Process of making lignocellulosic articles

Details Process of making lignocellulosic articles Process of making lignocellulosic articles

2002-08-20

2003-11-18

Lechert, Jr., Stephen J. (Department: 1752)

Plastic and nonmetallic article shaping or treating: processes

Forming articles by uniting randomly associated particles

C264S128000, C264S331110, C264S331120

Reexamination Certificate

active

06649098

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method for making compression molded or pressed lignocellulosic articles and, more specifically, a method for making compression molded or pressed boards using a binder resin comprising a polyisocyanate component and a synergist component.
BACKGROUND OF THE INVENTION
It is known to make compression molded or pressed lignocellulosic articles, such as particle board, Medium Density Fiberboard (MDF), agriboard (such as straw board, bagasse, etc.), and oriented strand board, by coating or contacting lignocellulosic particles with a binder resin to form a lignocellulosic mixture, optionally adding other additives including release agents or wood preservatives and compressing the mixture at elevated temperatures and pressures for a time sufficient to make commercially useful articles, such as, boards and panels.
The lignocellulosic particles can be in the form of chips, shavings, strands, wafers, fibers, sawdust, straw, and wood wool. When the particles are relatively larger in size, the boards produced by the process are known in the art under the general term of engineered wood. These engineered woods include laminated strand lumber, oriented strand board, parallel strand lumber, and laminated veneer lumber. When the lignocellulosic particles are relatively smaller, the boards are known in the art as particleboard and fiber board.
The engineered wood products were developed because of the increasing scarcity of suitably sized tree trunks for cutting lumber. Such products can have advantageous physical properties such as strength and stability. Another advantage of the engineered wood and particle boards and panels is that they can be made from the waste material generated by processing other wood and lignocellulosic materials. This leads to efficiencies and energy savings from the recycling process, and saves landfill space.
The binder used to make the lignocellulosic articles is typically a resinous material. One common class of binders are resins produced by polymerizing formaldehyde with other resin forming monomers, including urea, melamine, and phenol. In certain applications, articles made with such binders are deficient in some properties such as water resistance.
Another class of binders are the organic diisocyanate or polyisocyanate binders. One of the advantages of this class is its superior resistance to water. A disadvantage of the typical isocyanate binders is their relatively high viscosity, which can lead to problems with delivery of the binder onto the particles, and with wet out of the binder onto the particles. This high viscosity also requires that excess binder be used to fully coat the particles. Also these binders tend to ooze out of the particles during compression and are deposited on parts of the mold leading to further processing difficulties.
In the past various solvents have been added to the polyisocyanate binder compositions with the aim of achieving a lower viscosity and better handling properties. After application, the solvent generally evaporates during the molding process, leaving the bound particles behind. One major disadvantage of prior art solvents is that they cause a reduction in the physical properties of the formed board including a reduction in the internal bond strength of the formed board.
For example, it is known to use dialkyl carbonate solvents in isocyanate binder compositions for coating lignocellulosic particles prior to compression at high temperature and pressure to make manufactured lignocellulosic articles.
However, the use of these solvent systems do not lower the amount of isocyanate binder composition required for achieving best results, also the solvent systems generally lower the physical properties of the produced board.
It would therefore be advantageous to provide a synergist for a polyisocyanate binder resin, which will not only lower the viscosity of the binder resin but will also increase or maintain the efficiency of the binder resin when it is used to form lignocellulosic articles.
SUMMARY OF THE INVENTION
One embodiment of the present invention is a method for preparing a compression molded or pressed lignocellulosic article comprises the steps of: forming a binder resin by combining from about 75 to 98.0 weight percent based on the total weight of the binder resin of a polyisocyanate component with from about 25 to 2.0 weight percent based on the total weight of the binder resin of a synergist component selected from the group consisting of a C
1
to C
4
N-alkyl pyrrolidone, gamma-butyrolactone, and mixtures thereof; forming a resinated lignocellulosic mixture by combining from about 1 to 20 weight percent based on the total weight of the lignocellulosic mixture of the binder resin with from about 99 to 80 weight percent based on the total weight of the lignocellulosic mixture of lignocellulosic particles, the lignocellulosic particles having a moisture content of from 2 to 15 weight percent; and forming a compression molded or pressed lignocellulosic article by compressing the resinated lignocellulosic mixture.
In another embodiment, a method for preparing a compression molded or pressed lignocellulosic article comprises the steps of: forming a binder resin by combining from about 75 to 98.0 weight percent based on the total weight of the binder resin of a polyisocyanate component selected from the group consisting of diphenylmethane-2,2′-diisocyanate, diphenylmethane-2,4′-diisocyanate, diphenylmethane-4,4′-diisocyanate, polymeric diphenylmethane-diisocyanate, and mixtures thereof with from about 25 to 2.0 weight percent based on the total weight of the binder resin of a synergist component selected from the group consisting of a C
1
to C
4
N-alkyl pyrrolidone, gamma-butyrolactone, and mixtures thereof; forming a resinated lignocellulosic mixture by combining from about 1 to 20 weight percent based on the total weight of the lignocellulosic mixture of the binder resin with from about 99 to 80 weight percent based on the total weight of the lignocellulosic mixture of lignocellulosic particles, the lignocellulosic particles having a moisture content of from 2 to 15 weight percent; and forming a compression molded or pressed lignocellulosic article by compressing the resinated lignocellulosic mixture.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
In accordance with the present invention there is disclosed a method that utilizes a polyisocyanate binder resin for the preparation of compression molded or pressed lignocellulosic articles. The binder resin comprises a polyisocyanate component and a synergist component selected from the group consisting of a C
1
-C
4
N-alkyl pyrrolidone, gamma-butyrolactone, and mixtures thereof. Throughout the present specification and claims the terms compression molded or pressed are intended to refer to the same process whereby the article is formed by either compression molding the article in a mold or by using compression as between a pair of plates from a press. In both procedures pressure and heat are used to form the article and to set the binder.
In the present specification and claims the term polyisocyanate component is intended to include a single polyisocyanate and mixtures of polyisocyanates. The polyisocyanate component which may be used includes aliphatic, alicyclic and aromatic polyisocyanates characterized by containing two or more isocyanate groups. Such polyisocyanates include the diisocyanates and higher functionality isocyanates, particularly the aromatic polyisocyanates. Mixtures of polyisocyanates may also be used and include, crude mixtures of di- and higher functionality polyisocyanates produced by phosgenation of aniline-formaldehyde condensates or as prepared by the thermal decomposition of the corresponding carbamates dissolved in a suitable solvent, as described in U.S. Pat. No. 3,962,302 and U.S. Pat. No. 3,919,279, the disclosures of which are incorporated herein by reference, both known as crude diphenylmethane diisocyanate (MDI) or polymeric MDI. The org

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