Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-04-05
2003-10-21
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S014000, C524S487000, C524S489000
Reexamination Certificate
active
06635695
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an adhesive composition for lignocellulose-type hot-pressed forms (hot-pressing formed articles) which is comprised of an organopolyisocyanate and a wax emulsion, and also relates to a process for producing hot-pressed forms by using such a composition. More particularly, this invention relates, in the manufacture of hot-pressed forms making use of lignocellulose materials, to an adhesive composition having superior performances on releasability and resistance to hot water, and a process for producing hot-pressed forms by using such a composition.
2. Related Background Art
As adhesives for hot-pressed forms (boards such as particle boards and medium-density fiber boards) of lignocellulose materials such as wood chips and wood fibers, formalin-type adhesives of urea resin, melamine resin, urea melamine resin, phenolic resin or phenolic melamine resin have conventionally been used. However, as is seen in recent problems of, e.g., the sick building syndrome, it has become necessary to reduce formalin released from adhesives. As adhesives that can cope with such a problem to improve living environment, organopolyisocyanate resins have been put into use as non-formalin type adhesives because of their excellent adhesive properties such as resistance to heat and water, in addition to the feature that they do not contain any formalin originally in their structure. When, however, the organopolyisocyanate resins are used as adhesives for the above hot-pressed forms, a phenomenon may occur such that the formed material adheres strongly to the metal surface coming into contact therewith (hereinafter “heating platen”) at the time of hot-press forming by means of a continuous or batch-wise press, bringing about a problem that the hot-pressed forms can not stably continuously be produced.
To solve this problem of adhesion to the heating platen, a method is proposed as disclosed in Japanese Patent Application Laid-open No. 52-154875 in which a release agent (hereinafter “external release agent”) is directly applied on the heating platen before hot pressing. Meanwhile, not such an external release agent coating method but a method in which an additive (hereinafter “internal release agent”) is mixed in an organopolyisocyanate is proposed as disclosed in Japanese Patent Applications Laid-open No. 59-205175, No. 57-113053 and No. 1-198572. Japanese Patent Application Laid-open No. 4-232004 proposes a method in which a lignocellulose material is hot-press formed with addition of an orthophosphoric acid neutral ester as a compatibilizer of an emulsion wax with an organopolyisocyanate. In this method, however, any wax/orthophosphoric acid neutral ester mixture can not be obtained in a liquid form which is easy to handle at normal temperature, leaving a problem in the handling of the emulsion wax.
In the method using an external release agent, it is necessary to appropriately coat the heating platen with the external release agent in order to ensure releasability continuously, and there is such a problem that its coating is difficult and troublesome to operate. With the method using an internal release agent, it is necessary to use the internal release agent in a large quantity in order for the agent to exhibit the sufficient effect of releasing, causing such adverse effects that because of its use in a large quantity the physical properties deteriorate, and also, in an actual production process, involving difficulties in respect of long-time durability and also in respect of economical advantages. Thus, this method has not been applied in any existing manufacturing processes.
SUMMARY OF THE INVENTION
As a result of extensive studies, the present inventors have discovered that an adhesive composition comprised of an organopolyisocyanate compound and a wax emulsion having a specific formulation can solve the above various problems, as an adhesive composition for hot-pressed forms of lignocellulose materials. Thus, they have accomplished the present invention.
More specifically, the present invention provides an adhesive composition for lignocellulose-type hot-pressed forms which comprises;
(A) an organopolyisocyanate which is a polyisocyanate composed chiefly of from 20 to 70% by weight of a diphenylmethane diisocyanate having two benzene rings in one molecule and from 80 to 30% by weight of a diphenylmethane diisocyanate polynuclear condensate having at least three benzene rings in one molecule, and has a viscosity of 500 mPa·s or less in a state of solid content=100% by weight at 25° C.; and
(B) a wax emulsion prepared by emulsifying a wax (B1) which is a paraffin wax containing at least 80% by weight of a paraffin having 20 to 40 carbon atoms, and has a melting point of from 40° C. to 100° C., with an emulsifier (B2) which is an ethylene oxide polyaddition product of an aliphatic monoalcohol whose aliphatic chain has 14 to 20 carbon atoms.
In the above adhesive composition, the paraffin wax (B1) may have a molecular weight of from 100 to 1,200 in its molecular weight distribution measured by gel permeation chromatography and as molecular weight in terms of polyoxypropylene glycol as a reference substance.
In the above adhesive composition, the emulsifier (B2) may have a number-average molecular weight of from 250 to 3,000.
The adhesive composition may further contain (C) a formalin condensation resin.
The present invention also provides a process for producing lignocellulose-type hot-pressed forms, characterized by using the adhesive composition described above.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The adhesive composition of the present invention will be described below concerning its components.
The adhesive composition of the present invention is composed basically of (A) an organopolyisocyanate and (B) a wax emulsion.
(A) Organopolyisocyanate
The component-(A) organopolyisocyanate used in the present invention may preferably be of a type having a good compatibility with the component-(B) wax emulsion described later. Taking account of mixing performance of individual adhesive components and operability required when the composition is applied on lignocellulose materials, the organopolyisocyanate may preferably be those having a viscosity at 25° C. of 500 mPa·s or less, and particularly preferably from 10 to 400 mPa·s. The component-(A) organopolyisocyanate may also preferably have an isocyanate content of from 20 to 35% by weight, and particularly preferably from 28 to 32% by weight.
Since in this way the organopolyisocyanate is required to have a low viscosity and a high isocyanate content, a solvent and a plasticizer may be added thereto, but preferably none of them be added and the organopolyisocyanate may preferably have a viscosity of 400 mPa·s.
The component-(A) organopolyisocyanate is composed chiefly of a mixture of a diphenylmethane diisocyanate having two benzene rings in one molecule (hereinafter “MDI”) and a diphenylmethane diisocyanate polynuclear condensate having at least three benzene rings in one molecule. Hereinafter, the said mixture is referred to as “polymeric MDI”. In the organopolyisocyanate, the MDI or polymeric MDI account for 50% by weight or more, and other isocyanates may further be added thereto.
As will be detailed later, the component-(A) organopolyisocyanate usable in the present invention may be a prepolymer terminated with isocyanate groups, obtained by allowing an active-hydrogen-group-containing compound to react with MDI, polymeric MDI or a mixture of these in excess in MDI, polymeric MDI or a mixture of these in excess in equivalent weight ratio (isocyanate group/active hydrogen group). In such a prepolymer, too, the sum of the MDI or polymeric MDI may preferably account for 50% by weight or more.
The isocyanate which may be added to the organopolyisocyanate may include liquid MDI (carbodiimide-modified MDI), tolylene diisocyanate, xylylene diisocyanate, trimethylene xylylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, naphthalene diisocyanate,
Kanaya Masashi
Kimura Tadashi
Suzuki Seiki
Yoshida Mitsuhiro
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