US3801036A

US3801036A - Production of thermoplastic films

Info

Publication number: US3801036A
Application number: US00157306A
Authority: US
Inventors: R Hasler
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1970-07-06
Filing date: 1971-06-28
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02
Also published as: NL165969C; CA944682A; DE2133644B2; DE2133644A1; BE769589A; JPS5432102B2; NL7109083A; NL165969B; LU63474A1; JPS4833479A; GB1330863A; FR2100228A5; DE2133644C3

Abstract

An apparatus and method for producing rolls of film having no hard spots by slitting a tubular film with oscillating slitting knives and compensating for the fluctuation in the edges of the slit film due to the oscillation of the knives so as to obtain a reeled film having good edge register.

Description

United States Patent 1191 '11] 3,801,036 Hasler v Apr. 2, 1974 [541 R TI N F THERM L I 2,868,541 1 1959 KOlOdZiCj 242/57.1

FILMS 3,323,740 6/1967 Blessing.. 242 57.1 2,989,265 6/1961 SClSlOd 242 56.2 x [75] Inv Robm a g England 3,l88,856 6/1965 Schneider... 242 57.1 x 3,536,273 10 1970 Hawkins 242 57.1 x [73] Awgnee' 'I F chem'cal lndusmes 2,666,598 1/1954 Robinette 242 57.1 London England 3,570,735 3 1971 Kurz 242/57.1 122 Filed: June 28, 1971 Primary Examiner-John W. Huckert [21 I App! 157306 Assistant Examiner-Edward J. McCarthy Attorney, Agent, or Firm-Cushman, Darby & Foreign Application Priority Data Cushman July 6, 1970 @1661 131116111 32671/70 57 ABSTRACT [52] us. Cl 242/56.2, 83/428, 242/55 1 51 1111. c1 Bh 35/02, B65h /02 An apparatus and method for Producing rolls of film 58 Field Of Search 242/562, 56 R, 56.6, 56.7, having no hard Spots by slitting a tubular film with [5 6] References Cited UNITED STATES PATENTS 3,365,992 l/l968 Dreher 242/56 R cillating slitting knives and compensating for the fluctuation in the edges of the slit film due to the oscillation of the knives so as to obtain a reeled film having 1 PRODUCTION OF THERMOPLASTIC FILMS The invention relates to a process and apparatus for slitting a travelling web and winding the slit web into a roll. In particular the present invention is concerned with slitting tubular film.

When a stationary knife is used to slit a web which is wound up to form a roll having good edge register, by which is meant a roll in which the edges are substantially aligned, the roll often has hard areas across its width which extend partly or wholly through the depth of the roll. The reason is because the web being wound up often has thickness variations across its width which may be termed high spots and low spots." These tend to occur in the same position across the width of the web as a result of variations in the processing conditions such as the variation in the die gap producing tubular film or variation in the stretching conditions if an oriented film is being produced. When the web is wound up these high spots and low spots are superimposed upon one another in the reel so that the high spots reinforce one another. The hard areas resulting from the superimposed high spots, tend to stretch the web in localized regions so that when the roll is subsequently unwound, the web has areas that are wrinkled. These irregularities make the web visually unattractive and difficult to use in certain applications such as printing and packaging. Consequently, the parts of the web containing these irregularities often have to be cut out and discarded, leading to a substantial wastage of material.

It has been proposed that this disadvantage may be overcome by oscillating the reel onto which the web is being wound transversely with respect to the direction of travel of the web so that the high spots and low spots are distributed across the width of the reel. However, this technique suffers from the disadvantage that the edges of adjacent layers in the reel are not in register and it is necessary to cut off the edges to get a satisfactory reel. This also leads to wastage of material.

According to the present invention we provide a method for slitting a travelling web of material and winding the slit webs into a reel comprising slitting the web witha slitting means which oscillates across the direction of travel of the web, and adjusting the position of the web relative to the reel whereby successive layers of web wound onto the reel have their adjacent may be comprised of slitting units that are partly or completely rigidly linked together so that part or all of the slitting means assemblyv moves in unison.

Examples of slitting units of the slitting means of the present invention include the cutting edges of knives, hot gas jets, wires or laser beams. In one embodiment of our invention the slitting units comprise two knife edges which are rigidly linked together and move in a regular manner transversely to the forwardly moving direction of the film. By regular is meant that the movement of the slitting units is continuous rather than intermittent. However, it is not necessary for the slitting means to move transversely or in a regular manner and if desired the slitting means may move irregularly and/or obliquely to the forward motion of the film. The number of slitting units used depends on the number of separate pieces which are to be produced from the web; the separate strips so produced may then be wound up individually. In a preferred embodiment of our invention a tubular film is slit into two webs by two knives each of which slits only one thickness of film. By virtue of the tubular cross-section of the unslit film, each of the slit webs includes an overturned edge which should be unfolded before the slit web is reeled up. In this embodiment the knives are preferably oscillated out of phase with each other so that the widths of the two pieces of film produced by the slitting remain constant. The speed at which the slitting means moves is not critical providing there are several complete oscillations for each reel of film produced.

