deterioration in the elasticity of the products.

2 76020

In addition, a process for making heat-shrinkable, hollow plastic products from polyvinyl chloride plastics is known in the art (Encycl. Polym. Sci. London 1969 Vol. 9 pp. 106-126). This method comprises molding hollow preforms 5 from polyvinyl chloride plastics, structuring the preform, heating and orienting the products under mechanical load at a temperature between the alpha conversion temperature of the polymer and the pour point of the polymer, and cooling to secure the new shape of the preforms. which does not exceed 50%. The sequence of these steps in the method makes it possible to keep the production of defective products to a considerable extent and to reduce the need for labor to a certain extent due to the lower degree of crosslinking required. But since the manufacture of hollow plastic articles by this method involves their necessary additional structuring, the heat resistance of the obtained articles is reduced and the need for labor in their manufacture is still high. In addition, plastics 20 based on polyvinyl chloride contain a large amount of filler, which makes the degree of orientation of the different areas of the articles very uneven.

The device for carrying out the known method comprises, connected in series, the following parts: a chamber for heating the blanks, for thermally orienting the chamber molds by blowing, and a cooling chamber for fixing the new shape of the blanks. The second chamber has an internal cavity with a diameter corresponding to the required diameter of the blank in the final (thermally oriented) form. In the manufacture of articles from polyvinyl chloride plastics in this device, harmful distortion of the preform occurs prior to thermal orientation of the preform, which quite often results in uncorrected preform defects.

The object of the invention was to develop, by means of the physical structuring of a substance, a method for producing heat-shrinkable hollow articles from polyvinyl chloride plastic, and an apparatus for carrying out the method which do not require the use of a blank.

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3,76020 physico-chemical modifications, which reduces the need for labor in the manufacture of heat-shrinkable articles.

This object is achieved by the present invention, which relates to a process for producing heat-shrinkable, hollow plastic products from polyvinyl chloride plastic by molding said plastic, heating a polyvinyl chloride plastic molded, structured, hollow preform in a region of between the pouring temperature, and then cooling to stabilize the shape of the blank. The process according to the invention is characterized in that a polyvinyl chloride plastic is used which is mixed with an isoprene / styrene or divinyl / styrene or dimethyl / styrene block copolymer having from 20 to 40 mol% of styrene groups in the side chain: parts to a block copolymer of 2.5 to 3.5 parts by weight and that the cooling of the preform is carried out at a rate of 6-40 ° C / min.

By using polyvinyl chloride plastics, which additionally contain the above-mentioned block copolymers, and by cooling the blanks at a certain rate, it is possible to produce heat-shrinkable objects with as little deviation as possible from the arithmetic mean of stresses when samples are drawn 100%, e.g. 5 times.

30 residual deformation after heating and cooling.

When making heat-shrinkable, hollow plastic products in the form of a tube, according to the invention it is desirable to apply an axial load to the blanks before heating and orienting the pipe blanks so as to provide a tensile force of 20 to 50% of the blank fracture force and then perform convection-type heating. , while uniformly reducing the applied axial load to a value not exceeding 15% of the value of the breaking force of the blank, thereby providing a relative elongation of the blank of 2 to 8%.

The invention further relates to an apparatus for producing heat-shrinkable plastic products in the form of tubes, which according to the invention comprises a removable cooling jacket in which a heating part is arranged, on which a tubular blank is arranged, and means for supplying compressed air between the blank and the heating part. the same shape as the tube blank, and there is a spring between the end of the heating part and the end of the blank, which produces a tightening force. The device according to the invention makes it possible to produce heat-shrinkable tubes from polyvinyl chloride plastics in 98% yield.

The invention is further illustrated by the accompanying drawings, in which Figure 1 shows a vertical sectional view of an apparatus according to the invention for carrying out the method according to the invention for producing heat-shrinkable, hollow, tubular plastic products; and Fig. 2 shows a cross-sectional view along the line II-II in Fig. 1 (the cooling jacket is opened).

