ILPA SRL INDUSTRIA LEGNO PASOTTI S.r.l.

Panel for making poured concrete forms or the like

This invention relates to a panel, particularly for making poured concrete forms or the like, which panel comprises at least one layer having such mechanical properties as to be able to withstand the stresses of the concrete mass and at least one protective layer that is attached to the concrete-side face of the first layer, is made of a water- and/or moisture-proof, weather-resistant material and forms the layer in direct contact with the concrete mass.

Panels of this type are disclosed, for instance, in EP1426525 and EP668142. Typically, the layer with mechanical resistance to concrete mass stresses is made of wood or a similar material, whereas the outer protective layer may be a waterproofing coat of protective paint in certain panels or a layer of plastic material, such as a layer of polyolefin mixtures and particularly polypropylene in other types of panels .

The use of coats of protective paints involves the drawback that these paints can be scratched away and/or mechanically damaged thereby allowing moisture to penetrate to the mechanically resistant layer which is made of wood and hence prone to deterioration. Moisture infiltration causes important damages, because the wooden layer surface is almost totally covered with the protective paint, and moisture can remain trapped for a long time in the wooden layer once it penetrates it.

The panels in which the mechanically resistant layer , i.e. the wooden layer, is protected by outer plastic layers formed of plastic materials

incorporating various types of fillers, such as those described in the above mentioned documents , in which the protective layer is made of polypropylene filled with natural, vegetable fillers has the advantage that said protective or coating layers have a higher abrasion resistance, wherefore the outer surface of the panel is not damaged by being rubbed against the concrete or by rough handling of the panels during operation, and cracks or other passages for water or moisture infiltration are less likely to form. Furthermore, the panel has a multilayer structure, which provides advantages in terms of mechanical stresses. Therefore, these panels are the preferred solution for making poured concrete forms for walls , floors or the like. While these panels exhibit a good resistance to abrasion or other rough treatments occurring during casting and/or other handling operations required for making the form, they still suffer from certain drawbacks. These drawbacks consist in that, in view of achieving a good abrasion resistance of the outer surface, the protective layers have to be relatively hard. In these conditions, the protective layers have a brittle, non-ductile failure behavior, with potential cracking and veining. This behavior contrasts with the inevitable requirement for the panels to have a good behavior in response to nailing, which will be referred to herein as nailability behavior or simply nailability. Due to this requirement, the material will have to be softer and more ductile and failures shall not give rise to crack propagation .

In an attempt to solve these problems , compromise solutions have been proposed, which consist in

particular choices in terms of compositions of polymer mixtures and fillers . One of these solutions is proposed by the document.

Nevertheless, compromise solutions do not entirely fulfill the dual condition of enhanced scratch or abrasion resistance of the protective layer and better failure behavior in response to nailing or ductile failure mode .

Also, all prior art panels, regardless of their construction, have the drawback that the protective layer of waterproof material does not allow dissipation of the air bubbles that appear in the concrete mass in the area of contact with the protective layer of the panels. In this case, upon form removal, craters and bug holes may appear, possibly of considerable size, may appear in the finished concrete surface and jeopardize the aesthetic appearance of the wall.

One object of the present invention is to provide a panel of the type described hereinbefore in which the creation of craters and holes in the surfaces of the concrete walls due to air bubbles or air entrapments may be obviated using simple and inexpensive means .

A further object of the present invention is to provide a panel of the above type in which the protective layer, as a whole has both the highest abrasion and scratch resistance and an optimal nailability behavior, i.e. an optimal ductile fracture behavior, without requiring compromise solutions for each of the two characteristics and without requiring an excessively expensive and complex construction.

The invention fulfils the above objects by a panel of the type described hereinbefore, in which at least on one side of the panel the surface designed to be in

contact with concrete is treated to facilitate air discharge and/or dissipation along said contact surface .

This treatment is aimed at modifying the physical characteristics of the panel surface to increase wettability of such surface in contact with the concrete mass.

This result is known to be achieved by various treatments , including chemical , thermal and/or electric treatments or combinations thereof. Typically, flame hardening, plasma discharge and/or other known surface treatments may be used.

