Coating processes – Application to opposite sides of sheet – web – or strip – Roller applicator utilized
Reexamination Certificate
1999-03-12
2003-08-26
Bareford, Katherine A. (Department: 1762)
Coating processes
Application to opposite sides of sheet, web, or strip
Roller applicator utilized
C427S172000, C427S207100, C427S348000, C427S358000, C427S359000, C427S361000, C427S391000, C427S209000, C156S278000, C156S307400
Reexamination Certificate
active
06610358
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the manufacture of laminated products such as may be used for decorative flooring, counter and table tops, and wall panels, and more specifically to systems and methods for manufacturing such products by applying a coating of the same or different materials on opposing sides of a laminate material.
BACKGROUND
The ability to replicate natural materials has substantially improved over the years. For example, decorative laminates have replaced natural materials in the construction of furniture, cabinets, counter tops, flooring panels and other surfaces. In each of these applications, a decorative surface may be applied to a core layer or substrate, namely, plywood, particle board, chipboard, medium density fiberboard, etc. Often, a backing layer is secured to the opposite surface of the substrate to balance the laminates or provide other benefits.
Generally, the decorative surface and the backer layer will include one or more kraft paper layers which are adhesively laminated together using various materials, such as melamine formaldehyde and phenolic resins. As shown in
FIG. 1
, a high pressure laminate
11
may comprise a very thin overlay sheet
12
impregnated with melamine resin, a decorative sheet
13
disposed thereunder, and sheets
14
and
15
of kraft paper impregnated with phenolic resin disposed below the decorative sheet.
The melamine impregnated overlay sheet
12
forms a hardened layer on the surface of the decorative sheet. This hardened layer of the decorative laminate is used to protect the surface of laminate
11
, such as by making the laminate scratch and abrasion resistant. The melamine impregnated overlay also prevents discoloration or deformity of the laminate surface due to various external factors, such as high pressure and temperature and other ordinary stresses which occur in the environment where such laminates are typically used. Furthermore, the overlay sheet is also capable of easily withstanding the thermal or chemical strains occurring in these environments. For example, the melamine overlay sheet protects the laminate from discoloring when a very hot substance, such as tea or coffee, or a very cold substance, such as ice, spills on the surface of such a laminate. Thus, the melamine coating can withstand the very high and very low temperatures to which the laminate is exposed in everyday use.
However, the overlay sheet
12
itself may cause warping of the laminate panel under extreme hot, cold, or dry conditions. The conventional substrate or core layer
16
may not be able to withstand the pressure created by the movement of the melamine overlay of the decorative surface under these extreme conditions and may deform, delaminate, or in extreme cases, break due to the pressure exerted by the melamine overlay layer
12
. Therefore, backer type laminates may be used for many applications, such as to provide balancing sheets on the bottom of decorative laminates. These backer laminates may comprise a discrete melamine impregnated balancing layer
19
to balance the melamine layer of the decorative surface, and sheets of phenolic resin impregnated kraft paper
17
and
18
to correspond to the layers in the decorative laminate. The balancing layer
19
used in prior art systems is similar to the overlay sheet
12
of the decorative surface and uses the same material as the overlay sheet. However, the balancing layer
19
may or may not be transparent as it is usually not visible.
12
. The discrete melamine impregnated balancing layer
19
when used in a backer laminate prevents warping of the laminate due to the movement of the melamine layer
12
of the decorative surface under extreme conditions.
Typically, in prior art systems, sheets of kraft paper are impregnated with phenolic resin by submerging them in a vat which is filled with phenolic resin and then curing the phenolic resin impregnated kraft paper. The kraft paper soaks up a desired amount of phenolic resin based on the time it is left in the vat and the level of submergence. This method of impregnating the kraft paper is generally not cost effective as it requires large vats providing substantial resin pool surface areas in order to allow the proper immersion of a portion of a continuous roll of kraft paper. These large pool surface areas result in wasteful use of phenolic resin as the large vat surface area is prone to collection of contaminants and to the escaping of resin vapors thus causing variations in the percentage of solids and/or other controlled attributes of the resin requiring substantial portions of the resin to be disposed of from time to time. Moreover, when the resin impregnated kraft paper is being manufactured using such vats, fumes are created during the process which are harmful to the workers in the vicinity of the manufacturing process. All of this is compounded by the fact that such vats of phenolic resin, or other resins, are difficult to clean requiring an inordinate amount of time to properly clean the vats that have been used for impregnating the kraft sheets with phenolic resin.
The melamine impregnated sheet used in the decorative and backer layers is usually not a kraft paper sheet but rather a very thin sheet specifically adapted, such as by controlling strand orientation, density, and porosity to carry the melamine resin. Kraft paper sheets are typically not suitable to act as a carrier for melamine because the porosity, strand orientation, and density of kraft paper sheets are not adapted for this purpose although they are well suited for phenolic resin impregnation. Typically, a suitable sheet is impregnated with melamine by coating both sides of the sheet with melamine formaldehyde resin and then removing excess resin from the sheet. The melamine formaldehyde coated sheet is cured under controlled conditions to produce the melamine impregnated sheet which may be used both in decorative and backer laminates.
The laminates which are manufactured by using the phenolic resin impregnated kraft paper sheets and the melamine impregnated sheets as described above are made by a bulky manufacturing press which is expensive to operate. Thus, it is not cost effective or desirable to use the press to produce individual laminates. Therefore, in the typical manufacturing process a plurality of laminates are produced from each press during each press cycle to make the most efficient use of the press.
Typically, in such a press system pairs of laminate assemblies, similar to the laminate assembly shown in
FIG. 1
, with or without pattern layer
13
, are positioned back-to-back with the phenolic resin impregnated kraft paper sheet
15
of one laminate assembly facing the phenolic resin impregnated kraft paper sheet of a second laminate assembly with a discrete release sheet disposed there between as described below. These pairs of laminate assemblies are separated from other laminate assembly pairs by metal sheets or press plates. Usually during the manufacturing process each laminate assembly
11
also includes a sheet, known as release sheet. The release sheet is usually kraft paper which has been coated with a release agent on at least one side. This release sheet is placed at the end of each laminate assembly adjacent to the phenolic resin impregnated kraft paper layer
15
away from the press plates to provide a release mechanism between the paired laminate assemblies. The release sheet facilitates easy separation of the laminate assemblies after pressing as the release agent will not allow cross linking of the laminate assemblies at least with respect to the side of the laminate assembly to which the release sheet is applied.
Typically these laminate assemblies are subjected to a pressure and temperature for a time sufficiently long enough to cure the laminating resins impregnating the respective layers. The high temperatures and pressure cause the resins within the sheets to flow which consolidates the whole into an integral mass. Thus, typically the discrete melamine layer sticks to the phenolic resin
Mafoti Robson
Marshall Donald M.
Soudelier Earl
Williams Joel Lane
Bareford Katherine A.
Fulbright & Jaworski L.L.P.
Premark RWP Holdings Inc.
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