The process according to the invention for producing heat-shrinkable, hollow plastic products from polyvinyl chloride molds is carried out as follows: Hollow blanks, e.g. in the form of a tube, are formed from polyvinyl chloride plastics which additionally contain % ver-30 ran. The block copolymer is included in the composition in an amount of 2.5 to 3.5 parts by weight per 100 parts by weight of the polyvinyl chloride plastic. If the amount of the block copolymer is more than 3.5 parts by weight, the result is only a low-efficiency physical structuring, but if the amount is less than 2.5 parts by weight, it results in a greater unevenness of the properties of the block block-35 polymer articles. Reducing the content of styrene groups to less than 20 mol% does not ensure the required performance of the articles.

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5,76020, and if the content of styrene groups is more than 40 mol%, the result is a sharp reduction in the thermoforming of the articles, making their use impossible.

The extruded preforms are oriented under a mechanical load by blowing into various blow ratios at a temperature in the range between the temperature of the alpha change of the polymer and the pour point of the polymer.

The blowing of the blank is carried out under a vacuum provided on the outer surface side of the blank and / or at a pressure provided in the blank cavity by an air blower. The preforms are then cooled at a rate of 6-40 ° C / min from the final orientation temperature to a temperature that ensures the stability of the preform shape. When the cooling rate is above 40 ° C / min, the properties of the finished articles do not improve in practice, and the implementation of the method is quite complicated under these conditions due to the low thermal conductivity of the plastic; when the speed is less than 6 ° C / min, the shape achieved in the orientation cannot be made permanent.

The method according to the invention makes it possible to produce heat-shrinkable, hollow plastic products of any shape, e.g. pipes, installation gloves, lids.

The polyvinyl chloride plastics used in the process of the invention contain, per 100 parts by weight: 40 to 80 parts by weight of a plasticizer such as dibutyl phthalate, dioctyl 25 phthalate, tricresyl phosphate, trioctyltrimethylmethane, tetraoctyl pyromellitate, 0.5 to 5 parts by weight of stabilis , triphenyl phosphite, antimony trioxide, dibutyltin dilaurate, 0.5 to 5 parts by weight of an antioxidant such as calcium stearate-30, diphenylolpropane, 2,6-di-tert-butyl-4-methylphenol.

When making heat-shrinkable, hollow, tubular plastic products, an axial load is applied to the tubular preforms prior to heating and orientation so that the tensile force is 20 to 50% of the fracture force of the preform. Convection heating of the blank is then performed on the inner surface side.

During heating, the load is uniformly reduced to 6,76020, which is no more than 15% of the value of the breaking force of the blank, which ensures that the relative elongation is 2 to 8%. The best result can be achieved by reducing the load exponentially.

Numerous studies have now been carried out to obtain a method and apparatus suitable for making heat-shrinkable tubes with a closed end, for which purpose the blank was heated from the inside directly in a removable mold for a time sufficient to heat the blank 10 to the required temperature inside, compressed air , which blows the blank into contact with the mold relative to the cold wall, which ensures the shape stability of the blown object. However, it has been found that the blank loses its stiffness after heating, is distorted and partially contacts the surface of the heating part, causing the blank to heat unevenly; and for this reason the relaxation properties of the different areas of the blank also become uneven, which after blowing leads to a lower! valuable objects with defects such as different wall thicknesses and local blisters. To overcome this disadvantage, a small stretching force is applied axially to the blank. This method has made it possible to stabilize the relative position of the functional surfaces of the blank and the heating part, to achieve uniform relaxation properties for the blank before blowing and thus to produce first-class articles from heat-shrinkable materials.

The device for making heat-shrinkable tubes from polyvinyl chloride plastics comprises a removable cooling jacket 1 (Fig. 1), inside which there is a heating part 2, which is e.g. a rod. The tubular blank 3 is arranged on a heating part 2, to the end of which a spring 4 with a retainer 5 is attached to provide a tensile force. At the bottom of the device there is an inlet pipe 6 from which compressed air 35 is supplied between the blank 3 and the heating part 2. All parts of the device are mounted on the rotating table of the rotating machine (not shown) 7.

tl 7 76020

The device for producing heat-shrinkable, hollow plastic pipes works as follows:

The tubular blank 3 is placed inside a removable cooling jacket 1. A stretching 5 is applied to the closed end of the blank by bringing the blank into contact with the retainer 5, after which the jacket 1 is switched on and the heating is switched on. The load must produce a tensile force of 20 to 50% of the value of the breaking force of the blank.

