GB1579234A

GB1579234A - Process and apparatus for producing a thermoplastic film

Info

Publication number: GB1579234A
Application number: GB11091/77A
Authority: GB
Original assignee: Unilever PLC
Current assignee: Unilever PLC
Priority date: 1976-03-17
Filing date: 1977-03-16
Publication date: 1980-11-19
Also published as: JPS52111970A; SE7703006L; DE2611134A1; CA1086917A; DE2611134B2; IE45025B1; IE45025L; SU913926A3; FR2344395A1; ATA178777A; CH630557A5; ES456967A1; AT364525B; NO149379B; DD129416A5; LU76965A1; BE852561A; DK113877A; FI770839A; IT1082534B

Abstract

A film based on thermally unstable, thermoplastic materials, the film being formed on a calender at a temperature below the thermoplastic range and subsequently subjected to a heat treatment involving heating the film up to the thermoplastic range of the plastic used, is obtained by the film being oriented under tensile stress during the heat treatment, the tensile stress being set such that an elongation of the film of at least 25 per cent to 50 per cent is achieved. An apparatus for producing an oriented film based on thermally unstable, thermoplastic materials is also described. This apparatus is characterised in that a calender (k) for producing the film (K) is provided and is followed directly downstream by at least one melt cylinder (17 to 112), in that furthermore take-off rolls (113 to 115) are provided, which draw the film off the melt cylinder or cylinders at an increased rate, it being possible in each case for a further downstream melt cylinder to serve as the take-off roll. <IMAGE>

Description

(54) PROCESS AND APPARATUS FOR PRODUCING A THERMO-PLASTIC FILM (71) We, UNILEVER LIMITED, a company organised under the laws of Great Britain, of Unilever House, Blackfriars, London E/C 4, England, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to the particularly described in and by the following statement:- The present invention relates to a process of manufacturing a film from thermally unstable, thermoplastic materials at a temperature below the thermoplastic range, in which the film is subsequently heated to a value within the thermoplastic range of the material used, as well as to an apparatus for carrying out this process. The invention also relates to the films thus obtained.

By thermally unstable, thermoplastic materials are to be understood those plastics which can only be subjected for a short time to a temperature effecting thermoplasticity without thermal damage. Representatives of these unstable plastic materials are for example high polymers with a predominant amount of acrylonitriles. The best known representive of this group is polyvinyl chloride (PVC) that for example at a K value of 78 has to be subjected to a temperature of about 250"C so as to reach the plastic state. When this is done thermal destruction of the PVC occurs after about 10 sec. But also other. plastic materials with extremely long molecular chains belong to the group of these thermally unstable polymers.

In order, notwithstanding this, to be able to manufacture films from such plastic materials, a process for hard-PVC was found, known under the name LUVITHERN (registered Trade Mark), which is described in German Patent Specification 742,364.

In this process a film is formed on a calender at a temperature of about 1600C.

This film, however, only has extremely low strength values. Immediately behind the calender this film is subjected to a plasticizing temperature, as a result of which the real film of sufficient strength is formed only then. In the patent specification mentioned it is stated explicitly that while at this plasticizing temperature the film must be subjected neither to pressure nor to stretching.

Because of the relatively low temperature set in the calender it is only with great difficulty that a film having some degree of firm cohesion can be manufactured.

Likewise, because of this very low manufacturing temperature, extremely high working pressures and very high shearing forces between the calender rolls arise also, so that it is only possible to form the film very slowly and, in connection with this, only at very low production speeds.

So, in order to be able to manufacture these plastic films economically in spite of this, the so-called high temperature process (HT process) can be applied, in which PVC plastics with lower degrees of polymerization or lower K values are used which, on the one hand, permit higher manufacturing temperatures and have on the other hand a lower thermoplastic range, so that the film is already sufficiently strong when it leaves the calender and a thermal post-treatment of the films thus manufactured is therefore unnecessary with this process.

However, the films manufactured according to both of these processes have mechanical and physico-chemical properties widely differing from each other. For example, the solvent resistance of a film manufactured according to the Luvitherm process is much greater than that of a film manufactured according to the HT process. Also, with a so-called Luvitherm film a higher drying temperature can be used for the application of a coating; this possibility of adjusting to a higher drying temperature gives shorter drying times, which accelerates production and thus yields a clear economic advantage.

