SK35398A3 - Two-component glue system for the production of laminated wood panels - Google Patents

Abstract

A two-component glue system suitable for the production of laminated wood panels consists of (a) an aqueous hardener mixture (component (a)) which contains (a1) 3 to 15 wt % of a Brönsted acid; (a2) 20 to 40 wt % of a mineral filler; (a3) 2 to 8 wt % of a thickener; (a4) 40 to 60 wt % water; and (b) a melamine resin (component (b)).

Description

The present invention relates to a two-component adhesive system suitable for the manufacture of wood glued beams comprising

(a) an aqueous curing mixture [component (a)] comprising a1) 3-15 wt.% Bronstedtic acid; and2) 20-40 wt.% mineral filler; and3) 2-8 wt.% thickener; and4) 40-60 wt.% water; and

(b) melamine resins (component (b)).

The invention further relates to a process for the production of glued wood beams using a two-component adhesive system as well as the production of laminated wood.

BACKGROUND OF THE INVENTION

Wood-glued beams (BS-Holz) made from glued wood slats are known (see Informationsdienst Holz, Holzleimbau, Bauen mit Brettschichtolz, published by Arbeitsgemenschaft Holz e.V. and Zentrale Marketinggeselschaft, ISSN 0446-2114). These glued timber beams are mainly used as load-bearing structural parts of industrial, residential and public buildings.

In this field of application, high demands are placed on the mechanical strength of building components. Even after many years, the strength of the composite structure must be sufficiently high despite the effects of weather conditions such as e.g. temperature and humidity changes.

Adhesive systems used for the production of load-bearing components must therefore be subjected to extensive testing in state testing laboratories to ensure

- adherence to the necessary recommendations on suitability from the building supervisory authorities.

These tests are based on DIN 68141 together with DIN EN 301 and DIN EN 302 Parts 1 to 4. As part of the manufacturer's own supervision, the quality of the components produced must be demonstrated by a delamination test according to DIN EN 386 and DIN EN 391.

In addition to the requirements imposed on adhesive systems with respect to the performance of the components in the areas to which they are applied, manufacturers of wood glued beams are required to perform certain processing characteristics of the adhesive systems. On the one hand, the drying time of the adhesives must be long enough to allow the wood slats to which the adhesive has been applied for a certain period of time. On the other hand, the glued components should be mechanically loadable as soon as possible after production. This assumes that the adhesive will cure rapidly after joining the adhesive-coated panels.

It is well known in the art that phenol resorcinol resins can be used to produce wood glued beams that can be used to manufacture load-bearing building blocks. However, these glued wood elements have the disadvantage that the glued joints appear as black lines due to the dark color of phenol resorcinin resins on the finished component, which is often rejected for aesthetic reasons.

Liquid hardeners are known from Swedish patent 78 10 982. These are aqueous suspensions containing, based on the aqueous suspension, 1 to 25% by weight of an acid or acid breaker, 30 to 90% by weight of a filler, for example a mineral filler such as kaolin, 0.5 to 10% by weight of a chewing agent, and 0 to 50% by weight. % formaldehyde adsorber. The curing agent has a dry matter content of between 35 and 85% by weight and a viscosity of 2000 to 12000 mPa · s at 20 ° C.

It is recommended to use a curing agent to cure urea-formaldehyde resins. However, the wood glued beams produced by these blind and curing systems do not have the necessary strength especially when used outdoors.

¹ SUMMARY OF THE INVENTION The task of the invention is therefore the preparation of two-component adhesive systems for the production of glued wooden beams that have dark glued joints which have mechanical properties required by the construction industry.

Accordingly, two-component adhesive systems have been initially defined.

The curing composition [component (a)] preferably has a viscosity of 3000 to 10,000, in particular of 4,000 to 8,000 mPa.s, based on a measured temperature of 20 ° C and a shear rate of 30 s-1.

Preferably, the curing composition comprises a1) 5 to 12, in particular 7 to 10% by weight Bronstedtic acid, a2) 20 to 40, especially 25 to 35% by weight mineral filler a3) 2 to 8, most preferably 4 to 6% by weight thickener a4) 35 to 40 60, in particular 40 to 55% by weight of water.

Suitable Bronstedt acids are, for example, mineral acids such as phosphoric acid or organic acids e.g. acetic acid, propionic acid, oxalic acid or, in particular, formic acid.

Suitable mineral fillers are, in particular, kaolin or other layered aluminosilicates.