Studies have shown that a tensile force of less than 20% of the breaking load cannot completely eliminate the distortions of the billet caused by heating, leading to inferior products, whereas a force of more than 50% of the breaking load results in local thinning, which also leads to product-15 rejection. Inspection tests have shown that with a relative elongation of the product during molding of 2 to 8% and a residual tensile strength of up to 15% of the breaking load, the formation of wasted objects is substantially eliminated.

20 During heating, the load must be reduced evenly, as the mechanical properties of the preform deteriorate as the temperature rises. This reduction must be carried out without abrupt changes in the load, otherwise there is a greater risk of defective objects. When the blank 25 3 is heated, the tensile force decreases due to the slight elongation of the blank, so that the clearance between the outer surface of the heating part 2 and the inner surface of the blank 3 decreases and in the extreme case completely closes so that the blank is tightly against the heating part. This fact contributes to a more even heating of the blank 30, which ensures the production of high quality articles after blowing. The best results are obtained when the load is reduced exponentially, because experiments have shown that the change in the mechanical properties of heat-shrinkable materials with respect to temperature complies with this exponential law.

After the residence time of the blank has been sufficient to heat it to the required temperature, 8 76020 compressed air is passed between the blank 3 and the heating part 2 through the pipe 6; compressed air blows the blank up into contact with the cooled wall of the jacket 1. In this case, the cooling of the blank and the stabilization of its shape take place simultaneously. The Sa-5 racket stops the energy supply to the heating section and the air supply. The jacket 1 is opened, the finished object is taken out, a new blank 3 is placed on the heating part 2 and the whole cycle is repeated.

With the method and device according to the invention, it is possible to manufacture first-class objects from heat-shrinkable materials, whereby it is possible to improve the reliability of main and butt joints, reduce the amount of work and improve the quality of assembly and repair work in cable installations. The method according to the invention is preferably carried out with the blank in a vertical position (to eliminate the effect of gravity), although the method can in principle be carried out in any position of the blank.

To facilitate understanding of the invention, the following are a few examples that illustrate a method of making heat shrinkable hollow plastic products from polyvinyl chloride plastics.

Example 1 In this example, a polyvinyl chloride plastic having the following composition by weight is used; polyvinyl chloride 100.0; dioctyl phthalate 45.0; lead trioxide 5.0; calcium stearate 3.0; silica (SiO 2) 2.5.

The above-mentioned polyvinyl chloride plastic containing 100 parts by weight; 2.5 parts by weight of an isoprene-styrene-block copolymer containing 20 mol% of styrene groups in the side chains is extruded into tubes having an outer diameter of 20.0 mm and a wall thickness of 1.2 mm from an extruder having a screw diameter of 90 mm. The temperatures in the drum areas are as follows: I area 115 h 5 ° C; Region II 130 h 5 ° C; Zone III 140 ± 5 ° C; and the temperature of the spray head is 35 t 5 ° C. The extruded tube is subjected to orientation at a temperature of 100 to 5 ° C by blowing it at a gauge pressure of 101 ± 10 kPa to a blowing ratio of 2,5, which

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After 9,76020, the blank is cooled at a rate of 6 ° C / min. The quality of the objects obtained is evaluated by defining: 1) 2 ^ = deviation range from the arithmetic mean of the stress by 100% stretching of the samples cut from 5 oriented and cooled tubes. The dimensions of the sample are length (1) = 15 mm, thickness (b) = 4 mm. The samples are drawn in a traction machine. The separation speed of the machine jaws is 100 mm / min. 2) RDc ~ residual deformation after cooling of the sample, calculated from the following formula: 10 10 - 1 RD = -2-S. loo%, 1, -1 1 o where 1Q is the initial length of the sample; 1 ^ is the length of the sample after orientation; 1 ^ is the length of the sample after cooling.

3) RD ^ = residual deformation of the sample when the sample is heated to a temperature that ensures possible shrinkage.

RD ^ is calculated from the formula: i, -1, RD. = __ ± _ £ # loo%, h 1 - 1 20 L2 o where l ^ is the length of the sample after shrinkage.

