WO2004026588A1

WO2004026588A1 - Method and device for applying adhesive layers cured by radiation

Info

Publication number: WO2004026588A1
Application number: PCT/BR2003/000139
Authority: WO
Inventors: Ian Roycfe William Petrie Conzalez
Original assignee: Conzalez Ian Roycfe William Pe
Priority date: 2002-09-23
Filing date: 2003-09-23
Publication date: 2004-04-01
Also published as: AU2003260208A1; BR0204183A

Abstract

The present invention refers to a method for applying curable through high intensity ultraviolet radiation auto adhesive layers. The method comprises the positioning of a substrate in a serigraphy device having a serigraphy screen which temperature can be controlled, heat the adhesive until a sufficient temperature in such a way as to allow for the adhesive to be applied upon the substrate, selectively apply the adhesive upon the substrate, and cure the said adhesive upon the said substrate by the application of high intensity ultra violet radiation. A device for the actual conduction of the method is also revealed.

Description

"METHOD AND DEVICE FOR APPLYING ADHESIVE LAYERS CURED BY RADIATION" Background of the Invention Field of the Invention The present invention refers to the application of adhesive layers to a substrate and, more specifically, to a method for applying adhesive layers which are curable through the utilization of high intensity ("UV") ultraviolet radiation, particularly projected for the application upon substrates originally smooth or with textures, plastic and/or metallic. Description of the State of the Art

As it is widely known by the persons skilled in the art, the methods presently known for the manufacturing of, for instance, one-touch keyboards, plastic or metal front panels, signalling and patrimonial plates (in plastic, metal or in another substrate) , and a series of other artefacts, involve the step of applying these elements upon the surface of a substrate.

This application step, whether it is for a permanent or for a provisional fixture, demands the application of an adhesive sensitive to pressure.

Various methods are known and are used in the state of the art for applying auto-adhesive layers upon a substrate, and the following description is a brief summary of the main characteristics of some of the most well known methods . In the method of application by serigraphy, the adhesive, typically an adhesive based on water, solvent or even a bi- component adhesive, is applied to the substrate by means of a serigraphy screen and it is printed at room temperature. In the method of the adhesive' s layer transfer to the substrate by the method of hot fusion ("hot melt"), a polyester film or a polymeric film made out of another material or a film based on cellulose or another material with similar properties is provided with substantially uniform layers of an adhesive of the hot fusion type, which are previously applied to one or to both surfaces of the film.

When applying this film with the adhesive to the substrate surface, the said adhesive is previously heated until it reaches its specific fusion temperature and, with this, it is fixed upon the substrate surface .

A third used method, similar to the method of layer transfer by hot fusion ("hot melt") described above, is the transferable adhesive, according to which the auto adhesive layers are constituted by a sequence of layers comprising, from the bottom to the top, of a paper or similar layer based on silicone or polymeric film with a thin layer mainly composed by silicone in both sides, from herewith called "liner", and an adhesive layer in only one side. Typically, this type of auto adhesive layer is supplied in rolls, which have to be unrolled, cut and disposed upon the piece of the substrate to receive the auto adhesive layer, to be then conformed through a method of cut by printing. Following that, the auto adhesive layers suffer a method of lamination in room temperature so as to exert pressure upon the transferable adhesive to increase the contact of this transferable adhesive on the substrate on which it was applied e also to increase the initial adherence of the transferable adhesive upon the said substrate (in the case of this patent, a technical piece) .

For the adherence of this piece with the adhesive already applied and already laminated, the film with a fine layer of silicone must be removed to expose the transferable adhesive and then apply the piece to the desired surface.

The method of pulverizing or spraying is also known, which comprises the application of the adhesive by means of a pneumatic pistol specially designed to produce a mixture of air and adhesive in its discharge nozzle, resulting in the exit of the adhesive under the form of a cloud of drops through an appropriate hole for this very purpose. Inconveniences of the State of the Art

The known methods in the state of the art described above present some inconveniences, which will be discussed below. The present method of adhesive layers application by serigraphy present some limitations regarding the viscosity adjustment during the adhesive application due to the evaporation of the volatile part of these adhesives which causes the blocking of the screen, particularly when the utilization of adhesives based on water, solvent or bi-components .

The serigraphy screen cleaning difficulty and the deficiencies of the adhesive final behaviour properties after being applied upon the desired surface are also considered as some of the problems typically registered. In the layer transfer method by the hot fusion ("hot melt") method, the inconvenience is the need to repeat the adhesive' s heating method for the fixing of piece in the desired place. There are limitations with regards to the method of application and to the desired final properties of the hot fusion adhesive.

