GB2271961A

GB2271961A - Coating sheet-like objects with a plastic film

Info

Publication number: GB2271961A
Application number: GB9306101A
Authority: GB
Inventors: Raimo Tikka
Original assignee: Tikka-System Oy
Current assignee: Tikka-System Oy
Priority date: 1992-10-30
Filing date: 1993-03-24
Publication date: 1994-05-04
Anticipated expiration: 2013-03-24
Also published as: DK48093A; AU3512393A; DE4314030A1; FR2697531A1; GB9306101D0; SE9301431L; FI91225C; FR2697531B1; DK48093D0; RU2089392C1; NO931517D0; AU655874B2; SE9301431D0; ITRM930202A1; FI91225B; NO931517L; FI924936A0; IT1261219B; ITRM930202A0; GB2271961B

Abstract

The plastic film (10) is heated by a planar heating element (3) emitting radiation of sufficient wavelength, whereby the temperature of the plastic film remains sufficiently low. Heated, the plastic film is lowered on the object (5) to be coated a surface whereof has been treated with a heat activated adhesive, whereby, the film touching the surface of the object, the adhesive is activated and adheres the film to the object. The adhesion is further enhanced by low pressure. <IMAGE>

Description

2271961 1 Method and apparatus for coating sheet-like objects with a

plastic film The present invention relates to a method for coating sheet-like objects with a plastic film, said method comprising the steps of applying heat activated adhesive on a surface of the sheet-like object; heating the plastic film by a spaced-apart heat radiator; placing the plastic film on the object to be coated and causing the film to press against the surface of the object to be coated by sucking air from the space between the object and the plastic film until the film adheres to the surface of the object to be coated.

Further, the present invention relates to an apparatus for coating sheetlike objects with a plastic film, said apparatus comprising a heating hood defined by wall and top portions, a heat radiator provided in an upper part of the heating hood, and a low-pressure table for pressing the film to a surface of the object to be coated.

DE 38 19 434 teaches an arrangement in which a plastic film is heated in a heating chamber by means of rod-like heat radiators with a very high surface temperature, whereby the wavelength emitted by the heat radiator is very short. Further, on the bottom of the heating chamber there is a mould onto which the heated plastic film is pressed by overpressure applied from the side of the heat radiators, and sucked by low pressure applied correspondingly to the portion on the side of the mould. Said apparatus is a highly expensive and heavy arrangement. The overpressure in the heating chamber may rise to up to 10 bars, and the low pressure correspondingly approaches vacuum. This means that the walls of the heating chamber must be made very thick and firm. Opening of the heating chamber 2 and handling of the f inal product which is removed from the surface of the mould is very difficult, because the thick walls of the heating chamber render the mass of the apparatus very large. Still further, the low- and overpressure compressors required by the apparatus add to the total costs considerably. Since the wavelength of the heat radiation is very short and the heating process very fast, regulation of the heating process is very difficult. This causes non-uniform heating of the plastic f ilm, and in the worst case, when the heat radiation is non-uniformly distributed, it burns holes in the plastic film, whereby the object in question will be discarded from the line.

DE 32 20 416, DE 32 23 171 and DE 32 25 533 dis- close an apparatus and further applications of said apparatus in which a plastic material is heated by rod-like heat radiators with a very high surface temperature. The heated plastic sheet is placed on a mould, after which it is pressed against the mould by low pressure or overpressure. When the plastic sheet thus moulded has cooled down, it is detached from the mould for further treatment. It should be noted that said apparatus is not used for coating a material, but for moulding required objects from a plastic material. Said DE publications disclose how the plastic material is moulded industrially, and the production line is developed for industrial use. In addition, for its rapidity the heating process is very difficult to regulate, and because of the difficulty in the regulation, a uniform heating of the plastic material is practically impossible.

DE 27 45 395 discloses an apparatus in which the heated plastic material is forced into the shape of the mould by low pressure, and after the moulding product is detached from the mould. The document also 3 discloses a mould recycling system, which makes the production easy and flexible.

