GB2145964A

GB2145964A - Clear oriented polyester material

Info

Publication number: GB2145964A
Application number: GB08418996A
Authority: GB
Inventors: Ian Macmillan Ward; Alan Selwood
Original assignee: National Research Development Corp UK
Current assignee: National Research Development Corp UK
Priority date: 1983-07-29
Filing date: 1984-07-25
Publication date: 1985-04-11
Also published as: GB2145964B; JPH0470135B2; EP0133355A3; JPS6058832A; ATE58865T1; GB8320533D0; EP0133355B1; EP0133355A2; GB8418996D0; DE3483707D1

Abstract

A process for the preparation of clear, oriented polyester material, comprises providing an orientable thermoplastic workpiece of the polyester material, heated to a temperature from 55 DEG C to 110 DEG C, at the entry side of a reducing die; and deforming the workpiece by passage through the die in the solid phase at a nominal deformation ratio of at least 2:1, by means of hydrostatic pressure applied upstream of the die and/or by drawing the workpiece from downstream of the die. <IMAGE>

Description

1 GB 2 145 964 A 1

SPECIFICATION

Clear oriented polyester material This invention relates to oriented polyester mate- 70 rial; more particularly, this invention relates to a process for the preparation of oriented polyester material and to oriented polyester material, for ex ample tubing, produced thereby, especially such material of high transparency.

UK Patent No. 1311885 describes a process for reducing the cross-sectional area of an article of an orientable, thermoplastic polymeric material by drawing the article, at a temperature below its melting point, through a well-lubricated die of smaller cross-sectional area than that of the article, which process comprises forming an integral, pref erentially oriented nose at one end of the article by a solid phase deformation process, such that the tensile strength of the nose exceeds the draw ten85 sion to be applied to the article, gripping the nose and drawing the article through the die so as to in duce a substantial degree of molecular orientation throughout the drawn article.

This patent specification further discloses that the process is preferably performed by utilising the technique of hydrostatic extrusion; indeed, every example of the invention does use this technique.

However, and as the specification rightly points out, at the date of that specification simple hydro- 95 static extrusion was limited by a deformation ratio "boundary" above which further increase in the ra tio of the cross-sectional area of the polymer billet to that of the extruder die orifice had no useful ef fect; relaxation effects resulted in an extrudate ex- 100 hibiting die swell limiting the actual deformation ratio and orientation. The specification discloses overcoming this disadvantage by applying to the issuing extrudate a deforming draw tension, the complete process often being referred to as draw 105 assisted hydrostatic extrusion. UK Patent No.

1311885 discloses the application of its process to polyester materials such as polyethylene tere phthalate and polybutyiene terephthalate, including copolyester materials. A boundary deformation ra- 110 tio of 3.5:1 and highest previously attainable mod ulus of 11.4 x 105 p.s.i. are disclosed for polyester materials; and this is exceeded by draw assisted hydrostatic extrusion, to provide values of 5:1 and 20.55 X 10r p.s.i. (14.2 GPa) respectively. it is 115 stated that a temperature from 1000C to 200'C may be conveniently used for extruding polyethylene terephthalate material.

It is, however, found that oriented polyester material prepared by draw assited hydrostatic extrusion at the elevated temperatures exemplified in UK Patent No. 1311885 lack clarity. This invention seeks to provide a process in which this disadvantage is obviated.

According, therefore to one aspect of this invention, there is provided a process for the preparation of clear, oriented,. preferably unaxially oriented, polyester material, which process comprises providing an orientable thermoplastic work- piece of the polyester material, heated to a 130 temperature from 550C to 1100C, preferably from 60'C to 90'C, at the entry side of a reducing die; and deforming the workpiece by passage through the die in the solid phase at a nominal deformation ratio of at least 2:1, preferably of at least 3:1.

According to another aspect of this invention, there is provided a process for the preparation of oriented, preferably unaxially oriented, polyester material, which process comprises providing an orientable thermoplastic workpiece of the polyester material, heated to a temperature from 55'C to below 100'C, preferably from 600C to 90'C, at the entry side of a reducing die; and deforming the workpiece by passage through the die in the solid phase at a nominal deformation ratio of at least 2:1, preferably of at least 3:1.

