Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1996-07-16
2002-04-23
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S278000, C156S310000, C156S312000, C428S530000
Reexamination Certificate
active
06375788
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to substantially fully cured melamine formaldehyde resin coated decorative paper that can be adhesively bonded to particle board or other structural substrate. Resin on a decorative surface of paper is cured under temperature and pressure conditions for improving the wear characteristics of the paper without substantially reducing the capability of adhesively bonding the paper to structural substrate. Melamine formaldehyde resin coated decorative paper adhesively bonded to structural substrate is a decorative structural material with good stain and wear characteristics.
2. Description of the Related Art
Melamine resin impregnated decorative paper is commercially laminated to phenol formaldehyde resin impregnated kraft paper and liner board substrate for making high pressure laminate. Melamine resin impregnated decorative paper is also commercially laminated to particle board and other structural substrate for making low pressure laminate. Melamine resin in the impregnated decorative paper flows under laminating temperature and pressure conditions for bonding melamine resin impregnated decorative paper and substrate. Overlay paper impregnated with melamine resin can be laminated over decorative paper for improving the wear characteristics of the laminate. Overlay impregnated with melamine resin can be laminated over decorative paper that is not impregnated with resin. Melamine resin in the impregnated overlay flows under laminating temperature and pressure conditions for bonding overlay impregnated with melamine resin and non impregnated decorative paper. Melamine resin is clear when fully cured and has stain and wear characteristics that has made it the resin of choice for many commercially available laminates. Resistance to discoloration due to heat and light is also realized.
Melamine resins give a thorough impregnation and thereby insure a complete bond when employed in the production of laminates. Melamine resins have been used in the production of decorative, high pressure laminates wherein a plurality of phenolic resin impregnated kraft paper sheets have been used as a laminate core to which is bonded melamine resin impregnated decorative and overlay paper. These laminates are then adhesively bonded to a rigid substrate and used as partitions, walls, doors, table and counter tops, etc. Laminated panels that can readily be fabricated into furniture, kitchen cabinets and the like are produced by applying a single melamine resin impregnated decorative paper to a particleboard substrate at much lower pressure. These laminate panels have been designated “low pressure” panels. (U.S. Pat. No. 4,076,896, Bunkowski)
Decorative paper is made from bleached wood pulp that is at least 60% in alpha cellulose content. Decorative paper is pigmented in a known manner to obtain the desired levels of color and opacity. They range in basis weight from about 50-90 pounds per 3,000 square foot ream. The paper has a controlled pH due to the influence pH has on the reaction rate of the melamine resin after it is applied thereto. Variances in this pH range have adverse effects on the storage life of the treated paper and/or press cycle times when the panel is being produced. Porosity is controlled to assure proper treating of the paper with the resin and pressing of the panel. A paper having too high a porosity will allow too much resin to penetrate and will result in dry spots on the panel produced therefrom. A paper with too low a porosity will not enable sufficient resin to penetrate and the excessive resin on the surface will cause a mottled appearance and surface crazing and/or cracking of the resultant panel made therefrom. (U.S. Pat. No. 4,076,896, Bunkowski)
Impregnation of the paper and drying of the impregnated paper may be effected by conventional treaters and dryers known to those skilled in the art. The resin content of the impregnated paper generally ranges from about 55% to about 65% by weight based on the weight of the impregnated paper. Paper volatile levels are maintained at about 5%±0.5%. A balance between flow levels and treated weight of the treated paper is maintained to assure proper abrasion levels without reducing crack and/or craze resistance. Treated paper is beta-staged by drying at 150-360° F. for about 1 to about 15 minutes, and stored flat in a conditioned storage area. It has a nominal shelf life of at least about 3 months at 70-75° F. and 40-50% relative humidity. (U.S. Pat. No. 4,076,896, Bunkowski)
Core material, i.e., self-supporting substrates useful in producing the decorative low-pressure panels include medium density, mat-formed, wood particleboard and medium density, wood fiberboard. Useful core material, however, must enable the production of full-sized, smooth-faced, well-bonded, crack- and craze-resistant panels. Core materials should be stored for a sufficient time at ambient conditions to achieve an equilibrium temperature and an equilibrium moisture content of 7%±2%. (U.S. Pat. No. 4,076,896, Bunkowski)
The decorated layer may be placed on both sides or only on one side of the self-supporting substrate when panels are being produced. If the decorative sheet is placed only on one side of the substrate, it is preferred that a so-called balance sheet, i.e., a melamine-formaldehyde resin impregnated paper sheet, e.g. of kraft or other paper, sometimes called a cabinet liner, be placed on the other side in order to prevent the resultant panel from warping during pressing. (U.S. Pat. No. 4,076,896, Bunkowski)
In the formation of high pressure laminates, a decorative or print layer is superimposed upon a conventional, phenolic resin-impregnated core, and with a melamine type resin-impregnated overlay disposed protectingly thereupon. The formed stack is then loaded between the polished metal plate of a hydraulic press that is then closed and subjected to a sufficient pressure and heat for an adequate period of time for fusing the stack into a single sheet. A paper suitable for the decorative layer of laminate has requisite porosity for bleeding therethrough of the resins of the core and the overlay during fusing but without necessitating prior impregnation of said layer. For optimum laminate strength the decorative layer must absorb the resins from the overlay and the core to form durable adhesive bonds therewith. (Meiser, U.S. Pat. No. 3,816,232 and Santurri, et. al., U.S. Pat. No. 3,949,133)
In the making of laminated cement forming materials, precured bonded laminate overlay is formed and adhered to an underlying solid substrate. Thermosetting resin in the overlay is substantially cured prior to contact with the underlying substrate. The overlay is formed between two nearly perfectly smooth surfaces. Curing causes the resin material to become thermoset, thereby establishing a fixed final structure. Adhering the precured bonded laminated overlay to solid substrate may be accomplished through the use of pressure and adhesive alone. It is preferred that both pressure and heat be employed to ensure a more secure adhesion. In order to obtain proper adhesion in a hot press between the precured bonded laminate overlay and the solid substrate, a low water content adhesive must be applied between them. While many commercially available adhesives may be employed, a paper glue line sold under the trade name Plyocite PGL (Product No. 42-206) by Reichhold Chemicals, Inc. of Tacoma, Wash. has proven quite satisfactory for such use. Paper glue line consists of an extremely thin sheet of cellulose impregnated with a high amount of resin. Consequently, the paper glue line possesses the adhesion properties of production grade glue, but with a much lower water content. This lower water content is required or blisters will be formed beneath the surface of the overlay, thereby causing improper bonding and potential surface irregularities on the outside surface of the overlay. It is important that the laminate overlay of the present invention is substantially cured separately, away fro
Gaa Peter C.
Lay Timothy J.
Ma Muyuan M.
Oliver Jay T.
Gallagher John J.
Premark RWP Holdings Inc.
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