CA1123566A - Process and apparatus for stretching a tubularly-formed sheet of a thermoplastic material and the product produced thereby - Google Patents

Process and apparatus for stretching a tubularly-formed sheet of a thermoplastic material and the product produced thereby

Info

Publication number
CA1123566A
CA1123566A CA295,599A CA295599A CA1123566A CA 1123566 A CA1123566 A CA 1123566A CA 295599 A CA295599 A CA 295599A CA 1123566 A CA1123566 A CA 1123566A
Authority
CA
Canada
Prior art keywords
sheet
rollers
velocity
stretching
set
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA295,599A
Other languages
French (fr)
Inventor
Eckhard C.A. Schwarz
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BIAX-FIBERFILM Corp
Original Assignee
BIAX-FIBERFILM CORPORATION
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to US766,926 priority Critical
Priority to US05/766,926 priority patent/US4144008A/en
Application filed by BIAX-FIBERFILM CORPORATION filed Critical BIAX-FIBERFILM CORPORATION
Application granted granted Critical
Publication of CA1123566A publication Critical patent/CA1123566A/en
Application status is Expired legal-status Critical

Links

Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C55/00Shaping by stretching, e.g. drawing through a die; Apparatus therefor
    • B29C55/02Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
    • B29C55/023Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets using multilayered plates or sheets
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29LINDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2023/00Tubular articles
    • B29L2023/001Tubular films, sleeves

Abstract

PROCESS AND APPARATUS FOR STRETCHING A
TUBULARLY-FORMED SHEET OF A THERMOPLASTIC
MATERIAL AND THE PRODUCT PRODUCED THEREBY

.
ABSTRACT OF THE DISCLOSURE

There is described in a preferred embodiment of the present invention, a process and apparatus for bi-axially stretching a tubularly-formed sheet of thermo-plastic material in a first station and a plurality of second stations wherein the first and second stations are provided with sets of rolls having generally sinosoidally-shaped grooves perpendicular and parallel, respectively, to the axis of each set of rolls to produce hags of improved strip tensile breaking strength.

Description

~35~6 1 This invention rela-tes to a novel process and apparatus for the stretching of a tubularly--formed sheet of thermoplastic material and more particularly to a novel process and apparatus for the bi-axial stretching of a tubularly-formed sheet of orientable, polymeric thermoplastic material to form bags of improved strip tensile breaking strength.
Thermoplastic bags for diverse use, such as sandwich bags, garbage bags, leaf bags and the like, are produced by extruding a tube of thermoplastic ma~erial, such as high density polyethylene, with the resulting tubularly-formed material being cooled, heat sealed and 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. a~ 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 high strength characteristics.
It is an object oE the present invention to provide a novel process and apparatus for stretching a heat-sealable and tubularly-formed sheet of a s~nthetic material.
Another object of the present invention is to provide a novel process and apparatus for bi-axially strstching a collapsed heat-sealable and tubularly-formed sheet or web of thermoplastic material to form a bag having an improved strip tensile breaking strength of at least twice that of the tubularly formed sheet of thermoplastic material being trea-ted;

in effect, providing a significant and unexpected result in 3~

~3~

1 that both the heat seal area and the fold area increase in streng-th, in addition to the film area.
Various other objects and advantages of the present inven-tion will become apparent from the following detailed 5 description of an exemplary embodiment thereof with the novel features thereof being particularly pointed out in the appended claims.
In accordance with the present invention, there is provided a process and apparatus for the selective stretching 10 of a tubularly-formed sheet or web of thermoplastic material in a station provided with a set of groovecl, generally sinosoidally~shaped rolls, whereby the sheet or web of thermo-plastic material is stretched in a manner to effect uniform stretching thereby producing a sheet or web of larger dimension 15 in the direction of stretch.
`. In accordance with a preferred embodiment of the present invention, there is provided a process and apparatus for bi axially stretching a tubularly-formed and heat-sealed sheet o thermoplastic material in a first station 20 and a plurality of second stations wherein the first and second stations are provided with sets of rolls having grooves perpendicular and parallel, respectively, to the axis of each set of rolls. The groove pattern of each set of rolls is such that the distance between grooves is less than l.0 millimeters times the sheet or web basis weight in grams per square meter. The sheet or web of tubularly-formed thermoplastic material is stretched in a manner to effect uniform stretching to produce a thermoplastic bag of substantially improved strip tensile breaking strength.

