GB2164896A

GB2164896A - Process and apparatus for the production of bi-orientated thermo-shrinking hose

Info

Publication number: GB2164896A
Application number: GB08424244A
Authority: GB
Inventors: Tibor Cvikovzsky; Janos Dobo; Ivan Kalman; Imre Szakos; Gyula Madai; Zoltan Paricsi; Bela Kerekes; Endre Lakner; Laszlo Miskolczy
Original assignee: PAPIRIPARI VALLALAT; Muanyagipari Kutato Intezet
Current assignee: PAPIRIPARI VALLALAT; Muanyagipari Kutato Intezet
Priority date: 1984-08-20
Filing date: 1984-10-03
Publication date: 1986-04-03
Also published as: AT387540B; ATA265584A; GB8424244D0; GB2164896B; DE3430770A1

Abstract

In the process hose (1) extruded from polyethylene or ethylene copolymer, then reticulated, is led through a liquid bath (2), the temperature of which is approximately the same as the crystalline melting point of the hose material. An air bubble is blown from the hose emerging from the bath between two pairs of closing rolls (3, 7) and, during continuous expansion of the bubble, the extent of the expansion is controlled with deformation elements (10) arranged parallel or at variable angle to the direction of progress of the hose, the size of the bubble representing 50-500% longitudinal and transverse expansion in relation to the unexpanded hose. The hose is then passed via baffle plates (6) to the second pair of rolls (7). The apparatus enables increased safety and improved dimensional stability. <IMAGE>

Description

SPECIFICATION Improved process and apparatus for the production of bi-orientated thermo-shrinking hose The invention relates to an improved process and apparatus for the production of bi-orientated thermo-shrinking hose.

Thermo-shrinking packing materials are extensively used in the up-to-date packing technique mostly in the form of bag or foil produced mainly from hose. These packing materials shrink upon the effect of heat-shock, whereby the product is provided with protection and aesthetic appearance. The most suitable extent of the longitudinal and transverse shrinkage depends on the conditions of application.

The US patent specification No. 2 452 080 discloses the production method of polyvinylidene-chloride based (PVDC), bi-directionally shrinking hoses. Accordingly the PVDC is extruded vertically downwards into a liquid bath, then in supercooled condition it is guided between two pairs of rolls. The super-cooled PVDC tube is blown up between the two pairs of rolls to the required diameter. The drawback of the process-among others-is that it is suitable only for the production of PVDC-based shrink-hose, although the cold resistance and dimensional stability of the PVDC are poor, moreover its use in certain cases is contrary to the health regulations.

According to the English patent specification No. 1 390 430 gas (air) is injected through a tube arranged in the top of the extruder into the recently extruded tube, which is blown up to a bubble. The material is guided between two pairs of displaceable closing rolls, then on to a winding roll. The process is used for the orientation of non-reticulated foils. Such foils have to be orientated at a temperature much below the crystalline melting point. This is the reason that the longitudinal and transverse orientations are carried out relatively far from the extruder head, on cold material between two pairs of closing rolls, on the other hand the technical solution of the displaceable closing rolls-suitable for the high pressure required for orientation of the cold material-is complicated and burdened with sources of trouble.

The US patent specification No. 3 022 543 introduces reticulation with electron accelerator between the extrusion and expansion of the hose produced from polyethylene, ethylene-copolymer, or similar basic materials. This way the danger of melting of the hose material is eliminated in the expansion and shrinkage processes, and new possibility is opened up for the production of hoses and foils of higher shrink-force. Thus filling up the bubble with air used for the production of the hose connected to the extruder and ensuring the adequate pressure and air volume take place with conventional method through the head of the extruder, while the formation of the expanding (orientating) bubble takes place-similarly by conventional method-by passing a needle (injection needle) provided with hole through#the wall of the hose.The expansion process takes place mainly in expansion bath (water bath) the temperature of which is kept near the melting point of the reticulated material. The described apparatus is suitable for the production of reticulated shrink-hoses and shrinkfoils with high shrinking force. The drawback of the procedure is that the accurate adjustment of the size of the expanded hose is difficult with the described methods. Furthermore serious problems are caused by any trouble arising during the continuous operation mode, e.g. non-uniform thickness or reticulation of the extruded hose as a result of the operation of the electron accelerator, or the local inhomogeneity of the additives present in the hose, as well as if gas escapes the the expanding (orientating) bubble.In this case the amount of gas in the bubble is not sufficient to expand adequately the hose-part in the liquid bath and thus it results in indentation of the expanded hose. After a few seconds, as soon as the faulty hose-part leaves the bath, the expansion sets again to the required size.