If a measure of clarity may be sacrificed the workpiece may be heated above 11 OOC; for example to 115'C above which temperature the resulting product is both cloudy and of diminished modulus.

The polyester is one which is derivable from the reaction of at least one polyhydric alcohol, suitably a linear polyhydric alcohol, preferably a diol, with at least one polybasic acid, suitably a polycarbox- ylic acid. The alcohol is preferably an alicyclic or aliphatic such alcohol; for example, cyclohexanedimethanol or a linear C, to C, alkylene diol such as ethylene glycol, 1,3-propylene glycol or 1,4-butylene glycol, especially ethylene glycol. The acid is preferably an aromatic, alicyclic or aliphatic such acid; for example a mono- or poly carbocyclic aromatic acid such as o-, m-, or terephthalic acid; 2,6or 1,5- naphthalene dicarboxylic acid; or 1,2-dihydroxybenzoic acid, especially terephthalic acid. Examples of suitable polyesters include polyethylene 2, 6-naphthalate, polyethylene 1,5-naphthalate, polytetramethylene 1,2- dihydroxybenzoate, polyethylene terepthalate, polybutylene terephthalate and copolyesters, especially of ethylene terephthalate.

The term "workpiece" as used herein includes bars, strips, rods, multifilaments, tubes, films (including laminates thereof) and other cross-sections of solid or hollow stock. The term includes both billets and other forms of stock of greater length; indeed, continuous stock, which may be formed as the process is performed, may be utilised: exampies include a polymer sheathed continuous core such as a metal wire, or continuous polymer rod, film or filaments.

It has been found that oriented polyester material formed by the proces of the present invention has extremely good clarity; and that it is essential that the workpiece be heated to a temperature as aforesaid in order to achieve this desirable prop- erty. Thus, at temperatures of 11 O'C or above the oriented polyester material begins to exhibit opacity and at temperatures of below 55'C the workpiece is too brittle to be effectively deformed. The oriented polyester material can also exhibit en- hanced Young's modulus; resistance to creep; resistance to gas transport; and enhanced thermal conductivity in the machin direction.

Where clarity is not essential, certain of the mechanical properties (for example, Young's modulus) of the oriented polyester material may be 2 GB 2 145 964 A 2 further improved by incorporating a filler with the polyester to form the orientable thermoplastic workpiece. Examples of useful fibrous fillers include glass, asbestos, metal, carbon and ceramic whiskers, such as those formed from silicon carbide. Examples of useful laminar fillers include mica, talc and graphite flakes. Chalk and fly ash may also be included. The amount of filler which may advantageously be included depends on the nature of the filler, but up to 50% by weight, preferably less than 30%, especially less than 20%, may be incorporated.

It is preferred that the orientable thermoplastic workpiece is essentially unoriented before defor- mation: this is so that only intentional orientation is incurred with concomitant optimisation of properties.

The term "essentially unoriented" as used herein means that the workpiece has incurred no orienta- tion other than that minor amount which might be induced during formation of the workpiece, for example during billet moulding or melt extrusion, or during any subsequent shaping thereof, for example by machining, prior to the performance of the deformation process of this invention.

Where it is not possible to use the polyester material as received as a workpiece, the workpiece may be formed within the batch or continuously. In either case care must be taken to ensure that the workpiece cools at an appropriate rate, for example by quenching (suitably by immersion into a water bath at ambient temperature) the orientable thermoplastic workpiece, so that the resulting, oriented polyester material will be clear and without defects.

In the more crystalline polyesters too slow a cooling rate may result in a workpiece having coarse crystallinity which is not removed on orienting in accordance with this invention. Too fast a cooling rate may, however, result in voiding. Where crystallinity is present it is preferred that this amounts to no more than 10% to 25% by volume, especially less than 10% by volume.

For workpieces of tubular profile, it is found that blow-moulding is a satisfactory forming process. Where the tube thickness is greater than about 5 mm it may be necessary to coat the formed parison with further polyester material in at least one further forming step. Sheet may be formed by slit- ting tubular polyester material along the machine direction preferably after it has been oriented in accordance with this invention.

