AU2011202474B2

AU2011202474B2 - Laminate manufacture with novel solids application

Info

Publication number: AU2011202474B2
Application number: AU2011202474A
Authority: AU
Inventors: David Elwyn Price
Original assignee: Depco TRH Pty Ltd
Current assignee: Depco TRH Pty Ltd
Priority date: 2010-05-26
Filing date: 2011-05-26
Publication date: 2015-05-14
Anticipated expiration: 2031-05-26
Also published as: AU2011202474A1

Abstract

A method of manufacturing a laminate includes coating a substrate with a solvent/resin based slurry having a solids content including resin and colourants of at least 50% by weight of the slurry. The coating is dried to remove the majority of the solvent content 5 thereof within a time period sufficient to substantially avoid diffusion of the slurry into the substrate but without significantly advancing cure of the resin. The dried coating is overlaid with a layer comprising a partially cured resin-impregnated paper or non-woven and/or a slurry containing resin and fibrous material. The slurry is itself thereafter dried to produce a laminated assembly, which is treated to obtain a laminate in which the 10 resin therein is substantially fully cured. m 40 0 10 20 30 40 50 60 70 %TiO 2 Fig.1 TiO2 opacity chart

Description

P/00/0111 Regulaton 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Laminate manufacture with novel solids application The following statement is a full description of this invention, including the best method of performing it known to us: 2 Laminate Manufacture with Novel Solids Application Field of the Invention The invention relates to a method of manufacturing a decorative laminate using high density energy applied immediately after application of a high solids resinous slurry, as 5 well as decorative laminate products manufactured by the method according to the invention. Background of the Invention For the manufacture of decorative laminates, substrates, for example particleboard, fibreboard, orientated strand board (OSB), plywood, or impregnated kraft core paper, 10 are laminated with one or more resin impregnated overlaying papers or resin impregnated non-woven materials on one or both sides of the substrate in a hot press. Textured or smooth press tools or textured papers or composite films provide the desired structure and gloss or matte finish on the finished laminate. The overlaying materials serve as a carrier for a resinous starting material, pigments, additives, print or 15 any subset of those. The overwhelming majority of decor paper is impregnated in a one or 2 bath system during which the solvent mainly water is removed from the impregnated paper and the resin cure advanced to the b-stage. This process is well known in the industry and the majority of impregnation lines are supplied by either Vits Germany or Tocchio Italy. 20 Of the possible ways to decorate the surface of a wood-based panel only the low pressure melamine (LPM) process provides the adhesive and the final chemical resistant surface within the decor paper which under pressure and heat flows into the surface of the board. The step of impregnating the decor paper with resin is an energy intensive process starting with saturating the paper with a water based resin and 25 subsequently using an energy source to remove the majority of the water. The resin is usually manufactured at 60% solids 40% water and before the resin impregnated film can be placed on the board and in the hot press the water content is reduced to within a range of 4 - 7% and the cure of the resin advanced to so-called b-stage. The 3 expression b-stage generally means the polymer chains in the starting resin have grown in length, but have not yet reached the final thermoset point. The amount of energy to remove the water after impregnation and the cost of raw materials are a considerable economic burden in the manufacture of LPM woodpanels. 5 It is generally accepted that there needs to be a proportional combination of raw materials when making d6cor paper that enables adequate opacity and depth of colour from the cellulose fibres, colourant and fillers, and sufficient resin percentage during impregnation to provide the bonding of the paper to the woodpanel and provide a resin surface of the pressed panel that meets the desired technical requirement of mainly a 0 non-porous, chemical resistant surface. From experimentation it has been found that the aforementioned objectives are usually met using the following combinations D6cor paper - a mixture of short and long fibre pulp, usually more short fibre than long fibre. Basis weight usually ranges between 60 gsm to 120 gsm. 5 Colouration - usually measured as ash content, usually <20% for black, 20 - 30% for unicolours & print base paper, and > 30% for white, and due to colourant / filler retention issues in the papermaking process the ash content usually does not exceed 45%. The major colourants are titanium dioxide (TiO 2 ) and iron oxides. The high specific gravity of these type of colourants contributes to the difficulty of retention in the papermaking 20 process wherein the mass of material applied from the paper machine headbox to the wire section is usually about 98% water. Retention chemicals and control of parameters such as zeta-potential assist in the retention of the colourants which otherwise are lost in the wastewater or directed through a recovery loop. Resin - impregnation of an interior carcass white grade of decor paper of 75gsm is 25 usually a 2 resin system to reduce costs. Less expensive urea formaldehyde (UF) resin is employed for a first saturation where the resin forces the entrapped air out of the paper. The amount of UF resin is usually 40 - 60gsm and to enable fast and full saturation the water content of the UF resin is 45 - 55% and the resin mixture contains 4 a wetting agent and a catalyst. An advantage in using UF resins in the first impregnation step is that UF resins generally impregnate faster than melamine formaldehyde (MF) resin. After the decor paper has been saturated with UF resin it is partially dried and a coating of MF resin is applied to both sides of the UF impregnated paper. The reasons 5 for 2 side coating are that after the MF coating is dried the impregnated coated paper is cut into sheets and the sheets stacked for later use. The UF resin is hygroscopic and if not coated with MF resin will cause blocking, which is when several sheets stick together. The b-stage impregnated decor paper requires sufficient MF on the surface to provide a non-porous chemical resistant layer. Too little MF and there is a risk of the UF 10 core resin which is not