Technical field

The present document relates to a manufacturing method for a translucent display panel.

Background

Displays using back lighting, i.e. translucent panel displays, for

advertisements and instructional purposes are often made from glass or plastic panels. One example of such panels are those fabricated from a rigid or semi-rigid plastic sheet materials to which graphic design can be applied, for instance by silk screen techniques.

Another example of a back-lit display is disclosed in US5505801 , where the manufacture of a back-lit panel of film-to-glass composite is described.

These types of back-lit panels provide good color reproduction and printability, but they can be both heavy and quite costly to produce.

Summary

It is an object of the present disclosure, to provide an improved translucent or back lighted display panel, which eliminates or alleviates at least some of the disadvantages of the prior art back lighted display panels.

More specific objects include providing a method for manufacturing such a translucent display.

The invention is defined by the appended independent claims.

Embodiments are set forth in the appended dependent claims and in the following description and drawings.

According to a first aspect, there is provided a method for

manufacturing a translucent display panel, wherein said panel is formed as a sandwich structure, wherein said sandwich structure comprises a substrate sheet material, a first and second adhesive layer and a first and second surface structure layer, wherein the method comprises the steps of: providing a substrate sheet material, having a top and bottom side, providing a first and second adhesive layer onto the top and bottom side of the substrate sheet material, and providing a first and second surface structure layer onto said first and second adhesive layer respectively; thereby forming a sandwich structure precursor. The sandwich structure precursor is subsequently pressed in a calender to form the sandwich structure.

By forming a sandwich structure precursor and then pressing the precursor in a calender (i.e. between two bowls of a calander) the adhesive layer can be made to diffuse, i.e. be pressed, into the surface of the substrate sheet material, or completely through the substrate sheet material. This is preferably done while the adhesive is still in a plastic state. The adhesive layer further acts as an adhesive between the surface structure layer and the substrate sheet material. By pressing the adhesive layer or material into the substrate material the translucency of the substrate material is increased. Therefore, through this method, a strong and light display panel is provided, which is highly translucent and easily printable through for instance ink jet techniques. By the panel being highly translucent is meant that a light source can be provided on one side and that the light is held within the material, i.e. a back lighted (or back lit) material is formed. The light source may for instance be a LED light source, which may be placed at a distance from the panel.

According tone embodiment said calender operates at a pressure from 15 to 55 kg/cm ² , or from 20 to 50 kg/cm ² , or from 25 to 45 kg/cm ² .

This pressure may ensure that the adhesive layer is sufficiently pressed into the substrate sheet material to form the translucent panel.

The substrate sheet material may be a paper sheet material, wherein said paper sheet material is a dry coated paper.

The substrate sheet material may thus be a paper material which has slightly porous or rough surface, to allow for the adhesive layer to penetrate the surface, i.e. be pressed into the substrate sheet material or the surface thereof. The paper material should also allow for luminous or light

transmittance and preferably be white or substantially white paper.

The adhesive layer may be a hot-setting adhesive material.

The adhesive material may have a melting point around 100-160 ^° C. The adhesive layer is thus applied to the substrate sheet material when it is hot and the surface structure layer is provided, so as to contact the adhesive layer substantially immediately after the application of the adhesive layer onto the substrate sheet material. The adhesive may thus be a material with a relatively low melting point.

The adhesive layer may be any one of a, polyethylene (PE), a low-density polyethylene (LDPE) material and a polypropylene (PP) material. The surface structure layer may comprise a dimensionally stable material. According to one embodiment of the first aspect the surface structure layer may comprise a polyester (PET) material.

The polyester material provides for a surface structure layer which provides form or dimensional stability, which is strong and which is a clear, i.e. a transparent, material. The polyester may have a blank or matted surface. By matted surface is meant that the material does not reflect light. As the polyester is such a form stable and rigid material, it does not react with the LDPE, and it allows for the sandwich precursor to be calendered to form the panel display, while still maintaining its shape and structure.

The adhesive layer may be provided onto said substrate sheet material by means of extrusion and may be fed at a rate in a range of from 5 to 60 g/m ² , or in a range of from 5 to 50 g/m ² , or in the range of from 5 to 40 g/m ² , or in a range from 10 to 35 g/m ² .

The adhesive layer may be fed at the same rate or different rates, i.e. g/m ² for the first and second layer or side of the substrate.

The surface structure layer may be provided as a film and the film may have a thickness in the range of 10 to 25 micrometers, or in the range of 15 to 20 micrometers.

By using materials such as LDPE and PE for the adhesive layer and surface structure layer respectively, together with a paper sheet material, and in the thickness ranges as mentioned above, the panel will not only become strong, light and have excellent translucency properties, it will also be relatively thin, cheap and also environmentally friendly, as it can be sorted as recyclable paper.

