JPS6030262B2 - Pneumatic gauge adjustment of cast web for pinning helicopters - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a process in which when a cast web of thermoplastic web is cooled in close proximity to a moving quench surface and the edges of the web are pinned against the quench surface by electrostatic or other forces,
Regarding adjusting the gauge of this web.

The method of the present invention is directed to the cast web along the line of cut proximity between the cast web and the quenching surface prior to heli pinning, and is suitable for altering local web shrinkage during quenching. A more uniform quench web thickness is obtained using variable air forces applied at predetermined positions and speeds. The present invention is particularly suited for gauging the edge of a web near pinning. Widiger, U.S. Pat. No. 3,597,515, dated August 3, 1971, uses a vibrating air knife to direct a non-uniform air stream against a cast molten web of polymeric material that is fed to a quench drum. This is disclosed.

Because the web of this patent is not edge pinned, there is no substantial lateral tension during quenching. The method of this patent moves the thickened regions of the unpinned web from edge to edge across the web, without leaving irregular gauge non-uniformities in the same location, and moves the thickened areas of the unpinned web from edge to edge into the wound roll. It is concerned with creating thickened longitudinal tracks that create severe non-uniformities and thus result in poor quality wound rolls. H dated September 9, 1973
U.S. Pat. No. 3,904,725 to Uskey et al. discloses that a molten web of polymeric material is diagonally across the web from the edge of the web after the wafer is laid on a quench drum and its edges are pinned by electrostatic forces. , discloses a method of quenching by directing air forces in the direction of web movement.

Gas power is provided by individual closely spaced air jets that are individually adjustable. Because air forces are applied after the web meets the quench drum and is pinned, excess air can be locally entrained and sealed between the web and the quench drum.
This locally entrained air acts as an insulator between the web and the quenching drum, prevents sufficient heat transfer, and causes some gauge non-uniformity. Roth et al. Canadian Patent No. 848 dated August 11, 197
No. 852' discloses an arrangement for pinning and quenching a molten web of a viscous polymer, in which an electrostatic force is applied across the web at the line where the web comes into actual contact with a quench drum. The gas force is then applied uniformly around the quench drum extending from the contact line of the web to the point of immersion of the web in the cooling liquid and across the web.

Thermoplastic materials have long been fused and cast as webs, pinned at the web's edges to quench surfaces.

Such edge pinning eliminates web width loss due to shrinkage during quenching and prevents web edges from wandering over the quenching surface. The edges of the web are pinned during quenching,
This prevents changes in the width of the web so that lateral forces are generated across the web and the web is stretched to the extent that it contracts as it cools. Such stretching occurs at the weakest point of the web. In such points,
The following are combined: the hot edge directly adjacent to the pinning; the hottest web area; and excess air is entrained and sealed between the web and the quench surface, thereby creating a connection between the web and the quench surface. areas where heat transfer between is reduced. The present invention relates to a method of controlling the temperature of a web by controlling the proximity of the web to a quenching surface and then controlling the area of the web that is stretched during quenching, thus achieving gauge regulation. The present invention relates to a method of influencing a variable force across a molten web to control the local proximity of the web to a quenching surface. In methods where the molten web is cooled by proximity to a moving quenching surface, the web does not come into actual contact with the quenching surface.
Well established.

In the absence of some intimate pinning forces, such as electrostatic pinning forces, there is a thin layer of air entrained between the web and the quenching surface. For purposes of describing the present invention, the term "contact" refers to the relationship between the web and a moving quenching surface when the web is in close proximity to the quenching surface and separated from it by only a thin layer of air. means that To the extent that the entrained air layer has a uniform thickness across the web, the thermal conductivity between the quench surface and the web will be substantially uniform. Air entrained between the web and the quenching surface causes the layer to have non-uniform thickness, causing non-uniform heat transfer. For purposes of describing the present invention, the term "pinning" refers to the lateral movement of the edges of a web, regardless of the lateral tension that occurs across the web due to contraction as the web cools. means holding the web in physical contact with the quenching surface with a force adequate to prevent quenching.

According to the present invention, a molten thermoplastic web is extruded onto a quenching surface, each side edge of the web is pinned, and air is directed against the web along the line of initial contact between the web and the quenching surface. A method for rapidly cooling a web and adjusting its gauge is provided.

