HRP970066A2 - 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 proposed invention relates to a two-component adhesive suitable for the production of plywood, which consists of

a) aqueous mixture of hardener (component (a)), which contains

a1) 3 to 15 wt. % Bronstedt acid,

a2) 20 to 40 wt. % mineral filler,

a2) 2 to 8 wt. % thickening agent,

a3) 40 to 60 wt. % water

and

b) melamine resins (component (b)).

The invention further relates to the process for the production of plywood using a two-component adhesive, as well as to the plywood produced in this way.

Plywood constructed from glued wooden lamellas is generally known (compare Informationsdienst Holz, Holzleimbau, Bauen mit Brettschichtholz; Publisher Arbeitsgemeinschaft Holz e. V. und Centrale Marketingsgesellschaft, ISSN-Nr. 0446-2114). These plywood boards are mainly used as load-bearing elements in industrial, residential and public construction.

In this area of technical application, high demands are placed on the mechanical strength of construction parts. The strength of the joint must be sufficiently high even after many years despite the effects of weather conditions such as changes in temperature and humidity.

Therefore, in order to receive the necessary recommendation of suitability of the construction inspection, the adhesives used for the production of load-bearing construction parts must undergo extensive tests in state testing institutions.

The basis of these tests is represented by DIN 68141 together with DIN EN 301 and DIN EN 302, Part 1 to 4. Within the framework of the production plant's own control, the quality of the manufactured building part should be confirmed by delamination testing according to DIN EN 386 and DIN EN 391.

In addition to the requirements for adhesives with regard to the functional properties of the building parts produced with them, plywood manufacturers want certain properties related to the processing of the adhesive. On the one hand, the drying time of the glue must be long enough, so that wooden lamellas coated with glue can be processed in a certain period of time, while on the other hand, the glued construction parts must be ready for mechanical loads in the shortest possible time after their production. This assumes rapid hardening of the glue after joining the coated boards.

It is generally known among experts that phenol-resorcinol resins can be used for the production of plywood, which can be used for the production of load-bearing building elements. However, the disadvantage of layered wooden elements is that the adhesive joint, due to its own dark color of phenol-resorcinol resin, appears as a pattern of black lines in the finished construction part, which is often rejected for aesthetic reasons.

Liquid hardeners are known from Swedish patent 78 10 982. These are aqueous suspensions, which, in relation to the aqueous suspension, contain 1 to 25 wt. % acid or acid releasing substance, 30 to 90 wt. % filler, for example mineral filler such as kaolin, 0.5 to 10 wt. % thickening agent and 0 to 50 wt. % formaldehyde absorber. The hardener contains between 35 and 85 mass percent of dry matter and at 20°C has a viscosity of 2000 to 12000 mPa.

It is recommended to use a hardener for curing urea-formaldehyde resins. However, the plywood produced using this binder-hardener system does not have the necessary strength, especially if it will be used in external applications.

Therefore, the task of the proposed invention was to prepare a two-component adhesive for the production of plywood that does not have dark adhesive joints and that has the mechanical strength required by the construction industry.

Accordingly, the two-component adhesive defined in the introduction was prepared.

The hardener mixture (component (a)) at a temperature of 20°C preferably has a viscosity of 3000 to 10000, particularly usefully of 4000 to 8000 mPa s, and a shear rate of 30 s-1.

The hardener mixture contains first of all

a1) 5 to 12, especially useful 7 to 10 wt. % Bronstedt acid,

a2) 20 to 40, especially useful 25 to 35 wt. % mineral filler,

a3) 2 to 8, especially useful 4 to 6 wt. % thickening agent,

a4) 35 to 60, especially useful 40 to 55 wt. % water.

Suitable Bronstedt acids are, for example, mineral acids such as phosphoric acid or organic acids, such as acetic acid, propionic acid, oxalic acid or above all formic acid.

Kaolin or other aluminosilicates with a layered structure come into consideration as mineral fillers.

Polyvinyl alcohol or partially hydrolyzed polyvinyl acetate or a mixture thereof is suitable as a thickening agent. Polyvinyl alcohol can be obtained, for example, under the commercial name Moviol® (manufacturer Hoechst). With partially hydrolyzed polyvinyl acetate, at least 50%, preferably 80%, of the ester groups originally present in polyvinyl acetate are hydrolyzed. Component (c) is used in an amount of 1 to 20 wt. %, preferably 1 to 8 wt. %.