The type of treatment may be selected among those available to those of ordinary skill in the art, possibly depending on the specific composition of the protective layer whose surface has to be treated. The surface of the protective layer is treated to achieve a predetermined surface tension from 20 to 100 dine/cm, preferably from 35 to 80 dine/cm. Typical surface treatments are described in H. Saechting, Manuale delle Materie Plastiche, 8a edizione, Tecniche Nuove, ISBN 88 481 09152, 1999 chapter 3.4.4 page 324 et. e 3.4.5, pp. 331 et seq. and charter 3.4.5, pp. 331 et seq.

According to one improvement, the surface having the predetermined surface tension is the surface of the protective layer or the outer surface of an outer layer or an outer coating film. In this case, several different compositions may be used for the film, as described in greater detail below. A surface tension in a range from 20 to 100 dine/cm, preferably from 35 to 80 dine/cm allows a continuous water film to adhere to the panel surface, which forces air particles towards the side edges of

the panel or into the concrete mass to a certain depth.

In case of large air masses and/or when the concrete work is required to have a certain predetermined surface structure, then the invention provides, as an alternative, a three-dimensional shape on the concrete-side surface, at least on one side of the panel, to form a grid of air discharge or dissipation channels along said contact surface towards the peripheral edges of the panel. In one advantageous embodiment, this three- dimensional shape may be obtained by a satin finishing, embossing and/or knurling treatment on said surface.

Once again, the treatment may be carried out directly on the surface of the coating or protective layer/s of the panel or said layers may be covered by at least one film which is in turn formed with a three- dimensional shape as described above.

Three-dimensional shaping may be advantageously combined with the surface treatment that provides the above mentioned surface tension values.

According to an advantageous feature, the three- dimensional structure formed of these channels or micro-channels may have the form of a grid, in which said channels or micro-channels are oriented in at least two non-parallel directions or said channels or micro-channels are oriented substantially in one direction, so that air in the bubbles is only conveyed towards two opposite ends of the panels .

According to yet another feature, said three- dimensional structure can be formed as a pattern whose negative remains embossed on the surface of the concrete element upon removal of the form.

Such pattern may have any shape and structure and,

according to a preferred embodiment, the channels and/or micro-channels are formed in such a manner as to simulate wood grains .

Such three-dimensional shaping may also be provided as a number of micro-ridges or micro-teeth arranged all over the surface in spaced relationships , like a satin-finish or micro-knurling.

Advantageously, the micro-channels have a width of the order of 50um to lOOOum, preferably of 200um to 600um, and particularly, in a preferred embodiment a width of the order of 300um.

The depth is of the order of lOum to 500um, preferably of 20um to 200um, and particularly, in a preferred embodiment of the order of lOOum. The spacing between two adjacent grooves is of the order of lOum to 3 mm, preferably of lOOum to lOOOum, and particularly, in a preferred embodiment of the order of 500um.

When the three-dimensional structure is formed using a film having such structure on its surface, then such film can be made of any plastic material.

Particularly, preferred film types for the present invention are made of PP/PET, PP/PA, PP/PS, PP/ABS, PP/AN. The film may be applied by lamination on the application surface or on the surface of the coating and protective layer.

The film may be also coextruded with the coating and protective layer or applied using other known technologies that can be selected by those skilled in the art among various known preferred options for different types of coating and protective layers .

Thanks to these features , the invention allows

dissipation of air bubbles or inclusions that cause surface finishing defects in prior art concrete works , and also imparts an aesthetic finish to such surfaces, that can be selected among infinite options . Therefore, the film also provides further protection to the panel to damages and loss of waterproofness of the coating and protective layer and limits any cracks of the underlying layer during nailing. Concerning the second problem, the invention fulfils the relevant object by a panel as described hereinbefore in which the coating and protective layer/s are formed of at least two superimposed layers, i.e. an inner layer made of a plastic material that can, but need not (due to cost reduction purposes) be filled with an organic filler and designed to adhere to the mechanically resistant layer and an outer layer which is made of a plastic material filled with a mineral filler, the plastic material layer possibly filled with an organic filler being such that it has a ductile failure behavior, whereas the layer of plastic material filled with a mineral filler has a very hard and abrasion- and scratch-resistant surface, while being fragile. Particularly, the layer of plastic material possibly filled with the organic filler has the following characteristics:

- Elongation at break: > 4%

- Modulus of elasticity in bending: from 1000 MPa to 2000 MPa.