Suitable thickeners are polyvinyl alcohol or partially hydrolyzed polyvinyl acetate or mixtures thereof. Polyvinyl alcohol is commercially available e.g. under the designation Moviol.RTM. (Hoechst). For partially hydrolyzed polyvinyl acetate, at least 50%, preferably 80%, of the ester groups originally contained in the polyvinyl acetate are hydrolyzed. Component (c) is used in amounts of 1 to 20% by weight, preferably 1 to 8% by weight.

In addition to the mineral filler, the curing composition may also comprise an organic filler. These are generally fillers, usually contained in wood adhesives, preferably in the form of fibers, for example cellulose or wood flour.

The organic filler is usually present in amounts of 10 to 30% by weight, based on the mineral filler, in component (a).

In addition, the curing composition has the advantage that it contains 1 to 20, in particular 3 to 8% by weight, based on the total amount of resorcinol components (a1) to (a4), when wood glued beams particularly resistant to moisture are required. In addition, customary auxiliaries and additives, such as antifoams or emulsifiers, may be added to the curing composition in amounts of up to 3% by weight, based on the components of the mixture (a1) to (a4).

For component (b), melamine resins are commercially available resins which are known, for example, from Ullman's Enzyklopädie der technischen Chemie, 4th edition, Volume 7, pages 408 and 409.

These are, in particular, melamine resins from b1) melamine b2) 2.1 to 8.4, preferably 2.5 to 4.6 moles of formaldehyde per mole of meiamine b3) 0 to 10, preferably 0 to 0.5 moles of another compound, which is capable of reacting with formaldehyde in a polycondensation or polyadditive reaction, per mole of formaldehyde.

Melamine (component b1) is generally used in solid form.

Formaldehyde (component b2) is generally used in the form of a solution of 30 to 50% by weight or in the form of paraformaldehyde.

Suitable components (b3) are, in particular, those which are used together with formaldehyde in the production of aminoplast resins (see Uilman's Enzyklopädie der technischen Chemie, 4th edition, Vol. 7, pp. 403-422), e.g. urea, dicyandiamide, and guanamines such as benzoguanamine and acetoguanamine. They are also suitable

-5-bisguanamines such as adipoguanamine, glutaroguanamine or methylolglutarobisguanamine as well as compounds containing several e.g. condensed aminotriazine nuclei.

Component (b) comprises b1) 15 to 30% by weight of melamine b2) 15 to 30% by weight of formaldehyde b3) 5 to 25% by weight of urea, dicyandiamide and / or guanamines.

The preparation of the melamine resins is preferably carried out according to generally conventional procedures, which are known, for example, from Ullman's der technischen Chemie, 4th edition, Volume 7, pp. 403-422.

The conversion is usually carried out in an aqueous solution, the proportion of water in the solution being 25 to 50% by weight, based on the proportion by weight of components (b1) to (b3). The pH is generally 7 to 10.5, preferably 9.0 to 10.0 and the reaction temperature 60 to 110 ° C, most preferably 80 to 110 ° C.

Generally, the conversion is carried out until a starting melamine resin or an elastified melamine resin is formed. The conversion products exhibit, as aqueous solutions, 60% by weight at 20 [deg.] C., usually a viscosity of 350 to 1200, preferably 450 to 800 mPa.s. Under the above reaction conditions, general reaction times of 70 to 150 min are required.

The conversion may be completed by cooling the reaction mixture to temperatures below 50 ° C, preferably 20 to 30 ° C.

In general, aqueous elasticized melamine resins are required, especially those having a solids content of 50 to 70% by weight. If the melamine resins do not have the desired solids content before they are produced, it is possible to change the solids content by distilling off the water preferably under vacuum or by mixing with water.

To increase the elasticity of the adhesives, these preferably contain aliphatic polyols in amounts of 5 to 18, preferably 9 to 15% by weight, based on the solids content of the melamine resins. These polyols can already be added to the starting materials which are used for the production of melamine resins or to the finished melamine resin. Particularly suitable are C2-C20 polyols, preferably diols such as ethylene glycol, diethylene glycol, dipropylene glycol and butadiol, as well as triols such as glycerin.

Furthermore, modifying agents such as ε-caprolactam and other carbonic amides in amounts of 1 to 7, preferably 1 to 3% by weight based on the solids content of the adhesives may be added to the melamine resins to improve the application technical properties of the adhesives. melamine resins.

In addition, the melamine resins may optionally contain up to 20, preferably 9 to 15% by weight of organic fillers based on the solids content. Also suitable are the same organic fillers that may be included in component (a).

