JP2005517076A - Method for joining wood-based materials - Google Patents

Abstract

【the purpose】
The present invention relates to a step of preparing at least two pieces of a wood-based material, an adhesive composition (A) containing a curable resin, and a composition (B) containing a gel-forming substance. Separately applying to at least one of the at least two pieces, bonding the two pieces together to form an assembly having compositions (A) and (B) disposed between the pieces; Two or more pieces of wood-based material, comprising pre-pressing the resulting assembly without curing the resin, and then hot-pressing the assembly to cure the resin It relates to the combination method. The invention also relates to a wood-based product made by the method.

Description

  The present invention relates to a method for bonding wood-based materials wherein a curable adhesive composition and a composition comprising a gel-forming substance are applied separately to the wood-based material. The invention also relates to a wood-based product made by the method.

  Some methods of bonding wood based materials include a pre-pressing step followed by a hot pressing step. This is especially the case for bonding methods such as the production of plywood and laminated veneer lumber, where a thermosetting adhesive is applied to the veneer and they are assembled and usually pre-pressed at room temperature to form the veneer assembly. Form. The assembly is then usually hot pressed, in which case the curing of the adhesive occurs. It is important that the veneers are well bonded to each other after the pre-pressing process so that the assembly is not cut, thereby breaking its shape. If the veneers are poorly bonded together, the assembly may also stick in the hot press apparatus. Thus, poor cold bonding will result in some materials not being usable after pre-pressing and thus forming waste.

  When formulating a typical curable adhesive, various additives are usually mixed into the curable resin. Additives usually affect pot life, which can be as little as a few days or less for formulated curable adhesive compositions since it is up to a few weeks for the resin alone. Certain additives result in very short pot life, which creates handling problems. Thus, too short pot life problems are frequently present when formulating adhesive compositions.

  To improve cold adhesion, adhesives such as cereal-based materials including wheat flour, corn flour and the like are commonly used as a component in curable adhesive compositions. However, cereal-based adhesives can only be used to an amount that does not thicken the adhesive composition too much. Also, different natural or synthetic polymers were tested but did not produce satisfactory improvements. Thus, the performance of known adhesives for improving cold adhesion is inadequate and improves cold adhesion when bonding wood-based materials without causing too short pot life problems. There is a request about that.

  When bonding two surfaces together, there is some maximum assembly time available, i.e., the maximum length of time between application of the adhesive component and, for example, bonding of parts during pressing. The assembly time needs to be long enough to allow assembly and adjustment of the parts to be bonded in a practical manner.

  WO 89/05221 discloses a method for producing a wood product in which a curing agent is applied to the zone along the edge of the veneer layer. However, due to the rapid curing agent used, the assembly time before pre-pressing will be very short. Also, the method of WO 89/05221 can result in a change in the quality of the adhesive bond between the different parts of the adhesive bond, and more waste material.

  U.S. Pat. No. 4,824,896 discloses an adhesive for bonding wood pieces of high water content, which optionally includes borax. U.S. Pat. No. 2,889,241 discloses a phenolic resin composition containing a boron oxygen compound such as boric acid. EP 0259042 A2 discloses the use of esters as curing agents for phenol-formaldehyde resins. However, none of U.S. Pat. Nos. 4,824,896, 2,889,241 or EP 0259042 A2 disclose anything about cold bonding.

  It is an object of the present invention to provide a method for bonding wood-based materials that produces excellent cold bonding, minimizes pot life problems, and provides sufficient assembly time. Suitable methods for the method in which the curable adhesive composition is used include a pre-press step and a hot press step. A further object of the present invention is to provide a wood based product made by the method.

According to the present invention,
(a) providing at least two pieces of wood-based material;
(b) a step of separately applying an adhesive composition (A) containing a curable resin and a composition (B) containing a gel-forming substance to at least one of the at least two pieces;
(c) joining the two pieces together to form an assembly having compositions (A) and (B) disposed between the pieces;
(d) pre-pressing the resulting assembly without curing the resin;
(e) the object can be achieved by a method of joining two or more pieces of wood-based material, comprising the step of hot pressing the assembly to cure the resin I was surprised.