With a lateral deflection, the air is directed against the web before the pinning force is applied. This air is directed through a plurality of individually adjustable waps, and in one embodiment, the jets are directed at the pinned edges such that the aerodynamic force generally decreases inwardly from the pinning site.
be adjusted. In the central portion of the web, the jet is adjusted to be maximum for relatively thin regions of the web. In FIG. 1, a molten thermoplastic web 11 is extruded from an extrusion die 12 onto a steepening surface 13 moving in the direction of arrow 14.

The air jet pack 15 is mounted above the lining surface 13 (the mounting is conventional and not shown). Air is supplied to each row 61, 162, 163,...1 from a separate air source whose air pressure can be individually adjusted.
6n, and is introduced into the air jet pack 15. Air is directed from the air jet pack 15 to the web 11,
Line of initial contact 1 between surface 11 and surface 13
Directed along 7. After the web 11 has been subjected to the aerodynamic force of the air jet pack 15, but before the web has developed a substantial contraction force, the lateral edges of the web are pierced with an electrostatic probe 1.
8 pins. For purposes of this description, rows 61 and 162 and 16n with an IJ width of approximately 2 skins lateral to
and 16n-, are located directly above the portion of the web 11 to which the probe 18 pins. In practicing the method of the present invention, air jet packs provide aerodynamic forces to the molten web to achieve adjustment of the aerodynamic force gauge in at least two ways.

First, near the electrostatically pinned edge,
The air vents are positioned to direct air against the web prior to applying the pinning force and are adjusted so that the air force on the web is greatest at the location of the web being pinned and generally decreases inside that location. be done. Adjusting the aerodynamic forces in this manner forces the molten thermoplastic material adjacent to the electrostatic pinning site to move more closely to the pinning surface.
Cooling of the web will be more rapid in the area where the heli is pinned. More rapid cooling of the web closest to the area where the edges are pinned will alleviate overstretching and
This will eventually alleviate the thinning at the edges where shrinkage occurs upon cooling. The aerodynamic force applied near the area where the edge is pinned will generally spread inwardly towards the point in the web adjacent to the pinned edge, and the minimum weep thickness, in the absence of aerodynamic force, will generally be between 2 and 2. 15 skin, usually occurring at a distance of about 5 togs. Second, near the center of the web between the side edges, where the web may be cast with locally relatively thick or thin regions, the air openings are greatest in the relatively thin regions of the web. Adjusted to provide aerodynamics.

The adjustment creates non-uniformity in the entrained air layer, causing relatively thin web regions to cool more rapidly, and keeping relatively thick web regions at a higher temperature to allow for elongation during contraction during cooling. Make it even easier to wake up. Near the center of the web is where the helicopter is pinned...generally 2
It is generally considered to be the remainder of the inner web from around ~15 skins, typically a distance of 5 arcs. When the edge of the web is pinned against the quench surface, some amount of air from below the pinned edge is displaced to a position adjacent to the pinned edge.

This results in a relatively thick air layer adjacent to the pinning,
The aforementioned mechanism creates an overly thin condition. The air jets are positioned such that one or more of the air jets are positioned over the portion of the web that is to be quenched surface snaked. When the air force is directed against the area of the web to be pinned, some amount of air between the web and the quenching surface is displaced, so that when the web is pinned, the area of the web adjacent to the area being pinned is Less air is displaced below. In this way, the air layer is more uniform and the heat transfer is more uniform. The width of the web affected by applying electrostatic pinning forces is typically about 2-3 skins.

Air jets directed against the affected width of the pinned web are said to be directed directly above the pinning area. The outermost air jets, which are tailored to provide aerodynamic forces furthest from the central portion of the web, are said to be directed laterally. Referring to Figure 1, the gauge adjustment aero forces are typically 162 and 16n.
-1, and 163,164...
and 16n-2, 16n-3, . . . gradually decreases inwardly from each edge to a position directly above the area of the weave exhibiting minimum thickness in the absence of aerodynamic forces.

The aerodynamic forces from 161 and 16n are now adjusted to be less than the adjacent inner forces for pinning.