EP 179,374 teaches an apparatus with which different rubber surfaces may be vulcanised with one another in their mould and possibly e.g. car tyres coated. The solution of the publication concerns only the treatment of a rubber material.

DE 22 40 769 discloses an apparatus in which, by using over- and low pressure, the coating is moulded into the shape of the mould, after which a resilient material such as polyurethane is injected between the coating and the mould, whereby said apparatus may be used e.g. for manufacturing padding for car seats. Said document further describes an apparatus with which the production of such products may be industrialised to meet the requirements of car industry.

The object of this invention is to provide a method and apparatus enabling the coating of sheetlike objects with plastic films and enabling a light structure for the apparatus. This is achieved with the method of the invention, which is characterised in that the plastic film is heated by a planar heating element essentially having the size of that surface of the plastic film which is to be heated, the adhesive on the surface of the object being activated by the heated plastic film, which adheres to the object to be coated.

The apparatus of the invention is further characterised in that the heat radiator heating the plastic film is a sheet-like heating element essentially having the size of that surface of the plastic film which is to be heated.

Preferably the surface temperature of the heat radiators heating the plastic film is so low that the wavelength gener- 4 ated by the radiator is long enough, whereby the heat radiation absorbing factor of the plastic film is very good. Thereby the plastic film is uniformly heated throughout. It is also preferable that the heating hood is provided with an inner surface that absorbs as little heat radiation as possible, whereby it reflects the heat radiation to the object desired, in this case to the plastic film. Still another Pre ference is to make the surface of the heat elements facing the plastic film from a substance which emits the heat radiation well and, correspondingly, the sur face of the heat elements not facing the plastic film from a substance which emits heat radiation poorly, whereby the heat radiation can be directed straight to the plastic film. A further preference is to provide the highest point of the heating hood with a ventilating hole or ventilating holes enabling change of air heated by the heating elements when the plastic film is not attached to the heating hood. A still further preferential concept ls that in the heating phase the plastic film adheres to the hood at the edges of the hood by the effect of low pressure, whereafter the heating elements heat the plastic film and after this the heated plastic film is transferred onto a sheetlike door or the like to be coated, whereby the sheetlike object need not be heated. After this the plastic film is sucked tightly onto the sheet-like object by low pressure, whereby, the sheet being porous, the plastic f ilm is sucked by the low pressure so as to adhere to the whole area of the sheet to be coated. Furthermore, the surface of the sheet-like object is treated so that, by the effect of heat, it enables adhesion of the plastic film to the surface of the object.

An essential advantage of the invention is that when the plastic f ilm is heated at a lower temperature, the heat is more uniformly distributed in the plastic film and will thus not burn holes in the film or cause excessive stretching thereof. When a lower temperature is used for heating the plastic f ilm, it is possible to adjust the temperature of the plastic film to be uniform and ensure an accurate temperature for it. Another essential advantage is that the heating hood can be made very light and thus easily movable, because the hood need not be pressurised. Since the walls of the heating hood are made from a material which absorbs heat radiation poorly, the hood reflects the heat radiation uniformly on the plastic f ilm. It is also to be noted that said device heats only the plastic film and not the object to which the plastic f ilm is attached. Distortions of sheet-like blanks is thus avoided.

The invention will be described in greater detail in the attached figures wherein Figure 1 is a side view of an apparatus of the invention; and Figure 2 shows the cross-section of a preferred heating element.

Figure 1 shows an apparatus 1 for heating plastic films, said apparatus comprising a heating hood 2, heating elements 3, a low-pressure table 4 and a sheet-like object 5 to be coated, said object being located on the low-pressure table 4. The heating hood 2 comprises wall portions 6a and 6b and a top portion 6c. The wall and top portions 6a - 6c are made so that inner surfaces 7a, 7b and 7c are made from a material which absorbs heat radiation as little as possible, such as a burnished aluminium sheet. On the inner surface there is provided a heat-insulating layer which prevents unnecessary heat distribution to the 6 envIronment. The wall portlons 6a and 6b compri-se a low-pressure portion 8a and 8b with grooves 8a' and 8b' and sealings 9a and 9b. Further, Figure 1 shows a PVC plastic film 10 and ventilating holes lla and llb.

