METHOD FOR APPLYING NANOPARTICLES

Abstract

A method of producing a sheet including the photocatalytic nanoparticles by applying the particles in a freshly impregnated and wet surface. The method including the steps of impregnating the sheet with a polymer resin; spraying the sheet, freshly impregnated with the polymer resin in an uncured and wet state, with an impregnation fluid composition comprising dispersed photocatalytic nanoparticles; drying and/or at least partly curing the impregnated sheet comprising the polymer resin and the impregnation fluid.

Claims

1. Method of manufacturing a sheet comprising photocatalytic nanoparticles, the method comprising the steps of: impregnating the sheet with a polymer resin; spraying the sheet, freshly impregnated with the polymer resin in an uncured and wet state, with an impregnation fluid composition comprising dispersed photocatalytic nanoparticles; drying and/or at least partly curing said impregnated sheet comprising the polymer resin and the impregnation fluid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The disclosure will in the following be described in connection to preferred embodiments and in greater detail with reference to the appended exemplary drawing, wherein:

[0054] FIG. 1 Illustrates a production line for producing an overlay paper.

[0055] FIG. 2 Illustrates a production line for producing an overlay paper comprising spraying unit.

DETAILED DESCRIPTION OF EMBODIMENTS

[0056] The present invention is concerned with manufacturing of an overlay or boards or panels, such as laminate boards or panels, comprising different types of photocatalytic nanoparticles, which makes the manufactured products photocatalytic active. Each layer and process step can be preferred from the others e.g. depending upon the price of the laminate boards and panels (low cost/high cost product) and the facilities available by the laminate manufacturers.

[0057] Laminate boards and panels are typically made of a base of fibre board (mainly high density fibre board HDF) and 3 or more sheets: a décor sheet, an overlay sheet of cellulose on top and one or more backing sheets sitting on the opposite side of the fibre board base to balance the board and prevent it from curving. Other sheets are often placed between the fibre board and the décor sheet. The décor sheet could be monochromatic or patterned to look like e.g. wood, cork, stone, tiles or a more abstract pattern. The overlay sheet typically contains wear resistant particles, normally a certain amount of alumina oxide (Al2O3), to give the laminate better abrasive resistance. Furthermore, the overlay sheet is impregnated with a polymer resin, typically melamine formaldehyde resin. The other sheets, most often paper sheets, are also impregnated with resin. The décor sheet is typically impregnated with melamine formaldehyde resin whereas phenol formaldehyde resin often is used in the core of the laminate. The laminate board or panel is assembled applying heat and pressure, making the resin polymerise in a thermosetting reaction. After lamination the polymerised overlay sheet and décor paper constitute the top layer of the laminate board or panel and thus needs to be optically transparent right from the upper surface of the laminate through to the decorative print of the décor paper.

[0058] In one embodiment of the invention (FIG. 2) the photocatalytic nanoparticles are applied as a wet-in-wet spray coating (43, 40) to the upper and/or lower surface of the paper (10), after a first (42) and/or a second (41) impregnation of the paper (10) with a resin and wear resistant particles, preferably aluminium oxide. The paper may be dried (44,45) after each impregnation. Preferably the photocatalytic nanoparticles are applied after the impregnation step but before the drying step. In one embodiment the paper (10) is in a first step (46) moistened with a resin and/or impregnated in a resin through. This method of spraying the photocatalytic nanoparticles may be incorporated in any production line for producing overlay or décor paper, also in the line shown in FIG. 1 and described above under US2009/0208646. The spraying of the photocatalytic nanoparticles may in the FIG. 1 line be performed at any stage after the moistening (14) of the paper web (10).

[0059] A suitable type of spray nozzle for the spray coating of photocatalytic nanoparticles is an electronically controlled Autojet Pulsajet B10000jjau.

[0060] Preferred spray velocity of overlay or décor paper may be >1 m/s, such as >2 m/s, preferably a velocity of >5 m/s, such as >8 m/s, and even more preferably a velocity of >10 m/s.

[0061] In another embodiment the photocatalytic nanoparticles are applied as a wet-on-dry spray coating to the upper and/or lower surface of the overlay and/or décor paper, after a first or a second impregnation of the paper with resin and wear resistant particles, preferably aluminium oxide. The paper is normally dried after each impregnation.

[0062] In a preferred embodiment of the invention the photocatalytic nanoparticles may be mixed with a wetting agent and/or an alcohol prior to the spray coating step to improve the wettability of the impregnation fluid on the overlay and/or décor sheet.

[0063] In another embodiment of the invention the photocatalytic nanoparticles may be applied as a combination between wet-in-wet and wet-in-dry spray coating.

[0064] In another embodiment of the invention photocatalytic nanoparticles are applied as a polymer mixture in the resin impregnation step.

[0065] In another embodiment of the invention photocatalytic nanoparticles are incorporated into an overlay sheet, e.g., in the décor paper itself prior to polymer resin impregnation. Thus using said photocatalytic overlay sheet or décor paper a photocatalytic layer can be readily introduced applying the existing methods used for manufacturing laminate boards or panels i.e. polymer resin impregnation of the photocatalytic overlay sheet or décor paper followed by laminate board fabrication in a heat pressing laminating step.

[0066] Said photocatalytic nanoparticle impregnation and drying/curing steps may be incorporated into an existing production line immediately prior to the polymer resin impregnation of said overlay sheet or décor paper or said photocatalytic impregnated and cured overlay sheet or décor paper can be stored until needed.