Other aerodynamic force adjustments are made such that relatively large forces are directed to relatively thin web regions. Relatively thin web regions occur during conventional thermoplastic web manufacturing as a result of some local variations in the extrusion die closure. Thickness variations during web manufacturing can be detected by any of several well-known methods, such as non-contact radiation gauges or mechanical thickness measurement devices. The thickness of the web can be continuously monitored by non-contact means, and the indication of thickness variations can be used to automatically control and adjust the air force directed to the web to compensate for variations. . Of course, the variation can also be adjusted manually, and the aerodynamic force can be adjusted manually accordingly.
In FIG. 2, a four-part air jet pack 20 is shown, partially cut away to illustrate the interior of the device.

Air force is introduced into the jet pack through the port 21 from an individual adjustable air pressure source. The pneumatic source is not shown as it is conventional. Air enters the individual chambers 22 through the ports 21 and is then directed through the IJt closures 23 on the side of the pack facing the thermoplastic web in use. The chambers 22 are individually separated by walls 24;
Then, at the end of the slit, the wall 24 has a chamfered edge 25.
to provide continuity of air force between adjacent slit openings □23. Of course, air jet pack 20 can have fewer or the same number of individual adjustable air jets as required or desired for a particular use. Although as few as one jet on each side provides some of the benefits of the present invention, at least four on each side is preferred, with six to eight commonly used. The air jet back extends across the entire width of the web, and it has been found that for gauge adjustment, the slit should be about 5 cm or less long, usually 2 skins or less long. The stents can be as short or as short as desired, but the shortness of the slit baskets is dictated by economy and convenience of use since air is supplied to each slit from an individually controlled air source. For that reason, the slit generally should not be shorter than about 0.5 skin. The air jet packs should be located at a distance from the web to avoid contact with the web during operation, yet maintain a cohesive and individual air force from each square to the web.

The jet pack is typically located about 3 to 6 sides from the cast web. In FIG. 3, a preferred apparatus for carrying out the invention is shown in cross section.

Device 30 is of the same inventor as the present application. It consists of a combination of specific web manufacturing elements as disclosed in U.S. Pat. No. 4,017,575 to Heyer, issued April 12, 1977. An air bearing 31 is used in conjunction with a pressure chamber 32, and the pneumatic force of the present invention is applied between them before applying the pinning force. In the work, the web 33
is cast from an extrusion die 34 and then ejected from the catenary by air bearings 31 and then pressed into close proximity to a moving quenching surface 35 as shown. The molten web is held taut by and stretched around the air bearing 31, but does not move across the web into intimate contact with the quench surface 35 until it reaches point 36.

At point 36, air is directed to the web from an air jet pack 37, as disclosed. Following the aerodynamic force of air jet pack 37, pressure chamber 32 provides a constant air pressure to the web on the steep surface across the entire web from air bearing 31 to point 38. An electrostatic pinning force is applied to the web immediately after the air jet pack 37 to ensure that the lateral edges of the web 33 are secured to the quench surface 35. In the practice of the present invention, the aerodynamic force of the air jet back is directed toward the web at or near the point where the web makes initial contact with the quench surface to avoid excessive air entrainment and to create a desired gap between the web and the quench surface. It must be ensured that an air layer with a thickness of

In FIG. 4, the thickness profile of a cast web with and without the method of the present invention is graphically compared.

The abscissa is the distance from the lateral edge of the cast film web (
arc) and the vertical axis represents the thickness of the cast web. Curve 41 represents the thickness profile of a quenched web cast with the apparatus of FIG. 3 without applying air pressure to the air jet pack. To produce a web characterized by the curve of this Figure 4, polyethylene terephthalate was cast at a temperature of about 285°C onto a steep surface moving at about 35 m/min and having a surface temperature of about 25°C. did. The pressure on the air bearing is approximately 30kPa,
A uniform charging pressure of approximately 2 squares a existed. The nominal thickness of the web was 178 micrometers. This web was electrostatically pinned to Kagami approximately 10 mm inside the IJ (designated 42). Approximately 2-3 from these edges
It is observed that within a centimeter the thickness of the web is considerably thicker than the indicated thickness. The thickened heli 43 is
It is intended and necessary for the subsequent web handling equipment in the production of the film to provide the gripping material. In curve 41, an extreme thickness 44 occurs immediately inward from the thickened edge, followed by another thickened region 55, which is characteristic of webs made without the present invention. Yes, and especially noticeable. Curve 46 uses the same equipment and under the same conditions as above, but with an air jet pack positioned near each helicopter, so that the smallest of the eight slits on the 9.5 length side is in the web. The thickness profile of the cast quenched web is shown below.