According to the present invention,
(a) providing at least two pieces of wood-based material;
(b) An adhesive composition (A) containing a curable resin and a composition (B) containing a gel-forming non-curable material are separately applied to at least one of the at least two pieces. Process,
(c) joining the two pieces together to form an assembly having compositions (A) and (B) disposed between the pieces;
(d) pre-pressing the resulting assembly, then
(e) the object can be achieved by a method of joining two or more pieces of wood-based material, comprising the step of hot pressing the assembly to cure the resin I was surprised again.

  The “gel-forming substance” can cause the adhesive composition (A) of the present invention to form a gel by itself or a derivative thereof, and any resin in the adhesive composition (A) can be used. By this is meant a material that does not significantly cure during pre-pressing at relatively low temperatures, eg, room temperature, 20-25 ° C. (this is an example of the temperature range during pre-pressing).

  “Curing” the resin here means to convert the curable resin into a cured, cross-linked, preferably solid, state.

  "Pre-press" here means a press at a temperature below the required curing temperature of the applied thermosetting adhesive composition, so that no significant curing occurs during the pre-pressing time.

  “Cold adhesion” means here the adhesion after pre-pressing between two surfaces with a thermosetting adhesive layer between the surfaces.

  “Hot press” means here a press at a temperature above the required curing temperature of the applied thermosetting adhesive composition and higher than the temperature in the pre-press, so that the adhesive is cured .

  Suitable curable adhesive compositions (A) of the present invention include any curable adhesive composition that requires an increase in temperature to cure sufficiently quickly. The adhesive composition (A) may contain more than one resin. The adhesive composition (A) preferably contains a combination of a phenol resin or amino resin and a non-curable resin.

  A phenolic resin is a condensate of different phenolic compounds and aldehydes. The phenolic compounds may be phenolic itself, polyhydric phenols and alkylphenols such as resorcinol, alkylresorcinol, cresol, ethylphenol and xylenol, and natural source phenolic compounds such as tannins. Examples of suitable aldehydes include formaldehyde, acetaldehyde, glutaraldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde and furfural. The phenolic resin can be present as a solution in water or an alcohol such as ethanol. The phenolic resin is preferably present as an aqueous solution having various dry contents of the resin. The phenolic resin used in the adhesive composition (A) of the present invention is preferably a phenolic resin based on formaldehyde, for example, phenol-formaldehyde resin, resorcinol-formaldehyde resin and phenol-resorcinol-formaldehyde resin. is there. The adhesive composition (A) preferably contains a phenol-formaldehyde resin. The dry resin content in the phenolic resin is suitably from about 20% to about 80%, preferably from about 30% to about 60%, most preferably from about 40% to about 50% by weight. It is preferable that the remainder of the resin is substantially water. The molar ratio of formaldehyde to the total amount of phenolic compound (one or both of phenol and resorcinol) in making the resin is preferably from about 0.1 to about 4, and from about 0.5 for phenol-resorcinol-formaldehyde resin Preferably it is about 1. For phenol-formaldehyde resins, the molar ratio of phenol to formaldehyde is preferably from about 1 to about 3.

  Amino resins are carbonyl compounds such as condensates of aldehydes and compounds containing amino, imino or amide groups such as urea, melamine, thiourea, guanamine, ethylene urea, cyanamide, dicyandiamide and guanidine. Mostly, amino resins represent condensates of formaldehyde and amine-containing compounds, the most common of which are urea and melamine, yielding urea-formaldehyde and melamine-formaldehyde, and melamine-urea-formaldehyde. The amino resin used in the adhesive composition (A) of the present invention is preferably a urea-formaldehyde resin or a melamine-formaldehyde resin. The dry resin content in the amino resin is suitably from about 30 wt% to about 90 wt%, preferably from about 45 wt% to about 80 wt%, most preferably from about 55 wt% to about 75 wt%. It is preferable that the remainder of the resin is substantially water. The non-curable resin is suitably a polymer containing polar groups, preferably a polyvinyl ester or a polymer derived therefrom, most preferably polyvinyl acetate or polyvinyl alcohol. The amount of non-curable resin in the adhesive composition (A) is preferably about 0.1% by weight, calculated as dry non-curable resin in the total non-dry adhesive composition (A). To about 40% by weight, preferably about 0.5% to about 30% by weight, more preferably about 1% to about 15% by weight, and most preferably about 2% to about 10% by weight. The amino resin is preferably cured by using a normal curing agent at a high temperature, preferably 50 ° C. or higher, preferably 80 ° C. or higher.