chemical resistant bleeding through. The current practice is to have approximately 35gsm MF applied asymmetrically with 20gsm on the d6cor side and 15gsm on the board side. However if the film is not going to be turned, as may be the case with a carcass white decor paper, then both sides of the UF resin impregnated film are about 20gsm of MF resin. The total resin applied in the known paper 15 impregnation process is in the range of 100 to 120% of the paper weight, meaning 75gsm - 90gsm for a 75gsm paper. To obtain sufficient opacity in an economic sense and using TiO 2 as the opacifying medium the % TiO 2 to the total weight of the impregnated paper must be around 18 - 20%. See Fig. 1 for the chart of TiO 2 opacity. Examples of this % TiO 2 are 20 Decor paper #1: 75gsm with 35% ash = 26.25gsm TiO 2 plus 100% resin = 75g + 75g = 150gsm TiO 2 of 26.25g / 150g = 17.5% TiO 2 of total mass If 3gsm TiO 2 is substituted into the resin, then 25 TiO 2 of 29.25g / 150g = 19.5% TiO 2 of total mass 5 Decor paper #2: 80gsm with 40% ash = 32gsm TiO 2 plus 120% resin = 96g + 80g = 176gsm TiO 2 of 32g / 176g = 18.2% TiO 2 of total mass 5 If 3gsm TiO 2 is substituted into the resin, then TiO 2 of 35g / 176g = 19.9% TiO 2 of total mass It is known from European patent 1595718, and from International patent publication W02009/109003 that resins can also be applied directly to the surface of a woodpanel and partially cured. The resin envisaged in EP1595718 is a waterless dual cure resin 10 which may first be cured by UV radiation and later finally cured in a hot press. International patent publication W02010/048668 discloses applying resin (preferably UF) to a solid substrate, and then placing an overlay paper on which there is a further MF resin layer. Partial curing of the two resin layers may be effected before final treatment in a hot press. NIR is mentioned as enabling drying without significant curing 15 of the resin. It is not admitted that any of the information in this specification is common general knowledge, or that the person skilled in the art could be reasonably expected to have ascertained, understood, regarded it as relevant or combined it in anyway at the priority date. 20 It would be of great economic advantage if less water and less mass could be used to produce a LPM surface with technical and optical properties as achieved by the current state of the art process. Summary of the Invention This invention entails a realization that a satisfactory laminated end product can be 25 obtained by coating the required substrate with a resin slurry more laden with solids including colourants (with higher specific gravity than the resin solids) than is conventional in paper impregnation practice, rapidly drying the slurry without 6 significantly advancing cure of the resin, and then applying either a resin impregnated paper or non-woven or a further, fibrous, layer to the coating to provide a laminate assembly for final curing. The invention accordingly provides a method of manufacturing a laminate, comprising: 5 coating a substrate with a solvent/resin-based slurry having a solids content including resin and colourants of at least 50% by weight of the slurry; drying the coating to remove the majority of the solvent content thereof within a time period sufficient to substantially avoid diffusion of the slurry into the substrate but without significantly advancing cure of the resin; 10 overlaying the dried coating with a layer comprising a partially cured resin impregnated paper or non-woven and/or a slurry containing resin and fibrous material which slurry is itself thereafter dried, whereby to produce a laminated assembly; and treating the laminated assembly so as to obtain a laminate in which the resin 15 therein is substantially fully cured. The invention extends to a laminate made by the method of the invention. Embodiments of the Invention Preferably, a major proportion, e.g. greater than 50% and more preferably greater than 75%, most preferably 100% of the colourant in the end product is applied by the coating 20 step. The solvent may be water. The colourants may comprise one or more metal oxides, for example and typically titanium dioxide (TiO 2 ) and/or iron oxides. By employing this method, and by preferably using a suitable high density energy such as near infrared (NIR) or microwave radiation for the drying step in combination with a 7 low cost water-based resin for the coating, it is possible to significantly reduce the total mass that is required to obtain the desired opacity, depth of colour and technical surface characteristics in the end-product laminate. It is also possible to substantially reduce overall water and thereby energy usage relative to the aforedescribed current LPM 5 process. In an embodiment, these results are achieved by mixing an amino resin with a high proportion of colourants and or fillers to form a high solids slurry and immediately after applying the high solids slurry to the board applying high density energy to the slurry to remove the water content without significantly advancing the cure of the resin. This is 10 preferably done by using high density electromagnetic radiation in the near infrared wavelength immediately after the application of the water based high solids content slurry onto the board. Application of the high density energy to remove the solvent is preferably an inline process to minimize the time between the application of the slurry and the application of 15 the energy, thereby avoiding or minimizing diffusion of the slurry deeply into the woodpanel surface. An example would be that with a space of 1 metre between the application of the slurry and the application of the energy, and at a line speed of 60 metres per minute, the time lapse between application of the slurry and application of the energy is 1 second. Higher line speed or a shorter gap will reduce the dwell time 20 before the high density energy volatilizes the water from the slurry. By NIR is meant herein electromagnetic radiation in the wavelength range from 0.8 to 2.5pm. The preferred NIR source comprises one or more NIR emitters of the halogen type operating at >50% power, more preferably >70% power. The resins employed in the coating step and/or in the paper or overlay paper or non 25 woven are preferably amino resins. By amino resin is meant any combination of formaldehyde with one or more of urea or melamine. Suitable resins include urea formaldehyde (UF), melamine formaldehyde (MF), MUF, phenol formaldehyde (PF) or tannin formaldehyde (TF) Phenol or tannin may be added to the amino resin, or used as the coating resin.