When however the afore mentioned indentation reaches the upper, closing pair of rolls, it will force out less amount of air from the hose on account of the reduced size of the indented part. This amount of air is not sufficient for the adequate expansion, and thus the indentation becomes transposed to the hose just to be expanded in the expanding bath.

This way the system begins to pulsate, producing periodically indented useless product.

According to the experiences this phenomenon arises not only in case of local faults, but it may occur even when the operational parameters (velocity, water temperature) are slightly changed.

It was also experienced that this shortcoming can not be statisfactorily eliminated by air supply with injection needle. First of all by piercing of the hose, faults are introduced into the automatic machine producing ready-made hoses. Furthermore the supply of air-content of the expanded hose (bubble) through the injection needle is a more difficult problem, than the initial realization of the bubble from the still unexpanded reticulated hose. Namely during the initial realization of the expanding bubble a relatively thick wall nearly free from tension is pierced through, while the wall of the expanded hose is very thin, consequently it splits open easily upon piercing. The fine adjustment to size is particularly difficult under such circumstances.According to the experiences if indentation occurs during the hose expansion in the apparatus described in the US patent specification 3 022 543, and the system begins to pulsate as described earlier, then it is advisable to stop and restart the whole production line, because the parameters required for the production of the expanded hose can be reset only this way with the minimal loss of time and material. It stands to reason that the stopping and resetting of the production line are time-consuming and expensive.

The invention is aimed at the elimination of above shortcomings.

During the experiments such unexpected recognition was arrived at, that the reticulated hose of uniformly high quality and thermoshrinking in two directions to the controlled extent can be produced in such a way, that the hose extruded from polyethylene or ethylene copolymer, then reticulated is guided through a liquid bath, the temperature of which is nearly identical with the crystalline melting point of the hose material, then it is pulled with a second pair of closing rolls arranged above a pair of closing rolls, while such air bubble is formed from the hose between the two pairs of closing rolls, the size of which represents 50 to 500% expansion both in longitudinal and transverse directions in relation to the size of the extruded hose, and the extent of expansion along the bubble is set to the required value with deformation elements arranged parallel or at a variable angle to the direction of movement of the hose.

According to a further unexpected recognition dimensional stability of the expanded hose can be increased in certain cases by filling it up with liquid, suitably with water to the height of 5-50 cm in non-expanded condition above the pair of closing rolls immersed into the liquid. The optimal quantity of the water depending on the basic material, on the degree of reticulation and on the required extent of the expansion can be determined in each case.

In view of the foregoing the subject of the invention is a process for the production of a bi-orientated thermo-shrinking, reticulated shrink-hose of uniformly high quality, where a hose extruded from polyethylene or ethylene copolymer, then reticulated with electron accelerator is led through a liquid bath, suitably through water bath; the temperature of which is approximately identical with the crystalline melting point of the hose material, then guiding it with two baffle plates above the pair of closing rolls arranged in the liquid bath it is pulled out of the liquid bath with a second pair of closing rolls and such air bubble is formed from the hose between the two pairs of closing rolls, the size of which represents 50-500% expansion in longitudinal and transverse directions in relation to the nonexpanded hose, the essence of which is that the extent of expansion along the bubble is regulated with deformation elements arranged parallel or at variable angle to the direction of movement of the hose.

Subject of the invention is furthermore an apparatus for realization of above process, which consists of a liquid bath, suitably water bath, of a pair closing rolls arranged in the bath, as well as a pair of pulling closing rolls provided with baffle plates, and which is provided with deformation elements arranged parallel or at variable angle to the direction of movement of the part of the synthetic hose pulled though the liquid between the two pairs of rolls.

In a preferred construction of this apparatus according to the invention deformation elements are connected through a hinge to the hose guiding baffle plates, the angle of which is variable.

A further preferred construction of the apparatus according to the invention is provided with structurally independent deformation (flattening) elements parallel to the direction of movement of the hose.

