WO2001016246A2

WO2001016246A2 - Use of polyvinyl alcohol-stabilized polyvinyl acetate adhesives for bonding particle boards

Info

Publication number: WO2001016246A2
Application number: PCT/EP2000/008524
Authority: WO
Inventors: Bernd Schilling; Thomas Köhler
Original assignee: Wacker-Chemie Gmbh
Priority date: 1999-09-02
Filing date: 2000-08-31
Publication date: 2001-03-08
Also published as: WO2001016246A3; DE19941904A1; EP1222236A2

Abstract

The invention relates to the use of vinylacetate polymer-based synthetic dispersions that are modified with highly viscous polyvinyl alcohol for bonding particulate boards. The inventive use is characterized in that the aqueous synthetic dispersion has a solids content of 30 to 75 % by weight, based on the entire weight of the dispersion, and that the solids content includes a) 50 to 95 % by weight of one or more carboxylic group-containing vinylacetate polymers, b) 4.9 to 49.9 % by weight of one or more polyvinyl alcohols with a degree of hydrolysis of 95 to 100 mole- % and a Höppler viscosity of 0 to 120 mPas (4 % aqueous solution), and c) 0.1 to 10 % by weight water-soluble metal salts of monobasic acids with a pka value < 0. The indications in % by weight refer to the entire solids content.

Description

Use of polyvinyl alcohol-stabilized polyvinyl acetate adhesives for gluing wood chipboards

The invention relates to the use of plastic dipers modified with highly viscous polyalcohol on the basis of vinyl acetate polymers for gluing chipboard.

Formaldehyde condensation resins, for example urea-formaldehyde resins, are widely used for the production of chipboard. On the one hand, these resins are very inexpensive, on the other hand, they are also used because of their special adhesive properties (high crosslinking values, thermosetting properties). Although today the adhesives can be adjusted to be very low in formaldehyde using suitable manufacturing processes, when they are used in chipboard panels under unfavorable moisture conditions, hydrolysis can also occur in living areas and free formaldehyde can be emitted.

For this reason, dispersions without formaldehyde condensation resin based on vinyl acetate copolymers are frequently used, which contain small amounts of post-crosslinkable N-methylolacrylamide units. The disadvantage here is that even with these groups, when they are crosslinked, formaldehyde can be released under unfavorable circumstances.

It was therefore the task to provide high-quality wood adhesives for bonding chipboard, which lead to bonds with high water resistance and high heat resistance without the risk of formaldehyde being released.

The invention relates to the use of plastic dispersions modified with highly viscous polyvinyl alcohol and based on vinyl acetate polymers for the gluing of wood chipboard, characterized in that the aqueous plastic has a solids content of 30 to 75% by weight, based on the total weight of the dispersion, and in the solids content a) 50 to 95% by weight of one or more carboxyl group-containing vinyl acetate polymers, b) 4.9 to 49.9% by weight of one or more Polyvinyl alcohols with a degree of hydrolysis of 95 to 100 mol% and a Hoppler viscosity of 40 to 120 mPas (4% aqueous solution), and c) 0.1 to 10 Ge. I water-soluble metal salts of monobasic acids with a pks -Value <0, are included, the data in% by weight being based in each case on the total solids content.

The vinyl acetate polymers a) containing carboxyl groups contain from 0.1 to 15% by weight, preferably 0.1 to 5% by weight, particularly preferably 0.1 to 1.0% by weight, in each case based on the total weight of the vinyl acetate polymer, of carboxyl-containing Monomer units which are derived from monounsaturated mono- or dicarboxylic acids. Acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid units are preferred.

In addition to vinyl acetate, 5 to 50% by weight, based on the proportion of vinyl ester in the vinyl acetate polymer, of vinyl esters other than vinyl acetate or maleic acid and fumaric acid diesters can also be copolymerized. Vmyl pivalate, vinyl esters of alpha-branched monocarboxylic acids having 9 to 11 carbon atoms, for example VeoVa 9 or VeoVa 10 (trade names from Shell), and the diisopropyl, di-n-butyl, di-t-butyl, , Di-ethylhexyl and methyl t-butyl ester of fumaric acid and maleic acid.

Suitable polyhydric alcohols b) are polyhydric alcohols with a degree of hydrolysis of 95 to 100 mol% and a Hoppler viscosity from 40 to 120 mPas (4% aqueous solution, 20 ° C., Hoppier method according to DIN 53015), and also those which, in addition to the methyl alcohol and vinyl acetate units, also contain 0.1 to 10 mol% of 1-methyl methyl alcohol contain. Polyvinyl alcohols with a degree of hydrolysis of 98 to 100 mol% are preferred. Polyvinyl alcohols with a Hoppler viscosity of 40 to 60 mPas (4% aqueous solution) are also particularly preferred. The proportion of polyvinyl alcohol is preferably 5 to 10% by weight, based on the solids content of the dispersion.

