GB1598738A

GB1598738A - Receptacle formed from a tubularly-formed sheet of a thermo-plastic material

Info

Publication number: GB1598738A
Application number: GB24172/80A
Authority: GB
Original assignee: Biax Fiberfilm Corp
Current assignee: Biax Fiberfilm Corp
Priority date: 1977-02-09
Filing date: 1978-01-27
Publication date: 1981-09-23
Also published as: FR2380116A1; IT1092580B; GB1598737A; IT7820062A0; FI780340A; ES466802A1; AU3276978A; PT67610A; LU79030A1; BR7800746A; PT67610B; NL7801529A; NO780430L; DK57278A; DE2805440A1; DE2805440C2; BE863806A; SE7801484L; CA1123566A; JPS53124579A

Description

PATENT SPECIFICATION ( 11) 1 598 738

0 O ( 21) Application No 24172/80 ( 22) Filed 27 Jan 1978 ( 19), ^ 2 ( 62) Divided out of No 1598737 ( 31) Convention Application No 766926 ( 32) Filed 9 Feb 1977 in @ < Ad ( 33) United States of America (US) In ( 44) Complete Specification Published 23 Sep 1981 t t ' ( 51) INT CL 3 B 31 B 23/00 B 65 D 30/02 O ( 52) Index at Acceptance B 8 K 2 K 1 WC ( 54) A RECEPTACLE FORMED FROM A TUBULARLY-FORMED SHEET OF A THERMO-PLASTIC MATERIAL ( 71) We, BIAX-FIBERFILM CORPORATION, a corporation organized and existing under the laws of the State of Wisconsin, United States of America, of 1066 American Drive, Neenah, Wisconsin, United States of America, 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 be particularly described in and by the following statement: 5

This invention relates to a receptacle formed from a tubularly-formed sheet of thermoplastic material heated sealed at an end thereof.

Thermoplastic bags for diverse use, such as sandwich bags, garbage bags, leaf bags and the like, are produced by extruding a tube of thermoplastic material, such as high density polyethylene, with the resulting tubularly-formed material being cooled, heat sealed and 10 either scored or cut to the desired length The thus formed bag exhibits a strip tensile breaking length representative of the processed thermoplastic material The end use of the thermoplastic bag normally dictates the selection of the thermoplastic material, e g as a sandwich bag, a low porosity and normal strength thermoplastic material is selected whereas a garbage bag would require the selection of a thermoplastic material exhibiting 15 high strength characteristics.

The invention provides a receptacle comprising a cylindrically-shaped wall formed of stretched orientable polymeric material heat sealed at an end thereof; said wall being characterized by a strip tensile breaking length of at least twice the strip tensile breaking length of non-stretched orientable polymeric material 20 In a receptacle according to the invention the stretched polymer is preferably bi-axially stretched.

An advantage of the present invention is that it makes it possible to provide a receptacle formed by bi-axially stretching a collapsed heat-sealable and tubularlyformed sheet or web of thermoplastic material producing a bag having an improved strip tensile breaking 25 strength of at least twice that of the tubularly-formed sheet of thermoplastic material being treated; in effect, providing a significant and unexpected result in that both the heat seal area and the fold area increase in strength, in addition to the film area.

The invention will be more clearly understood by reference to the following detailed description of an exemplary embodiment thereof in conjunction with the accompanying 30 drawings wherein:

Figure 1 is a schematic side elevational view of the apparatus and process of the present invention; and Figure 2 is a schematic top elevational view of the apparatus and process of the present invention 35 Drive and support assemblies, timing and safety circuits and the like, known and used by those skilled in the art, have been omitted in the interest of clarity.

Referring to Figure 1, there is illustrated a preferred embodiment of the process and apparatus of the present invention including a circular blown film die assembly and a stretching assembly, generally indicated as 10 and 12, respectively The circular blown film 40 die assembly 10 forming the blown film 12 may be any one of the types of assemblies sold by the Sterling Extruder Corporation of South Plainfield, New Jersey The blown film 12 is passed about the roller 14 to form a flat two-layered sheet 16 prior to introduction into the heat sealing assembly, generally indicated as 18, as known and used by those skilled in the art, wherein the two layered sheet is heat sealed at selected intervals on a line perpendicular 45 1 598 738 to the movement of the sheet 16.