Prior to deformation, the orientable thermoplastic workpiece is desirably heated to a tempeature from 60'C to 90'C, suitably from 65' to 85', preferably from 700C to 80'. This may be effected by passage of the workpiece through a heated sleeve or in the case of a billet, by heating it in a temperature controlled chamber upstream from the die, as exemplified hereinafter. It is desirable that the reducing die is also heated to within the above temperature range. It is also desirable that the oriented polyester material passes through a heated sleeve downstream from the die which is suitable heated to provide a temperature within the above range.

While being deformed in accordance with this invention, it may also be desirable to subject the polyester material to a dielectric field as disclosed in US 3364294 and EPA 84274.

The deformation may be effected by extrusion processes; for example, by ram or hydrostatic extrusion (by analogy with the process dislcosed in UK 1480479) or by tensile processes; for example, by draw-assisted hydrostatic extrusion (by analogy with the process disclosed in UK 1311885) or die drawing, which latter process is preferred.

In accordance, therefore, with a preferred aspect of this invention there is provided a process in accordance with this invention wherein the deforma- tion is effected by applying to the workpiece from the exit side of the die a draw tension insufficient to cause tensile failure of the deforming workpiece; and drawing the workpiece through the die in the solid phase at a nominal deformation ratio of at least 2:1, preferably at least 3:1; for example at least 4:1.

It is feasible to use draw speeds greater than 1 cm min-' in the die drawing proces of this invention; indeed, speeds of 50 cm min-, or more, such as 60 to 80 cm min-,, are preferred.

Where hollow stock is being die drawn by the process of this invention it is essential to provide an appropriately dimensioned mandrel at the entry side of the die and protruding between the die lips to prevent collapse. In a continuous process this mandrel can suitably be of the "floating plug" type. In a batch process a fixed mandrel may be used.

A batch process may be converted to a continu- ous one by putting the upstream end of the deforming workpiece and downstream end of stock of the same cross-section both in contact with a hot, stainless steel plate; removing the plate and welding the two polymer surfaces. Preferably, such a weld should be at an angle of 45' or less to the axis of the stock.

The invention will now be further described, by way of example, with reference to the accompanying drawing and photographs, in which:

Figure 1 represents a schematic side elevation of the apparatus diametrically sectioned along the machine direction; Figure 2 is a photograph of the wide angle X-ray diffraction pattern of the initial billet; Figure 3 is a photograph of the wide angle X-ray diffraction pattern of the drawn product (radial Xradiation beam); and Figure 4 is a photograph of the wide angle X-ray diffraction pattern of the drawn product (tangential X-radiation beam).

In the drawing, the apparatus consits of a reduc- ing die 1 of 150 semi-angle and maximum reduc tion (or ideal deformation) ratio of 2.68 and, upstream thereof, an oven 2 from which a mandrel 3 (18 mm diametere and 10 mm length), having ta pered leading and trailing edges 4, 5, is supported by rod 6 (16 mm diameter) in the die exit 7 which is 1 cm in length and without taper. Haul off jaws 8 are connected downstream from the reducing die to a winch (not shown).

3 GB 2 145 964 A 3 In use, an initial billet 9 of polyethylene tere phthalate (intrinsic viscosity determined in o-chlo rophenol at 25'C of 0.75), produced by injection moulding to form a hollow cylindrical parison (26.0 mm O.D.; 19.7 mm I.D.), was machined at one end to 22 mm O.D. It was then inserted over the man drel and rod into the oven, maintained at a tem perature of 78'C, so that the machined end protruded through the die exit, the die also being maintained at 78C. The machined end was next gripped in the hauloff jaws and load applied, slowly at first such that the plastic strain of the bil let was progressively increased without causing tensile failure. After start-up a steady drawing speed of 65 cm min -1 at a drawing load of 280 kg wt was established. The drawn tube 10 emerged with 17.9 mm O.D. and 15.8 mm I.D., correspond ing to a deformation ratio of about 4. The resulting tube was completely transparent.