The slits were directly adjacent to each other and were 0.75 side wide. The air pressure in each air jet pack was adjusted so that the air velocity from the individual jets was as shown in Figure 4, and the slits were positioned 3.8 ribs from the cast web. Jets (jet L1, L2, L3,
The air velocity from R1, R2 and R3) was adjusted to be generally greater than the inner jet from the pinning.
The precise adjustment of the jets cannot be determined in advance for any given case. Inspect the web thickness profile and adjust the jets according to the teachings herein. Curve 46 reveals a cast web with a regular thinning profile without any reversal of thickness.

Curve 46 corresponds to 44 and 4 respectively in curve 41.
It is observed that it does not exhibit any extremely thinned or thickened areas such as those represented by 5. curve 4
A cast web with an improved thickness profile of 6 is the result of the present invention, and this result is even more pronounced in FIG.

Figure 5 shows that after biaxial orientation by stretching 3.4 times in the machine direction and 4.3 times in the transverse direction to produce a film with a nominal thickness of 12 micrometers. Shows a graph comparing cast webs. In FIG. 5, curve 51 represents the oriented film product of cast film 41 of FIG. 4, and curve 52 represents the oriented film product of cast web 46 in FIG. The thickness of the film of curve 51 is 10 mm from the inside from one edge.
~13 arc distance and 15-18 from inside the other edge
At skin distance, the deviation from the nominal thickness of 12 micrometers for a total of about 25 to 31 degrees of scrap. Such deviations represent significant waste in the film, which must be scrapped because it exceeds acceptable thickness limits. On the other hand,
The film thickness of curve 52 approaches and remains directly at the indicated thickness, and the total scrap is less than 13 arcs.
In FIG. 6, a graph comparing the thickness profiles of other cast webs with and without the method of the present invention is shown.

Curve 61 represents the thickness profile of a quenched web cast using the apparatus of FIG. 3 without supplying air pressure to the air jet pack. To produce a web characterized by the curve of this FIG. 6, polyethylene terephthalate was cast at a temperature of about 285 oO onto a steeple surface moving at about 8 shoes/min and having a surface temperature of about 16Qo.
The pressure on the air bearing was approximately 6 Pa and there was a uniform charging pressure of approximately 22 Pa. The nominal thickness of the cast web was 64 micrometers. The web was electrostatically pinned approximately one square inch inward from each side edge (indicated by 62). Approximately 4 to 5 degrees inward from the edge, the thickness of the web is observed to be significantly greater than the indicated thickness. In the curve 61, the thickness minimum 63 and the inner maximum 64
is recognized as the bias of the gauge to be adjusted by the method of the present invention.

Curve 65 uses the same equipment and conditions as above, but
Near each edge, the air jacket is positioned so that the first of the eight slits on the 6.2 length side is at the edge of the weave to define the thickness of the cast quenched film.

The slits were directly adjacent to each other and were 0.75 wide. The air pressure at the slit in each air jet pack was adjusted so that the air from the individual jets was present as shown in FIG. 6, and the slit was located 4.3 sides from the cast web. The air velocity from the jets above the pinning site is adjusted to be greater than the jets inboard from the pinning, and the air velocity from the jets at the lateral edges, LI and R1, is adjusted to be greater than the jets directly above the pinning, L2 and R2. Adjusted to be smaller than the air velocity from The air velocity from the jet adjacent to the pinning was reduced inward from the pinning. Curve 65 evidences a regularly thinning profile cast web that does not have the maxima and minima of curve 61.

The optimum pressure on the air jet back that is effective for practicing the present invention may vary depending on the type and properties of the thermoplastic material;
and changes significantly with changes in casting and drawing conditions.