On the other hand, the layer of plastic material filled with the mineral filler has the following characteristics :

- Elongation at break: < 4%

- Modulus of elasticity in bending: from 1000 MPa to 2000 MPa.

Polyolefin mixtures may be used as a plastic material and vegetable fillers, particularly wood flour, may be used as vegetable fibers, whereas several different mineral fillers or mixtures , preferably calcium carbonate , may be used as mineral fillers .

According to a preferred embodiment, in the layer formed of the polyolefin mixture and organic fillers , the polyolefin mixture is composed of 100% copolymer.

Concerning the organic filler, it represents 10% to 70%, preferably 40% to 60% by weight.

Concerning the mineral filler and particularly calcium carbonate, it represents 10% to 70%, preferably 40% to 60% by weight.

According to yet another embodiment, the coating or protective layer is advantageously composed of three layers, including an intermediate layer of a plastic material possibly filled with organic fillers, and two outer layers adhering to the two opposite faces of said intermediate layer and formed of a plastic material filled with an organic filler.

Said two layers have identical or different compositions .

The combined thickness of the coating layer is in a range from 0,6mm to 3mm, preferably from 0,8mm to

2,0mm, whereas the thickness of the mechanically resistant layer, particularly made of wood, is in a range from 9mm to 20mm, preferably from 15mm to 27mm.

The two or three layers that form the coating layer may be from 0,2mm to 1,5mm, preferably from 0,25mm to 1,0mm thick.

The coating or protective layer can be formed by lamination and/or coupling or co-extrusion, with a process as described, for instance, in EP 668142.

The coating or protective layer may be applied to the mechanically resistant layer, e.g. made of wood or another material, using any known physico-chemical bonding methods and/or using adhesives or intermediate anchoring layers .

It shall be noted that the panel having the above features may be additionally fitted with a three- dimensional surface structure as described hereinbefore, for air discharge along the surface in contact with the concrete mass. This can occur either by shaping the surface of the coating and protective layer or by applying a film thereon, as described above . Any combination or subcombination of features of the above embodiments is possible and shall be intended as part of the present invention.

Thanks to the provision of a coating or protective layer formed of two different layers or three layers, including two outer layers and an inner layer having different compositions and/or thicknesses, and hence having different failure and/or abrasion and/or scratch resistance behaviors, the panel affords surprising and unexpected nailability features. Particularly, hardness of the outer layer surfaces is ensured by using mineral fillers. Also, these outer layers have a very high abrasion resistance and, in spite of their hardness and substantially fragile failure behavior, they are less exposed to veining and cracking, due both to the above characteristics, and to reduced thickness, particularly of the layer in contact with concrete.

The layer formed of a copolymer matrix filled with

organic material remains relatively soft and ductile and has an optimal behavior in response to nailing or the like. Surprisingly, the lamination and/or co- extrusion or other combination of two or three layers generates a coating or protective layer that imparts excellent abrasion- or scratch-resistance to the outer surfaces, as well as optimum nailability. Mutual bonding of layers, within the above mentioned thickness ranges unexpectedly prevents veining, cracking or other damages in the outer layers .

This effect is advantageously achieved when the plastic materials employed for the various layers are compatible or identical and hence the bond of the plastic matrixes at the interfaces between the layers is stronger than simple adhesion, and allows the intermediate layer to keep the outer layer from breaking in case of penetration by a nail or the like .

In accordance with an advantageous improvement of the invention, the outer coating layer, formed of a plastic material filled with a mineral filler, further includes stiffening fibers incorporated in said mixture of plastic material and mineral filler.

Said stiffening fibers can have the form of individual long fibers mixed with the plastic material in random arrangement.

Otherwise, the fibers may be arranged and organized in a fibrous layer such as a fabric, a nonwoven fabric, wadding or the like, with fibers being impregnated and incorporated in the filled plastic material .

Glass fibers or the like can be advantageously used as stiffening fibers.