In addition to the mineral filler, the hardener mixture can also contain an organic filler. This is generally a filler that the glue usually contains, for example in the form of fibers, for example cellulose or wood flour.

In relation to the amount of mineral filler in component (a), the mixture usually contains from 10 to 30 wt. % organic filler.

If you want a plywood that will be particularly resistant to the effects of moisture, the hardener mixture further usefully contains 1 to 20, especially usefully 3 to 8 wt. % of resorcinol in relation to the total amount of components (a1) to (a4).

The mixture of hardeners can be further added with the usual auxiliaries and additives, such as anti-foaming agents or emulsifiers in an amount of 3 wt. % in relation to the amount of components (a1) to (a4).

As component (b), the melamine resin, common commercial resins, which are known for example from Ullmann's Encyclopedia of Technical Chemistry, 4th edition, volume 7, pages 408 and 409, come into consideration.

This is primarily about melamine resin from

b1) melamine,

b2) 2.1 to 8.4, preferably 2.5 to 4.6 moles of formaldehyde per mole of melamine,

b3) 0 to 10, preferably 0 to 0.5 moles of a further compound per mole of formaldehyde, which can enter into a polycondensation or polyaddition reaction with formaldehyde.

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

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

As components (b3) come into consideration above all those that can be used together with formaldehyde in the production of aminoplastic resins (compare Ullmann's Encyclopedia of Technical Chemistry, 4th edition, volume 7, pages 403 to 422), so for example urea, dicyanamide and guanamines such as benzoguanamine and acetoguanamine. Bisguanamines such as adipo-, glutaro- or methylolglutarobisguanamine are suitable, as well as compounds containing several, for example condensed, amino-triazine nuclei.

Especially useful component (b) contains

b1) 15 to 30 wt. % melamine,

b2) 15 to 30 wt. % formaldehyde,

b3) 5 to 25 wt. % of urea, dianamide and/or guanamine.

The preparation of melamine resin is primarily carried out according to general customary procedures, known for example from Ullmann's Encyclopedia of Technical Chemistry, 4th edition, volume 7, p. 403 to 422.

The chemical conversion takes place in the usual way in an aqueous solution, where the proportion of water, in relation to the mass proportion of components (bi) to (b3), is 25 to 50 wt. %. In this case, the pH value is generally 7 to 10, preferably at 9.0 to 10.0 and the reaction temperature takes place at 60 to 110, preferably at 80 to 110°C.

The chemical conversion is generally carried out as long as the final melamine resin, i.e. elastified melamine resin, is formed. At a temperature of 20°C, 60% wt. the aqueous solution of the product of this chemical conversion usually has a viscosity of 350 to 1200, preferably 450 to 800 mPa-s. Under the stated reaction conditions, the reaction generally lasts from 70 to 150 minutes.

The chemical conversion can be completed by cooling the reaction mixture to a temperature below 50°C, preferably to 20 to 30°C.

Water elastified melamine resins are generally preferred, especially those with a solids content of 50 to 70 wt.%. If melamine resin with the desired solids content is not available immediately after its production, it is possible to change the solids content by removing water by distillation in a vacuum, or by adding water with mixing.

To increase the elasticity of the adhesive, it usefully contains aliphatic polyols in an amount of 5 to 18, preferably 9 to 15 wt.%, in relation to the solids content of the melamine resin. Polyols can be added already to the starting materials, which will be used for the production of melamine resin, or they can be added to the finished melamine resin. First of all, C2- to C20-polyols come into consideration, primarily diols such as ethylene glycol, diethylene glycol, dipropylene glycol and butanediol, as well as triols such as glycerin.

To improve the application-technological properties of the glue, for example, reactivity and flexibility, modification agents, such as ε-caprolactam and other amides of carboxylic acids, can be added to the melamine resin in an amount of 1 to 7, preferably 1 to 3 wt. % in relation to the solid content of melamine resin.

In addition, melamine resin can contain up to 20, preferably 9 to 15 wt. % of organic filler in relation to solid matter. The same organic fillers that can also be contained in component (a) are suitable for this.