  The adhesive composition (A) can be formulated in any suitable manner of the state of the art. Suitably, the adhesive composition (A) may contain various additives such as curing catalysts and fillers such as nut shell powder or other starch-containing materials known in the art. . The preferred viscosity of the adhesive composition (A) when applied to the surface of a wood-based material depends on the application method used. It is preferred that the adhesive composition (A) has a Brookfield viscosity at 25 ° C. of from about 100 cP to about 150,000 cP, preferably from about 300 cP to about 50,000 cP.

  It is preferred that the gel-forming material is a non-curable material, which here indicates that the curable adhesive composition containing the material should not be irreversibly crosslinked at 20 ° C. even after several hours. means. Examples of suitable gel forming materials of the present invention include inorganic gel forming materials and organic gel forming materials. Examples of inorganic gel forming substances include boron-containing compounds and metal ions. The boron-containing compound of the present invention preferably contains oxygen, and most preferably the boron-containing compound is selected from the group of boric acid, borate, or combinations thereof. As borate, all types of borates such as metaborate, triborate, tetraborate and the like are mentioned here. The boron-containing compound is preferably dissolved in water or an organic solvent such as glycerol, ethylene glycol, diethylene glycol, methanol or ethanol. The boron-containing compound is preferably dissolved in water. The metal ions preferably belong to group 3A of the periodic table of elements, or transition metal ions belonging to any of groups 3B to 8B, such as zinc, zirconium and chromium. The metal ion is preferably dissolved in water. When one or more inorganic gel-forming substances are used, composition (B) is preferably an amount up to saturation of the one or more gel-forming substances in the solvent used, preferably about 0.01% by weight. One or more from about 0.1% to about 50%, preferably from about 0.1% to about 30%, more preferably from about 0.5% to about 25%, most preferably from about 1% to about 20% A gel-forming substance.

Examples of the organic gel-forming substance of the present invention include compounds having an ester functional group. Organic gel-forming substances are suitable when phenolic resins are used in the adhesive composition (A). Such a gel-forming substance is preferably selected from the group consisting of esters, lactones, organic carbonates, or mixtures thereof. Suitable esters include, but are not limited to, methyl formate, methyl acetate, ethyl acetate, N-butyl acetate, butylene glycol diacetate, ethylene glycol diacetate, and glycerol triacetate (triacetin). Other aliphatic C ₁ -C ₄ monoesters, for example, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, butyl acetate, propyl acetate, methyl propionate, ethyl propionate, propionic acid Propyl, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, propyl butyrate, methyl pentanoate, ethyl pentanoate, propyl pentanoate, butyl pentanoate can be used. Also, multi-esters such as ethylene glycol di-alkyl ester, diethylene glycol di-alkyl ester, propylene glycol di-alkyl ester, butylene glycol di-alkyl ester, glycerol alkyl ester, 1,3-propanediol alkyl ester, 1,3 - butanediol alkyl esters, 1,4-butane diol esters can be used, wherein the alkyl is C ₁ -C _4. Suitable organic carbonates include propylene carbonate, ethylene glycol carbonate, glycerol carbonate, 1,2-butanediol carbonate, 1,3-butanediol carbonate, 1,2-pentanediol carbonate, and 1,3-pentanediol carbonate. However, it is not limited to these. Propylene carbonate is preferably used. Lactones include, but are not limited to, gamma-butyrolactone, beta-propiolactone, beta-butyrolactone, beta-isobutyrolactone, beta-isopentyrolactone, gamma-isopenthilactone, and delta-pentyrolactone. When an organic compound, such as a compound having an ester functional group, is used as the gel-forming material, the composition (B) is suitably from about 1% to about 100%, preferably from about 10% to about 40%. Contains up to wt% gel-forming material. It is preferred that the balance of the composition (B) is substantially water.

  Preferably, the Brookfield viscosity of the adhesive composition (A) gelled by the gel-forming material at 20 ° C. should be reduced when the gel is heated moderately, for example to 50 ° C. This indicates that gelation is reversible and no significant irreversible cross-linking occurred in the adhesive composition (A).

  The weight ratio of applied adhesive composition (A) to applied composition (B) is preferably from about 100: 1 to about 2: 1, preferably about 50: 1, calculated per unit area. To about 5: 1, most preferably about 30: 1 to about 10: 1.

