DE7017571U - DEVICE FOR COOLING FILMS BY ELECTROSTATIC ADHESION TO A COOLING SURFACE. - Google Patents

Description

BI. DU PONT DE NEMOURS AND COMPMY 10th and Market Streets, Wilmington, Delaware 19 898, V.St.A.

Device for cooling foils by electrostatically adhering them to a cooling surface

When casting molten, crystallizable, thermoplastic webs, the molten web must be cooled rapidly below its glass transition temperature in order to suppress the crystallization as far as possible. It is assumed that excessive crystallization in the film web adversely affects the orientation, as a result of which cloudy areas and irregularities develop in the thickness of the oriented product. The extruded web is generally cooled by pouring the molten thermoplastic material onto a cooled, moving surface, usually a rotating drum. Attempts to increase the speed of this process to achieve a more effective and efficient way of working, have a poor uniformity in thickness and from repetitive patterns turbidity education to regular training

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leads, referred to in the art as "blind clouding" will. Furthermore, the increased speed often leads to "necking", a lateral shrinkage of the cooled film. In order to borne these difficulties: 'r., One has to be different Methods are used which aim to bring the web into closer contact with the cooling drum.

One of the best ways to adhere the molten web to the cooling surface is to electrostatically charge the film across its entire width. This method is described in US Pat. No. 3,223,757, '.', 'If, however, even higher casting speeds are used, "this leads to a reduction in the ability of a given electrostatic force to adhere the web to the cooling surface, because then be introduced larger amounts of air between the sheet and the cooling drum the trapped between the 3ahn and the drum air layer prevents the wirkssisen Wärn eiiber ^ir sn ^{|:.! r} to Trosmel and thereby reduced the efficiency of the cooling process Further, the occurrence of "Anheftblasen ¹¹ lists. the interface between the film web and the drum leads to undesirable surface irregularities in the finished film.

Attempts have been made to increase the electrostatic force generated by the tacking wire by increasing the voltage. However, these attempts have not been successful, since when the voltage is increased, it is generally electric Strikethrough between the electrode and the drum could occur before a sufficient charge was applied to the web v / can ground to produce a substantial increase in the attachment force. The spark formation is nasal temporarily interrupted the electrostatic field of the electrode contributing to the adhesion force.

The invention provides an apparatus for electrostatically adhering a plastic web along its entire width a cooling surface is available, which on the one hand

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increased tension can be applied to provide higher adhesion force and which, on the other hand, is adjustable in relation to the width of the diffracted electrostatic field.

The invention relates to a method for cooling polisn by electrostatic attachment to a cooling surface by means of one near the point of impact of the foil on the cooling surface arranged wire electrode, which consists in attaching the electrode to rigid, conductive supports that have no sharp points or surfaces with a small radius of curvature on v / iron, in tensioned Condition and all parts of this carrier as well as all parts of the wire electrode, which are in the vicinity of the cooling Are located on the surface and protrude beyond the film, isolated by an axially movable, dielectric Yferkstoff, the adjustment of this insulating material being made by shifting it sideways as required during cooling will. Furthermore, the invention relates to a device sun electrostatic attachment of foils to a cooling surface, consisting of one connected to a high voltage source and between side supports approximately above the point of impact of the film web on the cooling surface tensioned wire electrode, the film web having a smaller width has as the cooling surface, the side supports are equipped with electrically insulated, conductive rods, extending towards the cooling surface are substantially circular in cross-section, i.e. none Have points or surfaces with a small radius of curvature at which spark formation could take place, and in one at a time section directed inside and parallel to the cooling surface .end the wire electrode with the ends of the parallel sur cooling surface extending portions of the support rods is connected, and the connection points between the wire electrode and the Support rods of axially displaceable collars made of dielectric V / Erkstoff are surrounded, which extends from the edges of the film web along the wire electrode and the rods to the outside extend.

P-2051

Zig. 1 shows a cross section through an embodiment of FIG Electric carrier arrangement according to the invention.

Pig. Fig. 2 shows a device according to the invention in connection with a pouring and cooling device.

? ig. Figure 3 is a plan view of the Pig device. 2.

. In the drawings, the same parts are given the same reference numbers,
ji

II The terms "inwardly" and "outwardly" relate to

Directions along a line parallel to the plane of the cooling surface and perpendicular to its edge and give "the Towards the center or towards the edges in this surface.

The basic form of the slectrode carrier is in Pig. 1 shown. The rod 10 provided with the insulating layer 11 has at its inner end holes 12 through which the electrode wire 13 is pulled through in a loop shape and fastened. The rod can be made of any conductive material such as brass, copper, stainless steel and the like should be thick enough - to place the electrode wire under the desired To keep tension. A 3-4 mm thick brass rod has proven to be particularly useful for many purposes proven according to the invention.

The rod 10 is connected to the high-voltage connection 14 (e.g. in Commercially available from Gremar Manufacturing Co. of Wakefield, Massachusetts, Y.St.A., as Model No. 8731) connected to a high voltage source (not shown). This connection conductor is soldered to the end of the rod 10 and engages in a matching rope of the high voltage source. The electrode rod 10 fits snugly into the insulator 15 and is held in place in the adjoining frame by an internally threaded bushing 16 shown in engages an externally threaded file (not shown).