~23~

1 The inven-tion will be more clearly understood by reference to the following de-tailed description of an exemplary embodiment thereof in conjunction with the accompanying drawi.ngs wherein:
Figure l is a schematic s.ide 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.
Drive and support assemblies, timing and safety 1~ circuits and the like, known and used by those skilled in the art, have been omitted in the interest of clarity.
Referring to Figure l, there is illustrated a preferred embodiment o the process and apparatus of the present invention including a circular blown film die assembly 15 and a stretching clssembly, generally indicated as lO and 12, respectively. The circular blown film die assembly lO forming the blown film 12 may be any one of the types of assemblies sold by the Stexlin~ Extrucler Corporation of South Plainfield, New Jersey~ The blown film 12 is passed about the roller 14 20 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 i.ntervals on a line perpendicular to the movement of the sheet 16.
The thus heat-sealed, two-layered sheet 20 i5 coursed in a first station, generally indicated as "I" between a nip 22 of a palr of rollers 24 having a plurality of grooves 2~
perpendicularly formed to the axis of the rollers 24, as seen 3~

3~

in Figure 2. The sheet 20 is maintained against the lower grooved roller 2~ by a pair of press rollers 28 to hold the sheet 20 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 laterally, such as by means of tenter clamps or curved 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 "~" of the groove divided by the original length of the web "~ " between contact points of each respective groove tip as disclosed in Canadian Patent No. 1,075,870 issued April 22, 1980 to E.C.A. Schwarz.
The ~raw ratio,~/~ is calculated by the following ~ equation where ; a = ~ d/2 ~ , and the sinus wave of the groove is ~ .
~/~ 1 1 + a cos x dx D ~

Thus ~or d/~ ratios of 1.0, 0.75 and 0.5 the draw ratios are 2.35, 2.0 and 1.6, respectively.

~ - 5 -~ 5~

1 ~ laterally s~retched 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.
5 The sheet 32 is maintained against the lower grooved roller 42 by a pair of press rollers 46 to ensure that the velocity V
of the sheet 32 is substantially identical to the surface velocity Vl of the grooved rollers 42. The grooves 44 of the rollers 42 are intermeshed like gears, as known to those 10 skilled in the ar-t. 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 " ~ " of the groove divided by the original length o~ the web " ~ "
between contact points of each respective groove tip, as ~5 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 V2 greater than the surface velocity 20 of the rollers 42, but not greater than a factor of the draw ratio affected in the nip 40 of the rollers 42.
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 25 extended, as is the case with conventional roller systems.
In a preferred embodiment of the present invention, the sheet 3~ is passed through two further pairs of grooved 3~

,, .......... , . .... ...... ,. ..... ..... . ....... .. ~ ........... ~
:

~3~

1 rollers 42 to further stretch lengthwise the sheet 34 which is eventually collected on a roller 50.
The maximum permissible draw ratio can easily be determined by measuring the residual elongation of the thermo-plastic ma-terial. For best resul-ts, 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 orientedO
From experience, good results are obtained~ if the distance between grooves ( in mm) is less than 1.0 times the fabric 10 basis weight (in gram/m2). With 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 ~ilm bag.
; Operation of the process and apparatus is described 15 in the following examples which are in~ended to be merely : illustrative, and the invention is not to be regarded as limited thereto.

Exam~le l A 7" x 7" double layer sheet is for~ed by extruding a mixture of 90% polypropylene ~melt flow rate of 0.5 gjmm~ and l0~ clay and had the following properties:
; thickness 0.050" : 127 micron film basis weight: 125 g~m2 STBI. . 3570 m break elongation ; 1600%
initial modulus : 1600 m STBL over seal : ~560 m STBL over fold : 3050 m 3~1 , _ -- . . . .. ... ... ......

1 The bag was lleat-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 5 area also stretched. The stretched bag had the following properties:
STBI. : 23550 m break elongation : 40%
initial modulus : 185500 m 1~ STBL over seal : 15500 m STBL over fold : 16600 m Exampl e I I

The process of Example I was repeated on a similar 15 7l~ x 7" sheet with heat sealing being effected after st.retching vice before wi.th the STBI, over seal being 2200 m ; i.e~ less than the STBL over seal of a bag heat sealed hefore 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" : 150 micron film basis weight: 142g/m

2~ STB~ : 3200 m break elongation : 1400%
initial modulus : 14500 m STBI. over seal : 14500 m STBL over fold : 3040 m

3~

~3~

1 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-5 sealed area also stretched. The stretched bag had the following properties:
thickness : 25 microns basis weight : 21 g/m2 STBL : 35700m(length~ -lCI break elongation : 25%
initial modulus : 225000 m STBI. over seal : 18400 m STBI, over ~ol~ : 22050 m Exam~)le IV

