Arrangement in an apparatus for forming a windscreen interlayer

Abstract: The invention relates to an arrangement in an apparatus for forming a windscreen interlayer, comprising a heating unit for heat treating a moving web (20). The heating unit comprises individually adjustable radiation units (1 - 18) for directing radiation towards the moving web (20) and radiation restriction means (25) for suppressing the radiation output in desired areas (24). According to the invention, the radiation restriction means (25) comprises a board (5) which is essentially perpendicular to the plane of the web (20), the board being aligned essentially in the travel direction of the web (20) and positioned at the level of the radiation sources (1 - 18) at its upper end and at a distance from the web (20) at its lower end such that no direct radiation output is directed towards the desired area (24) of the web (20) from the closest radiators (5, 6, 7) in operatio.

Description: The invention relates to an arrangement according to the preamble of claim 1 in an apparatus for forming a windscreen interlayer. The polyvinyl butyral films used in the manufacture of screen glass are worked in a continuous process by heat treating films reeled off rolls. The heat treatment is carried out as radiation heat in a multi-lamp radiation unit such that a temperature difference is created between the different margin areas of the web in the cross direction of the web. The hot margin area is typically heated to a temperature of about 90 °C whereas the cold margin area is typically at 30 to 50 °C. By providing stretching in the thus heat treated material web the curvatures needed in screen glass are obtained. The curvature is controlled by means of both the temperature and the stretching. Today, a shaded film is increasingly often used a an anti-dazzle barrier at the brim of the film. During the heat treatment, this dark brim is the cool section of the web. As the shaded portion of the web absorbs a greater portion of the radiation than the clear section, the excess temperature rise constitutes a problem during the heating process. The problem has been approached by putting out radiation sources at the cool brim of the web and by placing at the dark brim a radiation-barrier board which is aligned parallel with the plane of web. In the case of new shading materials, sufficiently good process control properties have not been attained by this method, and it has not been possible to form the desired temperature distribution in the web. The present invention aims at eliminating the drawbacks of the above-described prior art and at achieving an entirely novel type of arrangement in an apparatus for forming a windscreen interlayer. The invention is based on fitting a radiation-barrier board essentially parallel to the travel direction of the web, the board extending through the entire heating unit and at least essentially being perpendicular to the plane of the web, in the vicinity of the cool brim in the heating unit, whereby the radiation-barrier board is of a material of poor thermal conductivity, such as Teflon. In more detail, the arrangement according to the invention is characterized by what is stated in the characterizing part of Claim 1. The invention offers considerable benefits. The heat-insulation board does not generate any harmful radiation to the cool area. By means of the vertical board, even the radiation distribution can be accurately controlled by adjusting the height of the board. In the following, the invention is examined in closer detail in the light of the exemplifying embodiments illustrated in the annexed Figures. Fig. 1 is a front view of the arrangement according to the invention. Fig. 2 is a side view of the arrangement according to Fig. 1. Fig. 3 is a flattened top view of the arrangement according to Fig. 1. In accordance with Fig. 1, the heating unit of the film-forming apparatus comprises radiation sources 1 to 18, there being 18 sources in the exemplifying unit. The radiation sources 1 to 18 are arranged essentially in the travel direction of the web, the angle between the travel direction and the radiation sources being about 5 to 10°. In addition, the radiation sources are arranged with regular intervals in the transverse direction. The radiation sources 1 to 18 typically comprise halogen lamps. Other alternatives include, e.g. ceramic infrared radiators or IR gas radiators. The maximum effect of one radiation element is typically about 1 to 3 kW. The radiation output of each element is separately adjustable. A typical target for the temperature distribution of the polyvinyl butyl web 20 is 90 to 40 °C from the hot brim to the cool brim. The distance between the radiation sources 1 to 18 and the web 20 is typically 10 to 15 cm. The width of the radiation unit is typically 125 cm and its length is 100 cm. The typical total output of radiation is about 30 kW. A ventilated space is provided above the radiation sources 1 to 18, a 1000 to 1500 m 3 /min air circulation being provided from said space in order to achieve improved temperature control. The radiation sources in the Figures are numbered such that the first radiation source on the right has the reference numeral 1. The initial output of the radiation sources 1 to 3 on the right is zero when a film 20 is used having a shaded brim. The shaded portion 24 coincides with these radiation elements 1 to 4. The aim is also to keep the shaded portion 24 the coolest, that is, at about 40 °C. According to the invention, a radiation-barrier board 25 is placed between the radiation sources 4 and 5 at least essentially perpendicularly to the plane of the film web 20 and at least essentially in the travel direction of the web 20. As an alternative to the vertical alignment, the radiation-barrier board may be slightly tilted, e.g. 1 to 15° from the vertical position. The radiation-barrier board 25 may also be parallel with the radiation sources. The radiation-barrier board 25 is made of a heat-resistant material of poor thermal conductivity, such as Teflon. At the top, the board 25 is placed in close proximity with the lamps 1 to 18 and extends thus far down towards the web 20 that sufficient radiation suppression is achieved in the area 24. In this example the distance between the web 20 and the lower edge of the board 25 is 2 to 5 cm. The distance is typically the same throughout the entire radiation unit. Thus, the distance is approximately half of the mutual distance between the radiation elements which is typically 7,5 cm. As a general rule, it can be stated that the distance between the lower edge of the radiation-barrier board 25 and the web is selected such that the direct radiation output of the closest radiation elements 5 to 7 in operation does not reach the shaded zone 24. The distance between the film web 20 and the radiation-barrier board 25 is adjustable according to the controlled output of the radiation sources 1 to 18 and/or the properties and width of the web used in each case. Even the transverse position of the radiation-barrier board 25 can be altered because the width of the shaded area 24 varies according to the type of the web. However, the radiation-barrier board 25 is arranged in the vicinity of the border of the shaded area 24. Fig. 2 is a side view of the structure of Fig. 1. It emerges that the radiation-barrier board 25 is rectangular in shape. Fig. 3 is a top view of the radiation unit. In the Figure, the radiation unit is flattened in the longitudinal direction. The slightly oblique alignment of the radiation elements 1 to 18 in relation to the travel direction of the web 20 will emerge from the Figure. The radiation-barrier board 25 is also slightly inclined in relation to the travel direction of the web.