With regards to the application method by means of a transferable adhesive, the layer cutting method or the cutting of the auto adhesive layers when disposed upon the piece's substrate results in the loss of a considerable volume of material, considering the high cost of the said material .

Other negative aspects associated to the method of application by transferable adhesive are: (i) loss of material in the method of conformation for the collage upon the target substrate to be applied in a selective form; (ii) the waste of time and labour with the previous preparation of the auto adhesive layer and the cutting method; (iii) rejections caused by blisters and other superficial defects incorporated during the method of lamination; (iv) limitations in the adhesive behaviour when already applied upon the desired surface; and (v) costs with the confection of the cutting knife for each type of the desired product .

The layer application method by pulverizing or spraying generates the loss of a considerable volume of the adhesive considering the fact that part of the sprayed volume ends up not being transferred to target substrate surface. Another limitation is the lack of efficient control of the layer's thickness and the difficulty of the selective application of such adhesive layer. Summary of the Invention

There is, therefore, the need for a method for applying an adhesive layer to a substrate which does not present the inconveniences of the known and used methods in the state of the art discussed above, which is one objective of the present invention.

Another objective of the present invention is to provide for such a method for applying an adhesive layer to a substrate which surpasses the inconveniences associated to the application methods of the present state of the art, particularly the problems resulting from the characteristics of the adhesive behaviour.

Another objective of the present invention is to provide for such a method for applying an adhesive layer to a substrate which generates material economy without compromising the finishing and the resistance standard of the applied product nor the application versatility of the materials presently available.

According to the present invention, these objectives are accomplished by the combination of the use of an adhesive cured by radiation to an application method which provides a source of heating for the said adhesive, which presents a high viscosity under room temperature, to reduce the adhesive viscosity in such a way that the same can be applied upon the substrate, but without the need to reheat it to be applied on the target substrate after the cure by radiation.

The preferred method to heat the adhesive and, in this form, turn its application viable, is the serigraphy method, which traditionally allows for the adhesive application in a selective way, avoiding its application upon parts of the target substrate which should not receive the adhesive.

As used in the method of the present invention, the application by serigraphy is slightly modified in such a way as to allow for the adhesive to reach an appropriate viscosity state which will make possible its application by serigraphy. Once heated, something which causes the adhesive' s viscosity reduction to an adequate state for the application by serigraphy, the adhesive is applied upon a substrate and afterwards cured by radiation and then, if desired, is covered by a polymeric or based on cellulose film which contains a thin silicone layer on the film's surface, known in the state of the art as the "liner".

During the time of the effective application of the auto adhesive layer upon the substrate, the liner is removed, the auto adhesive layer is disposed in its final application position upon the target surface and a pressure is applied so that an adhesion is provided.

The present invention allows for a manufacturer of auto adhesive plates or identifying labels to deliver to its client a technical piece (one touch keyboard, frontal panel and others) and an auto adhesive layer having a protection cover (film with silicone) , which will be detached for the collage of the technical piece with the auto adhesive layer on the desired place.

A presently preferred application could be, for instance, the conversion of the original substrates in command interface plates of_ machines and equipment of general use and identifying labels . Brief Description of the Drawings

The present invention will be described hereinafter in greater details with reference to a non-limitative example of its currently preferred embodiment as shown in the attached drawings, wherein:

The Figure 1 is a frontal elevation view of the device used in the method of the present invention illustrating the general aspect of this example of embodiment; and

The Figure 2 is a plane view of an auto adhesive identifying label according to the present invention. Detailed Description of the Preferred Embodiment A currently preferred specific embodiment of the present invention is shown in the attached drawings as a non-limitative example of the invention and will be described in details hereinafter. However, it is to be understood that the present invention is susceptible to several modifications and alterations in its form and dimensions, and that the present specification does not intend to limit the invention to the particular forms and/or dimensions here shown and described but, on the contrary, to cover all the modifications and alternative embodiments that are within the spirit and scope of the invention, as defined by the accompanying claims.

With reference now more particularly to the drawings, the preferred embodiment of the present invention comprises a serigraphy mesh 1 which wires are composed by a thermal and electric conducting material, a wooden rigid frame 2 or another similar electricity non-conducting material, copper conducting bars 3 or other electricity conducting material, fixing screws 4 and electrical terminals 5 for the electric transformer terminals' fixing (not illustrated) which output tension is regulated by a rheostat (not illustrated) . The method begins with the heating of the serigraphy mesh 1. The mesh used can be made out of steel or other conductive metal or even a metallic synthetic wire (the most common being the metallic polyester) , or other electricity conducting material which can be used in a serigraphy screen.