The thus heat-sealed, two-layered sheet 20 is coursed in a first station, generally indicated as "I" between a nip 22 of a pair of rollers 24 having a plurality of grooves 26 perpendicularly formed to the axis of the rollers 24, as seen in Figure 2 The sheet 20 is maintained against the lower grooved roller 24 by a pair of press rollers 28 to hold the sheet 5 against the lower roller 28 to thereby prevent the sheet 20 from narrowing prior to introduction Once in the nip 22, the sheet 20 assumes the shape of the groove pattern and becomes stretched by a factor of the draw ratio as hereinafter more clearly described.

In the first station, in effect, lateral stretching, the sheet 20 is wound up at about the same velocity as the feed velocity The crimp pattern is flattened out by stretching the sheet 20 10 laterally, such as by means of tenter clamps or curve Mount Hope rolls, generally indicated as 32, such as known and used by one skilled in the art.

The grooves 26 of the rollers 24 are intermeshed like gears, as known to those skilled in the art As the sheet 20 enters the nip 22, the sheet 20 assumes the shape of a groove 26 and is stretched by a factor determined by the length of the sinus wave "ie" of the groove 15 divided by the original length of the web "(o" between contact points of each respective groove tip as disclosed in British Patent Specification No 1,521,183.

The draw ratio el/ is calculated by the following equation where 20 a = N d/2 co, and the sinus wave of the groove is 25 eiw = N 1 + a 2 CO 52 x dx 0 30 Thus for d/o ratios of 1 0, 0 75 and 0 5 the draw ratios are 2 35, 2 0 and 1 6, respectively.

A laterally stretched sheet 34 is passed from the rollers 32 and is coursed between a nip 40 of a first pair of rollers 42 of a second station "II" with said rollers 42 having a plurality of grooves 44 parallel to the axis of the rollers 42 The sheet 32 is maintained against the lower 35 grooved roller 42 by a pair of press rollers 46 to ensure that the velocity V 1 of the sheet 32 is substantially identical to the surface velocity V, of the grooved rollers 42 The grooves 44 of the rollers 42 are intermeshed like gears, as known to those skilled in the art As the sheet 34 enters the nip 40, the sheet 34 assumes the shape of a groove 44 and is stretched by a factor determined by the length of the sinus wave "C' of the groove divided by the original 40 length of the web "co" between contact points of each respective groove tip, as hereinabove discussed with reference to the passage sheet 20 through station I rollers 24.

The sheet 34, after passage through the nip 40 of the rollers 42, is pulled away by a pair of tension rollers 48 having a surface velocity V 2 greater than the surface velocity of the rollers 42, but not greater than a factor of the draw ratio affected in the nip 40 of the rollers 42 45 Accordingly, the length of the sheet 34 is therefore increased by such factor It is noted that the sheet 34 does not undergo narrowing while being longitudinally stretched or extended, as is the case with conventional roller systems In a preferred embodiment of the present invention, the sheet 34 is passed through two further pairs of grooved rollers 42 to further stretch lengthwise the sheet 34 which is eventually collected on a roller 50 50 The maximum permissible draw ratio can easily be determined by measuring the residual elongation of the thermoplastic material For best results, the grooves 44 of the rollers 42 should be as fine as possible, with groove distance being increased if heavy basis weight factors are to be oriented From experience, good results are obtained, if the distance between grooves (in mm) is less than 1 0 times the fabric basis weight (in gram/M 2) With 55 the process and apparatus of the present invention, a bag is produced having a much higher strip tensile breaking length (STBL expressed as meters) than a normal produced blown film bag.

