Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2002-10-18
2004-05-11
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S155000, C528S176000, C528S256000, C525S328700, C525S328800, C525S489000, C525S501000, C525S508000, C428S505000, C428S506000, C428S511000, C428S528000, C156S335000
Reexamination Certificate
active
06734275
ABSTRACT:
The present invention relates to a method of gluing wood based materials whereby a urea based amino resin is cured by a hardener composition comprising an acid and a phenolic resin. The present invention also relates to an adhesive system and a hardener composition. Furthermore, it also relates to a wood based product obtainable by the method. Finally, it relates to the use of an adhesive system for making a wood based product.
BACKGROUND
When gluing wood, it is common to use an adhesive system based on a curable resin, such as a formaldehyde resin, which, for example, can be an amino resin or a phenolic resin. Important properties of an adhesive include adhesive strength, curing time and temperature, water-resistance and emission of formaldehyde.
Urea based amino resins are condensates of carbonyl compounds, such as aldehydes, with urea or thiourea. Other compounds containing amino, imino or amide groups may also be co-condensed into the urea based amino resin. Mostly, urea based amino resins refer to condensates of formaldehyde and urea giving urea-formaldehyde (“UF”). Urea based amino resins are usually cured by using acidic hardener compositions. The water-resistance is moderate for UF resin based adhesives as compared with pure melamine-formaldehyde (“MF”) resin based adhesives. Therefore, the use of UF resins is usually limited to indoor applications.
It is known to improve the water-resistance of UF resin based adhesives by adding different melamine based compounds. For example, an MF resin can be mixed into a UF resin thereby forming a melamine-urea-formaldehyde (“MUF”) resin. Also, the addition of melamine powder to a UF resin improves the water-resistance of the adhesive bond. Furthermore, SE 505134 describes the use of melamine salts to improve the water-resistance of UF resins.
However, all the methods of improving the water-resistance above lead to slower curing than for the UF resin alone. The use of melamine powder in UF resins has limitations since the powder has a poor solubility in water. Solubility problems occur as well when using melamine salts in UF resins.
JP Laid Open No. 1997-278855, discloses a thermosetting resin composition comprising a UF resin having a molar F/U ratio of 2.5 to 6. This is the molar ratio formaldehyde to urea used when making the resin. At ratios of 2.5 or less, the UF resin is said to be remarkably poor in stability and having poor mixability with the phenolic resin. The problem solved is how to achieve a thermosetting resin composition, which is stable for a long time at room temperature.
However, it would be desirable to provide a method of gluing wood based materials, an adhesive system, and a hardener composition, which give water-resistant and fast curing adhesive bonds.
It is therefore an object of the present invention to provide a method for gluing wood based materials which provides fast curing and water-resistant adhesive bonds. It is another object of the present invention to provide an adhesive system, as well as a hardener composition intended for use in an adhesive system, which is fast curing and gives water-resistant adhesive bonds. Finally, it is an object of the present invention to provide a wood based product which adhesive bonds cure fast, and are water-resistant.
INVENTION
It has surprisingly been found possible to meet these objects by a new method of gluing wood based materials using a new adhesive system and a new hardener composition. The method according to the invention comprises gluing wood based materials by providing an adhesive system onto wood based materials followed by curing, the adhesive system comprising a urea based amino resin and a hardener composition, wherein the hardener composition comprises an acid and a phenolic resin, which is a resorcinol resin or a tannin resin, or a mixture thereof. The adhesive system according to the invention comprises a urea based amino resin and a hardener composition, wherein the hardener composition comprises an acid and a phenolic resin resin, which is a resorcinol resin or a tannin resin, or a mixture thereof, the molar ratio aldehyde to amino compound used when making the urea based amino resin is less than 2.4.
The hardener composition according to the invention comprises an acid and a phenolic resin, which is a resorcinol resin or a tannin resin, or a mixture thereof. The invention further relates to a wood based product obtainable by the method which can be a flooring material, plywood, a laminated beam and a fibre-, chip- or particleboard material. Finally, the invention further relates to the use of an adhesive system according to the invention for making a wood based product which can be a flooring material, plywood, a laminated beam and a fibre-, chip- or particleboard material. The present invention provides a hardener composition which is storage stable before mixing with a curable resin.
By the term “adhesive system”, as used herein, is meant a curing formulation containing a curable resin and a hardener composition.
By the term “hardener composition”, as used herein, is meant a composition, not intended to cure by itself, comprising a curing promoter intended to cure, or harden, a curable resin.
In the urea based amino resin of the invention, it is suitable that at least 30 mole % of the one or more amino compounds used when making the amino resin is urea or thiourea or derivatives thereof, preferably at least 50 mole %.
The combination of a urea based amino resin with a hardener composition according to the invention makes it possible to provide an adhesive system with similar curing time as an adhesive system comprising the amino resin and an acidic hardener without phenolic resin, at the same time the water-resistance is greatly improved.
Another advantage with the present invention is that urea based amino resins, having very low contents of free aldehyde, particularly UF resins having very low contents of free formaldehyde, can be used in order to achieve adhesive bonds with high water-resistance at short curing times. This makes it possible to provide an adhesive system that is fast curing, water-resistant and which also has very low emission of aldehyde, particularly formaldehyde.
The urea based amino resin used in the method and the adhesive system of the invention can be any urea based amino resin, such as urea-formaldehyde (“UF”), melamine-urea-formaldehyde (“MUF”), melamine-urea-phenol-formaldehyde (“MUPF”), thiourea resins, alkyl urea resins such as ethylene urea, and condensates of formaldehyde and urea together with other compounds containing amino, imino or amide groups such as thiourea, substituted urea, and guanamines. The preferred urea based amino resin is UF. The urea based amino resin is made by reacting an aldehyde and an amino compound. The “aldehyde to amino compound ratio”, which is the molar ratio aldehyde to amino compound used when making the amino resin of the claimed adhesive system, is less than 2.4, preferably from about 0.5 to about 2.3, most preferably from about 0.7 to about 2. Optionally, fillers, thickeners or other additives, including aldehyde catchers, can be added to the amino resin. Examples of fillers are inorganic fillers such as kaolin and calcium carbonate or organic fillers such as wood flour, wheat flour, starch and gluten. Examples of thickeners are polyvinyl alcohol, and cellulose compounds such as hydroxy ethyl cellulose and carboxy methyl cellulose. Other additives can be, for example, polyols, polysaccharides, polyvinylalcohol, acrylates, and- styrene-butadiene polymers. Homopolymers or copolymers of vinylesters may also be used as components, such as vinyl acetate, vinyl propionate, and vinyl butyrate. These polymers may also comprise post-crosslinking groups. Also aldehyde catchers such as urea and guanamines may be added. If components, like fillers or other additives according to above, are present, their amount can usually be less than about 70 weight %, suitably from about 0.1 to about 70 weight %, preferably from about 1 to about 60 weight %, most preferably from about 5 to about 40
Lindh Ingvar
Nasli-Bakir Benyahia
Pirhonen Salme
Akzo Nobel N.V.
Serbin David J.
Truong Duc
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