CN115895566A - An adhesive used for bonding flame-retardant density boards to veneer veneers - Google Patents

Abstract

The adhesive for sticking the veneer facing on the flame-retardant density board comprises a component A, a component B, a component C and a component D, wherein the component A is a silicon-containing acrylate polyol prepolymer with hydroxyl, the component B is a polyisocyanate curing agent, the component C is a catalyst, the component D is a flame-retardant filler, the mass content of the component A is 60-90%, the mass content of the component B is 5-30%, the mass content of the component C is 0.05-0.5%, and the mass content of the component D is 1-10%. The adhesive contains the silicon-containing acrylate polyol prepolymer with hydroxyl, so that the adhesive has higher adhesive force, better weather resistance and certain flame retardance.

Description

Adhesive for bonding flame retardant density board to veneer

Technical Field

The invention relates to an adhesive, in particular to an adhesive used for attaching veneer to flame retardant density board.

Background Art

Flame retardant density board is a kind of flame retardant board. It is generally made by mixing wood fiber, flame retardant and adhesive, and hot pressing to obtain a "plain board". The plain board and the veneer are then bonded with adhesive to improve the aesthetics of the board. Traditional density board (non-flame retardant density board) is mainly bonded with veneer (veneer) by white glue. However, since flame retardant density board has been flame retardant treated, the board contains a certain amount of flame retardant, which reduces its surface energy. At this time, the traditional white glue cannot meet the requirements of bonding veneer, and it is easy to cause peeling problem.

Summary of the invention

The present invention overcomes the drawbacks of the prior art and provides an adhesive for affixing veneer to flame retardant density board, which contains a silicon-containing acrylic polyol prepolymer with hydroxyl groups, so that the adhesive has higher bonding strength, better weather resistance and certain flame retardancy.

The technical solution adopted by the present invention to solve the technical problem is:

An adhesive for affixing veneer to a flame retardant density board, the adhesive comprising component A, component B, component C and component D, wherein component A is a silicon-containing acrylic polyol prepolymer with hydroxyl, component B is a polyisocyanate curing agent, component C is a catalyst, component D is a flame retardant filler, the mass content of component A is 60-90%, the mass content of component B is 5-30%, the mass content of component C is 0.05-0.5%, and the mass content of component D is 1-10%.

The adhesive for flame retardant density board with veneer, the hydroxyl-containing silicon-containing acrylic polyol prepolymer is prepared by free radical polymerization of methacrylate monomer, acrylate monomer, vinyl monomer, hydroxy acrylic monomer and silicon-containing monomer, and has a number average molecular weight _Mn of 30000-70000 and a hydroxyl value of 5-15 mgKOH/g.

In the adhesive for attaching veneer to flame retardant density board, the addition ratio of methacrylate monomer, acrylate monomer, vinyl monomer, hydroxy acrylate monomer and silicon-containing monomer is 10-20:30-40:5-15:5-15:25-35.

The adhesive for flame-retardant density board with veneer, the ester group of the hydroxyl-containing silicon-containing acrylic polyol prepolymer is located at the side chain of the molecular chain, and the preparation process is: in a three-necked flask equipped with a stirrer, a condenser, and a constant pressure titration funnel, ethyl acetate is added, heated to 80°C, and a mixture of methacrylate monomer, acrylate monomer, vinyl monomer, hydroxy acrylate monomer, silicon-containing monomer, and initiator azobisisobutyronitrile is added dropwise through the constant pressure titration funnel, stirring while adding dropwise, and the rotation speed is 90-120rpm.

The above-mentioned adhesive for flame-retardant density board with veneer, the isocyanate curing agent includes at least one of toluene diisocyanate trimer, diphenylmethane diisocyanate trimer, hexamethylene diisocyanate trimer, isophorone diisocyanate trimer and meta-xylylene diisocyanate.

In the adhesive for attaching veneer to flame retardant density board, the adding ratio of the isocyanate curing agent to the hydroxyl-containing silicon-containing acrylic polyol prepolymer is 1:5 to 1:20.

The hydroxyl groups in the hydroxyl-containing silicon-containing acrylic polyol prepolymer can react chemically with the isocyanate group -NCO in the polyisocyanate to generate a carbamate bond -NHCOO-, thereby extending the molecular chain, increasing the molecular weight, and enhancing the cohesive force of the adhesive. Since the hydroxyl group and the isocyanate group react in an equimolar ratio, it can be known from the bonding theory that if the adhesive is to have good adhesion, a certain active group must be retained after the reaction, so the molar ratio of the active groups provided by the two components cannot be 1:1. On the other hand, if the ratio of the two is too different, there will be more small molecules in the system, which will reduce the cohesive force of the adhesive and cause the adhesion to decrease. Therefore, the present invention adjusts the ratio of the polyisocyanate curing agent to the hydroxyl-containing silicon-containing acrylic polyol prepolymer so that the molar number of one reactive functional group is slightly greater than that of the other, and finds the ratio range that makes the adhesive bonding performance reach the best. It should be noted that the ratio stated above is the molar ratio of the active functional groups, which is converted into the mass ratio in the actual operation process by taking into account factors such as the molar ratio of the active functional groups in each molecule, the molar molecular weight, and the solid content.

The above-mentioned adhesive for flame-retardant density board with veneer, the catalyst is at least one of an organic metal catalyst and an organic amine catalyst.

The above-mentioned adhesive for flame-retardant density board with veneer, the flame-retardant filler is one or more of calcium carbonate, magnesium hydroxide and aluminum hydroxide powder, and the particle size of the powder is 0.1-30 μm.