The deformation elements of both apparatuses are suitable for automatic control through electrical, pneumatic or other signal transmitter sensing the size of the hose. The sensor and the automaton can be produced with conventional elements, their technical solution does not affect the essence of the invention, and they do not represent the subject of the invention.

An important characteristic of the bidirectionally expanded, reticulated shrink-foils is the transverse and longitudinal expansion and the required ratio of the related shrinkage parameters. Its setting and keeping it on the specified level (e.g. according to the ratio of 1:1) is a phase associated with the up-to-dateness of the technological system and characteristic to the technological process control. The process and apparatus according to the invention are particularly suitable for the controlled, strict observance of this important ratio.

The simple and safe adjustability of the hose expansion with deformation elements according to the invention is surprising, because the bubbly hose expansion process is similar to the production of the hose with bubble following the extrusion. However the deformation elements according to the invention can not be used for adjustment to size of the hose during its production.

The role and function of the deformation elements according to the invention can be better enlightened by comparison of the conventional hose extrusion and the reticulated hose expansion. The conventional hose extrusion which is the basic process of the foil production takes place from melt. The temperature of the hose material emerging from the tool is by 50-80'C over the crystalline melting point. On the other hand the reticulated material is to be expanded in the form of infinite hose. The cold hose is heated in liquid bath, mainly in water bath: meanwhile the crystals melt fully or at least to a considerable extent, but the temperature of the hose remains close to the melting point of the crystals.The strength of the hose in the hot water bath is ensured by the reticulated bonds, but emerging from the water bath after a very short, a few cm, cooling phase the condition sets in when the strength of the hose is provided by the crystalline particles. As a result of this the elasticity modulus of the hose material increases by two-three-times within a few seconds, or along the a few cm long path, depending on the extent of reticulation (see: P. Forgacs, J. Dobo: Radiat.Phys. Chem.

11, 123-127/1978). In case of the production or orientation of hoses produced from non-reticulated material, the process is not analogous, because these materials over the crystalline melting point are in viscous liquid state.

Upon emerging from the hot water bath the fast increase of the elasticity modulus of the reticulated hose results in that the final size of the hose will be reached in or immediately above the water bath. Along the following part of the hose neither the circumference nor its length will vary, not even upon change of the expanding air volume or pressure. Thus the change of the air volume or pressure of the air in the hose affects only the shape and size of the hose part with small elasticity modulus submerging into the hot water or immediately above the water bath. This explains the efficiency of the dimensional adjustment by deformation of the hose.

Thus the surprisingly sensitive simple adjustment of the size of the hose with deformation elements according to the invention can be traced back to the fact, that by changing (e.g.

flattening) the shape of the hose, the air volume of the hose between the deformation elements, i.e. the air volume in the cooled crystalline part is changed without changing the surface, and thus the possibilities given by the change of the physical state and geometry are utilized simultaneously.

A preferred construction of the improved hose expanding apparatus is shown in Fig. 1.

An extruded hose 1 reticulated with an electron accelerator is admitted into a liquid bath 2, preferably into a water bath and pulled through between a pair of rolls 3. The pair of rolls revolves at 2-10 m/min peripheral velocity. A few cm high water column 4 above facilitates the uniform expansion. Upon starting an expanding bubble 5 is formed on the hose with pressurized air; the bubble is conducted with roller baffle plates 6 between the extruding rolls of a pair of pulling rolls 7 revolving at 4-40 m/min peripheral velocity, then the expanded hose 8 is wound up. Deformation elements 10 join the roller baffle plates 6 at the hinged straps 9, their angular position is adjustable through a push rods 11 in directions 12, whereby the expansion in and immediately above the water bath is adjustable and the expanded hose can be adjusted to the accurate size.

Another preferred construction of the apparatus according to the invention is shown in Fig. 2. Here the size of the hose is adjustable with parallel functioning deformation elements 13; the adjustment is carried out by an automaton 15 with the aid of hydraulic cylinders 14 according to the correction signal transmitted by a transmitter 16 sensing the size of the hose.

The best advantage of the deformation elements according to the invention is the balanced process control, the uniform dimensional stability and the resultant constant quality. The intervention or control system with suitable feedback can be interlinked with the characteristic size of the expanded reticulated hose measurable at a certain distance after the water bath, whereby the automatic process control is ensured. Further advantage of the process and apparatus according to the invention is that in case of continuous operation mode the expanded size of the product can be changed over to a following different size, and the required new wall thickness is adjustable without stopping the production system.