8 The solids content of the resin based slurry is preferably at least 50% by weight, better at least 60%, more preferably at least 65%, most preferably 70% or higher. Such a high solids amino resin slurry would not be able to saturate a d6cor paper at high line speeds employed in modern impregnation machinery nor could the colourants with high specific 5 gravity be able to be easily kept in suspension, however it is possible to apply it to the surface of a substrate such as a woodpanel and by using high density NIR radiation immediately after the slurry has been applied the water is removed before the slurry can penetrate deeply into the surface of the woodpanel and the cure of the resin is only slightly advanced due to the very low amount of time the resin is exposed to the high 10 density NIR radiation. An example of a "very low amount of time" in this context is as follows: by using near infrared emitters that are 25cms long and positioned parallel to the direction of the substrate, and moving the substrate at 60 metres per minute, there is direct line of contact with the emitted radiation for 0.25 sec. Alternatively the NIR emitter may extend across the line of travel. 15 In general, the aforementioned time period of the drying step is preferably less than 5 seconds, more preferably 1 second or less. The substrate is preferably a woodpanel such as particleboard, fibreboard, orientated strand board, plywood, or impregnated kraft core paper. The overlaying layer may be an amino resin containing colourant, filler or fibrous 20 material or any combination of these. The method may be applied to both sides of the substrate to provide a coating on both sides. The resin employed in the coating step may be a urea formaldehyde (UF) resin. The partially cured resin-impregnated paper or non-woven may be a paper or non 25 woven impregnated with melamine formaldehyde (MF) resin, advanced to b-stage. The final treatment may typically entail placement of the laminated assembly in a hot press and under pressure to fuse the assembly to make the final product.