An electric transformer (not shown) is used to supply energy, which tension generating terminals are connected to a pair of conducting bars 3, which in its turn are fixed in opposing sides of the rigid frame 2 and in contact with the serigraphy mesh

1.

The mesh is fixed to the rigid frame 2 by means of stapling grips or glue. It is essential that the rigid frame 2 be made out of a stable material independently from the variations of temperature, so as not to bend, and yet being able to support the traction strains applied by the mesh 1.

The screws 4 which fix the mesh 1 and the conducting bars 3 to the rigid frame 2 are inserted from outwards to inwards, that is to say, firstly going through the conducting bars 3, afterwards the rigid frame 2 and finally the mesh 1, with which the end tip of the screws 4 make contact .

This disposition allows for the electrical current intensity adjustment which runs through the mesh 1 to adjust itself to the positioning of the transformer rheostat, thus adjusting the serigraphy screen temperature.

As the electrical energy intensity conducted by the wires which composes the serigraphy mesh 1 increases, the screen temperature increases and, therefore, reduces the adhesive viscosity in the serigraphy screen, due to the existing relation between the adhesive viscosity and its temperature.

The preferable range of temperature for the adhesive application is between 40o C and 140o C, depending on the formulation of the adhesive to be applied, this temperature being directly controlled by the rheostat (not shown) fitted to the transformer.

According to the adhesive formulation, an excessively high temperature of the serigraphy screen could result in a premature polymerisation or transforming the adhesive in the screen in a gel. Additionally, an excessively high temperature value will also cause the adhesive to seep out through the serigraphy mesh' s wires between one printing and the next, due to the adhesive viscosity turning excessively low. By the other hand, a low serigraphy screen temperature and, consequently, a high adhesive viscosity will unnecessarily reduce the amount of adhesive which effectively goes through the serigraphy mesh. In this latter case, that is to say, in the case of a high viscosity, the operator will observe irregularities on the surface of the adhesive layer when lifting the serigraphy screen after the end of the printing by serigraphy.

According to the present invention the method of serigraphy can take place in a manual way, semi automatic, totally automatic or by rotation serigraphy. Independently of the serigraphy method to be used, it is necessary to previously prepare the serigraphy screen. This is done by fixing, in a tensioned form, the chosen mesh to the edges of the rigid frame which will compose the serigraphy screen.

After the application, the serigraphy material suffers a method of cure by means of high intensity ultraviolet radiation or any other form of adequate radiation. In the case of the material applied by serigraphy being an adhesive, the substrate covered by the adhesive will be covered by a film of polymeric nature or based on cellulose which is covered with a thin layer of silicone or another polymeric film for the protection of the adhesive in such a way that it is not touched and to allow for its handling for storage and/or subsequent stages of the production or delivery to a client.

Independently from the degree of automation of the used method, different layers thickness (and therefore different degrees of adherence) can be obtained by the characteristics variations of the serigraphy screen (mesh density, roller pressure during the application, profile of the roller which makes contact with the adhesive for applying the adhesive, the roller's angle, etc.) . Therefore, a serigraphy mesh with a greater density of wires by linear centimetre will deposit a smaller layer of adhesive and vice-versa. The present invention does not entail the protection of the various forms of preparation of a frame for applying adhesive by serigraphy as an objective, considering the fact that the state of the art presents various methods and configurations of frames capable of such a role. The innovative fact incorporated to the method according to the present invention is the modification of the adhesive viscosity through the heating of the serigraphy screen and its posterior cure by radiation. The heating of the applied material during the application by serigraphy, utilizing for such a function a device (serigraphy screen) specifically developed for this method.

As previously discussed above, the preferable method for applying the adhesive is the serigraphy one, but nevertheless incorporating some improvements in relation to the conventional serigraphy method.

By traditional serigraphy it should be understood the application method which uses a frame ( of wooden, metal or other rigid material which acts as a rigid supporting frame) , typically of a rectangular shape which presents a screen (usually composed by a polyester fabric forming a mesh) .

The serigraphy is usually used for ink application, special coverings, varnishes and adhesives having the most various chemical compositions.

The posterior drying of the applied materials through serigraphy is done in the open air, in an oven with thermal curing or through hot air or even utilizing cure by radiation incidence. It is worth reminding the fact that the more wires the serigraphy mesh has by linear unit of measurement, the smaller amount of material (varnish, ink, covering or adhesive) which will effectively go through the screen and will end up applied upon the target surface. This relation remains valid when inverted: the smaller the screen density, greater the amount of material (varnish, ink, adhesive) , is effectively deposited.

