Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27N—MANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
  • B27N7/00—After-treatment, e.g. reducing swelling or shrinkage, surfacing; Protecting the edges of boards against access of humidity
  • B27N7/005—Coating boards, e.g. with a finishing or decorating layer

Definitions

• the present invention relates to a method for the three-dimensional wrapping of wood panels and the like with a surface-enhancing sheet of thermoplastics material which is glued to the faces of the panel.
• PVC polyvinyl chloride
• ABS acrylonitrile-butadiene-styrene
• the coating process is carried out to as to wrap the board, whereby the side faces and the upper face of the board are coated.
• a membrane press is typically used for such a purpose; more recently, a membraneless coating process has been introduced which makes use of a membraneless coating press, wherein the thermoplastics foil to be coated act as the press membrane.
• the pressing is carried out with heat in order to thermally reactivate the adhesive and consequently achieve uniform contact between the two adherent members constituted by the MDF board and the coating plastics material.
• the adhesive is constituted by an aqueous-based polyurethane emulsion, possibly associated with additional vinylic or acrylic aqueous emulsions according to the requirements.
• the adhesive is pre-mixed with a certain percentage of an isocyanate hardener which has a cross-linking effect on the adhesive bond.
• thermoplasticity that is its ability to adapt itself perfectly to the shaped surfaces of the board as a result of heating.
• the coating material most widely used today is PVC, but other polyolefin materials, particularly polypropylene and ABS are making their appearance on the market, rendering the gluing problems more complicated.
• the surface-enhancing sheet whether it consists of PVC, polypropylene or other thermoplastics, is always provided with a coating layer of a primer on its surface which is to be glued, the primer typically consisting of chlorinated polymers in a solvent-based carrier suitable to promote, during the pressing step the adhesion of the thermoplastics sheet onto the board faces on which the adhesive is applied.
• the present invention provides a method for the three-dimensional wrapping of wood panels and the like with a surface-enhancing sheet of thermoplastics material which is caused to adhere to the side faces and upper face of the panel by gluing, characterised in that a layer of adhesive is applied both to the faces of the panel to be coated and to the face of the surface-enhancing sheet and gluing is achieved by contact between the adhesive layers by pressing of the sheet onto the side faces and upper faces of the panel.
• the method of the invention uses a thermoplastics sheet having a pre-applied layer of adhesive coated onto its face intended to adhere to the board.
• the adhesive is spread onto the MDF board in the conventional manner, the adhesive layer is dried under ambient or hot conditions and the board is wrapped with the sheet of plastics material which carries a previously applied and dried layer of adhesive compatible with the adhesive applied to MDF board.
• adhesion develops by direct contact between the two adhesive films and not by transfer of adhesive from the panel to the coating sheet as occurs in the prior art.
• the adhesives used in the method of the invention include any adhesive in aqueous emulsion, which can develop adhesion by direct film-to-film contact.
• adhesives include aqueous emulsions of polyurethane, polyethylene-vinyl acetate, polychloroprenes, nitrile rubbers, SBS, SBR, emulsions of vinylic polymers and copolymers, emulsions of acrylic polymers and copolymers.
• Preferred adhesive systems include polyurethane emulsions and emulsions of polyurethane and polyethylene-vinyl acetate in a ratio of 1:2 to 2:1 to each other.
• the adhesive advantageously comprises an anti-blocking agent suitable to prevent the accidental adhesion of the turns of the sheet with each other, thereby to avoid blocking events in the unwinding process.
• the anti-blocking agent is to be selected so as not to jeopardise the contact adhesion properties of the adhesive.
• the anti-blocking agents which are used for such a purpose are non-thermoplastics polymers which are compatible with the adhesive system being used.
• High molecular weight polyvinylalcohol is preferably used in combination with polyurethane-based adhesive systems; however, also cellulose and starch ethers, such as hydroxypropyl or hydroxyethyl cellulose or starch could be used if sufficiently compatible with the adhesive system.