9 The layer overlayed on the dried coating may comprise a slurry of a second amino resin with additives such as a colourant, fillers and fibrous material which may be applied directly over the dried first amino resin slurry and itself dried and partially cured using high density NIR radiation or an alternative source of energy. Other combinations of 5 slurry and fibrous material are also practical. The fibrous material may be, e.g. cellulose, synthetic polymers or glass, or any combination of these. It is also practical that the woodpanel having been coated with the first slurry and immediately afterwards dried, is then printed. Printing may be by any known means, for 10 example but not limited to flexographic or inkjet. It is preferred that a primer or print receptive layer is applied before the printing process. To provide a hard, non-porous surface with a smooth or textured, gloss or matte surface finish, the coated woodpanel and optionally a paper or non-woven impregnated with melamine formaldehyde resin are placed in a hot press and under pressure the final 15 panel surface is achieved. Usual parameters in the hot press are: temperature between 150 0 C and 210 0 C, pressure between 25 and 45 bar, and dwell time usually between 10 - 35 seconds. The range of parameters has to be broad as there are many old presses in operation which are not able to operate as efficiently as a modern short cycle or continuous press. 20 As used herein, except where the context requires otherwise the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude other additives, components, integers or steps.

10 Example 1 A slurry of 40g water, 60g UF resin & 20g TiO 2 = 66.6% solids was applied to a 16mm particleboard. The majority of the water was vapourized using NIR emitters operating at 100% power with a distance between the NIR emitters and the substrate particleboard 5 of 50mm, leaving approximately 80gsm solid matter on or at the surface of the particleboard. A decor paper 50gsm @ 20% ash = TiO 2 of 10gsm impregnated with 20g MF resin advanced to b-stage was applied onto the coated particleboard and pressed in a hot 10 press to achieve the desired final curing and surface texture. The ratio of TiO 2 being 30g / 150g = 20% TiO 2 of total mass provided desired opacity and the MF surface resin the desired technical features of the laminate surface.

Claims

1. A method of manufacturing a laminate, comprising: coating a substrate with a solvent/resin-based slurry having a solids content including resin and colourants of at least 50% by weight of the slurry; 5 drying the coating to remove the majority of the solvent content thereof within a time period sufficient to substantially avoid diffusion of the slurry into the substrate but without significantly advancing cure of the resin; overlaying the dried coating with a layer comprising a partially cured resin impregnated paper or non-woven and/or a slurry containing resin and fibrous 10 material which slurry is itself thereafter dried, whereby to produce a laminated assembly; and treating the laminated assembly so as to obtain a laminate in which the resin therein is substantially fully cured.

2. A method according to claim 1 wherein a proportion greater than 50% of the 15 colourant in the end product is applied by the coating step.

3. A method according to claim 2 wherein said proportion is greater than 75%.

4. A method according to claim 1, 2 or 3 wherein the colourants comprise one or more metal oxides such as titanium dioxide (TiO 2 ) and/or iron oxides.

5. A method according to any preceding claim wherein said drying is effected by 20 application of near infrared (NIR) or microwave radiation.

6. A method according to any preceding claim wherein the heating step is an inline process to minimize the time between the application of the slurry and the drying step, thereby avoiding or minimizing diffusion of the slurry deeply into the substrate surface. 12

7. A method according to claim 6 wherein the drying is effected by application of NIR or microwave radiation, and the time lapse between application of the slurry and application of the energy is less than 5 seconds.

8. A method according to any preceding claim, where resins employed in the 5 coating step and/or in the paper or overlay paper or non-woven are amino resins.

9. A method according to any preceding claim when the solids content of the resin based slurry is preferably at least 60% by weight.

10. A method according to any preceding claim wherein the duration of the drying step is less than 5 seconds. 10

11. A method according to any preceding claim wherein the duration of the drying step is 1 second or less.

12. A method according to any preceding claim wherein the substrate is a woodpanel.

13. A method according to any preceding claim wherein the resin employed in the 15 coating step is a urea formaldehyde (UF) resin.

14. A method according to any preceding claim wherein the layer overlayed on the dried coating comprises a slurry of a second amino resin with additives including a colourant, fillers and fibrous material.

15. A method according to claim 14 wherein the second amino resin is applied 20 directly over the dried first amino resin slurry and itself dried and partially cured.

16. A method according to any preceding claim wherein the fibrous material is cellulose, synthetic polymers or glass, or any combination of these.

17. A method according to any preceding claim wherein the substrate after drying of the first coating is then printed. 13

18. A method according to any preceding claim wherein the overlaying layer is an amino resin containing colourant, filler or fibrous material or any combination of these.

19. A method according to any preceding claim wherein the final treatment includes placing the coated substrate and optionally a paper or non-woven impregnated with 5 melamine formaldehyde resin in a hot press whereby under pressure a final panel surface is achieved.

20. A method according to any preceding claim carried out on both sides of the substrate.