Water-soluble metal salts of embasic acids are to be understood as those whose water solubility is at least 10 g per liter of water under normal conditions. Preferred metal salts c) are salts of Al (III), Cr (III), Zr (IV). Aluminum chloride, aluminum nitrate, chromium nitrate and zirconium oxychloride are particularly preferred. These hardener salts are preferably used in an amount of 0.5 to 5% by weight, based on the solids content of the dispersion.

To produce the polyvinyl alcohol-stabilized polyvinyl acetate adhesive, the procedure can be such that the corresponding amount of highly viscous polyvinyl alcohol is mixed in with the polyvinyl acetate dispersion together with the hardening agent. It is also possible to proceed in such a way that the aqueous polyvinyl acetate dispersion is prepared in the presence of a mixture of partially saponified polyalcohol as protective colloid and the highly viscous polyvinyl alcohol according to customary methods of free-radical, aqueous emulsion polymerization.

The polymerization to produce the polyvinyl acetate

Dispersion is preferably carried out in a temperature range from 40.degree. C. to 120.degree. C. and initiated using the methods usually used for emulsion polymerization. The initiation takes place by means of radical formers, preferably in quantities of 0.01 to 1.0% by weight, based on the total weight of the monomers. Examples include ammonium and potassium persulfate, alkyl hydroperoxides such as tert-butyl hydroperoxide, and hydrogen peroxide. If appropriate, the radical initiators mentioned can also be combined in a known manner with 0.01 to 0.5% by weight, based on the total weight of the monomers, of reducing agents. Formaldehyde-free reducing agents such as sodium bisulfate or ascorbic acid are suitable.

Suitable protective colloids are polyvinyl alcohols, with a specification typical for use as a protective colloid (degree of hydrolysis 70 to 95 mol%, Hoppler viscosity 5 to 30 mPas). The proportion of protective colloid used in the polymerization is usually 5 to 15% by weight. -%, based on the total mass of the monomer phase. The solids content of the aqueous dispersions obtainable using this procedure is generally 30 to 75% by weight. %.

If polymerization is carried out in the presence of the highly viscous polyalcohol, a residual amount of highly viscous polyvinyl alcohol can optionally be added to the dispersion together with the metal salt portion c) after the end of the polymerization.

The carboxyl-functional comonomers can be used in the form of their free acid or as anhydrides for the polymerization. The carboxyl-functional comonomers are preferably metered in completely.

With the use according to the invention of plastic dispersions modified with highly viscous polyalcohol on the basis of vinyl acetate polymers for the glueing of chipboard, the required high bending tensile strengths of about 15 N / mm ² and transverse tensile strengths of about 15 N / mm ^{2 are} obtained even without the addition of formaldehyde condensation resins in the production of chipboard 0.3 N / mm ² . The adhesive based Plastic dispersions modified with highly viscous polyvinyl alcohol are particularly suitable for gluing chipboard for furniture production and interior construction.

The production of the chipboard can m known

Done with wood shavings. For example, the wood chips can be glued with the adhesive dispersion in a free-fall cascade mixer with glue resin wide-area spraying. Then is pressed at a pressure of 90 ° C to 150 ° C, under a pressure of 50 to 100 bar.

The following examples serve to further explain the invention:

Example 1 (preparation of the polymer dispersion):

120 kg of an 8.5% strength polyvinyl alcohol solution were placed in a 500-liter reactor with automatic metering devices, temperature controls and a stirrer. The polyvinyl alcohol had a degree of hydrolysis of 90 mol% and a viscosity of 28 mPas (4% aqueous solution). Then 34 kg of vinyl acetate were emulsified and the mixture was heated to 55 ° C. The polymerization was then started using the Ascorb acid / t-butyl hydroperoxide initiator system. After 1/2 hour of polymerization, 100 kg of vinyl acetate were metered in together with 0.8 kg of maleic anhydride within 3 hours. The resulting dispersion had a solids content of 51.7%.

Example 2 (preparation of the adhesive):

To prepare the adhesive, 880 g of the polyvinyl acetate dispersion from Example 1 were mixed with 25 g of aluminum chloride

Hexahydrate and 120 g of a polyalcohol with a Hoppler viscosity of 56 mPas (4% aqueous solution, 20 ° C) and a degree of hydrolysis of 98 mol% mixed.

The adhesive strength was determined according to DIN EN 204/205 and the heat resistance of the bonds determined according to WATT 91.

Test methods:

Adhesive strength according to DIN EN 204/205:

The test specimens were produced in accordance with DIN EN 205. To this end, two 5 mm thick, 130 mm wide and 600 mm long beech wood panels with the adhesive dispersion to be tested were evenly distributed over the adhesive surface

Pressure glued together, the glued plates divided into 150 mm long test specimens and stored according to DIN EN 204. A part of the test specimens was hot pressed at 120 ° C for 15 minutes.