Also, from the considerably more recent German Patent Specification 11 20 684 an apparatus is known for carrying out the Luvitherm process. Therein it is also explicitly set out that in such a process, while at the relatively high temperaturc for fusing or plasticizing, the film only has a small degree of cohesion, for which reason here too it must be passed through the calender without any substantial tension.

Only after completion of this plasticizing can the film be subjected, at considerably lower temperatures, to stronger pulling forces, whereby as a result of the stretching of the film carried out at these temperatures this film gets considerable strength values.

It is known, for example, to bring this film to a temperature in the thermoelastic range and to carry out stretching with orientation of the molecules.

It is the aim of the present invention to develop a process with which plastic films can be manufactured not only as economically as with the HT process, but also with which these films at least obtain or if possible even surpass the favourable properties of the so-called Luvitherm films.

According to the invention this problem is solved, in one operating step, by heating the plastic material used, under stretching and orientation, to its thermoplastic temperature and subsequently subjecting it to further orientation by deformation within the range of its thermo-elastic temperature or its crystalline melting point.

Here this tension applied is such that no damage is done to the film that is not yet heated to the thermoplastic temperature, but that at the same time as this temperature is reached a plastic stretching of the film is obtained. As a result, a considerably higher end speed is obtained and, attendant thereon, the economic advantages in production are immensely increased.

Moreover, with this process a double orientation of the film is obtained which cannot be achieved with the otherwise usual treatments alone. This additional orientation imparts to the film improved mechanical and physico-chemical properties at a comparatively lesser or equal degree of subsequent thermo-elastic stretching.

From a publication of Schönbuch, "Neuzeitliche Fertigung von Kunststoff Folien", in NEUE VERPACKUNG, Volume 21, No. 3, 1969, illustration 25 and the explanation thereof, it is known to draw off a film from a calender at increased speeds; involved here, however, is the manufacture of PVC raw material with a low K value, that is to say the HT process, in which an already finished, ready-for-use film is obtained. According to Schönbuch, here a speed of the film up to 150 /" of the end speed of the calender is possible. Still greater speeds can be achieved, according to Schönbuch, only by stretching in the elastic range of the film, for which the roller stretching apparatus illustrated can serve.

Through this withdrawal of the film from the calender at a higher temperature, however, the present invention was not obvious, because the film, as described, is already manufactured in finished state on the calender, whereas the film manufactured according to the Luvitherm process is, on the contrary, by no means ready after leaving the calender and cannot be subjected to any kind of stretching, as is explicitly indicated in both of the patent specifications mentioned.Also in the Schonbuch publication "Neuzeitliche Fertigung von Kunststoff-Folien" in NEUE VERPACKUNG, Volume 21, No. 3, 1969, on page 9, left-hand column, 5th and 6th paragraphs ("The film is melted there at a constant thickness at a higher temperature on melting rollers"; see also Fig. 18), it is explicitly stated that this Luvitherm film after leaving the calender is thermally upgraded with retention of its thickness, which is equivalent to saying that this film may not be subjected to any kind of stretching or orientation.

According to a favourable embodiment of the invention the stress acting on the film during heating to the thermoplastic temperature is such that an elongation of the film of at least 25 to 50%, preferably 100 to 200 /n and more is obtained, depending on the type of orientation aimed at and on the plastic material used. In the same degree the end speed of the film is then also higher, whereby a correspondingly greater thickness of the starting film, i.e. the calender film, must be taken into account. Furthermore, the degree of orientation increases with the degree and the speed of the stretching in the plastic range.

For further orientation, according to the invention a mono- or biaxial stretching of the film can be carried out in the range of thermo-elasticity or the crystalline melting point, which additionally increases the orientation already present.

The advantage of the first orientation is that it is less sensitive to temperature, i.e. compared with the second orientation, it only leads to shrinking of the film on application of considerably higher temperatures.

According to the invention the heating to the plastic temperature should be effected for a short period only, preferably for just a few seconds, e.g. I to 10 seconds. In that way thermal damaging of the plastic mass is avoided under all circumstances.