According to a second aspect there is provided a translucent display panel obtainable by the method according to the first aspect.

According to a third aspect there is provided use of the translucent display panel according to the second aspect for printing.

According to a fourth aspect there is provided use of the translucent display panel according to the second aspect as an advertising or

informational display panel, wherein said panel is back lighted.

Brief Description of the Drawings

Embodiments of the present solution will now be described, by way of example, with reference to the accompanying schematic drawings. Fig. 1 is a schematic perspective view of a display panel.

Fig. 2 is a schematic side view of the manufacturing method.

Fig. 3 is a schematic top view of a panel and a mounting arrangement.

Fig. 4 is a schematic perspective view of a mounting arrangement.

Figs 5a and 5b are schematic side and perspective views of an alternative mounting arrangement.

Description of Embodiments

Fig 1 illustrate a translucent display panel 1 , having a sandwich structure 2. The sandwich structure 2 of the panel is formed from a substrate sheet material 3, having a top side 6 and a bottom side 7. On each side 6, 7 an adhesive layer 4 is provided or arranged. The first layer 4' is provided on the top side 6, and the second layer 4" is provided on the bottom side 7. The adhesive layer is interposed between the substrate sheet material 3 and a surface structure layer 5. The surface structure layer is provided or arranged on the adhesive layer such that first layer 5' is in contact with the first layer of the adhesive layer 4', and the second layer 5" is in contact with the second layer 4" of the adhesive layer.

The adhesive layer thus acts as an adhesive or glue between the substrate sheet material and the surface structure layers.

Fig 2 illustrates the manufacturing of the sandwich structure 2 and the translucent display panel 1 . The manufacturing method may be performed in a continuous manner. The manufacturing may take place at room

temperature. The first 4' and second 4" adhesive layers are provided on the top 6 and bottom 7 side of substrate sheet material 3.

According to one embodiment the adhesive layers may be extruded onto the substrate sheet material. The material forming the adhesive layer may thus be fed from an extruder (not shown) and applied onto the substrate sheet material 3.

According to one embodiment the adhesive layer is applied at a rate in the range of from 5 to 60 g/m ² . According to an alternative embodiment the adhesive layer is applied at a rate in the range of from 5 to 50 g/m ² .

According to another embodiment the adhesive layer is applied at a rate in the range of from 5 to 40 g/m ² . According to yet an embodiment the adhesive layer is applied at a rate in the range from 10 to 35 g/m ² . According to one embodiment adhesive layer is applied at a rate of approximately 15 g/m ² . By applied at a rate is meant that the adhesive is extruded onto the substrate sheet material at a specific weight per square meter level or ratio. According to one embodiment this rate or level is depending on the grammage of the paper.

According to one embodiment the thickness of the adhesive layers may be at least substantially the same on both sides of the substrate sheet, i.e. the adhesive layer may be fed onto the substrate sheet material at substantially the same rate (i.e. weight (gram) per m ² ) on both sides of the substrate.

According to an alternative the thickness may be different on different sides of the substrate sheet material .

It is desirable to have a relatively thin layer, preferably fed onto the substrate in the range of 10-20 g/m ² . In this range there is provided the optimum amount of adhesive for penetrating into the substrate sheet material or surface thereof, and to glue the surface structure layer to the substrate sheet material. If the layer is too thick the panel will be too heavy and too expensive to manufacture. Further the thickness is dependent on the grammage of the paper.

When the adhesive layer has been provided or applied to the substrate sheet material, the surface structure layers 5' and 5" are provided or arranged on each of the adhesive layers. This may either be performed simultaneously or after the adhesive layers have been applied on each side of the substrate sheet material. According to one embodiment the surface structure layer is provided as a film. According to one embodiment the surface structure layers are preferably provided or arranged while the adhesive material is still hot, i.e. still plastic, such that when the sandwich precursor is processed in the calender the surface structure layers help pressing the adhesive material into the substrate material to achieve the optimum level of translucency of the panel material.

The surface structure layers are thus provided such that a sandwich structure precursor 2' is formed. According to one embodiment this can be done by pressing the layers together between a pair of bowls or pressure cylinders 1 1 , 12.

If the surface structure layer is provided as a film it is fed to a pressure nip formed between the pressure cylinder 1 1 , 12. The substrate sheet material 3 is thus sandwiched between the adhesive 4', 4" and surface structure 5', 5" layers respectively. The surface structure film may thus be fed from a supply roll (not shown). According to one embodiment the film may have a thickness in the range of range of 10 to 25 micrometers (μιτι). According to another

embodiment the film may have a thickness in the range of 15 to 20 μιτι. It is important that the film is not too thick, i.e. preferably below 25 μιτι because otherwise it will make the panel too heavy, and not too thin, i.e. preferably above 10 m to provide the proper strength and stability to the panel.