The two-component adhesive according to the invention can be applied by mixing components (a) and (b) to produce a liquid adhesive and applying it to at least one of the two surfaces to be joined by gluing.

Liquid glue consists primarily of components (a) and (b) with a mass ratio of 0.1:1 to 0.5:1, and especially useful from 0.2:1 to 0.4:1.

The preparation of liquid glue from components (a) and (b) is not critical and is done purposefully by mixing one component in another.

Particular preference is given to adhesives for casting with the following composition, whereby the listed ingredients are added to 100 wt. parts:

0.5 to 2.5 wt. part of formic acid,

0.3 to 1.5 wt. part of the thickening agent,

12 to 25 wt. parts of melamine in the form of melamine resin,

4 to 21 wt. part of urea in the form of melamine resin, 12 to 25 wt. parts of formaldehyde in the form of melamine resin,

4 to 12 wt. parts of organic filler,

3 to 13 wt. parts of C2 to C20-polyol,

0 to 5 wt. parts of means for modification,

0 to 4 wt. part of resorcinol,

3 to 9 wt. parts of mineral filler,

the rest up to 100 wt. is parts of water.

The two-component adhesives according to the invention are primarily suitable for gluing massive wooden parts. They are particularly suitable for the production of plywood made of several, primarily 5 to 70 wooden lamellas, for example wooden planks with a thickness of 10 to 43 mm.

The gluing of wooden lamellas is done purposefully according to one of the procedures generally known in the wood industry.

At the same time, one can, for example, act in such a way that

Ia: by mixing components (a) and (b), prepare liquid glue.

IIa: coated wooden slats are prepared, whereby liquid glue is applied on one or both sides to the wooden slats, and

IIIa: the coated wooden lamellas are brought into contact with each other or they are brought into contact with uncoated wooden lamellas so that the glue layer is between the two wooden lamellas to be glued,

on the condition that work procedures Ia to III are carried out within a time period of 45 to 150 minutes, preferably from 60 to 120 minutes,

or

Ib: coated wooden lamellas are prepared, whereby separately components (a) and (b) are applied to the wooden lamellas on one or both sides, so that component (a) and also component (b) are applied to one or on both sides of the wooden lamella, i

IIb: coated wooden lamellas are brought into contact with each other, or with uncoated wooden lamellas, so that both components of the glue are always between 2 wooden lamellas, or

Ic: coated wooden lamellas are prepared, whereby components (a) and (b) are applied to the wooden lamellas separately, on one side or on both sides, so that only one component of the two-component adhesive system is always on the same side of the wooden lamella, and

IIc: the coated wooden lamellas are brought into contact with each other in such a way that both components (a) and (b) are always located between the two coated wooden lamellas.

When components (a) and (b) are applied separately, in phase IIb or IIc, components (a) to (b) are applied in a ratio of 0.2:1.0 to 0.5:1.0 to the surface unit of the wooden lamella. , preferably 0.3:1.0 to 0.4:1.0.

The total amount of components (a) and (b), i.e. liquid glue that is applied to wooden lamellas in procedures IIb, IIc, and Ia, is usually 350 to 500 g/m2.

Wooden lamellas, coated with liquid glue, or individual components, are brought into contact with each other by procedures IIIa, IIb, or IIc, generally under the action of pressure from 0.6 to 1.0 N/mm2. This pressure is generally maintained during the time period required for the glue to harden, which at 20°C is approx. 112 - 2 p.m. Curing is usually carried out at room temperature, and at higher temperatures it is shortened according to the curing time.

Liquid adhesives are specially marked by the time of their use after their preparation, i.e. mixing the relevant components (a) and (b). Furthermore, they are characterized by special rheological properties. Based on their structural viscosity and thixotropy, they do not leak down the vertically placed wooden lamella and no threads are pulled out.

Plywood produced with two-component adhesives has particularly excellent mechanical properties, which are retained also in external use.

EXAMPLES

Example 1

Preparation of hardener mixtures

Hardener mixture I

One after the other, 4000 g of 10% polyvinyl alcohol solution, 642 g of water, 1058 g of 85% formic acid, 200 g of propylene carbonate, 600 g of resorcinol, 3000 g of kaolin and 500 g of cellulose fibers were thoroughly mixed with a high-speed mixer and completely homogenized.