According to the invention it is also very favourable if the film, after completion of at least one of the two elongation processes, preferably the last, is subjected to a higher temperature, or is not immediately cooled to ambient temperature, but is kept at a temperature between thermo-elasticity and ambient temperature. As a result thereof a so-called tempering of the film is effected, yielding a further improvement of the properties of the film, particularly an improvement in its resistance to the action of temperature and solvents.

A further favourable embodiment of the process according to the invention is obtained, immediately after the elongation and orientation of the film in the thermoplastic range, with subsequent cooling to a temperature in the range of thermo-elasticity or the crystalline melting point, by stretching the film at this temperature by at least 50%, preferably 100 to above 200%, for the purpose of achieving a second, superimposed orientation. Through this super-imposed orientation a very considerable and additional improvement of the mechanical and physico-chemical properties of the film is obtained.

Yet another favourable embodiment of the process according to the invention consists in processing adjuvants being added to the raw plastic material, for example external lubricants, emulsifiers, waxes. At the relatively low temperatures of the calender the raw plastic material can only be processed with great difficulty.

Through the addition, according to the invention, of processing adjuvants this processing is facilitated somewhat and a film is obtained that is already transportable and transmittable, although as far as the strength is concerned initially inferior.

In another favourable embodiment of the process according to the invention, for the manufacture of a PVC film there is added to the PVC raw material an external lubricant.

In another favourable embodiment of the process according to the invention, for the manufacture of a PVC film there is added to the PVC raw material an external lubricant based on E-wax (ex Farbwerke Hoechst AG, West Germany; ethylene glycol ester of montanic acids with drop point 78-820C; OP-wax (ex Farbwerke Hoechst AG, West Germany, partly saponified ester wax of montanic acids; drop point 100--1050C); hydrowax (ex Fett- und Oelraffination AG, West Germany); hydrogenated sperm oil, consisting of 75 parts wax esters and 25 parts hydrogenated triglycerides; drop point 48-510C and/or polymer waxes based on polyethylene or polypropylene in an amount of from 0.5 to 1% or more, preferably more than 1%, calculated on the weight of the raw plastic material.

Moreover it was found that the addition of about 0.5 to 1% of emulsifier has a favourable effect during the manufacture of the raw film.

Quite surprisingly, it could be confirmed that film manufactured according to the invention with a minimum amount of about 0.5 to 1% of emulsifer and 0.5% of E-wax can be provided with a silicone coating which, with a further coating to form adhesive tape, proves satisfactory as release layer.

Surprisingly, such silicone layers could not be applied to PVC films without these adjuvants. The application of a release layer is, however, of great importance for' the manufacture of adhesive tape films. In the further processing of the coated adhesive tape films manufactured according to the invention, this release or anti-adhesive layer makes it possible, without disturbance and tearing, to cut up these films more easily to small rolls of ready-to-use adhesive tape Another favourable embodiment of the process according to the invention for the manufacture of a PVC film consists in the K value of the PVC raw material being 65 or more, preferably 70 to 78, in the film being formed on a calender at a temperature below 1800C and during the subsequent heating, with tensile stress on and orientation of the film, in the PVC temperature being at least 2000C, preferably 220 to 2500 C. With such a process optimum values for strength and optimum chemical properties are obtained for a PVC film.

An apparatus for carrying out the process according to the invention is characterized in that a calender is provided for manufacturing the film, immediately behind which at least one melting roller, preferably at least two or three melting rollers are connected, and that there are also draw-off rollers which draw off the film from the melting roller(s) at increased speed, in which arrangement each time a following melting roller, connected behind the previous one, can serve as draw-off roller.

With such an apparatus a foil can be relatively simply manufactured and given a first orientation.

Here the film is first manufactured on the calender. On a melting cylinder the film is heated to a temperature of 240"C and subjected to elongation by 200%.

These melting cyclinders can be adjusted to temperatures up to 3000 C. Their speed is infinitely variable. In this respect it appeared to be very favourable if the first melting cylinders have approximately the same speeds and these are comparable with the speeds of the calender rollers.

On the other hand the speeds of the other melting cylinders are linear or even raised so over-proportionately high that the desired elongation and orientation of the film are obtained.