When the sandwich structure precursor 2' has been formed the precursor is pressed in a calender 10 or between two bowls 13, 14 or cylinders to form the sandwich structure 2.

According to one embodiment, the sandwich structure precursor is immediately processed in the calender 10.

According to one embodiment the calender operates at a pressure P in the range of from 15 to 55 kg/cm ² . According to another embodiment the calender operates at a pressure in the range of from 20 to 50 kg/cm ² .

According to yet an alternative the calender operates at a pressure in the range of from 25 to 45 kg/cm ² , which is the preferred range. At this pressure it is certain that the adhesive layer, or the adhesive material, will be pressed into the substrate sheet material or the surface thereof. By pressed into the substrate sheet material or the surface thereof is meant that through the pressure from the calender the adhesive layer or material is made to penetrate between the porous fibers of the substrate material.

According to one embodiment the substrate sheet material 3 may be a paper sheet material. According to one embodiment the paper sheet material is a dry coated paper. According to one alternative the paper material is an uncoated paper. According to one embodiment the paper sheet may have a Bendtsen value between 200 - 1500 mls/min. This means that the surface of the paper has certain porosity. It is further important that the paper is not completely smooth, i.e. that it is heavily coated, to allow for the adhesive layer material to penetrate the surface. According to one alternative the paper has a grammage of from 80 to 200 g. According to one alternative the paper has a grammage of less than 180 g. According to yet an alternative the grammage of the paper is in the range of from 120 to 130 g.

According to one alternative the adhesive layer is made from a hot- melt adhesive material. According to one embodiment the adhesive layer, i.e. the material forming the adhesive layer, may have a melting point in the range of from 100 to 160 ^° C. According to one embodiment the melting point is in the range of from 140 to 160 ^° C. The adhesive material may thus be a material with a relatively low melting point.

According to one embodiment the adhesive layer is polyethylene (PE) or low density polyethylene (LDPE). According to another alternative the adhesive layer is polypropylene (PP).

According to one embodiment the surface structure layer, i.e. the material of the surface structure layer, is polyester (PET). The surface structure layer may further be an optically clear film. The surface structure layer may have a blank or a matted surface, or it may even have a blank surface on one side of the panel and a matted surface on the other. The surface structure layer provides the panel with the desired form or

dimensional stability and makes the panel strong, yet light.

The surface structure layer also provides a printable surface. This means that when the panel 1 has been manufactured it can be transported to a printing facility and there provided with the desired print.

According to one embodiment the translucent display panel may be used for printing advertisements and displaying for instance in a store.

The display panel may be placed in a frame or placed or hung, e.g. on a wall or from the ceiling, on its own.

According to one embodiment the translucent display panel can be lighted from the back, i.e. so called back-lit or back lighted.

As illustrated in Fig 3 the panel 1 may be attached to a frame or backing portion 20. As shown in Fig 4 the frame or backing portion is provided with a light source 21 . In Fig 4 the lighting source is depicted as a light strip, but it may of course be spotted or continuous. According to one embodiment the light source may be LED.

As illustrated by Figs 3 and 4 the panel 1 may be arranged at a distance D from the light source. The distance D can be altered depending on the translucency of the display panel and the desired appearance of the display panel. According to one embodiment the distance D is in the range of from 10 to 50 mm. According to one embodiment the distance D is in the range of from 25 to 40 mm.

According to one embodiment the light source 21 may be placed directly adjacent to, i.e. at a very short distance e.g. < 10 mm, the panel 1 , which is illustrated by Figs 5a and 5b.

The light source may also have different luminance depending on the desired appearance of the display panel. The display panel of the invention allows for the use of a light source having a fairly strong luminance while still providing an even scattering of the light throughout the panel. Example 1

As an example a translucent display panel was manufactured by using as a surface sheet material a paper sheet material which is a wood free coated 2- side fine paper, a matted mineral coated, on both sides, paper. The adhesive layer was formed from LDPE, melt flow index (MFI) 4,5, with a melting point of approximately 1 10 ^° C.

The surface structure layer was formed from a polyester (PE) film, a biaxially orientented transparent polyester, which had a melting point of approximately 250 ^° C.

The LDPE was extruded onto the paper material and the polyester film was applied when the LDPE was still hot to form a sandwich precursor. The precursor was then pressed in a calender to form a translucent display panel.

Example 2

A translucent display panel was produced according to example 1 above. The panel was printed with an advertising image (color). The panel was placed at a distance of approximately 40 mm from a light source, which was a LED lighting in the form of a light strip as back lighting. The translucent display panel was evenly back lighted, and gave an excellent appearance, light scattering and color representation.