The two-component adhesive system according to the invention can be used by preparing the adhesive bath by mixing components (a) and (b) and applying it to at least one of the two surfaces to be bonded with the adhesive.

Preferably, the adhesive bath composition of components (a) and (b) is in a weight ratio of 0.1: 1 to 0.5: 1, in particular 0.2: 1 to 0.4: 1.

The preparation of the adhesive baths of components (a) and (b) is non-critical and is expedient by mixing one component into the other component.

In particular, the following adhesive bath composition is suitable, with the components added to 100 parts by weight:

0.5 to 2.5 parts by weight of formic acid

0.3 to 1.5 parts by weight of a thickener to 25 parts by weight of melamine in the form of a melamine resin

- 74 to 21 parts by weight of urea in the form of melamine resin up to 25 parts by weight of formaldehyde in the form of melamine resin up to 12 parts by weight of organic filler up to 13 parts by weight of c2 - to c20 polyols up to 5 parts by weight of modifying agent up to 4 parts by weight of resorcinol up to 9 parts by weight parts of mineral filler per 100 parts by weight of residual water

The two-component adhesive systems according to the invention are particularly suitable for bonding solid wood parts. In particular, they are suitable for the production of wood glued beams composed of several, preferably 5 to 70, wooden lamellas, for example boards of 10 to 43 mm thickness.

The gluing of the wooden slats is expediently carried out by a method generally known in the wood-processing industry.

For example, it is possible to form an adhesive bath by mixing components (a) and (b), to prepare wood lamellas with an adhesive layer by applying the adhesive bath to one or both sides of the wood lamellas and to the wood lamellas with the adhesive layer is bonded to one another or to the wooden lamellas without the adhesive layer so that there is always an adhesive layer between the two glued wooden lamellas, the working steps 1a to 11a being carried out in a range of 45 to 150 minutes, preferably 60 to 120 minutes, or

-δΙό to prepare wood slats with a layer of glue by applying components (a) and (b) separately to one side or both sides of the wooden slats, so that both component (ä) and component (b) are applied on both sides or on one side of the wooden slats and the wood slats with an adhesive layer are joined to one another or to the wooden slats without an adhesive layer such that the two adhesive components are each between two wooden slats, or lc 'to prepare the wooden slats with adhesive layer so that the components (a) and (b) are applied separately to one or both sides of the wooden slats, so that only one component of the two-component adhesive system is located on the same side of the wooden slat and the wooden slats are glued to each other. components (a) and (b) are each located between two glued wooden slats.

In the separate application of components (a) and (b), components (a) and (b) are applied to the wood lamellas of step IIb or IIc in a ratio of 0.2: 1.0 to 0.5: 1.0, preferably 0.3: 1 to 0.4: 1.0.

The total amount of components (a) and (b), respectively of the adhesive bath, which are applied in steps IIb, 11c or 1a to the wooden slats is usually 350 to 500 g / m 2.

The joining of the wooden slats to the adhesive bath layer or the individual components according to step IIIa, IIb or 11c is generally carried out at a pressure of 0.6 to 1.0 N / mm 2. This pressure is generally maintained during the time it takes the adhesive to cure, which is about 112-114 hours. at 20 ° C. Curing is usually carried out at room temperature, at higher temperatures the curing time is correspondingly shortened.

Adhesive baths are particularly characterized by their usability after preparation, i.e. after mixing components (a) and (b). They are further characterized by suitable rheological properties.

-9 Because of their structural viscosity and thixotropy, they do not flow on the vertical wooden slats coated with glue and do not form fibers.

In particular, the wood glued beams produced by the two-component adhesive system according to the invention are characterized by excellent mechanical properties, which are retained even when used outdoors.

DETAILED DESCRIPTION OF THE INVENTION

Preparation of curing mixtures

Curing mixture 1

4000 g of a 10% solution of polyvinyl alcohol, 642 g of water, 1058 g of 85% formic acid, 200 g of propylene carbonate, 600 g of resorcinol, 3000 g of china clay and 500 g of cellulosic fibers were gradually mixed inside with a fast rotating stirrer. homogenized.

The finished curing composition had the following characteristic values of properties:

density at 20 ° C (g / mI) 1.315 viscosity at 20 ° C, cut 30 / s (mPa.s) 4802 pH at 20 ° C, measured with glass electrode 1.3

Curing mixture 2

5320 g of a 10.6% solution of polyvinyl alcohol, 239 g of water, 941 g of 85% formic acid, 3000 g of china clay and 500 g of cellulose fibers were gradually stirred inside with a rapidly rotating stirrer and thoroughly homogenized.