The above teachings are the best presently contemplated mode of carrying out the invention, and for varying materials or conditions, air pressure and other process conditions may simply test the web thickness profile. The gauge can then be varied and adjusted by adjusting the air pressure according to the teachings disclosed herein. Although the present invention can be used in the production of thermoplastic cast webs in accordance with the teachings herein, the present invention is most suitable for producing cast webs from the following materials: preolefins, such as polyethylene and polypropylene; polyamides, such as polyhexane. Methylene adipamide and polycaproamide; vinylidene chloride: and polyesters such as polyethylene-2,6-naphthalene and polytetramethylene-1,2-dioxybenzoate.

Polyethylene terephthalate is particularly useful.

[Brief explanation of drawings]

FIG. 1 represents the apparatus used to carry out the invention. FIG. 2 represents a cross-section of the air jet used in the present invention. FIG. 3 is a cross-sectional view of an apparatus used when preferably carrying out the present invention. Figures 4 and 6 represent the as-cast film thickness across a web of thermoplastic material made using the apparatus of Figure 3 with and without the method of the present invention. This is a comparison graph. FIG. 5 is a comparison graph showing the film thickness of the web depicted in FIG. 4 after Nito stretching. 11...
- Molten thermoplastic web, 12... Extrusion die, 13... Quenching surface, 14... Arrow, 15... Air jet pack, 161, 16
2,163...16n-3,16n-2,16
n-1, 16n...mouth, 17...line,
18... Electrostatic probe, 20... Air jet pack, 21... Mouth, 22... Chamber, 23... Slit opening □, 24... Wall, 25... Chamfering Edge, 30
....device, 31...air bearing, 32
...pressure chamber, 33...web, 34...
...Extrusion die, 35...Quiet cooling surface, 36...
... point, 37 ... air jet pack, 38
...Point, 41...Curve, 42...Sideward,
43...Thickened edge, 44...Extreme thickness, 45...Thickened area, 46...
Curve, 51...Curve, 52...Curve, 61
...Curve, 62 ... Electrostatic pinning point, 63 ... Minimum thickness, 64 ... Maximum inside, 65. ·…·curve. FiG. 1 fiG. 2 ``16.3 fiG.4 FiG.5 FIG.6

Claims (1)

Claims: 1. Quenching a molten thermoplastic web and measuring its gauge by extruding the molten thermoplastic web onto a quenching surface and pinning each lateral edge of the web onto a quenching surface. A method of conditioning, characterized in that air is directed against the web along the line of initial contact between the web and the quenching surface, and the air is directed against the web through a plurality of individually adjustable air jets. How to do it. 2. The air jet is adjusted to supply air in the vicinity of the edge being pinned before pinning, so that the aerodynamic force on the web is greatest at the point where the web is being pinned and decreases inwardly from that point. A method according to claim 1. 3. The air jet in the vicinity of the center of the web between the transverse hems is adjusted to provide air such that the aerodynamic force on the web is greatest in the region of the relatively thin web. Method described. 4 The vicinity of the helicopter to be pinned is determined from each surrounding helicopter.
The minimum web thickness in the absence of aerodynamic forces is the area up to a point in the web near the pinned edge, and the area around the center of the web between the surrounding edges is the area from near the pinned edge to the inner web. The method according to claim 3, which is the remaining part of the method. 5. The method of claim 4, wherein the vicinity of the pinned hem is about 2 to 15 cm inwardly from each lateral hem. 6. A method according to claim 1, in which the air jet in the vicinity of the center between the lateral hems is adjusted to supply air such that the aerodynamic force on the web in that vicinity is greatest in a region of the web that is relatively thin. . 7. The method of claim 1, wherein the air is directed at the web along the entire line of initial contact between the web and the quenching surface. 8. A patent claim that adjusts the air jet to supply air in the vicinity of the edge to be pinned before pinning so that the aerodynamic force on the web is greatest at the location where the web is being pinned and decreases inward from that location. range 7th
The method described in section. 9. Adjusting the air jet near the center of the web between the lateral hems to supply air so that the aerodynamic force on the web in that vicinity is greatest in the relatively thin web region. the method of. 10 Air is directed into the web along the line of initial contact between the pre-pinned web and the quenching surface and to a point in the web near the edge to be pinned where maximum web thickness occurs in the absence of aerodynamic forces. A method according to claim 1.