The effect of the stiffening fibers in the outer

coating layer of plastic material filled with mineral fillers is to obtain a stiffness of the coating layers similar to the stiffness of wood. Thus, as compared with traditional prior art panels , in which the whole panel is made of wood, the thickness part that has been replaced, in the coated panel, by the plastic coating layer has a reduced stiffness as compared with the panel made of wood only, due to the lower stiffness and particularly the different elastic modulus of the plastic material and the wood.

In the case of the present invention, the stiffening fibers reduce to a certain extent the loss of stiffness of the laminated panel with respect to the panel made of wood only, without affecting the abrasion-resistance and nailability features of the laminated panel of the present invention.

Further features and improvements of the invention will form the subject of the subclaims .

The characteristics of the invention will appear more clearly from the following description of a few embodiments, which are shown without limitation in the annexed drawings , in which :

Fig. 1 shows a sectional view of an enlarged detail, as taken in a plane perpendicular to a panel of the present invention, in which a surface of the coating and protective layer is shaped with a three- dimensional structure composed of a set of thin grooves or channels .

Fig. 2 shows a variant embodiment in which said three-dimensional structure is formed on a film attached to the outer side of the coating and protective layer.

Fig. 3 shows an enlarged detail in which the

individual superimposed layers are staggered to show their order and the outer layer has the three- dimensional shaping formed of a number of thin grooves that form a pattern resembling wood grains . Fig. 4 is a sectional view of a detail of the inventive panel , in which the coating or protective layer is composed of two layers .

Fig. 5 is a variant of the embodiment of Figure 4, in which the coating or protective layer is composed of three layers .

Fig. 6 shows the same embodiment as shown in Figure 5, a film with a three-dimensionally shape as described in the example of Figure 2 being applied to the outer surface of the coating and protective layer. The panel as shown in Figure 1 is composed of two layers , one layer 1 whereof has such mechanical properties as to withstand the stresses of the concrete mass, and is covered on at least one side by a coating or protective layer 2. According to one variant, the coating or protective layer can be provided on both sides of the layer with mechanical resistance properties 1 as indicated by the layer 2 ' , outlined by broken lines .

The layer with mechanical properties affording resistance to the pressures and/or weight of the concrete mass, also referred to as bearing layer and designated by numeral 1 , can be made of any material whatever. In one embodiment, such layer may be a wooden layer consisting of a board of solid wood and/or a number of strips glued together in one or more layers with either the same orientation or a criss-cross orientation within said layers and/or a number of superimposed wooden sheets like in multilayer plywood

and/or wood fibers in the form of chips or shreds pressed and glued together, like in the so-called particleboard or the like . The bearing layer 1 may be also formed of any combination of the above embodiments, depending on both mechanical resistance requirements and desired thicknesses as well as the expected use of the panels .

The coating or protective layer may be formed of any plastic material, particularly a thermoplastic material, such as a polyolefin mixture and particularly polypropylene. The plastic material may be filled with various amounts of one or more organic and/or mineral fillers or mixtures of said one or more fillers and particularly wood flour as organic fillers and/or talc or calcium carbonate as mineral fillers , or the like .

Referring to Figure 1, the outer surface 102 of the coating or protective layer 2 and the layer 2 ' , if any, which is designed to contact the poured concrete, is shaped with a three-dimensional structure including a plurality of channels and/or microchannels or a grid of such channels or microchannels , which extend all over the panel and create discharge or dissipation passages for the air trapped in the concrete mass and the panel. These channels or microchannels can be formed by various surface processing treatments, such as embossing or stamping and may have any shape. Particularly, said channels or grids of channels may be also formed by satin finishing of the outer surface of the coating and protective layer 2.

Depending on specific requirements and applications, three-dimensional structures may be formed with grooves or channels having a depth H in a

range from lOμm to 500μm, particularly from 20um to 200um. According to a preferred embodiment, the depth is of the order of lOOum.

The widths L of such recesses or troughs or channels or grooves that form the three-dimensional surface shaping 102 are in a range from 50um to lOOOum, particularly from 200um to 600um. According to a preferred embodiment, the width is of the order of 300um. If desired, the three-dimensional shaping may be formed with a predetermined pattern which may simulate wood grains, as shown in Figure 3. In this case, the depth H of the troughs or grooves or channels is of the order of lOOum, whereas the width L is of the order of 500um.