[0067] A suitable type of nanoparticle for use in the coating fluid composition is Titania. The nanoparticles of Titania may according to some aspects of the present invention further comprise other elements. In some embodiments such elements may be introduced into said nanoparticles with the aim to improve the photocatalytic activity of said nanoparticles by altering the absorption range of said Mania photocatalytic nanoparticles.

[0068] The solvent of said coating fluid composition may comprise water, methanol, ethanol or isopropanol or combinations thereof, or may just be water.

[0069] The particle concentration of said photocatalytic nanoparticles in the manufactured board or panel may be increased by repeating said coating step several times.

[0070] A preferred embodiment of the produced impregnated paper comprises discrete photocatalytic nanoparticles on and in said overlay sheet or décor paper. Said nanoparticles or clusters of nanoparticles may in many applications according to the present invention be of substantially the same size as the effective particle size in said impregnation fluid composition.

[0071] The produced impregnated paper, comprising the photocatalytic nanoparticles, may be used in all known process, to produce laminated building panel, preferably floorboards, wall panels and kitchen tabletops

[0072] The photocatalytic composition to be dispersed in the polymer resin may preferably comprise photocatalytically active nanoparticles of Titania (TiO2). In a preferred embodiment said nanoparticles comprise the anatase and/or the rutile and/or the brookite crystal form of Titania or a combination thereof. Further, said photocatalytically active nanoparticles are according to the present invention predominantly present in their final crystal form in said composition i.e. no heat treatment is required for transformation of said nanoparticles into their active form. The average primary particle size or crystallite size of the nanoparticles, e.g. Titania expressed as an equivalent spherical diameter may preferably be below 30 nm, such as below 20 nm, and preferably below 15 nm, such as below 10 nm. The average primary particle size or crystallite size may be measured by X-ray Diffraction (XRD) using Scherer's formula. It is further preferred that the particle size distribution of said nanoparticles is relatively narrow.

[0073] The photocatalytic composition to be dispersed in the polymer resin, whether it is introduced as a powder, a paste or a suspension, may be added to the polymer resin at any given time. In one embodiment of the invention the photocatalytic composition is dispersed into the polymer resin immediately prior to the impregnation of overlay sheets or décor papers with polymer resin. Said dispersion process may be aided by a specially designed machine or apparatus.

EXAMPLES

[0074] Having described the basics aspects of the invention, the following examples are given to illustrate specific embodiments thereof.

Example 1

Wet in Wet

[0075] This example illustrates the production of a polymeric surface containing embedded nanoparticles. The particles were applied as dispersion via a spray system onto the freshly impregnated polymeric surface while still wet.

[0076] The following dispersion was used as a feedstock. 30% TiO2 dispersion in water containing particle agglomerates of no bigger size than 80 nm as determined using the Particle Matriz Nanotrack NPA 252. The stock solution was then sprayed onto freshly impregnated melamine paper right after the paper had left the impregnation roller. The dispersion was applied onto the paper using an autojet spray system, pumping the fluid to the nozzles via a low pressure tank whit a pressure of 1.8 bar. The nozzles were pulsejet nozzles with air atomizing tips (air pressure 1.5 bar) placed 35 cm above the freshly impregnated paper right in front of the entrance to the first drying oven.

[0077] The autojet system was set to deliver 30 ml fluid/m2 of paper; the paper was then dried in two consecutive heating ovens. This yielded a melamine paper with embedded TiO2 agglomerates of a very small size, penetrating approximately the first couple of hundred micrometers of the melamine paper.

Example 2

Wet on Dry

[0078] This example illustrates the production of a polymeric surface containing embedded nanoparticles. The particles were applied as dispersion via a spray system onto the polymeric surface after this was dried in the heating oven.

[0079] The same liquid and spray system as used in Example 1 was used in this experiment.

Example 3

Wet on Raw Paper

[0080] This example illustrates the production of a polymeric surface containing embedded nanoparticles.

[0081] The particles were applied as dispersion via a spray system onto the raw paper before the paper was impregnated with melamine.

[0082] Test Results

[0083] The table below shows the result of different methods to apply the photocatalytic particles: [0084] Test I: Applying a photocatalytic top layer by impregnation of overlay paper wet-in-wet by spraying. [0085] Test II: Applying a photocatalytic top layer by impregnation of overlay paper wet-on-dry by spraying. [0086] Test III: Applying a photocatalytic top layer by impregnation of overlay paper wet-on-dry by spraying on raw overlay paper before melamine impregnation.

[0087] The appearance, the stability and the distribution are evaluated.

TABLE-US-00001 Treatment Appearance (a) Stability (b) Distribution (c) Blank-Reference 1 1 — Test I: Wet-in-wet 1 1 1 Test II: Wet-on-dry 2 1 3 Test III: Wet-in-dry 4 4 2

[0088] a) The appearance on a scale from 1-5, as judged by transparency and haziness, where 1 is no visible difference from non-embedded laminate and 5 is very hazy.

[0089] b) The process stability was evaluated on a scale from 1-5, as judged by material lifetime and flexibility, where 1 is no difference from non-embedded laminate and 5 is very sensitive to process changes.

[0090] c) The distribution of embedded particles was evaluated on a scale from 1-5, where 1 is complete homogenous distribution of photocatalytic nanoparticles.