  Application of the adhesive composition (A) and the composition (B) can be performed in any order of application. The adhesive composition (A) is preferably applied to the surface before the composition (B). Application of the adhesive composition (A) and the composition (B) to the wood-based material is any suitable method known in the art, for example spraying, brushing, extrusion, roll coating, curtaining This may be done by forming a shape, such as a droplet, one or several strands, beads or a substantially continuous layer using a coating or the like. The adhesive composition (A) is preferably applied by using an extrusion, roll application or curtain coating method, while the composition (B) is preferably applied by spraying.

  Suitably, from about 20% to about 100%, preferably from about 50% to about 100%, most preferably from about 80% to about 100% of the surface to which the adhesive composition (A) has been applied. The composition (B) is applied. “Coated surface” means herein a surface that has been exposed to any application method without requiring some degree of coating of either composition (A) or (B).

In the method of the present invention, two or more pieces of wood-based material are combined to form a piece assembly, which is suitably from ambient temperature, preferably from about 0 ° C. to about 40 ° C., most Preferably, it is subjected to a pre-pressing step at about 5 ° C to about 30 ° C. The pre-pressing step of the present invention is suitably performed at a pressure of about 1 to about 50 kg / cm ² , preferably about 2 to about 25 kg / cm ² , most preferably about 4 to about 15 kg / cm ² . The pre-press time depends on the resin used and the type of assembly being pressed, and is preferably from about 0.1 minutes to about 30 minutes. For phenolic resins, the pre-press time is preferably from about 0.1 to about 15 minutes, more preferably from about 1 to about 10 minutes, and most preferably from about 3 to about 5 minutes. For amino resins, the prepress time is preferably from about 5 minutes to about 30 minutes, most preferably from about 8 minutes to about 15 minutes.

The assembly of pieces is further subjected to a hot pressing process, which is preferably at a temperature above the curing temperature of the adhesive composition (A). The hot pressing process of the present invention is suitably performed at a pressure of about 1 to about 50 kg / cm ² , preferably about 2 to about 25 kg / cm ² , most preferably about 4 to about 15 kg / cm ² . The temperature of the hot pressing process depends on the resin used and is preferably from about 50 ° C to about 200 ° C. For phenolic resins, the hot press temperature is suitably from about 80 ° C to about 200 ° C, preferably from about 120 ° C to about 170 ° C. For amino resins, the hot pressing temperature is suitably from about 50 ° C to about 150 ° C, preferably from about 90 ° C to about 130 ° C. The hot pressing time depends on the resin and the thickness of the assembly, preferably from about 0.01 to about 5 minutes per mm of assembly thickness, preferably from about 0.1 to about 2 minutes per mm of assembly thickness, Most preferably from about 0.2 minutes to about 1 minute per mm thickness of the assembly.

  In one preferred embodiment of the present invention, a curable adhesive composition comprising a phenolic resin is applied to a wood veneer followed by an application comprising a composition comprising boric acid. Two or more veneers are pre-pressed to form an assembly that is subsequently hot pressed, thereby curing the adhesive composition.

  In another preferred embodiment of the invention, an adhesive composition comprising a curable adhesive composition comprising a combination of an amino resin and a polyvinyl ester is applied to a wood veneer followed by a composition comprising boric acid. Applied. Two or more veneers are pre-pressed to form an assembly, which is subsequently hot pressed, thereby curing the adhesive composition.

  The wood-based material of the method of the present invention may be of any kind that can be bonded by an adhesive system. The wood based material is preferably a veneer or other wood based sheet.

  The wood-based products obtained by the method of the present invention may be of any kind for which a pre-pressing process is suitable, examples of such products are plywood, laminated veneer lumber and flooring.

  The invention will be further described with reference to the following examples, which should not be construed as limiting the scope of the invention.