A 7" x 7" double layer sheet is formed by ex~ending a mixture of 95~ high density polypropylene (melt flow rate of 2.0 g/lOmm) and 5~ titanium dioxide and had the following properties:

thickness : 200 micron film basis weight : 170 g/m2 STBL : 3800 m break elongation : 1800~

initial modulus : 12000 m :STBL over seal : 2600 m STBL over fola : 2650 m 3~ 6 1 , The bag ~as 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" wide and 25" long. It was noted that 5 the heat-sealed area also stretched. The stretched bag had the following properties:
thickness : 22 microns basis weight : 18 g/m STBL : 38500 m break elongation : 40~
initial modulus : 17500 m STBL over seal : 28500 m STBL over fold : 30400 m Thus, it is readily apparent to one skilled in 15 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 passiny a 20 tubularly-formed thermoplastic sheet, preferably heat-sealed, either through laterally or longitudinally grooved rollers or sequentiall,y through such grooved roller~ or as described herein with reference to the preferred embodiment.
While the invention has been described in connection 25 with an exemplar.y embodiment thereof, it will be understobd that many modifications will be apparent to those of ordinary skill in the art and that this application is intended to cover any adaptations or variations thereof.

.:

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for longitudinally stretching a tubularly-formed sheet of orientable polymeric material which comprises:
(a) introducing said sheet into a nip of inter-digitating rollers having grooves parallel to the axis of said rollers;
(b) controlling the velocity of introduction of said sheet into said nip to substantially the rotational velocity of said rollers thereby to longitudinally stretch incremental portions of said sheet;
(c) withdrawing said sheet from said rollers at a velocity greater than the rotational velocity of said rollers; and (d) collecting the thus stretched sheet.
2. The process as defined in claim 1, wherein the withdrawal velocity of step (c) is not greater than a factor of the draw ratio of said nip.
3. The process as defined in claim 1, wherein said tubularly-formed sheet is heat-sealed at preselect intervals perpendicular to the movement of said sheet prior to stretching.
4. A process for bi-axially stretching a tub-ularly-formed sheet of orientable polymeric material which comprises:
(a) introducing said sheet into a nip of inter-digitating rollers having grooves parallel to the axis of said rollers;
(b) controlling the velocity of introduction of said sheet into said nip to substantially the rotational velocity of said rollers thereby to longitudinally stretch incremental portions of said sheet;
(c) withdrawing said sheet from said rollers at a velocity greater than the rotational velocity of said rollers;
(d) introducing said sheet into a nip of inter-digitating rollers having grooves perpendicular to the axis of said rollers;
(e) controlling the velocity of introduction of said sheet into said nip to substantially the rotational vel-ocity of said rollers thereby to laterally stretch incremental portions of said sheet;
(f) laterally elongating and withdrawing said sheet from said rollers at a velocity substantially corres-ponding to the velocity of introduction; and (g) collecting the bi-axially stretched sheet.
5. The process as defined in claim 4, wherein steps (d) to (f) are again repeated prior to step (g).
6. The process as defined in claim 5 wherein steps (d) to (f) are twice repeated prior to step (g).
7. An apparatus for producing thermoplastic bags which comprises:
(a) means for extruding a tube of orientable polymeric material;
(b) means for forming said tube into a sheet;
(c) means for heat sealing said sheet at preselected portions thereof;
(d) a first station means for stretching said sheet in a first direction and including a first set of interdigitating rollers formed with grooves, said first set of interdigitating rollers stretching incremental portions of said web in a first direction;
(e) first regulator means for controllably introducing said sheet into said first set of interdigitating rollers at a velocity substantially identical with the surface speed thereof;
(f) a first take-up means for elongating said sheet in said first direction upon withdrawl of said sheet from said first set of interdigitating rollers;
(g) a second station means for stretching said sheet in a second direction and including a second set of interdigitating rollers formed with grooves, said second set of interdigitating rollers stretching incremental portions of said sheet in a second direction;
(h) a second regulator means for controllably introduc-ing said sheet into said second set of interdigitating rollers at a velocity substantially identical with the surface speed thereof;
(i) a second take-up means for elongating said sheet in said second direction upon withdrawal of said sheet from said second set of interdigitating rollers; and (j) collecting means for receiving said sheet.
8. The apparatus as defined in claim 7, wherein said first and second set of interdigitating rollers are formed with grooves which are perpendicular and parallel, respectively, to said first and second sets of inter-digitating rollers.
9. The apparatus as defined in claim 8, wherein said second take-up means are press rollers operated at a rotational velocity proportional to the draw ratio effected in said second set of interdigitating rollers.
10. The apparatus as defined in claim 7, wherein said second regulator means include a roller rotating at substantially the same rotational velocity as that of an associated interdigitating roller.
CA295,599A 1975-03-31 1978-01-23 Process and apparatus for stretching a tubularly-formed sheet of a thermoplastic material and the product produced thereby Expired CA1123566A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US766,926 1977-02-09
US05/766,926 US4144008A (en) 1975-03-31 1977-02-09 Apparatus for stretching a tubularly-formed sheet of thermoplastic material