Claims: An arrangement in an apparatus for forming a windscreen interlayer, comprising a heating unit for heat treating a moving web (20), the heating unit comprising individually adjustable radiation units (1 - 18) for directing radiation towards the moving web (20), and radiation restriction means (25) for suppressing the radiation output of the radiation units (1 - 18) in desired areas (24), characterized in that the radiation restriction means (25) comprises a board (25) which is essentially perpendicular to the plane of the web (20), the board being aligned essentially in the travel direction of the web (20) and at the level of the radiation sources (1 - 18) at its first edge and at a distance from the web (20) at its second edge, being opposite to said first edge, such that no direct radiation output is directed towards the desired area (24) of the web (20) from the closest radiators (5, 6, 7) in operation. The arrangement according to Claim 1, characterized in that the radiation restriction means (25) is of Teflon® or some other heat-resistant material having poor thermal conductivity. The arrangement according to Claim 1, characterized in that the distance between the radiation restriction means (25) and the web (20) is about half of the mutual distance between the radiation elements (1 - 18). The arrangement according to Claim 1, characterized in that the distance between the radiation restriction means (25) and the web (20) is adjustable. The arrangement according to Claim 1, characterized in that the transverse position of the radiation restriction means (25) is adjustable in accordance with the respective width of the shaded area (24).

Inventors: SUOMI PIRKKO, SUOMI, PIRKKO
Applicants: SOFTECO OY
Application year: 1997
Main classification: B29B13
IPC codes: B29C35, B32B17, B29B13