A three-point bend test of the intact tube was carried out between supports 40 cm apart. A small correction was made for the deformation of the tube during testing. The deflection was determined seconds after application of the load, giving a value of 11.3 GPa for the 10 second isochronal ax- 90 ial modulus of the tube. An empirical test of the crushing strength was undertaken by compressing a 5 mm length in a vice. The outside diameter could be crushed until the vice jaws were only 5 mm apart without tube cracking, stress whitening 95 or any other sign of failure being observed.

The injection moulding of the initial billet in volved rapid cooling from the melt so that a com pletely amorphous structure would be expected.

Figure 2 confirms that there was no crystaline structure.

Wide angle X-ray diffraction patterns were taken with the X-ray beam direction radially and tangen tially respectively with respect to the tube axis. The patterns depicted in Figures 3 and 4, respectively, 105 were very similar to those observed for one-way drawn polyethylene terephthalate films (see M.

Kashiwagi, A. Cunningham, AJ. Manuel and I.M.

Ward, Polymer 14, 111 (1973); Figures 2G and 2H correspond to Figures 4 and 3 respectively). This 110 suggests that the tube has an uniaxial planar struc ture where the molecular chain axes are preferen tially oriented along the tube axis (the machine direction) and crystalline units are preferentially oriented with their 100 planes close to the tangential direction (i.e. the local plane of the tube) than in the radial direction.

Claims

1. A process for the preparation of clear, ori ented polyester material, which process comprises providing an orientable thermoplastic workpiece of the polyester material, heated to a temperature from 55'C to 11 O'C, at the entry side of a reducing die; and deforming the workpiece by passage through the die in the solid phase at a nominal de formation ratio of at least 2A.

2. A process for the preparation of oriented po lyester material, which process comprises provid- ing an orientable thermoplastic workpiece of the polyester material, heated to a temperature from 55C to below 100C, at the entry side of a reducing die; and deforming the workpiece by passage through the die in the solid phase at a nominal de- formation ratio of at least 2:1.

3. A process according to Claim 1 or 2 wherein the polyester comprises residues of at least one polyhydric alcohol. 75

4. A process according to Claim 3 wherein the polyester comprises residues of at least one linear C2 to C, diol.

5. A process according to any preceding claim wherein the polyester comprises residues of at least one polycarboxylic acid.

6. A process according to Claim 5 wherein the polyester comprises residues of at least one aromatic dicarboxylic acid.

7. A process according to any preceding claim wherein the orientable thermoplastic workpiece is essentially unoriented before deformation.

8. A process according to any preceding claim wherein the orientable thermoplastic workpiece is heated to a temperature from 700C to 80'C.

9. A process according to any preceding claim wherein the reducing die is heated to a temperature from 60'C to 90'C.

10. A process according to any preceding claim wherein the oriented polyester material passes through a heated sleeve downstream from the die.

11. A process according to Claim 10 wherein the heated sleeve provides a temperature from 60'C to 90'C.

12. A process according to any of Claims 1 to 11 wherein the deformation is effected by a tensile process.

13. A process according to Claim 12 wherein the deformation is effected by applying to the workpiece from the exit side of the die a draw tension insufficient to cause tensile failure of the deforming workpiece; and drawing the workpiece through the die in the solid phase at a nominal deformation ratio of at least 2:1.

14. A process according to Claim 13 wherein the draw speed is greater than 50 cm min-'.

15. A process according to Claim 13 or 14 which is continuous.

16. A process according to Claim 15 wherein the upstream end of a discrete workpiece being deformed in accordance with Claim 13 or 14 is welded to the downstream end of continuous stock of the same polyester and cross-section.

17. A process according to Claim 15 or 16 wherein the workpiece is continuously formed in 120 situ.

18. A process according to any preceding claim wherein the workpiece is a filament, film or tube.

19. A clear oriented homo- or copolyester material which has been deformed by passage 125 through a die in the solid phase.

20. An oriented polyester material according to Claim 19 which is a film or tube.

Printed in the UK for HMSO, D8818935, 2,185, 7102. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.