It is preferred that the amplitude of the oscillation of the knife is from 10 to 25 percent of the width of the advancing web as thisrange gives a suitable spread of any irregularities in the slit web. Other amplitudes may also be used with good results but if the amplitude is less than about 10 percent of the width of the web, any

edges lying in a plane substantially perpendicular to the I longitudinal axis of the reel.

The present invention is applicable to the slitting and winding of webs of any material. In particular it is concerned with films of thermoplastic materials which may be oriented or unoriented. The invention may be used for trimming the edges of fiat film or for slitting tubular film. ln slitting tubular film the slitting means may operate to slit through one or both thicknesses of the film. When only one thickness is slit it is necessary to unfold the overturned edge of the slit film before it is wound into a reel.

A reel made according to the present invention has substantially no defects such as hard spots extending partly or wholly through the roll since the high and low spots in the web are distributed across the width of the roll.

The slitting means may further be composed of one or more slitting units which may each move independently of each other. Alternatively, the slitting means thickness variation may not be dispersed enough while if the amplitude approaches about half the width of the web, the subsequent winding-up of the web becomes increasingly cumbersome.

The position of the slit web may be adjusted relative to the reel to give good edge register on the reel either by oscillating the take up reel in response to the oscillatory movements of the slitting means or by means of a compensating device located between the slitting means and the reel. The compensating device may be actuated in response to the oscillating movements of the slitting means by any suitable means, for example a simple mechanical coupling between the slittingmeans and, compensating device, or preferably by an independent drive mechanism operating in response to signals received from the slitting means to indicate the extent of the movement thereof. However, because of variations in the speed of travel of the web and the thickness of the web, and the short period of time taken v by the web to pass from the slitting device to the compensating device, which requires virtually instanta-.

neous response of the compensating device, we prefer that activation of the compensating device be effected in response to signals received from a sensor which senses the position of an edge of the slit web, preferably as it passes from the compensating device to the take up reel.

The position of one or both edges of the web or webs produced by the slitting operation may be sensed in any suitable manner. For example their position may be sensed by light beams, by a pneumatic sensing gauge, mechanically or by capacitance determination.

The information obtained by the sensing means is relayed to a compensating device which adjusts the path of travel of the film to ensure edge register on the reel. Our preferred form of compensating device consists of at least two web guiding members which are capable of pivoting in the plane of the forwardly moving web so that some or all of the film guiding members of the compensating device may pivot as one unit in a plane parallel to the forwardly moving film. The web is wrapped around the guiding members as it passes from the slitting means to the reelv Accordingly, the position of the web as it leaves the guiding members may be adjusted by altering the angle at which the web guiding members is inclined to the edge of the film as it is fed 'to the members. Thus, by sensing the position of the edge of the web as it leaves the guiding members and relaying this information to a device which controls the inclination of the guiding members to the web, this inclination may be adjusted to compensate for the oscillation of the slitting means thus giving edge register in the reel.

The web guiding members of the compensating device may consist of rigid bars, rotatable rollers, sheets, or wires. It is important that the web surface does not become crinkled by thefilm guiding members and for this reason we prefer that the guide member is a rigid bar rather than a roller. We prefer to maintain a thin cushion of air between the film and the bar to prevent the film being scratched; this can conveniently be supplied'through holes in the bar. An assembly of such air bearing bars rigidly mounted on to a rotatable carriage as hereinbefore described is commonly known as a bar guide. In one embodiment of our invention the bar guide consists of two such air bearing bars rigidly mounted on a rotatable carriage so that they may be rotated as a single unit in a plane parallel to that of the oncoming film, in this way the transverse position of the film issuing from the second bar may be displaced from the transverse position of the film approaching the first bar.

The compensating device is linked with a pneumatic sensing device and in the particular embodiment of the bar guide type of compensating device, the sensing device is located such that the film passes through it al most immediately after passing around the second bar of the bar guide. The information received from the pneumatic sensor causes the bar guide to rotate as a single unit in a plane parallel to that of the oncoming web so that the web is transversely displaced as is necessary to result in a roll having good edge register.

The techniques of the present invention are: particularly suitable for slitting tubular film to flat form and may be used to produce one slit in a tube so that the tube may be opened out to a single sheet or to produce two slits in the tube so that two sheets are produced. If two sheets are produced we prefer that each sheet is passed through a web guiding member as described to produce two reels each having good edge register.

