Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-12-29
2002-10-15
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S062200, C156S331400, C156S331700, C264S109000
Reexamination Certificate
active
06464820
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for making compression molded or pressed lignocellulosic articles by adding a binder resin including a parting agent to lignocellulosic particles and thereafter either pressing the mixture between plates or compressing it in a mold at an elevated temperature and pressure and, more specifically, a method for making compression molded or pressed boards using a binder resin comprising a polyisocyanate component, a parting agent 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) agrifiber board (such as straw board or 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 parting 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.
The lignocellulosic particles can be in the form of chips, shavings, strands, wafers, fibers, sawdust, bagasse, 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 panels, 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 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 property 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. This high viscosity also requires that excess binder be used to fully coat the particles.
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. The isocyanate binder compositions with dialkyl carbonates are reported to have a lower viscosity than the free isocyanates, leading to advantages in their use in the process.
In the above examples, however, the use of the solvent system does 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 is therefore an object of the present invention to provide a solvent system for an isocyanate binder composition, which will not only act as a diluent but also increase the efficiency of the binder resin when it is used to coat or contact lignocellulosic particles prior to pressing at high temperature and pressure.
Another common disadvantage of the use of isocyanate binder resins is their poor release properties from molds or press parts used to form lignocellulosic articles, which can lead to problems during manufacture of the lignocellulosic articles when the mold or press parts stick to the articles.
To overcome the sticking, it is desirable to use a parting agent either internally as a component of the binder resin, or externally by applying it to the press parts between runs. External parting or release agents are less preferred because their use involves the extra step of applying the agents to the press parts.
It is therefore, an object of the present invention to provide a parting agent for an isocyanate binder resin, which will not only display the desired parting properties but will also be compatible with an isocyanate binder resin.
SUMMARY OF THE INVENTION
In one embodiment, the present invention is a method for preparing a compression molded or pressed lignocellulosic article comprising the steps of: forming a binder resin by combining from about 75 to 99.5 weight percent based on the total weight of the binder resin of a polyisocyanate component with from about 25 to 0.5 weight percent based on the total weight of the binder resin of a parting agent, comprising the reaction product of an isocyanate compound and an isocyanate-reactive compound of the general structure
R—(ao)
n
Y
wherein R is a hydrophobic group containing alkyl, alkaryl, polyaryl, or siloxane moieties, wherein the alkyl moieties comprise straight chain or branched hydrocarbons with 6 or more carbon atoms, the alkaryl moieties comprise monoalkyl, dialkyl, or trialkyl substituted aromatic hydrocarbons with 9 or more carbon atoms, the polyaryl moieties comprise a polyphenyl structure that is either alkyl substituted or unsubstituted, and the siloxane moieties comprise a trisiloxane or higher polysiloxane; (ao) is an alkylene oxide or mixture of alkylene oxides selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, and mixtures thereof; n is from 1 to 25; and Y represents a monofunctional isocyanate-reactive group. In a second step a resinated lignocellulosic mixture is formed by combining from about 1 to 10 weight percent based on the total weight of the lignocellulosic mixture of the binder resin with from about 99 to 90 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. Then a compression molded or pressed lignocellulosic article is formed by compressing the resinated lignocellulosic mixture at an elevated temperature and under pressure. It is particularly preferred that the binder resin further include a synergist selected from the group consisting of C
1-4
N-alkylpyrrolidones, gamma-butyrolactone, and mixtures thereof. The most preferred synergist is N-methyl-2-pyrrolidine.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
In accordance with the present invention there is disclosed a process that utilizes an isocyanate binder resin for the preparation of lignocellulosic articles. The binder resin comprises an organic di- or polyisocyanate, a parting agent and optionally, a synergist selected from the group consisting of C
1
-C
4
N-alkyl pyrrolidones, 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 specifi
Lu Li-Mei
Mente Donald C.
Peters David D.
Schaefer Anthony G.
Wilson Joe C.
BASF Corporation
Borrego Fernando A.
Yao Sam Chuan
LandOfFree
Binder resin and synergist composition including a parting... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Binder resin and synergist composition including a parting..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Binder resin and synergist composition including a parting... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2969548