The present invention utilizes metallic serigraphy screen or meshes or with wires covered by an electricity conducting material and, consequently, heat, of the pressed, simple or double mesh type. In principle, any of the three types of mesh can be used for the adhesive' s application.

Preferably, the radiation for the cure is conducted through high intensity ultraviolet radiation although other methods can also be used. The present invention offers multiple advantages in comparison to the present state of the art, according to the following below:

The reduction of adhesive loss, as in the case of application by pulverizing or by transferable adhesive or yet by transferable adhesive by hot fusion. Once the use of the curable by radiation adhesive is finished, whatever was not applied in the graphic work can be replaced in its recipient of origin contrary to the bi-component adhesives or based on solvents or water.

The improvement of the viscosity adjusting system, specially if compared to the cases of the use of adhesives based on water and solvents of the state of the art, considering the fact that the viscosity is directly influenced by the serigraphy screen temperature, which in its turn is adjusted through the rheostat controlling the output tension of the electric transformer, without the addition of diluents .

The elimination of the risk of blisters formation and/or other imperfections on the surface which damage the total adherence of the adhesive on the substrate, which is very common in the method of lamination in room temperature of the state of the art with transferable adhesives .

The elimination of the inconvenience of adhesive drying on the screen, for this will only be cured when exposed to a source of radiation which effectively conducts the curing method. This inconvenience is common in the method which utilizes adhesives based on solvents and on water or bi-components of the state of the art . The adhesive can be applied utilizing the same production line in which the serigraphy inks are applied, thus facilitating the adhesive application in a continuous form of production. This advantage eliminates the cutting around the contour of the piece's cutting step which will receive an auto adhesive layer in the case of the transferable adhesive type, the adhesive of fusion by heat type and also eliminates the method of lamination at room temperature in the case of transferable adhesives .

A better control of the final layer thickness, thus providing a better degree of superficial uniformity contrary to what happens with adhesives which needs to be applied by pulverizing in accordance to the state of the art.

After the cure, the adhesive cured by radiation dispenses with the re heating when it is transferred to the substrate, contrary to what happens with the transferable adhesive of hot fusion of the state of the art.

The invention allows for yet a much more exact control of whichever the areas of selective application of the adhesive upon the substrate, allowed by the use of a polymeric material mascara in the preparation method of the serigraphy screen previously described.

It is also avoided the need for the production of knives to conform the piece to its finished state in terms of external dimensions and internal cuttings . Having been described and illustrated the best form of embodiment presently contemplated for the present invention to come true, various modifications and variations in its form of embodiment will be readily apparent to those specialized in the art. Therefore, it must be understood that the present invention is not limited to the practical aspects of the embodiment presently preferred illustrated and described, and that all of such modifications and variations must be considered enveloped within the spirit and the scope of the invention, such₄ as defined in the annexed claims .

Claims

1. The method for applying curable by radiation auto adhesive layers, characterized by the fact that it comprises the steps of: providing a substrate upon which a curable by radiation adhesive layer must be applied; positioning the said substrate in a serigraphy device having a serigraphy screen which temperature can be controlled; applying to the said substrate, through the said serigraphy screen, an adhesive which when cured presents the properties of an adhesive which can be used immediately after the cure; heating the said adhesive, through the temperature control of the said serigraphy screen, until a sufficient temperature as to reduce its viscosity to an adequate point so that it can be applied upon the substrate, the temperature adjustment allowing for the adjustment of the adhesive viscosity; selectively applying the adhesive upon the substrate, avoiding its application upon parts of the substrate which should not receive the adhesive; and, curing the said adhesive upon the said substrate by radiation.

2. The method according to claim 1, characterized by the fact that the temperature which the referred serigraphy screen is heated depends on the adhesive' s formulation to be applied.

3. The method according to claim 2, characterized by the fact that the referred temperature for the adhesive' s application varies between 40o C and 140o C, depending on the formulation of the adhesive to be applied.

4. The method according to claim 1, characterized by the fact that it additionally comprises the step of covering the adhesive layer applied upon the substrate with a layer of polymeric film.

5. The method according to claim 1, characterized by the fact that it additionally comprises the step of covering the adhesive layer applied upon the substrate with a layer of polymeric film or based on cellulose having a fine layer of silicone on the film's surface .

6. The device for applying curable by radiation adhesive layers, characterized by the fact that it comprises: a serigraphy mesh (1) which wires are composed by a thermal and electrical conducting material; a wooden rigid frame (2) or other similar electricity nonconducting material; copper conducting bars (3) or other electricity conducting material;

fixing screws (4) and electric terminals 5 for the fixing of an electric transformer terminals which output tension is adjustably controlled.