In a situation in which the PVC plastic film 10 is not attached to the heating hood 2, hot air heated by the heating elements 3 within the heating hood 2 can flow out through the ventilating holes lla and llb, whereby, when a new PVC plastic f ilm is being attached to the heating hood 2 by means of the low-pressure grooves 8a' and 8b', no excessive heated air remains in the heating hood which possibly burns holes in the PVC plastic film 10. The film 10 being attached to the heating hood 2 by means of the low-pressure portions 8a and 8b, air flow through the ventilating holes lla and llb is finished. When the film 10 is sufficiently warm, it is lowered onto the low- pressure table 4 and the object 5 to be coated. The surface of the object 5 is treated with an adhesive which is activated by heat, whereby, when the hot film 10 touches the adhesive, it makes the adhesive capable of adhesion for a moment. When the adhesive cools down the film 10, the film 10 starts to adhere, whereby a solid coating is formed on the sheet. In order to make the film press against the sheet-like object 5 as efficiently as possible, air is sucked from under the film by the low-pressure table 4, whereby the atmospheric pressure presses the film 10 as tightly as possible against the sheet-like object 5 to be coated. When desired, the heating may be continued, whereby the f ilm 10 is made to adhere to the sharp angles of the sheet-like object.

Figure 2 shows by way of example a preferred apparatus according to the heating element 3, said apparatus comprising heating resistors 12a - 12c and t 7 two mutually corresponding members 14a and 14b having grooves 13a - 13c of a square cross-section cut therein for the resistors 12a - 12c. Further, the surfaces of the members 14a and 14b have been treated in such a manner that the half with its surface facing the plastic f ilm 10 is made to emit heat radiation well, being typically black, and, correspondingly, the other surf ace 10, not f acing the plastic f ilm, is made to emit heat radiation poorly, i.e. in practice this means that it is left bright. In this case the heat radiation is directed straight to the plastic film 10.

Further, the heating element halves 14a and 14b may preferably be made from aluminium, which has a very good heat transfer capacity, whereby, with the res istors 12a - 12c becoming hot, the heat is distrib uted as uniformly as possible in the halves 14a and 14b. It should however be noted that it is mainly one surface which emits heat radiation from the heating element 3, whereby the radiation occurs only through the desired surface. Most preferably the temperature used is 200 to 3000C, whereby the wavelength of the heat radiation is greater than 4 um. The heating ele ment may also be of the type of heat exchanger, where by e. g. hot oil may be led to the heating element, said oil having been heated outside the heating hood and led, after heating, along the piping to the heating element. Further, other liquids are also possible as a medium in the heat transfer. The surface of the heating element may be so formed as to have a serrated cross-section, whereby the heat radiation moves through the coating of the wall portions by being reflected to the plastic film. It is however to be taken into account that the heating element is a planar sheet with an essentially straight surface, whereby the heat radiation is uniform.

8 It should be noticed that this method is easy to bring into production, because the required length of e.g. PVC plastic film may be pulled under the heating hood from the roll, whereafter the film is heated, and after this the sheet-like object to be coated is moved onto the low-pressure table 4. This makes the process fast and efficient.

The figures and the descriptions related thereto are intended merely to illustrate the concept of the invention, and in its details the invention may vary within the scope of the claims. Therefore, in some cases the heating element may be an aluminium sheet on which the heating resistors are provided. Preferably the surface temperature of the heat-emitting object is sufficiently low. It is still to be noted that Figure 1 is only a cross-section of the apparatus in question and that in reality the apparatus is a three-dimensional apparatus which takes account of depth also, whereby, when looked at from the corner, the apparatus resembles a cube. The heating element is schematically depicted as one piece in the Figure, but it can be formed of a plurality of sheet-like element portions so that together they form a sheetlike radiator essentially having the size of that surface of the plastic film which is to be heated.