Example 1 A hose of 63 mm diameter and 0.25 mm wall thickness is extruded from ethylene-vinylacetate copolymer containing 7.5% vinylacetate (Hostalen LD/EVA FV 2430 VP; Hoechst A.G., Frankfurt am Main), then irradiated by 50 kGy dosage with a 2 MeV electron power and 400 W van de Graaff electron accelerator.

Thereafter the hose is expanded to 130 mm diameter on the apparatus shown in Fig. 1.

The peripheral velocity of the first pair of rolls is 3 m/min, that of the second one is 8 m/min, the temperature of the water bath is 92 C, the superpressure in the bubble is 25t2 mbar. The hose in unexpanded state is filled up with water to a height of 20 cm above the pair of rolls arranged in the water bath. The dimensional stability of the expanded hose is +2%; the size of the hose has to be readjusted with the deformation elements on 10 occasions during the 6 hour continuous operation mode. The longitudinal shrinkage of the expanded hose in 950C water bath is 40%, and the transverse shrinkage is 45%.

Example 2 A hose of 45 mm diameter and 0.2 mm wall thickness is extruded from low density polyethylene (Tipolen FA 1718; Tiszai Vegyi Kombinat, Leninvaros), followed by irrediation with 100 kGY dosage to 28% reticulation as shown in example 1, then expanded to 180 mm diameter on the apparatus shown in Fig.

2. The peripheral velocity of the first pair of rolls is 4 m/min, that of the second one 14 m/min. Temperature of the ethylene-glycol bath is 105 C, the superpressure 40+5 mbar.

The dimensional stability of the expanded hose is + 1 %, its longitudinal shrinkage in the boiling water bath is 50%, the horizontal shrinkage is 35%.

Example 3 The procedure is the same as in example 2 but ethylene-vinylacetate copolymer containing 12.5% vinylacetate (Alkathene EVA 555; Imperial Chemical Industries, London) is used as basic material. The applied dosage is 40 kGy, the reticulation 36%, a water bath is used for heating of the hose the temperature of which is 85 C, the super-pressure is 20 t 1 mbar.

The dimensional stability of the expanded hose is +2%, its longitudinal and transverse shrinkage in a water bath of 860C is 29%.

Claims

1. A process for the production of a uniformly high quality, bi-orientated thermoshrinking, reticulated shrinkhose, in which a hose extruded from polyethylene or ethylene copolymer, then reticulated, is guided through a bath of liquid such as water, the temperature of which is the same, or substantially the same, as the crystalline melting point of the hose material, then by guiding it with baffle plates above a pair of closing rolls arranged in the liquid bath, it is pulled out of the liquid bath by a second pair of rolls so that an air bubble is formed with the hose between the two pairs of closing rolls, the size of which represents 50-500% longitudinal and transverse expansion in relation to the extruded unexpanded hose, characterized in that the extent of expansion along the bubble is adjusted with deformation elements arranged parallel or at a variable angle to the direction of progress of the hose.

2. A process as claimed in claim 1, characterised in that the unexpanded hose above the pair of closing rolls into the liquid bath is filled up with liquid, suitably with water, to a height of 5-50 cm.

3. Apparatus specifically for carrying out the process as claimed in claim 1 or 2, which consists of a heatable bath for liquid such as water, a pair of closing rolls arranged within the bath, and baffle plates and a second pair of closing rolls arranged above said bath for guiding and pulling the hose out of the bath, characterized in that said apparatus is provided with deformation elements arranged between the two pairs of rolls parallel or at variable angle to the direction of progress of the synthetic hose pulled through the bath.

4. Apparatus as claimed in claim 3, characterized in that its deformation elements are formed by two sets of rollers hinged to the end of the baffle plates.

5. Apparatus as claimed in claim 3, characterised in that its deformation elements are formed by two parallel moving, structurally independent sets of rollers.

6. Apparatus as claimed in claim 4 or 5, characterized in that it is provided with an automaton controlling the movement of the deformation elements, and sensing the size of the hose.

7. A process, or apparatus specifically adapted for the process, substantially as hereinbefore described with reference to the accompanying drawings.