The finished hardener had the following features:

density at 20°C [g/ml]: 1.315,

viscosity at 20°C, shear 30/s, [mPa s] 4802

pH value at 20°C, measured with a glass electrode, 1.3.

Hardener mixture I

One after the other, 5320 g of 10.6% polyvinyl alcohol solution, 239 g of water, 941 g of 85% formic acid, 3000 g of kaolin and 500 g of cellulose fibers were thoroughly mixed with a high-speed mixer and completely homogenized.

The finished hardener had the following features:

density at 20°C [g/ml]: 1.265

viscosity at 20°C, shear 30/s, [mPa-s]: 5659

pH value at 20°C, measured with a glass electrode: 1.4.

Preparation of melamine resin

Melamine resin A

A mixture of 2515 g (33.5 moles) of a 40% formaldehyde solution, 2575 g of urea-formaldehyde precondensate (10.7 moles of urea and 42.9 g of formaldehyde), 300 g of water, 15 g of diethanolamine and 2380 g (18, 9 moles) of melamine is heated to 95°C and condensed at that temperature for 75 minutes. It is then cooled to 87°C and further condensed to a viscosity of approx. 900 mPa s (measured at 20°C). Throughout the duration of the condensation, the pH value is constantly kept constant at approx. 9.5. When it cools to 50°C, 415 g (6.9 moles) of urea is added and it is further cooled to room temperature. The viscosity of the mixture is 715 mPa-s (measured at 20°C) and it contains 62.5 wt.% solids. 100 g of caprolactam, 600 g of ethylene glycol and 850 g of cellulose were homogeneously mixed into that resin.

The finished resin had the following features:

viscosity: 2480 mPa-s

solid content: 65.2 wt. %

pH value: 9.2

gelation time (3 g of 34% formic acid, 40°C): 5 minutes.

Melamine resin B

A mixture of 2515 g (33.5 moles) of a 40% formaldehyde solution, 2575 g of urea-formaldehyde precondensate (10.7 moles of urea and 42.9 moles of formaldehyde), 300 g of water, 15 g of diethanolamine and 2380 g (18, 9 moles) of melamine is heated to 93°C and condensed at that temperature for 90 minutes to a viscosity of approx. 600 mPa s (measured at 20°C). Throughout the duration of the condensation, the pH value is constantly kept constant. When it cools to 50°C, 415 g (6.9 moles) of urea is added and it is further cooled to room temperature.

The viscosity of the mixture was 548 mPa s (measured at 20°C) and it contained 62.4 wt.% solids. 850 g of diethylene glycol and 950 g of cellulose were homogeneously mixed into that resin.

The finished resin had the following features:

viscosity: 2380 mPa s

solid content: 65.6 wt. %

pH value: 9.1

gelling time (3 g of 34% formic acid, 40°C): 58 minutes.

Melamine resin C

A mixture of 4550 g (60.7 moles) of a 40% formaldehyde solution, 350 g of urea-formaldehyde precondensate (1.5 moles of urea and 5.8 formaldehyde), 15 g of diethylethanolamine and 2700 g (21.4 moles) of melamine is heated is at 97°C and condenses at that temperature to a viscosity of approx. 580 mPa s (measured at 20°C). All the time during the condensation, the pH value is constantly kept constant. When it cools to 50°C, 438 g (7.3 moles) of urea are added and it is further cooled to room temperature. The viscosity of the mixture was 450 mPa s (measured at 20°C) and it contained 59.1 wt.% solids. 200 g of caprolactam, 300 g of 1,4-butanediol, 500 g of ethylene glycol and 947 g of cellulose were homogeneously mixed into that resin.

The finished resin had the following features:

viscosity: 2270 mPa-s

solid content: 63.5 wt. %

pH value: 9.4

gelation time (3 g of 34% formic acid, 40°C): 42 minutes.

The physical properties of the mixture of hardener and melamine resin are determined as follows:

Viscosities were measured according to DIN 53019 with a rotary viscometer at 20°V. The solids content was measured according to DIN 12605, whereby 1 g of the substance was weighed into a flat weighing container with a diameter of 3.5 cm and dried for 2 hours at 120°C in an oven.