Thus, pipes with the following properties are produced: Δ = 5.5%, RDc = 100%, RD ^ = 100%. Table 1 shows the properties of the articles made of polyvinyl chloride plastic to which an isoprene-styrene-block copolymer has been added.

Example 2 100 parts by weight of a polyvinyl chloride plastic having the composition defined in Example 1 to which 30 parts by weight of a divinylstyrene-block copolymer containing 20 mol% of styrene groups in its side chains have been extruded are tubes having an outer diameter of 30.0 mm. and a wall thickness of 1.5 mm, in the same manner as described in Example 1 above. The tubes are oriented at a temperature of 60 h 35 5 ° C by blowing 400 to 670 Pa under a vacuum developed from outside the tubes. The tubes are then cooled at a rate of 6 ° C / min. Table 2 shows the properties of articles 10,76020 made of polyvinyl chloride plastic to which a divinylstyrene-block copolymer has been added.

Example 3 100 parts by weight of a polyvinyl chloride plastic having the composition defined in Example 1 to which 2.5 parts by weight of a dimethylstyrene-block copolymer containing 20 mol% of styrene groups in its side chains have been extruded are tubes extruded with an outer diameter of 8.0 mm. and a wall thickness of 1.0 mm, in the same manner as described in Example 1. The tubes are directed at a temperature of 95 h at 5 ° C by blowing at a gauge pressure of 81 kPa and cooled at a rate of 6 ° C / min. Table 3 shows the properties of the articles made of polyvinyl chloride plastic to which dimethylstyrene-block copolymer has been added.

Example 4 100 parts by weight of a polyvinyl chloride plastic having the composition defined in Example 1 to which 3 parts by weight of a dimethylstyrene-block copolymer containing 30 mol% of styrene groups in its side chains have been extruded into tubes by the method described in Example 1. heated from the inner surface to 110 ° C. Prior to heating, an axial load is applied to the pipe, which ensures an axial force of 30 kg / cm, which is reduced to 5 kg / cm during heating. The relative elongation of the tube in this case is 5%. The change in axial load is performed exponentially. The yield of acceptable objects is up to 98%.

As can be seen from the following tables, the articles made according to the invention are not inferior to those produced by the prototype method K (closest prior art) in terms of residual deformation (RDc and RD 2), while the uniformity of thermal orientation (Δ) of different parts of the products is much better than the latter. Thus, an important advantage of the method according to the invention is that it can be used to produce thermally oriented articles from polyvinyl chloride plastics which have the best properties without laborious, additional structuring.

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II

Claims (3)

A process for producing heat shrinkable, hollow plastic articles from a polyvinyl chloride plastic by forming said plastic, heating the textured hollow blank formed from the polyvinyl chloride resin, and orienting the polyvinyl chloride resin under a mechanical load at a temperature within the range. transition temperature and flow temperature and then by cooling 10 to stabilize the form of the substance, characterized in that a polyvinyl chloride resin is used which is mixed with an isoprene / styrene or divinyl / styrene or dimethyl / styrene block copolymer with 20 to 40 mol% of styrene groups in the side chain, wherein the polyvinyl chloride resin and the block copolymer are used in the following ratio: polyvinyl chloride resin 100 parts by weight block copolymer 2.5 - 3.5 parts by weight and the cooling of the blank is carried out at a rate of 6-40 ° C / min. 20 2. A method according to claim 1, characterized in that, in the production of heat shrinkable, hollow polymer articles, pipe blanks are subjected to an axial load prior to heating and orientation, which provides a tensile force of 20 - 50% calculated on. the breaking force of the blank 25, after which the inner surface of the blank is heated by convection, and the axial load is evenly reduced to a value of not more than 15% of the breaking force of the blank, which ensures for the blank a relative breaking elongation of 2-8%. Device for carrying out the method according to claim 2, characterized in that it comprises partly a detachable cooling jacket (1), on which is arranged a heating element (2), whereby a pipe blank (3) is placed, and a means ( 6) for injecting compressed air into a gap between the pipe blank (3) and the heating element (2), which has the same shape as the pipe blank (3), and that a spring (4) for providing a pulling force is arranged between the heating element (3). 2) the end surface and the end surface of the substance (3).