The finished curing composition had the following characteristic values of properties:

density at 20 ° C (g / ml) 1.265 viscosity at 20 ° C, cut 30 / s (mPa.s) 5659

PH value at 20 ° C, measured with a glass electrode 1.4

Preparation of melamine resins

Melamine resin

A mixture of 2515 g (33.5 mol) of a 40% formaldehyde solution, 2575 g of urea-formaldehyde polycondensate (10.7 mol of urea and 42.9 mol of formaldehyde), 300 g of water, 15 g-diethylethanolamine and 2380 g (18.9 mol) Melamine was heated to 95 ° C and allowed to condense at this temperature for 75 minutes. The mixture was then cooled to 87 ° C and allowed to condense further to a viscosity of about 900 mPa · s (measured at 20 ° C). The pH was constant throughout the condensation period - about 9.5. After cooling to 50 ° C, 415 g (6.9 mol) of urea was added and the mixture was further cooled to room temperature. The viscosity of the mixture was 715 mPa · s (measured at 20 ° C) and the mixture had a solids content of 62.5% by weight. 100 g of caprolactam, 600 g of ethylene glycol and 850 g of cellulose were mixed homogeneously into this resin.

The finished resin had the following characteristic property values:

viscosity 2480 mPa.s solids content 65.2% by weight pH value 9.2 gelation time (3 g 34% formic acid, 40 ° C) 55 minutes

Melamine resin

A mixture of 2515 g (33.5 mol) of a 40% formaldehyde solution, 2575 g of urea-formaldehyde polycondensate (10.7 mol of urea and 42.9 mol of formaldehyde), 300 g of water, 15 g of diethylethanolamine and 2380 g (18.9 mol) of melamine was heated to 93 ° C and condensed at this temperature for 90 minutes to a viscosity of about 600 mPa · s (measured at 20 ° C). The pH was constant throughout the condensation period. After cooling to 50 ° C, 415 g (6.9 mol) of urea was added and the mixture was added

11 was further cooled to room temperature. The viscosity of the mixture was 548 mPa · s (measured at 20 ° C) and had a solids content of 62.4% by weight. 850 g of diethylene glycol and 950 g of cellulose were mixed homogeneously into this resin.

The finished resin had the following characteristic property values:

viscosity solids content pH value

2380 mPa.s

65.6% by weight

9.1 gelation time (3 g 34% formic acid, 40 ° C) 58 minutes

Melamine resin C

A mixture of 4550 g (60.7 mol) 40% formaldehyde solution, 350 g urea-formaldehyde polycondensate (1.5 mol urea and 5.8 mol formaldehyde), 15 g diethylethanolamine and 2700 g (21.4 mol) melamine was heated to 97 ° C and condensed at this temperature for 90 minutes to a viscosity of about 580 mPa · s (measured at 20 ° C). The pH was constant throughout the condensation period. After cooling to 50 ° C, 438 g (7.3 mol) of urea was added and the mixture was further cooled to room temperature. The viscosity of the mixture was 450 mPa.s (measured at 20 ° C) and had a solids content of 59.1% by weight. 200 g of caprolactam, 300 g of 1,4-butanediol, 500 g of ethylene glycol and 947 g of cellulose were homogeneously mixed into this resin.

The finished resin had the following characteristic property values:

viscosity 2270 mPa.s solids content 63.5% by weight pH value 9.4 gel time (3 g 34% formic acid, 40 ° C) 42 minutes

The physical properties of the curing mixture and melamine resins were determined as follows:

The viscosity was measured according to DIN 53019 with a rotary viscometer at

20 ° C.

The solids content was measured according to DIN 12605, whereby 1 g of substance was weighed into a 3.5 cm flat weighing bottle and dried for 2 hours. at 120 ° C in a drying oven.

The pH was measured according to DIN 53785 / ISO 1148.

To measure the gelation time, 100 g of melamine resin was mixed with 3 g formic acid 34 wt% and the mixture was heated to 40 ° C. The gelation time is the time between the addition of the curing agent and the curing of the sample.