9

Claims

1. A method for coating sheet-like objects (5) with a plastic film (10), said method comprising the steps of applying activated adhesive on a surf ace of the sheet-like object (5); heating the plastic film (10) by a spaced-apart heat radiator; placing the plastic film on the object (5) to be coated and causing the film to press against the surface of the object (5) to be coated by sucking air from the space between the object (5) and the plastic film (10) until the film adheres to the surface of the object (5) to be coated, c h a r a c t e r i s e d in that the plastic film (10) is heated by a planar heating element (3) essentially having the size of that surface of the plastic film which is to be heated, the adhesive on the surface of the object (5) being activated by the heated plastic film (10), which adheres to the object (5) to be coated.

2. A method according to claim 1, c h a r a c t e r ú s e d in that the plastic film (10) is heated by a heating element (3) provided in an upper part (6c) of a space defined by wall and top portions (6a, 6b).

3. A method according to claim 1 or 2, c h a r a c t e r i s e d in that the plastic film is placed against the lower edge of the wall portions (6a, 6b) of said space for heating, and the film is supported during the heating by sucking air through channels provided in the wall portions (6a, 6b) so that the plastic film is pressed against the underside of the wall portions (6a, 6b), whereby the distance between the plastic film (10) and the heat- ing element (3) during the heating essentially remains unchanged.

4. A method according to claim 2 or 3, c h a r a c t e r i s e d in that the heated air in the space defined by the wall (6a, 6b) and top (6c) portions is exchanged through ventilation ducts in the top portion (6c) after the coating of the object (5).

5. A method according to any one of the preceding claims, c h a r a c t e r i s e d in that the surface temperature of the heating element (3) is maintained at 200 to 3000C so that the wavelength of the heat radiation emitted thereby is approx. 4 to 10 um.

6. A method according to any one of the preceding claims, c h a r a c t e r i s e d in that the heating of the plastic film (10) is continued when pressing against the surface of the object (5) to be coated.

7. An apparatus for coating sheet-like objects (5) with a plastic film (10), said apparatus comprising a heat- ing hood (2) defined by wall (6a, 6b) and top (6c) portions, a heat radiator provided in the upper part of the heating hood (2), and a low- pressure table (4) for pressing the film (10) to a surface of the object (5) to be coated, c h a r a c t e r i s e d in that the heat radiator heating the plastic film (10) is a sheet-like heating element (3) essentially having the size of that surface of the plastic film (10) which is to be heated.

8. An apparatus according to claim 7, c h a r a c t e r i s e d in that the heating element (3) is a sheetlike plane to the surface whereof, on the side facing away from the plastic film (10), are attached the heating resistors.

9. An apparatus according to claim 7 or 8, c h a r a c t e r i s e d in that the heating element (3) is made from at least two portions (14a, 14b), of which the side facing away from the plastic film (10) emits heat radiation poorly and the side facing the plastic film (10) emits heat radiation well, and that the heating resistors are mounted 4 11 in grooves (13a - 13c) between the portions (14a, 14b) of the heating element (3).

10. An apparatus according to any one of the claims 7 tog, characterised in that the surface temperature of the heating element (3) is 200 to 3000C, whereby the wavelength of the heat radiation is 4 to 10 um.

11. An apparatus according to any one of the claims 7 to 10, c h a r a c t e r i s e d in that inner surfaces (7a, 7b, 7c) of the wall (6a, 6b) and top (6c) portions are made from a bright material, whereby they absorb heat radiation poorly.

12. An apparatus according to any one of the claims 7 to 11, c h a r a c t e r i s e d in that the top portion (6c) of the curing hood (2) is provided with ventilating holes (11a, llb) for removing hot air from the curing hood (2).

13. An apparatus according to any one of the claims 7 to 12, c h a r a c t e r i s e d in that the underside of the wall portions (6a, 6b) is provided with low-pressure portions (8a, 8b) for attaching the plastic film (10) to the underside of the wall portions (8a, 8b) f or the time of the heating thereof.

14. An apparatus substantially as hereinbefore described with reference to the accompanying drawings.

15. A method substantially as hereinbefore described.