Adhesive bonding and miscellaneous chemical manufacture – Surface bonding means and/or assembly means therefor – With work feeding or handling means
Reexamination Certificate
2002-07-15
2004-03-16
Sells, James (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Surface bonding means and/or assembly means therefor
With work feeding or handling means
C156S308200, C156S582000, C156S583500
Reexamination Certificate
active
06705375
ABSTRACT:
The present invention relates to a sealing device for using heat to form a weld between a first layer of plastic and a second layer of plastic, provided with heating means for heating the layers of plastic and conveyor means for conveying the layers of plastic past the heating means, and separation means for forming a separating layer between the heating means and the layers of plastic while the latter are being heated, the separation means being displaceable in the direction of movement of the layers of plastic past the heating means.
A device of the type which is described in the preamble is known from Dutch patent NL 1015127. The sealing device according to the prior art is provided with heating means which are designed as a sealing wire. This sealing wire is held taut between two stationary sealing elements which are responsible for supplying current to the sealing wire. The sealing wire is made from resistor material and will become hot when current is passed through it. The width of the sealing wire is a few millimetres. This width corresponds to the width of the weld which is to be formed between a first layer of plastic and a second layer of plastic. Beneath the sealing wire, there is a support block allowing pressure to be exerted on the layers of plastic which are guided through beneath the sealing wire.
In use, two layers of plastic are guided through beneath the sealing wire. The heat which is introduced into the layers of plastic will cause the plastic to at least partially melt, so that bonding can take placed between the first and second layers. If no further measures were to be taken, the molten plastic material could stick to the sealing wire. Therefore, what are known as separation means are described in NL 1015127. These separation means are designed as a teflon strip which is guided in an endless loop around the heating means by the device. In use, the speed of movement of the teflon strip is the same as that of the layers of plastic which are moved through beneath the sealing wire, i.e. the teflon strip is stationary with respect to the plastic layers and moves over the sealing wire. The teflon is able to withstand the relatively high temperature of the sealing wire and will not melt as a result of the introduction of heat. The presence of the teflon strip substantially avoids the problem of possible sticking of the plastic material to the sealing wire or to the sealing elements between which the wire is held taut.
According to the prior art, the plastic belt or strip is guided underneath a sealing wire via guide rolls. After it has left the downstream section of the sealing wire, the teflon strip will be guided back to the upstream start of the sealing wire via the rolls. While it is being conveyed, the teflon strip will cool and will return to ambient temperature. From initial contact between the sealing wire and the teflon strip, the teflon will have to be heated from ambient temperature until the temperature of the teflon is the same as the temperature of the sealing wire itself. Then, the heat is transferred to the plastic below it by the teflon. It is desirable to keep the sealing wire as short as possible, i.e. within a relatively short distance it is necessary both to heat the teflon and to supply heat to the plastic layers below it. Therefore, a relatively high temperature of the sealing wire is used. Since a relatively high temperature is used, what is known as a hot spot will occur at the downstream end of the sealing wire. Both the teflon and the plastic below it are heated with the aid of the sealing wire over the downstream section. The sealing wire cannot readily release heat at the location of the hot spot. This leads to the sealing wire being subjected to thermal loads at the location of the hot spot and to the teflon material and the plastic layers below it being excessively heated at this location. Furthermore, dust and dirt will bake on at the hot spot. This dirt is relatively sharp. The teflon strip which runs passed this sharp dirt will as a result become worn more rapidly. This represents a drawback.
In view of the drawbacks of the prior art, the object of the present invention is to provide a device of the type described in the preamble in which the above drawbacks are avoided as far as possible.
According to the invention, this object is achieved by the fact that preheating means are provided for the purpose of preheating the separation means before they are fed to the heating means.
According to the invention, it is provided that the separation means, which are designed, for example, as a teflon belt or strip, are preheated at a section which lies upstream of the heating means. When the layers of plastic, together with the separation means, reach the heating means, the separation means are already preheated. This means that the heat which is fed to the separation means and the layers of plastic by the heating means can pass directly to the plastic layers themselves, i.e. it is possible to use a sealing wire which is at a relatively low temperature. The preheating of the separation means means that there is no need to supply excessive heat to a starting section of the heating means, i.e. a hot spot at the end of the heating means is also eliminated.
According to the invention, it is possible for the heating means to form a guide for the separation means, in which case the heating means comprise a first section for preheating the separation means which adjoins a second section for heating the layers of plastic. In this case, it is possible for the preheating means to comprise a first section for bringing the separation means up to temperature, which first section adjoins a second section for further increasing the temperature of the separation means.
According to these measures, it is possible to design the heating means as a simple sealing wire, with the separation means being guided past this sealing wire. The sealing wire may, for example, have a first section which is at a relatively low temperature and adjoins a section which is at a higher temperature, i.e. the separation means, such as for example a strip of teflon, are gradually heated from room temperature towards the temperature of the sealing wire itself. When the separation means together with the plastic reach the heating means, the separation means have been heated to such an extent that they are at a temperature which substantially corresponds to that of the sealing wire itself.
According to the invention, it is possible for the separation means to form a belt or strip which can be displaced along the heating means. In this case, it is possible for the belt or strip to comprise teflon. Furthermore, according to the invention it is possible for the belt or strip to be of endless design.
As has already been stated above, it is advantageous for the heating means to be designed as a resistor.
In this case, it is possible for the resistor to have a first section having a first resistance and a second section having a higher resistance, in order, in use, to form a first section which is at a relatively low temperature and a second section which is at a relatively high temperature.
According to the invention, it is furthermore provided that the resistor has a core of resistor material, the first section being coated with a conductive material in order to reduce the resistance at the location of the coating. According to this embodiment, the heating means are designed as a sealing wire comprising, for example, resistor material. The first section of this sealing wire is coated with a material which reduces the resistance of the material. This coating means that the resistance will be lower, and the temperature which is to be generated when current is passed through will also be lower.
According to the invention, it is possible for the coating to comprise nickel or copper.
A further preferred embodiment is characterized in that the device comprises first heating means and second heating means, which heating means are positioned opposite and at a distance from one another, so
Aarts Anna Maria
Freriks Marcel
Renkens Johannus Henricus
Van De Rijt Johan Henricus
Pieter Theodorus Joseph Aquarius
Sells James
Young & Thompson
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