An essential component according to the invention is the J§

Slidably arranged insulating sleeve 25> which exactly over the 1st

Sta "b 10 fits and through its plug 26 over the wire 13 |

slide kar_; i, the latter o -.- ■ - · .: a small hole in the ||

Plug is passed through- Di »· * · ¹ ··? ! '.- tnsGbette enables the S

Sin control of the effective width of the electrode. D. the Han- J

cuff may be of any dielectric material \

stand that can be deformed into a rigid cylinder;

e.g. made of hard guns or resins, e.g. fluorocarbon resin / ( zen, Carnstoff-iormaldehyd-Karzen, filled phenol-formaldehyde

hyd resins, polyamides and cast epoxy resins. ^{Polytetramethylene:} fluoroethylene has proved for this purpose to be particularly suitable f * because it is resistant to the temperatures of the extruder occur near the "■ '· Kund piece and has an i excellent insulating capacity The size of the Man-. `` The sleeve depends on the size of the support rod 10; for
a rod with a diameter of 3-4 mm can use a cuff with a clearance of 3-4 mm and an outside diameter of 4-6 mm. The length of the cuff! depends on the distance that is normally between: the point of the extruded film and the end of the support rod
is present to which the wire is attached.

Pig. 2 and 3 show a device according to the invention in FIG
Connection with a melt extrusion plant. The molten flat sheet 18 is from the extrusion die 17 on the
metallic cooling drum 19 pressed out. On the frame 20
the electrode carriers 21 and 22 are arranged, which the wire
13 wear in the manner shown in Fig. 1 so that he
over the roller 19 and the film web 18 in a tensioned state
is held. The carriers 21 and 22 are electrically connected to the
High voltage source 23 connected, one side of which is grounded,
so that the roller 19 grounded at 24 forms an electrical circuit with the high voltage source. The chill roll 19
is wider than the track 18, so that? bare metal would be exposed to the action of the electrode device 3, if not

the insulating cuffs 25 would be present, which the setting the effective length of the electrode.

Pig. Fig. 3 is a plan view with the extrusion molding apparatus omitted for clarity. The effective one The length of the electrode wire 13 is limited by the cuffs 25 so that it is over one t inn t with the width of the web 18, and the sleeves extend outward from this point so that they are the junction between wire and cover the stick.

example 1

A polyethylene terephthalate film is by means of a device extruded according to FIG. 1 of US Pat. No. 3,223,757 and electrostatically attached to a cooling drum. After the biaxial orientation, the thickness of the film is 23 μ. The voltage applied to the tacking device is adjusted to the maximum attainable cLine electrical breakdown and the maximum generation speed is determined in kg / hour, at which a film of remains the same:.! high quality can be produced. This generation speed is denoted by R.

You now replace the tacking device according to the above USA patent by the one according to the invention and again sets the voltage to the maximum value, the one without electrical breakdown can be applied. This device has support rods from measurement with a diameter of 3-4 mm and sleeves made of polytetrafluoroethylene. the highest production speed with which with this device a film of 23 μ thickness and consistently high Quality grade is 1.23 R.

Example 2

y.an works according to Example 1, but with a film of one such an initial thickness that the foil dioke after uo.:.

Orier tiür-r ·? 6 μ. The maximum production speed P-Ir ₁ C.- ¹ lolie of a consistently high quality grade with the device according to the USA patent 3 223 7 ^ 7 is denoted by H "." \ P maximum production speed for the Manufacturing-. a film with a consistently high quality grade six aid of the device ρ sm according to the requirement is then 1.45 R ¹ .

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Claims (2)

EGG. du Pont de Nemours May 11th, 1997 and Company P-2051 Protection against 1. Device for the electrostatic attachment of foils a cooling surface, characterized by one connected to a high voltage source (23) and between lateral supports (21, 22) approximately above the point of impact the film web (18) on the cooling surface (19) tensioned wire electrode (13), wherein the film web (18) a Has a smaller width than the cooling surface (19), the side supports (21, 22) with electrically insulated (11), conductive rods (10) are equipped, which extend towards the cooling surface (19), an im have a substantially circular cross-section and each one directed inwards and parallel to the enveloping surface (19) End section, the wire electrode (13) with the ends of the sections running parallel to the cooling surface of the support rods (10) are connected, and the connection points (12) between the wire electrode (13) and the support rods (10) are surrounded by axially displaceable collars (25) made of dielectric material, which extend from the The edges of the polien web (18) extend outwards along the wire electrode (13) and the rods (10). 2. Device according to claim 1, characterized in that the sleeves (25) made of a fluorocarbon resin or consist of hard rubber. >ι> j I P-2051 3. Device according to claim 1 or 2, characterized in that the rods (10) are made of brass, have a diameter of about 3-4 and are insulated by an outer layer (11) made of a poly carbon heart «