Application-technical tests

For application testing, a homogeneous adhesive bath was prepared in a ready-to-use state from 100 parts by weight of melamine resin and 20 parts by curing mixture. The tests were carried out according to the regulations given in DIN 68131, October 1969 edition and DIN EN391, November 1990 edition in conjunction with DIN EN 386, issued November 1990. The following tests were carried out in particular:

Test I Durability, DIN 68141 Paragraph 2.1.2

Test II Open drying time, DIN 68141, paragraph 2.1.3

Test III Influence of joint thickness and different bearing order on jointability, DIN 68141, paragraphs 2.1.1 (A) and 2.2.3 (B)

Test IV Effect of room climate on solidification rate, DIN 68141, paragraph 2.3 (a) after 24 hours

Test V Delamination resistance, DIN standard EN 386

Test VI Optical assessment of bonded joints and their darkening

- 13 The tests were carried out on the following adhesive baths:

Adhesive bath 1

Melamine resin A with curing mixture 1

Adhesive bath 2

Melamine resin C with curing mixture 2

Adhesive bath 3

Phenol-resorcinol-formaldehyde resin (Kauresin.RTM. Leim 460 flussig BASF AG), available commercially, with a commercially available paraformaldehyde phenolic resin curing agent and a small amount of carbonic acid (Karesin.RTM. Hertter 466, Pulver BASF AG).

The results of the application testing are given in Tables 1 and 2.

Table 1:

Adhesion (N / mm2) to DIN 68141 with different joint thickness according to DIN 53254, January 1987 edition.

adhesive Test IIIA Test IIIB Test IV bath save order save order 1 13 14 1 13 14 1 10.6 6.67 10.14 8.90 6.21 7.84 6.26 2 10.39 7.08 9.38 8.40 6.22 6.91 5.21 3 11.30 8.11 10.94 11.22 6.84 9.02 5.24

- 14Table 2:

Results of durability tests and open drying times according to DIN 68141, delamination according to DIN pr EN 391 and 386 and optical assessment of the glued joint color

Adhesive bath Lifetime (min) 20 ° C / 65% rel. humidity Open drying time (min) 400g / m ² delamination after 3 days optical assessment Oak spruce tot. gaps are unit. gaps are 1 105 120 130 2.4 10.4 light crack, slight darkening 2 120 - 167 150 0 0 light crack, no darkening 3 235 135 135 0 0 dark red- brown

Claims (8)

PATENT CLAIMS A two-component adhesive system suitable for the manufacture of wood glued beams, characterized in that it consists of: a) an aqueous curing mixture [component (a)], comprising a1) 3-15 wt.% Bronstedtic acid; and2) 20-40 wt.% mineral filler; and3) 2-8 wt.% thickener. (a4) 40 to 60% water by weight; and (b) melamine resin (component (b)). The two-component adhesive system of claim 1, wherein the aqueous curing composition (a) further comprises an organic filler. The two-component adhesive system of claim 1 or 2, wherein component (a) further comprises resorcinol. A two-component adhesive system according to claims 1 to 3, characterized in that component (b) of b1) melamine b2) is 2.1 to 8.4 moles of formaldehyde per mole of melamine b3) 0 to 1.0 moles of another compound, which is also capable of reacting with formaldehyde in a polycondensation or polyadditive reaction, per mole of formaldehyde. Method for producing wood glued beams from wood slats using a two-component glue system according to claims 1 to 4, characterized in that Ia forms an adhesive bath by mixing components (a) and (b). - 16lla the wood slats with an adhesive layer are prepared by applying the adhesive bath to one or both sides of the wooden slats and 11lla the wooden slats with an adhesive layer are connected to each other or to the wood slats without glue so that they always connect between two glued wooden slats wherein the steps of 1a to IIIa are carried out in the range of 45 to 150 minutes, preferably 60 to 120 minutes. A method of manufacturing wood glued beams using a two-component adhesive system according to claims 1 to 4, characterized in that Ib, the wood slats with an adhesive layer are prepared by separately applying components (a) and (b) to one side or both sides of the wooden slats, so that both component (a) and component (b) are applied on both sides or on the one hand, the wooden lamellae and the wooden lamellae with the adhesive layer are joined to each other or to the wooden lamellas without the adhesive layer, so that the two adhesive components are each between two wooden lamellas. A method for producing wood glued beams using a two-component adhesive system according to claims 1 to 4, characterized in that Ic slats are prepared with a layer of glue by applying components (a) and (b) separately to one side or both sides of the slats so that only one component of the two-component adhesive system is located on the same side of the slat and llc The wooden lamellas with the adhesive layer are joined to each other such that the two components (a) and (b) are each between two glued wooden lamellas. Wooden glued beams produced by the process according to claims 5 to 7.