It is particularly favourable when the first rollers have a maximum temperature of for example 220 to 2500C and the following melting rollers a temperature dropping to for example 220 to 2000C. Subsequently the film can be conducted through a range of cooling rollers.

In another embodiment of the invention, in such an apparatus a stretching device can be mounted immediately behind the draw-off/melting rollers, where the film is stretched at a temperature in the range of its thermo-elasticity or its crystalline melting point. As a result of this stretching device connected behind the draw-off rollers, the film undergoes a second orientation in which a film is manufactured with values thought impossible up to now as far as their mechanical and physico-chemical properties are concerned.

Another favourable embodiment of the invention is an apparatus in which the melting or drawing-off rollers and the rollers of the stretching device have the same form, as well as being mounted horizontally behind each other and preferably in a row, with only the surface temperatures differing from each other. In that way a relatively simple construction of such an apparatus is possible in which substantially similar building elements can be used.

It is also very favourable if in the apparatus according to the invention the melting or draw-off rollers and/or the stretching rollers have a length: diameter ratio of less than 10:1. It has appeared that with such diameter ratios a relatively favourable and uncomplicated stretching of the film in longitudinal direction can be obtained.

According to the invention, here too the speed of the melting rollers is infinitely variable and they are provided with adjustable heating members which make surface temperatures of up to about 300"C possible.

The stretching rollers are here generally mounted so that they run clear of each other.

Starting from the known Luvitherm process a number of comparative tests were carried out in respect of the process according to the invention.

Example 1 This example describes the manufacture according to the Luvitherm process of a hard PVC film on a classic Luvitherm apparatus from the known state of the art.

Here a hard PVC film coming from the calender is conducted over the melting roller of the Luvitherm apparatus and subsequently stretched with the aid of a stretching cyclinder. In order to prevent the hot, melted film from sticking to the surface of the melting roller, this melting roller has a somewhat higher speed than the film, through which, however, no appreciable stretching of the film takes place.

The following technical data characterize the manufacture of the film on the calender, in manufacture according to the Luvitherm process and stretching, as well as the properties of the film after the three processing steps mentioned: A) Raw material, calender and technical data concerning the C film (calender film) PVC raw material E-PVC with K value=78 Kind of calender process Low temperature or Luvitherm process Temperature of the calender rollers about 160 to 1700C Thickness of the C film about 200 M Production speed of the C film V,=10 m/min.

Tear strength of the C film in longitudinal direction about 430 kp/cm2 Tear strength of the C film in transverse direction about 510 kp/cm2 Stretch at breaking point of the C film in longitudinal direction about 10% Stretch at breaking point of the C film in transverse direction about 12% Impact resistance* of the C film at O"C no impact resistance, extremely brittle, not measurable Capability of the C film for being deep-drawn none Extensibility of the C film not extensible Number of pores of the C film 0 Number of holes of the C film 0 Optical appearance of the C film milky, opaque, cloudy *The impact resistance was measured according to DIN 53372 (draft standard) B) Technical data concerning the manufacture according to the Luvitherm process and the US film (unstretched film) Speed of run-on of the C film on to the melting cylinder V,=10 m/min.

Speed of rotation of the melting cylinder V2=about 11.5 m/min.

Diameter of the melting cylinder 500 mm Run-off speed of the US film from the melting cylinder V2=l I m/min.

Temperature of the melting cylinder about 240"C (With increase of the speed of rotation of the melting cylinder or, particularly, of the speed of the draw-off rollers, withdrawal of the film takes place on the melting cylinder).

Thickness of the US film about 180,u Tear strength of the US film in longitudinal direction about 480 kp/cm2 Tear strength of the US film in transverse direction about 440 kp/cm2 Stretch at breaking point of the US film in longitudinal direction about 70 /n Stretch at breaking point of the US film in transverse direction about 60 /n Impact resistance* of the US film at 0 C 100% in order in longitudinal and transverse direction Capability of the US film for being deep-drawn good Extensibility of the US film good Number of pores of the US film 0 Number of holes of the US film 0 Optical appearance of the US film milky, opaque, cloudy, very streaky *The impact resistance was measured according to DIN 53372.