In the variant of Figure 3 , unlike Figure 2 , the three-dimensional shaping is not formed directly on the coating or protective layer 2 , but on the surface of an additional layer 3, i.e. a film that is glued or otherwise applied to the outer side of the coating or protective layer 2 and/or possibly to the coating or protective layer 2', if any, on the opposite face of the bearing layer 1.

The film may be made of any thermoplastic material, such as PP/PET, PP/PA, PP/PS, PP/ABS, PP/AN. Adhesion to the coating or protective layer/s may be obtained by physic-chemical bonding using the known methods typically used for the specific materials of the film and the coating or protective layer. In this case, the troughs, channels, grooves or the like, designated by numeral 103, may be formed by embossing, as described hereinbefore.

Figures 4 to 6 show a panel of the present

invention, in which at least the coating and protective layer facing towards the concrete, but preferably both coating and protective layers 2, 2' adhering to the faces of the bearing layer 1 are in turn composed of two layers: one layer 202 adhering directly to the bearing layer 1 and one outer layer 102 adhering to the layer 202 and whose surface is the surface in contact with the concrete mass and/or with the outside, depending on the side of the panel on which the coating or protective layer is provided.

Referring now to Figure 4, the combined thickness of the panel, designated by S5, may be in a range from 2,1 mm to 33 mm and preferably from 2,6 mm to 2,9 mm.

The thickness Sl of the bearing layer 1 is typically in a range from 9 mm to 30mm, preferably from 15mm to 27mm.

The combined thickness S4 of the coating or protective layer 2 is typically in a range from 0 , 6 mm to 3 mm, preferably from 0,8 mm to 2,0 mm. Obviously, the thicknesses S2 and S3 of the layers 102 and 202 may be identical and corresponding to half the combined thickness S4.

The two layers 102 and 202 that form the coating or protective layer 2 differ from each other by having different features, that is: the layer 102 has a high surface hardness, imparting abrasion- and scratch- resistance, but also a glass-like failure behavior; the layer 202, according to the invention, is softer, and hence has a ductile failure behavior. These features are obtained using different compositions for the plastic materials that form such layers. The layer 102 is formed of a polyolefin mixture filled with an organic filler, preferably a mineral

organic filler and particularly a calcium carbonate filler.

The polyolefin mixture is polypropylene and the mineral filler and particularly calcium carbonate represents 10% to 70%, preferably 40% to 60% by weight.

This composition imparts high surface hardness to this outer layer.

The inner layer 202 is formed of a polyolefin mixture filled with organic fillers and particularly wood fibers, preferably wood dust.

The organic filler represents 10% to 70%, preferably 40% to 60% by weight.

In order to obtain the required ductility for optimal nailability, the polyolefin mixture is composed almost exclusively, preferably of 100% copolymer.

Thanks to the chemical compatibility of the polyolefin matrices of the two layers 102 and 202 and to the mutual adhesion of these layers , while the outer layer has a glass-like failure behavior and is prone to veining and cracking in response to nailing, such veining and cracking do not occur thanks to the action of the layer 202.

Therefore, the coating or protective layer 2 has both an optimal surface abrasion- or scratch-resistance and an optimal failure behavior in response to nailing.

The variant of Figure 5 is an embodiment in which the coating or protective layer is composed of three layers. In this case, the intermediate layer is the layer 202 with the above mentioned ductility properties, which has layers 102 of higher surface hardness, having identical compositions, on both faces.

Said coating or protective layers 2 may be formed by lamination or co-extrusion or in any other known

manner .

In the variant of Figure 6 , a layer 3 having a three-dimensional shaping 103 as described with reference to Figures 1 to 3 is applied to at least one face of the bearing layer 1 and/or to both faces of said bearing layer 1 (as shown by numeral 2 ' ) .

Obviously, also with reference to the embodiment of Figure 6, the three-dimensional shaping may be directly formed by stamping and/or embossing of the surface of the outermost layer 102 that forms the coating and protective layer 2. Such embossing or stamping may be carried out during lamination of the layers 102, 202 and the third layer 102, if any, for forming the coating or protective layer 2 , wherefore the advantages associated to the characteristics of Figures 1 and 3 add to the advantages associated to the characteristics of Figures 4 and 5.