• the amount of the anti-blocking agent in the adhesive emulsion is typically from 0.3 to 2% by wt., or from about 1 to about 6% by wt. referred to the dry adhesive.
• the adhesive which is pre-applied to the coating sheet preferably comprises a surfactant suitable to provide adequate wetting properties to the thermoplastics sheet thereby to foster the good anchoring of the adhesive and exclude the need for the traditionally used primer coating.
• the surfactant is preferably an anionic surfactant.
• the surfactant is preferably incorporated in the adhesive emulsion in a concentration ranging from 0.3 to 1% by wt. referred to 100 parts of the emulsion, most preferably of from 0.3 to 0.6 by wt..
• thermoplastics surface-enhancing sheet which, in the method of the invention, is preferably PVC or some other polyolefin materials, particularly polypropylene and ABS.
• the adhesive advantageously comprises a carefully controlled amount of a cross-linking isocyanate hardener which has been found to provide for an improved anchoring of the adhesive to the thermoplastics sheet and which allows to exclude the use of traditional solvent-based primer coating.
• the amount of the isocyanate hardener must be carefully controlled in order not to jeopardise the thermal-activation properties, that is the possibility to develop the adhesion by contact.
• the amount of isocyanate hardener should preferably not exceed 2.5% by wt. referred to 100 parts of the wet adhesive emulsion.
• the adhesive which is applied to the faces of the board to be coated may have the same nature as the adhesive applied onto the coating sheet or a different nature.
• the adhesive to be spread onto the board surfaces is selected among those mentioned hereinbefore.
• the performance of the wrapped panel in terms of its being water-proof or heat-proof may be improved by pre-mixing the adhesive spread onto the board with an isocyanate hardener which can induce suitable cross-linking over the entire adhesive bond formed by the contact adhesion.
• the isocyanate hardener is present in a concentration of from 1 to 10% with reference to 100 parts of aqueous adhesive emulsion.
• Polyvinylalcohol 40-88 is a high molecular weight polymer having a hydrolysis degree of 88% and 40 Hoeppler viscosity; it provides anti-blocking properties to the adhesive spread onto the coating sheet.
• Lumiten AFK (trademark) is an anionic surfactant which is chemically defined as the sodium salt of a fatty acid condensation product; it is employed as an aqueous solution including 55% by wt. solids and with an alkaline pH; the anionic surfactant improves the anchoring properties of the adhesive to the thermoplastics sheet and allows to avoid the use of a conventional primer coating.
• thermoplastics sheet of material other than PVC such as polypropylene
• the use of a conventional primer may be avoided by pre-mixing the adhesive composition with a controlled amount of isocyanate hardener.
• Example 1 without hardener
• Example 2 with hardener present in the adhesive composition applied to the board in quantities of 5% by wt. with respect to 100 parts of adhesive
• Example 1 without hardener
• Example 2 with hardener
• Coating sheet PVC without primer As 1 - Thickness of adhesive 2 on PVC: 40 ⁇ m As 1 - Drying of adhesive: under ambient conditions
• Panel MDF As 1 - Adhesive 1 on panel: Spread (60-80 g/m2)
• Drying of adhesive on panel Ambient conditions for 30 minutes As 1 - Bonding T: 60°C As 1 - Bonding pressure: 5 kg/cm2 As 1 - Pressing time: 3 seconds
• the adhesives described above at 1 and 2 were used in coating tests to coat doors in a membrane press with the use of PVC as the coating sheet without primer coating.
• the test conditions were as follows:
• adhesive 2 - before being applied onto the polypropylene sheet - was mixed with 2% by wt. of the isocyanate hardener Desmodur DA (trademark), thereby to obtain an adequate anchoring onto the polypropylene without compromising the thermal reactivation properties of the adhesive layer.

Applications Claiming Priority (2)

Publications (1)

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Citations (5)

• 1994
  • 1994-07-01 IT IT94TO000545A patent/IT1266151B1/it active IP Right Grant
• 1995
  • 1995-06-26 DE DE0689911T patent/DE689911T1/de active Pending
  • 1995-06-26 EP EP95109906A patent/EP0689911A1/de not_active Withdrawn
  • 1995-06-26 ES ES95109906T patent/ES2082736T1/es active Pending

Patent Citations (5)

Non-Patent Citations (1)

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