For the test to be assigned to stress group D2, the test specimens were glued for 7 days in a normal climate (23 ° C, 50% humidity), then for 3 hours in cold water at 23 ° C, and finally for a further 7 days in a normal climate stored.

For the test to assign stress group D3, the test specimens were stored in normal climate (23 ° C, 50% humidity) for 7 days after gluing, then in cold water at 23 ° C for 4 days. For the test to be assigned to stress group D4, the test specimens were stored after the gluing for 7 days in a normal climate (23 ° C, 50% humidity), then for 6 hours in boiling water, and finally for a further 2 hours in 23 ° C cold water. After storage, the adhesive strength was determined with the test specimens in the tensile-shear test, with the tensile test specimens being pulled apart with a tensile testing machine at a pull-off speed of 50 mm / min and subjected to stress until they broke. In the event of breakage, the maximum force F _] ι _a χ that occurred was determined. The adhesive strength T is calculated according to DIN EN 205 from T = F _Max / A, where A is the glued test area m mm ² .

Heat resistance test according to WATT 91 (Wood Adhesive Temperature Test): The test specimens were produced and divided in accordance with EN 205 and stored for 7 days in a standard climate. Some of the test specimens were hot pressed at 120 ° C. for 15 minutes before storage. The test specimens were then stored in a warm cabinet preheated to 80 ° C. at a temperature of 80 ° C. for 1 hour. Immediately after the warm storage, the heat resistance was determined in the tensile-shear test in accordance with DIN EN 205, with the tensile test specimens being pulled apart with a tensile testing machine at a peeling speed of 50 mm / min and bs stressed to break. In the event of breakage, the maximum force F _Max occurring was determined.

The heat resistance is calculated from F ^ _ax / A, where A is the bonded test area in mm ² .

The test results are summarized in Table 1:

Table 1:

Example 3:

With the adhesive dispersion from Example 2, pine chips were glued in an amount of 7% by weight of solid resin per atro chip and a single-layer plate with 510 mm × 510 mm × 21 mm was pressed by pressing at a temperature of 140 ° C. for a pressing time of 4 minutes manufactured. 10 test specimens were produced from this plate and the following property profile was determined: transverse tensile strength 0.35 N / mm ² , bending tensile strength 15.3 N / mm ² , ² h thickness swelling 36%, ² h water absorption 101%.

Claims

Claims:

1. Use of plastic dispersions modified with high-viscosity polyvinyl alcohol on the basis of vinyl acetate polymers for gluing chipboard, characterized in that the aqueous plastic dispersion has a solids content of 30 to 75% by weight, based on the total weight of the dispersion, and in the solids -

a) 50 to 95% by weight of one or more carboxyl group-containing vinyl acetate polymers, b) 4.9 to 49.9% by weight: one or more polyvinyl alcohols with a degree of hydrolysis of 95 to 100 mol% and a Hoppler viscosity of 40 to 120 mPas (4% aqueous solution), and c) 0.1 to 10% by weight of water-soluble metal salts of embolic acids with a pks value <0, are contained, the details in% by weight in each case based on the total solids content are related.

2. Use according to claim 1, characterized in that the carboxyl group-containing vinyl acetate polymers a) contain a proportion of 0.1 to 15 wt .-%, based on the total weight of the vinyl acetate polymer, of carboxyl group-containing monomer units which are monounsaturated Derive mono- or dicarboxylic acids.

3. Use according to claim 1 or 2, characterized in that the carboxyl group-containing vinyl acetate polymers a) still contain 5 to 50% by weight, based on the proportion of vinyl ester in the vinyl acetate polymer, of vinyl acetate different from vinyl acetate or maleic acid and fumaric diesters.

4. Use according to claim 1 to 3, characterized in that the Polyvmylalkohole b) have a degree of hydrolysis of 98 to 100 mol%.

5. Use according to claims 1 to 4, characterized in that the polyalcohols b) have a Hoppler viscosity of 40 to 60 mPas (4% aqueous solution).

6. Use according to claim 1 to 5, characterized in that salts of AI (III), Cr (III), Zr (IV) are used as metal salts c).

7. Use according to claims 1 to 6, characterized in that the metal salts c) are used in an amount of 0.5 to 5% by weight, based on the solids content of the dispersion.

8. Use according to claims 1 to 7, characterized in that the carboxyl group-containing vinyl acetate polymers a) are prepared in the presence of a polyvinyl alcohol b) by means of emulsion polymerization.

9. Use according to claim 1 to 8, characterized in that the modified with highly viscous polyvinyl alcohol plastic dispersions are used for gluing chipboard for the furniture industry.

10. Use according to claim 1 to 8, characterized in that the modified with highly viscous polyvinyl alcohol plastic dipersions are used for gluing chipboard for interior construction.