The present invention is particularly useful for slitting films of thermoplastic materials. Examples of suitable therrnoplastic materials which may be slit include polymers and copolyrners of olefines such as ethylene, propylene, butene and 4-methyl pentene-l; polymers and copolymers of vinyl chloride; polymers and copolymers of vinylidene dichloride; polymers and copolymers of styrene; polymers and copolymers of methyl methacrylate; cellulose and cellulose derivatives such as the cellulose-acetates; polyamides such as the various nylons and polyesters such as polyethylene terephthalate. The thermoplastic materials may also be coextruded so as to form film laminates. Other ingredients that may be incorporated in the thermoplastic material include, for example, plasticisers, stabilizers, lubricants, antioxidants, processing aids, impact modifiers, dyes, pigments and antistatic agents.

The film may be unoriented or oriented as is desired. A common method for producing an oriented film is one in which the thermoplastic material is extruded through an annular. die orifice in the form of a thin walled tube or a tubular film, and stretched in the longitudinal direction by passage through two pairs of nip rollers, the second of which rotates at a greater speed than the first. The film may be stretched concurrently in the lateral direction by expanding it with internal gas pressure.

The oriented film may be heat set by the techniques of roller heat setting or by stenter heat setting, both of which are well known in the art. In theprocess of the present invention an oriented film may optionally be heat set before or after passage through the compensating device. If the oriented film is to be heat set in a stenter, it is preferably passed through the compensating device before passing into the stenter.

The present invention is illustrated but by no means limited by reference to the accompanying drawings in which:

FIG. 1 is a schematic view of a flattened tubular film being slit with a pair of rigidly linked knives that are moving in phase with each other in a transverse direction to that of the movement of the flattened tubular film.

FIG. 2 is a plan view of one layer of flat film issuing from the slitter knives shown in FIG. 1'.

FIGS. 3 and 4 are schematic plan views of the layer of fiat film shown in FIG. 2 being laterally displaced by a bar guide and subsequently being wound up into a roll of film.

FIG. 5 is a schematic view of a flattened tubular film being slit with a pair of knives moving out of phase with each other in a direction transverse to that of the movement of the flattened tubular film, each knife cutting only one thickness of the film.

FIG. 6 is a perspective view of one of the slit films issuing from the slitter knives shown in FIG. 5.

FIG. 7 is a simplified schematic view of a fluid logic sensing system for detecting the portion of an edge of a flat film and actuating a compensating device to adjust the position of that edge. I

Referring to FIGS. 1 and 2, a flattened tubular film 1 is slit into two separate layers of film by

knife edges

2 and 3 rigidly linked together. The knives edges oscillate across the direction of travel of the tubular film and the extreme positions of the knives are represented by 2, 3 and 4, S. The oscillation of the knives produces lay flat film 6 having the configuration shown in FIG. 2

. With reference to FIG. 3, the layer of film 6 is fed to a barguide as illustrated in FIG. 3 which comprises two

bars

7 and 8 rigidly linked together on a carriage 9 and are provided with air holes 37 in the surfaces of

bars

7 and 8 in communication with a source of air (not shown). Issuance of air through air holes 37 provides an air cushion between the layer of-film 6 and each of the compensator bars 7 and 8. The bar guide system is capable of rotational movement about a line through 10 perpendicular to the plane of the film. The film passes around the upper bar 8 and around the lower bar 7 as shown and on leaving the bar 7, the film 6 passes through a pneumatic sensing device 11 which is linked with the bar guide and causes it to rotate in such a way that the film always issues from the second bar along substantially the same path and is thus wound up into a roll 12 having good edge register. FIG. 4 illustrates the bar guide at the opposite end of its rotational movement from that shown in FIG. 3. Accordingly, due to the oscillation of the slitting

knives

2 and 3 any thick spots in the film are distributed across the reel and film that was produced according to this embodiment of our invention was free from stretched areas caused by thickness variations.

Referring to FIG. 5, a flattened tubular film 13 is slit into two separate layers of film by knife edges 14 and 15 which oscillate out of phase with each other across the direction of travel of the tubular film, the extreme positions of the knives being represented by 14, 15 and 16, 17. v

The out of phase oscillation of the knives produces two lay flat films 18, of which one is shown in FIG. 6.

.The overturned edge 19 of the film is then unfolded to yield a flat film suitable for winding into a reel.