Operation of the process and apparatus is described in the following examples which are intended to be merely illustrative, and the invention is not to be regarded as limited thereto 60 1 598 738 Example 1

A 7 " x 7 " double layer sheet is formed by extruding a mixture of 90 % polypropylene (melt flow rate of 0 5 g/mm) and 10 % clay and had the following properties:

thickness 0 050 " film basis weight STBL break elongation initial modulus STBL over see STBL over fold : 127 micron : 125 g/m 2 : 3570 m : 1600 % : 1600 m : 2560 m : 3050 m The bag was heat-sealed and stretched in the apparatus 1 5 times on a lateral direction and 3 3 times on a longitudinal direction ( 3 passes) to a final dimension of 10 5 " wide and 23 " long It was noted that the heat-sealed area also stretched The stretched bag had the following properties:

STBL break initial STBL STBL elongation modulus over seal over fold : 23550 m : 40 % : 185500 m : 15500 m : 16600 m Example II

The process of Example I was repeated on a similar 7 " x 7 " sheet with heat sealing being effected after stretching vice before with the STBL over seal being 2200 m; i e less than the STBL over seal of a bag heat sealed before stretching.

Example III

A 7 " x 7 " double layer sheet is formed by extruding a 100 % polypropylene (melt flow rate of 6 0 g/10 mm) and had the following properties:

thickness 0 050 " film basis weight STBL break elongation initial modulus STBL over seal STBL over fold : 150 micron : 142 g/m 2 : 3200 m : 1400 % : 14500 m : 14500 m : 3040 m The bag was heat-sealed and stretched in the apparatus 1 5 times on a lateral direction and 4 5 times on a longitudinal direction ( 3 passes) to a final dimension of 10 5 " wide and 31.5 " long It was noted that the heat-sealed area also stretched The stretched bag had the following properties:

thickness basis weight STBL break elongation initial modulus STBL over seal STBL over fold : 25 microns : 21 g/m 2 : 35700 m (length) : 25 % : 225000 m : 18400 m : 22050 m 4 1 598 738 4 Example IV

A 7 " x 7 " double layer sheet is formed by extending a mixture of 95 % high density polypropylene (melt flow rate of 2 0 g/l Omm) and 5 % titanium dioxide and had the following properties:

5 thickness: 200 microns film basis weight:170 g/m 2 STBL: 3800 m break elongation: 1800 % initial modulus:12000 m 10 STBL over seal: 2600 m STBL over fold: 2650 m The bag was heat-sealed and stretched in the apparatus 2 0 times ( 2 passes) on a lateral direction and 5 0 times on a longitudinal direction ( 3 passes) to a final dimension of 14 0 " 15 wide and 25 " long It was noted that the heat-sealed area also stretched The stretched bag had the following properties:

thickness: 22 microns basis weight:18 g/m 2 20 STBL: 38500 m break elongation: 40 % initial modulus:17500 m STBL over seal: 28500 m STBL over fold: 30400 m 25 Thus, it is readily apparent to one skilled in the art that a novel bag is produced of a light weight per dimension exhibiting substantially improved strip tensile breaking length It will be readily apparent to one skilled in the art, that depending on end use, that a bag of improved strip tensile breaking length may be produced by passing a tubularly-formed 30 thermoplastic sheet, preferably heat-sealed, either through laterally or longitudinally grooved rollers or sequentially through such grooved rollers or as described herein with reference to the preferred embodiment.

Reference is made to our copending British Patent Application No 3293/78 (Serial No.

1598737), on which the present application is divided, and which claims a process and 35 apparatus for the bi-axial stretching of a tubularly-formed sheet of orientable, polymeric thermoplastic material for forming into bags.

Claims

WHAT WE CLAIM IS:

1 A receptacle comprising a cylindrically-shaped wall formed of stretched orientable polymeric material heat sealed at an end thereof; said wall being characterized by a strip 40 tensile breaking length of at least twice the strip tensile breaking length of non-stretched orientable polymeric material.

2 A receptacle according to claim 1 wherein the polymeric material is stretched in two different directions.

3 A receptacle according to claim 2 wherein said directions are parallel and 45 perpendicular, respectively, to the axis of said cylindrical wall.

4 A receptacle as claimed in claim 1 and substantially as described herein with reference to the accompanying drawings.

MICHAEL BURNSIDE & PARTNERS 50 2 Serjeants' Inn Fleet Street London EC 4 Y 1 HL England.

Agents for the Applicants 55 Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon Surrey 1981.

Published by The Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.

1 598 738