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

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

Applied technological tests

For applied-technological tests from 100 wt. parts of melamine resin and 20 wt. parts of the hardener mixture, ready-to-use liquid glue is prepared. The tests were carried out according to the regulations DIN 68141, edition from October 1969, as well as DIN EN 391, edition from November 1990, connected with DIN EN 386, edition from November 1990. The following were tested individually:

test I, service life, DIN 68141, point 2.1.2,

test II, outdoor drying time, DIN 68141, point 2.1.3,

test III, influence of layer thickness and different order of layers on joint strength, DIN 68141, point 2.1.1 (A) and 2.2.3 (B),

test IV, the influence of the room climate on the joining speed, DIN 68141, point 2.3a) after 24 hours,

test V, resistance to delamination, DIN, proposal EN 386,

test VI, optical evaluation of the color of the adhesive joint and its darkening.

Tests were performed on the following liquid adhesives:

liquid glue 1,

melamine resin A with hardener mixture 1,

liquid glue 2,

melamine resin C with hardener mixture 2,

liquid glue 3.

A common commercial phenol-resorcinol-formaldehyde resin (liquid adhesive Kuresin® 460 from BASF AG) with a common commercial hardener for phenolic resins based on paraformaldehyde and a small amount of carbonic acid (powder hardener Kuresin® 466 from BASF AG).

The results of applied technological tests can be seen in tables 1 and 2.

Table 1:

Joint strengths (N/mm2) by bonding according to DIN 68141 with different joint thicknesses after the laying sequence according to DIN 53254, January 1987 edition.

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Table 2:

Test results of service life and outdoor drying time according to DIN 68141 as well as delamination according to DIN pr EN 391 and 386 and optical evaluation of the color of the adhesive layer.

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Claims (8)

1. A two-component adhesive suitable for the production of plywood, characterized by the fact that it consists of a) aqueous mixture of hardener (component (a)), which contains a1) 3 to 15 wt. % Bronstedt acid, a2) 20 to 40 wt. % mineral filler, a3) 2 to 8 wt. % thickening agent, a4) 4 0 to 60 wt. % water and b) melamine resins (component (b)). 2. Two-component adhesive according to claim 1, characterized in that the aqueous mixture of hardener (a) additionally contains an organic filler. 3. Two-component adhesive according to claim 1 or 2, characterized in that component (a) additionally contains resorcinol. 4. Two-component adhesive according to claims 1 to 3, characterized in that it contains component (b) consisting of b1) melamine, b2) 2.1 to 8.4 moles of formaldehyde per mole of melamine, b3) 0 to 1.0, preferably 0 to 0.5 mol of further compound per mole of formaldehyde, which can enter into a polycondensation or polyaddition reaction with formaldehyde. 5. Process for the production of plywood made of wooden lamellas using a two-component adhesive according to claims 1 to 4, characterized by the fact that Ia: by mixing components (a) and (b), prepare liquid glue, IIa: coated wooden slats are prepared, whereby liquid glue is applied on one or both sides to the wooden slats, and IIIa: the coated wooden lamellas are brought into contact with each other or they are brought into contact with uncoated wooden lamellas so that the glue layer is between the two wooden lamellas to be glued, under the condition that work procedures Ia to Lila are carried out within a time period of 45 to 150 minutes. 6. Method for the production of plywood using a two-component adhesive according to claims 1 to 4, characterized in that Ib: preparation of coated wooden lamellas, whereby separate components (a) and (b) are applied to the wooden lamellas on one or both sides, so that component (a) and also component (b) are applied to one or both sides of the wooden lamella, i IIb: coated wooden lamellas are brought into contact with each other, or with uncoated wooden lamellas, so that both components of the glue are always between 2 wooden lamellas. 7. Process for the production of plywood made of wooden lamellas using a two-component adhesive according to claims 1 to 4, characterized by the fact that Ic: preparations of coated wooden lamellas, whereby components (a) and (b) are applied to the wooden lamellas separately, on one side or both sides, so that only one component of the two-component adhesive system is always on the same side of the wooden lamella, and IIc: the coated wooden lamellas are brought into contact with each other so that both components (a) and (b) are always located between the two coated wooden lamellas. 8. Plywood indicated by the fact that it was produced by one of the procedures according to requirements 5 to 7.