Referring to FIG. 7, air or gas under pressure is introduced to a control unit 20 from a supply conduit 21 and passes into a manifold 22 from which it flows into

jets

23, 24 and 25 in sensing head 26 through which travels an edge of film 27 in a direction perpendicular to the plane of the paper. The sensing head operates on the interruptable jet principle, the edge of the film, depending on its position, either preventing or permitting air to pass from any or all

ofjets

23, 24 and 25 respectively to

corresponding orifices

28, 29 and 30, and thence back to control unit 20, where the return flow of air is monitored and valve 31 or valve 32 actuated as appropriate to pressurize either of

chambers

33 and 34 respectively in actuating cylinder 35 whereby piston 36, which is coupled to the pivotable frame of the compensating device (not shown), is driven in the appropriate direction to compensate for wander of the edge of the film as it travels through head 26.

It will be understood that all displacements shown, as well as the shape shown in FIG. 2, have been greatly exaggerated to illustrate the principle of the invention.

1 claim:

1. A method for longitudinally slitting a travelling web of material into a number of separate slit webs and winding each of the slit webs into a reel, comprising contacting the traveling web with a slitting means, oscillating said slitting means across the direction of travel of the web, the amplitude of the oscillation being within the width of the web, sensing the position of an edge of the slit web, adjusting the position of the slit web relative to the reel, and winding the adjusted slit web onto the reel, whereby the adjacent edges of successive layers of slit web wound onto the reel lie in a plane substantially perpendicular to the longitudinal axis of the reel.

2. A method according to claim 1 in which a travelling web of material is slit into a plurality of strips by slitting the web with a slitting means comprising a plurality of slitting units which oscillate across the direc-- tion of travel of the web.

3. A method according to claim 1 in which the web is a thermoplastic polymeric film. I

4. Apparatus for slitting a travelling web of material into a number of separate slit webs and winding each of the slit webs into a reel comprising web-slitting means for oscillation transverse to the direction of travel of the web, means for sensing the position'of an edge of the slit web, and compensating means responsive to said sensing means to adjust the position of the slit web relative to the reel, whereby the adjacent edges of successive layers of slit web wound onto the reel lie in a plane substantially perpendicular to the longitudinal axis of the reel.

5. Apparatus according to claim 4 in which the slitting means comprises a plurality of slitting units.

6. Apparatus according to claim 4 in which the slitting means comprises a pair of knife edges which are rigidly linked together and are movable in a regular manner transversely to the forward direction of travel of the film.

7. Apparatus according to claim 4 in which the edge sensing means is a pneumatic sensor.

8. A method for longitudinally slitting a travelling tubular web into two separate slit webs and winding each of the slit webs into a reel, comprising contacting the travelling tubular web with two slitting units each of which slits only one thickness of the tubular web, oscillating said slitting units across the direction of travel of the web, the amplitude of the oscillation being within the width of the web, sensing the position of an edge of each slit web, adjusting the position of each slit web relative to its reel, and winding each adjusted slit web into its reel, whereby the adjacent edges of successive layers of slit web in the reel lie in a plane substantially perpendicular to the longitudinal axis of the reel.

9. A method for longitudinally slitting a travelling web into a number of separate slit webs and winding each of the slit webs into a reel, comprising contacting the travelling web with a slitting means, oscillating said slitting means across the direction of travel of the web, the amplitude of the oscillation being within the width of the web, wrapping the slit web around a compensating device, sensing the position of an edge of the slit web as it leaves the compensating device, and pivoting said device in the plane of the forwardly moving slit web to give edge register of adjacent layers of slit web wound into the reel.

10. A method according to claim 9 in which a cushion of gas is provided between the compensating device and the web.

11. Apparatus for slitting a travelling web of material into a number of separate slit webs and winding each of the slit webs into a reel comprising web-slitting means for oscillation transverse to the direction of travel of the web, means for sensing the position of an edge of the slit web, and compensating means including at least two web guiding members which are capable of pivotal movement in the plane of the forwardly moving slit web, said compensating means being responsive to said sensing means to adjust the position of the slit web relative to the reel, whereby the adjacent edges of successive layers of slit web wound into the reel lie in a plane substantially perpendicular to the longitudinal axis of the reel.

Claims

2. A method according to claim 1 in which a travelling web of material is slit into a plurality of strips by slitting the web with a slitting means comprising a plurality of slitting units which oscillate across the direction of travel of the web.

3. A method according to claim 1 in which the web is a thermoplastic polymeric film.

4. Apparatus for slitting a travelling web of material into a number of separate slit webs and winding each of the slit webs into a reel comprising web-slitting means for oscillation transverse to the direction of travel of the web, means for sensing the position of an edge of the slit web, and compensating means responsive to said sensing means to adjust the position of the slit web relative to the reel, whereby the adjacent edges of successive layers of slit web wound onto the reel lie in a plane substantially perpendicular to the longitudinal axis of the reel.