C) Technical data concerning the longitudinal stretching and the S film (stretched film) Thickness of the US film at run on on to the stretching cylinder about 180,u Speed at run-on of the US film on to the stretching cylinder V3=about 11 m/min.

Run-off speed of the S film from the stretching cylinder V4=about 44 m/min.

Stretching ratio 1.4=300% Stretching temperature about 110"C Thickness of the S film after leav ing the stretching cylinder about 40 to 45 M Tear strength of the S film in longitudinal direction about 1980 kp/cm2 Tear strength of the S film in transverse direction about 460 kp/cm2 Stretch at breaking point of the S film in longitudinal direction about 19% Stretch at breaking point of the S film in transverse direction about 80 /n Impact resistance* of the S film at 0 C 100% in order in longitudinal and transverse direction Capability of the S film for being deep-drawn can no longer be deep drawn Extensibility of the S film not further extensible Number of pores of the S film about 10 per m2 Number of holes of the S film about 2 to 3 per m2 Optical appearance of the S film slightly milky, some what opaque, somewhat cloudy and streaky Example 1 shows the defective mechanical properties of C films of hard PVC, which are particularly manifest in the great brittleness of these films, in their limited stretching capacity and also in their unsuitability for being deep-drawn and stretched.

But also the optical properties of the C films not manufactured according to the Luvitherm process are unsatisfactory and even worse than those of the US and S films.

Example 1 also shows, however, that these unsatisfactory properties, particularly the mechanical properties can be quite definitely improved by manufacture according to the Luvitherm process, in which the US films are formed from the C films. The properties of the US films of interest here can be seen in Example 1.

Noteworthy too in Example I is the relatively large number of pores and holes in the thin S film. This large number of pores and holes is to be attributed to the unilateral and therefore unsatisfactory manufacture according to the Luvitherm process with one melting cylinder. Because of this, of late tests have become known in which manufacturing of.C films according to the Luvitherm process is carried out with two melting cylinders immediately following each other.

These tests have brought about a certain improvement in the optical appearance of the film; the number of pores too, although only to a slight degree, has been reduced. Moreover, the second melting cylinder has brought no advantages with it; on the contrary, there are higher investment costs connected with its installation.

Example 2 The test from Example I was repeated under exactly the same conditions with only this difference that, instead of a melting cylinder as in Example 1, two Luvitherm cylinders were used. Both melting cylinders follow immediately after each other and have approximately the same speed of rotation. Only the second melting cylinder can be adjusted to a somewhat higher speed with respect to the first melting cylinder, not, however, with the intention of stretching the film, but in order to prevent sticking to the cylinder.

The C film manufactured according to the Luvitherm process under exactly the same conditions as in Example 1 has in its various stages, as C film, as US film and as S film, the same properties as in Example 1. Only with respect to the number of pores and its optical properties does the S film show a slight improvement, which can be attributed to the use of two melting cylinders.

Number of pores of the S film about 6 to 8 per m2 Number of holes of the S film about I to 2 per m2 Optical properties of the S film slightly milky, somewhat opaque, somewhat, but evenly cloudy and streaky In the same test 2 the speed of rotation of the second melting cylinder was increased additionally with respect to that of the first melting cylinder.

At this increased speed ratio the C film broke, so that the test had to be discontinued.

Example 3 In Example 3 a test is described that was carried out with a Luvitherm machine as in Figure 2 with several melting cylinders or melting rollers. A C film with a thickness of about 200 y was used. The melting rollers had the same diameter of 500 mm, their speed of rotation could, however, be adjusted as desired, and they could be adjusted to any desired melting roller temperature with circulating liquids of which the temperature could be regulated with the aid of thermostats.

While the manufacture of the C film according to the Luvitherm process was now initially carried out in principle as in Examples 1 and 2, that is with constant speeds of rotation of the melting rollers, now, in contrast with Examples 1 and 2, the speeds of rotation, particularly of the third melting roller and the following one, were greatly increased with respect to those preceding them. Contrary to expectation, no breaking or other damaging of the film occurred, neither on or between the first two cylinders nor, particularly, between and on the second and third cylinder and the following cylinders.