Example

By adhering veneer to a two-ply panel with a standard adhesive composition made from 100 parts by weight phenol-formaldehyde resin, 1 part by weight sodium carbonate, 9 parts by weight flour and 5 parts by weight water The method of was tested. The resin had a dry content of 45% by weight. The formulated adhesive composition had a Brookfield viscosity of about 3000 cP at 25 ° C. The veneer tested was a radiata pine with a thickness of 3 mm. The adhesive composition was applied to the strands by extrusion in an amount of 220 g / m ² . A composition (B) of the present invention containing about 5% by weight of sodium tetraborate decahydrate and 95% by weight of water was made. Composition (B) was sprayed onto the applied adhesive composition in an amount of about 10 g / m ² . Pre-pressing was performed at a pressure of 10 kg / cm ² at a temperature of 21-25 ° C. for 60 seconds. Three identical test panels were made and tested. The amount of the upper and lower surfaces of the two-ply panels separated from each other ("release") was recorded after 30 minutes. A release value of 100% means complete separation, 0% means that the veneer is still sticking together.

Comparative example:
The test was conducted as in Example 1 except that the composition (B) was not sprayed onto the applied adhesive.

  It is concluded that separate application of the composition of the present invention results in a significant improvement in cold adhesion.

  Samples of a combination of PF resin and UF resin and polyvinyl alcohol (PvAl) were tested with the gel-forming material of the present invention and the citric acid curing agent (for UF) described in WO 89/05221. 15 g of a composition containing 10% by weight of a gel-forming substance or 20% by weight of a curing agent according to WO 89/05221 was mixed with 180 g of an adhesive containing a PF resin or UF / PvAl resin system. The UF / PvAl system also contained a conventional curing agent, the component relationships being 100 parts UF, 6 parts PvAl (17% by weight), and 20 parts curing agent. The mixture was then left for 1 minute at 20 ° C., after which the appearance and viscosity were recorded. The temperature was then rapidly raised to about 50 ° C. and the sample appearance and viscosity were recorded again.

* Combination not valid for testing It is concluded that the gel-forming material of the present invention does not irreversibly crosslink the resin at room temperature. Furthermore, the combination of citric acid / aluminum sulfate curing agent and UF / PvAl as described in WO 89/05221 already produced a hard gel after 1 minute at 20 ° C., which does not soften when heated and causes irreversible curing. Show.

Claims (15)

(a) providing at least two pieces of wood-based material;
(b) separately applying an adhesive composition (A) containing a curable resin and a composition (B) containing a gel-forming substance to at least one surface of the at least two pieces;
(c) joining the two pieces together to form an assembly having compositions (A) and (B) disposed between the pieces;
(d) pre-pressing the resulting assembly without curing the resin;
(e) A method for joining two or more pieces of wood-based material comprising the step of hot pressing the assembly to cure the resin. (a) providing at least two pieces of wood-based material;
(b) An adhesive composition (A) containing a curable resin and a composition (B) containing a gel-forming non-curable material are separately applied to at least one surface of the at least two pieces. The process of
(c) joining the two pieces together to form an assembly having compositions (A) and (B) disposed between the pieces;
(d) pre-pressing the resulting assembly, then
(e) A method for joining two or more pieces of wood-based material comprising the step of hot pressing the assembly to cure the resin.   The method according to claim 1, wherein the adhesive composition (A) is applied before the composition (B).   4. The method according to claim 1, wherein the wood based material is veneer.   The method according to claim 1, wherein the adhesive composition (A) contains a phenol resin.   The method according to any one of claims 1 to 4, characterized in that the adhesive composition (A) comprises a combination of polyvinyl acetate or polyvinyl alcohol and an amino resin.   The process according to claim 6, characterized in that the amino resin is a urea-formaldehyde resin or a melamine-formaldehyde resin.   The method according to any one of claims 1 to 7, characterized in that the gel-forming substance is boric acid, borate, or a combination thereof.   6. The method according to claim 5, wherein the gel-forming substance is a metal ion belonging to group 3A of the periodic table of elements or a transition metal ion belonging to any of groups 3B to 8B.   10. A method according to any of claims 8 to 9, characterized in that the composition (B) comprises from about 0.5% to about 30% by weight of a gel-forming substance.   6. A method according to claim 5, characterized in that the gel-forming substance is selected from the group consisting of esters, lactones, organic carbonates, or mixtures thereof.   12. A method according to claim 11, characterized in that the composition (B) comprises from about 10% to about 40% by weight of a gel-forming substance.   The weight ratio of the applied adhesive composition (A) to the applied composition (B) is about 30: 1 to about 10: 1 calculated per unit area. The method according to any one of 1 to 12.   A wood-based product obtained by the method according to claim 1.   15. A wood-based product according to claim 14 which is a plywood, laminated veneer lumber or flooring.