Publications (1)

Publication Number Publication Date
CA1123566A true CA1123566A (en) 1982-05-18

Family

ID=25077949

Family Applications (1)

Application Number Title Priority Date Filing Date
CA295,599A Expired CA1123566A (en) 1975-03-31 1978-01-23 Process and apparatus for stretching a tubularly-formed sheet of a thermoplastic material and the product produced thereby

Country Status (18)

Country Link
JP (1) JPS53124579A (en)
AU (1) AU3276978A (en)
BE (1) BE863806A (en)
BR (1) BR7800746A (en)
CA (1) CA1123566A (en)
DE (1) DE2805440C2 (en)
DK (1) DK57278A (en)
ES (1) ES466802A1 (en)
FI (1) FI780340A (en)
FR (1) FR2380116A1 (en)
GB (2) GB1598738A (en)
IT (1) IT1092580B (en)
LU (1) LU79030A1 (en)
NL (1) NL7801529A (en)
NO (1) NO780430L (en)
PT (1) PT67610B (en)
SE (1) SE7801484A (en)
ZA (1) ZA7800643B (en)

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0218977B2 (en) * 1981-07-04 1990-04-27 Sumitomo Electric Industries
GB8424062D0 (en) * 1984-09-24 1984-10-31 Mackley M R Oriented polymer films
GB2362351B (en) * 2000-03-18 2004-01-14 Harris Parts Ltd Extruded packaging material
US7932196B2 (en) 2003-08-22 2011-04-26 Kimberly-Clark Worldwide, Inc. Microporous stretch thinned film/nonwoven laminates and limited use or disposable product applications
US7651653B2 (en) 2004-12-22 2010-01-26 Kimberly-Clark Worldwide, Inc. Machine and cross-machine direction elastic materials and methods of making same
GB0721410D0 (en) * 2007-10-31 2007-12-12 Rasmussen O B Method and apparatus for longitudinal orientation of thermoplastic film material
GB0907755D0 (en) * 2009-05-06 2009-06-24 Rasmussen O B Method for longitudinal stretching a film in solid state and apparatus to carry out the method

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2773285A (en) * 1947-11-06 1956-12-11 Continental Can Co Method of making sterile containers
GB756476A (en) * 1954-03-19 1956-09-05 Ici Ltd Improvements in the seaming of films
DE1504502B2 (en) * 1962-03-17 1971-08-12 Stretching unit for biaxial stretching of a thermoplastic plastic film web
DE2037574A1 (en) * 1970-07-29 1972-02-10 Wolff Walsrode Ag Drawn plastics film - by drawn flatterned film tube without bonding surfaces of the flattened film tube
GB1526722A (en) * 1974-07-05 1978-09-27 Rasmussen O Method for producing a laminated high strength sheet
CA1082508A (en) * 1974-11-26 1980-07-29 Charles R. Walitalo Tear resistant separable end-connected bags
CA1075870A (en) * 1975-03-31 1980-04-22 Eckhard C.A. Schwarz Process and apparatus for stretching a non-woven web of an orientable polymeric material
DE2641533A1 (en) * 1975-09-17 1977-03-31 Biax Fiberfilm Corp A method of stretching a thermoplastic material

Also Published As

Publication number Publication date
SE7801484A (en) 1978-08-10
FI780340A (en) 1978-08-10
PT67610B (en) 1979-07-16
JPS53124579A (en) 1978-10-31
LU79030A1 (en) 1978-09-28
DE2805440C2 (en) 1981-09-17
ES466802A1 (en) 1979-01-16
ZA7800643B (en) 1978-12-27
NL7801529A (en) 1978-08-11
NO780430L (en) 1978-08-10
DE2805440A1 (en) 1978-08-10
FR2380116A1 (en) 1978-09-08
BR7800746A (en) 1978-09-12
AU3276978A (en) 1979-08-02
IT1092580B (en) 1985-07-12
IT7820062D0 (en) 1978-02-07
GB1598737A (en) 1981-09-23
DK57278A (en) 1978-08-10
BE863806A1 (en)
BE863806A (en) 1978-08-09
PT67610A (en) 1978-03-01
GB1598738A (en) 1981-09-23
CA1123566A1 (en)

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