Below, the technical data of test 2 are given, as well as the properties of the film before and after the relevent steps in the manufacture according to the Luvitherm process.

A) Raw material and calender data as well as technical data concerning the C film The same as the values in Examples 1 and 2.

B) Technical data concerning the manufacture according to the Luvitherm process and the US film Speed at run-on of the C film on to the 1st melting cylinder VE=10 m/min.

Speed of rotation of the 1st melting cylinder V51=about 11.5 m/min.

Temperature of the 1st melting cylinder 240"C Speed of rotation of the 2nd melting cylinder V52=about 13 m/min.

Temperature of the 2nd melting cylinder 240"C Speed of rotation of the 3rd melting cylinder Vs3=20 m/min.

Temperature of the 3rd melting cylinder 230"C Speed at run-on of the US film from the 3rd melting cylinder on to the 1st cooling or draw-off roller VA=26 m/min.

Although a speed increase of about 160% was reached between the speed VE or V5 of the first melting cylinder and the speed VA of the cooled run-off roller, no breaking of the film occurred. Only the width of the film band was some-what reduced.

Thickness of the US film about 90 u Tear strength of the US film in longitudinal direction about 640 kp/cm2 Tear strength of the US film in transverse direction about 420 kp/cm2 Stretch at breaking point of the US film in longitudinal direction about 50% Stretch at breaking point of the US film in transverse direction about 110% Impact resistance of the US film at 0 C 100% in order in longitudinal and transverse direction Capability of the US film for being deep-drawn good Extensibility of the US film good Number of pores of the US film 1 Number of holes of the US film 0 Optical appearance of the US film slightly milky, some what opaque, barely cloudy and streaky C) Technical data concerning the longitudinal stretching and the S film Thickness of the US film at run on on to the stretching device about 90 M Speed at run-on of the US film on to the stretching device 26 m/min.

Run-off speed of the S film from the stretching device 106 m/min.

Stretching ratio about 1:4=300% Stretching temperature 110 C Thickness of the S film after leaving the stretching device about 2023 M Tear strength of the S film in longitudinal direction about 2400 kp/cm2 Tear strength of the S film in transverse direction about 445 kp/cm2 Stretch at breaking point of the S film in longitudinal direction about 10% Stretch at breaking point of the S film in transverse direction about 100% Impact resistance of the S film at 0 C 100In in order in longitudinal and transverse direction Capability of the S film for being deep-drawn can no longer be deep-drawn Extensibility of the S film not further extensible Number of pores of the S film 5/m2 Number of holes of the S film l/m2 Optical appearance of the S film barely milky and opaque, no longer cloudy and streaky With respect to the resistance to solvents of the films manufactured according to Examples I to 3 there also appear to be considerable and surprising differences: films manufactured according to Examples I and 2 were, in comparison with the films manufactured according to Example 3 with an equal degree of orientation, i.e. at an equal tear strength in longitudinal direction, clearly less resistant to solvents. This better resistance to solvents in the manufacture of films according to the invention is extremely important in their further processing to adhesive tape films by application of a coating based on solvents.

In the drawings three examples of embodiments are illustrated: Fig. I shows a schematic diagram of an apparatus for manufacturing a Luvitherm or LT film. Instead of the stretching cylinder shown, a roller stretching range is also often used, especially for technical reasons.

Fig. 2 shows schematically an apparatus with six melting or draw-off cylinders and a connected roller stretching device.

Fig. 3 shows, also schematically, an apparatus arranged as a unit with similar melting and stretching cylinders.

In Fig. 2 a calender K is shown, built up of six rollers k1 to k6. On this calender a plastic film K is formed which, after leaving the last roller gap, is conducted to the melting roller part of Luvitherm part 1, consisting of six melting cylinders 17 to 112.

Subsequently the plastic film passes over each of these cylinders. The melting cylinders are staggered each time under each other, as a result of which there are relatively short pieces of film between two adjacent cylinders. The following melting cylinder simultaneously serves at any given time as draw-off roller for the preceding melting cylinder. Behind the last melting cylinder 112, three draw-off rollers 113 to lis are mounted.

After leaving these draw-off rollers the film is conducted to a stretching device r. This device consists of a pair of holding rollers r,6, r", nineteen superimposed stretching rollers r,8 to r36, as well as a pair of pinching rollers r37, r38.

From the pair of pinching rollers the film runs to a coil winder where it is wound up to a roll.

In the embodiment according to Fig. 3 the calender k is shown in the same manner as in Fig. 1 with six rollers k, to k6. This calender can, however, also be built up differently. The Luvitherm station I is in this embodiment built up of melting cylinders 17 to 1,, arranged in series. Connecting directly with this series is the stretching device r in which the stretching rollers r,2 to r20 are mounted in series. The melting cylinders 17 to lii and the stretching rollers r12 to r20 do not differ from each other outwardly; only the surface temperatures are different. The stretching rollers r12 to r20 are provided with pressure rollers and, just as shown in Fig. 1, take over the function of the pairs of holding and pinching rollers. Naturally, the number of melting cylinders 1 and stretching rollers r is a matter of choice.

After leaving roller r20 the film runs to a coil winder where it is wound up to a roll.

WHAT WE CLAIM IS: 1. Process of manufacturing a film from thermally unstable, thermoplastic materials at a temperature below the thermoplastic range, and subsequent heating of the film to within the thermoplastic range of the material used, characterized in that, in the same operating step, the film is heated, while subjected to stress and orientation, to the thermoplastic temperature of the thermoplastic material used and is subsequently subjected to further orientation by deformation within the range of its thermo-elastic temperature or its crystalline melting point.

2. Process according to claim 1, characterized in that the stress acting upon the film during heating to the thermoplastic temperature is such that an elongation of the film of at least 25 to 50%, preferably of 100 to 2009/" or more is achieved, depending on the type of orientation aimed at and the thermoplastic material used.

3. Process according to claim I or 2, characterized in that the deformation effecting the further orientation consists in a mono- or biaxial stretching of the film carried out in the range of thermo-elasticity or the crystalline melting point.

4. Process according to any one of claims I to 3, characterized in that the heating is effected for a short period, preferably for I to 10 seconds.

5. Process according to any one of claims 1 to 4, characterized in that, after completion of at least one of the two elongation processes, the film is subjected to an elevated temperature, which is above ambient temperature, preferably below the thermoelastic temperature.

6. Process according to any one of the preceding claims, characterized in that immediately after the elongation and orientation of the film in the thermoplastic range, the film is cooled to a temperature in the range of thermo-elasticity or the crystalline melting point, and while being at this temperature the film is stretched by at least 500/,, preferably by 100 to 200%, for the purpose of achieving a second, superimposed orientation.

7. Process according to any one of the preceding claims, characterized in that processing adjuvants, for instance external lubricants, internal lubricants, emulsifiers, waxes, are added to the thermoplastic raw material.

8. A film from thermally unstable, thermoplastic material, whenever obtained by a process according to any one of claims 1--7.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Luvitherm or LT film. Instead of the stretching cylinder shown, a roller stretching range is also often used, especially for technical reasons. Fig. 2 shows schematically an apparatus with six melting or draw-off cylinders and a connected roller stretching device. Fig. 3 shows, also schematically, an apparatus arranged as a unit with similar melting and stretching cylinders. In Fig. 2 a calender K is shown, built up of six rollers k1 to k6. On this calender a plastic film K is formed which, after leaving the last roller gap, is conducted to the melting roller part of Luvitherm part 1, consisting of six melting cylinders 17 to 112. Subsequently the plastic film passes over each of these cylinders. The melting cylinders are staggered each time under each other, as a result of which there are relatively short pieces of film between two adjacent cylinders. The following melting cylinder simultaneously serves at any given time as draw-off roller for the preceding melting cylinder. Behind the last melting cylinder 112, three draw-off rollers 113 to lis are mounted. After leaving these draw-off rollers the film is conducted to a stretching device r. This device consists of a pair of holding rollers r,6, r", nineteen superimposed stretching rollers r,8 to r36, as well as a pair of pinching rollers r37, r38. From the pair of pinching rollers the film runs to a coil winder where it is wound up to a roll. In the embodiment according to Fig. 3 the calender k is shown in the same manner as in Fig. 1 with six rollers k, to k6. This calender can, however, also be built up differently. The Luvitherm station I is in this embodiment built up of melting cylinders 17 to 1,, arranged in series. Connecting directly with this series is the stretching device r in which the stretching rollers r,2 to r20 are mounted in series. The melting cylinders 17 to lii and the stretching rollers r12 to r20 do not differ from each other outwardly; only the surface temperatures are different. The stretching rollers r12 to r20 are provided with pressure rollers and, just as shown in Fig. 1, take over the function of the pairs of holding and pinching rollers. Naturally, the number of melting cylinders 1 and stretching rollers r is a matter of choice. After leaving roller r20 the film runs to a coil winder where it is wound up to a roll. WHAT WE CLAIM IS:

1. Process of manufacturing a film from thermally unstable, thermoplastic materials at a temperature below the thermoplastic range, and subsequent heating of the film to within the thermoplastic range of the material used, characterized in that, in the same operating step, the film is heated, while subjected to stress and orientation, to the thermoplastic temperature of the thermoplastic material used and is subsequently subjected to further orientation by deformation within the range of its thermo-elastic temperature or its crystalline melting point.

9. Process according to any one of claims 1--7 for preparing a PVC-film,

characterized in that to the PVC raw material is added an external lubricant, on the basis of E-wax, OP-wax, hydrowax and/or polymer waxes on the basis of polyethylene or polypropylene in an amount of from 0.5 to 1% or more, preferably over 1%, calculated on the weight of the thermoplastic raw material.

10. Process according to claim 9, characterized in that from 0.5 to 1% of emulsifier is added to the PVC raw material.

11. Process according to any one of claims 1--7 and 9-10 for preparing a PVC-film, characterized in that the K-value of the PVC raw material amounts to 65 or more, preferably 70 to 78, that the film is formed on a calender at a temperature below 1800C and that during the subsequent heating, effected with tensile stress and orientation of the film, the PVC temperature is at least 200"C, preferably 220 to 2500 C.

12. A PC-film, whenever obtained by a process according to any one of claims 1-7 or 9-Il.

13. Apparatus for carrying out the process according to any one of claims I to 7 or 9--11 characterized in that a calender is provided for manufacturing the film, behind which at least one melting cylinder (17 to 112), preferably two to three melting cylinders are connected in series, and draw-off rollers (113 to 115) are provided which draw off the film from the melting cylinder(s) at increased speed, in which arrangement each time an additional melting cylinder can serve as draw-off roller.

14. Apparatus according to claim 13, characterized in that immediately behind the draw-off rollers (1,3 to l,5) a stretching device is provided, in which the film is stretched at a temperature in the range of its thermo-elasticity or its crystalline melting point.

15. Apparatus according to claim 14, characterized in that the melting cylinders (17 to 112), the draw-off rollers (113 to 1,,) and the rollers (rl8 to r36) of the stretching device have the same form and are arranged behind each other and preferably in a row, only the surface temperatures of the rollers being mutually different.

16. Apparatus according to claim 14 or 15, characterized in that the melting cylinders (17 to 112) and/or the draw-off rollers (113 to 115) and/or the stretching rollers (r,a to r36) have a length: diameter ratio of about 10:1.

17. Apparatus according to any one of claims 13 to 16, characterized in that the melting cylinders (17 to 1,2) are provided with an infinitely variable heating device, allowing surface temperatures of up to about 300"C.

18. Apparatus, substantially as hereinbefore described with reference to Figure 2 or Figure 3 of the accompanying drawings.

19. PVC-film from a PVC raw material having a K-value of at least 65, containing at least 0.5 parts of a lubricant wax and at least 0.5 parts of an emulsifier, manufactured on a calender at temperatures below 180"C, which film while being stretched, has been subjected to a first orientation by means of an elongation of at least 50'in at temperatures above 200"C, and to a second orientation at temperatures of its thermo-elastic range by means of an elongation of at least 100%.

20. PVC-film according to claim 19, characterized in that said film has been silicone-coated on at least one side.

21. A process of manufacturing a film from thermally unstable thermoplastics materials substantially as hereinbefore described with reference to Figure 2 or Figure 3.