The beneficial effects of the present invention are as follows: Component A in the adhesive of the present invention is a silicon-containing acrylic polyol prepolymer with a hydroxyl group, and the -OH in the prepolymer undergoes a cross-linking and curing reaction with the -NCO group in the polyisocyanate curing agent to form a cross-linked network structure, thereby improving the bonding strength of the adhesive; in addition, the ester bond in the molecular chain of the adhesive of the present invention is in the side chain of the molecular chain, so that it has better weather resistance. The adhesive of the present invention contains silicone, which makes it have excellent flame retardancy. The flame retardant board made by bonding the flame retardant board and the veneer together using the adhesive of the present invention has better bonding strength, no peeling phenomenon, and better flame retardant performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a structure in which 100 squares are drawn on the veneer of a flame retardant board.

DETAILED DESCRIPTION

The adhesive of the present invention has improved bonding strength and better weather resistance, because the -OH in the synthesized hydroxyl-containing silicon-containing acrylic polyol prepolymer undergoes a cross-linking curing reaction with the -NCO group in the isocyanate curing agent to form a cross-linked network structure, thereby improving the bonding strength of the adhesive. Traditional polyester and polyether polyurethane adhesives also react through -OH and -NCO, but their ester bonds or ether bonds are located on the main chain of the molecule, which are easily hydrolyzed in a hot and humid environment, resulting in a decrease in bonding strength, so some anti-hydrolysis agents have to be added to reduce hydrolysis. The adhesive involved in the present invention not only has improved bonding strength, but also exhibits better weather resistance, because the ester bond of the adhesive of the present invention is on the side chain of the molecular chain, and even if hydrolysis occurs in a hot and humid environment, its impact is much smaller than that of traditional polyester or polyether polyurethane adhesives.

The hydroxyl-containing silicon-containing acrylic polyol prepolymer is prepared from methacrylate monomers, acrylate monomers, vinyl monomers, hydroxyl acrylic monomers and silicon-containing monomers through free radical polymerization, and the ester group of the silicon-containing acrylic polyol is located in the side chain of the molecule. Because these monomers have a common feature of containing carbon-carbon double bonds, the initiator azobisisobutyronitrile generates free radicals when heated, and the carbon-carbon double bonds are opened under the action of free radicals, and free radical polymerization occurs to form macromolecules. The parts other than the double bonds of each monomer form "pendants" on the side of the macromolecule chain. The ester group of the acrylic ester monomer is in the side chain of the macromolecule, and the side chain of the silicon-containing acrylic ester monomer is a silicon-containing acrylic ester. As follows:

In addition, the adhesive involved in the present invention also has a certain flame retardancy. This is because during the preparation of the adhesive, a certain amount of reactive organic silicon monomer is grafted onto the polymer molecular chain. After the adhesive is burned, a dense and stable silicon-containing (main component SiO ₂ ) carbon layer will be formed on the surface of the substrate. This silicon-containing carbon layer not only prevents the escape of combustible substances that are burned and decomposed, but also plays a role in heat insulation and oxygen isolation, preventing the thermal decomposition of polymer materials, and achieving the purpose of flame retardancy, low smoke, and low toxicity. In addition, the present invention also uses a certain amount of inorganic flame retardant filler, which can absorb a large amount of heat and slow down the temperature increase of the flame-retardant material, thereby achieving a flame retardant effect. Adding a certain amount of inorganic filler can appropriately increase the viscosity of the adhesive, prevent the liquid adhesive from flowing on the substrate, and allow the adhesive to fully infiltrate the substrate, which is conducive to improving the adhesion, thereby achieving the perfect compatibility of the adhesive adhesion and flame retardancy.

The monomers selected in the polymerization process of the hydroxyl-containing silicon-containing acrylic polyol prepolymer of the present invention are: methacrylate monomer, acrylate monomer, vinyl monomer, hydroxy acrylate monomer. In order for the adhesive to have good adhesion, two conditions must be met: 1. Good wetting with the adhered substrate; 2. Forming a chemical bond with the adhered substrate. The adherends in this experiment are flame retardant boards and thin veneers. The flame retardant boards are mainly made by introducing flame retardants into ordinary density boards, and the outer surface may be urea-formaldehyde resin or melamine-formaldehyde resin containing flame retardants. The main components of wood are: cellulose, hemicellulose and lignin, and there are hydroxyl groups on their surfaces. Therefore, increasing the polarity in the adhesive component is beneficial to improving the adhesion. The hydroxy acrylate monomer in the adhesive makes the adhesive main agent also have hydroxyl groups, which can form hydrogen bonds with the hydroxyl groups on the wood surface; the isocyanate curing agent in the adhesive component can form urethane bonds with hydrogen bonds, thereby improving the adhesion; the cyano group in the adhesive main agent is a nitrogen-containing polar group that can form chemical bonds with urea-formaldehyde resin and melamine-formaldehyde resin layers; the ester bond in the adhesive main agent is a polar bond that can form hydrogen bonds with the hydroxyl groups on the wood surface; in addition, the adhesive main agent has a suitable glass transition temperature (Tg) by compounding the relatively rigid methacrylate monomer and the relatively flexible acrylate monomer. In summary, the selected monomers are connected into a macromolecular chain through free radical polymerization, so that the adhesive main agent has a suitable glass transition temperature and can form chemical bonds with the flame retardant board and the thin veneer. At the same time, due to the introduction of silicon-based monomers in the flame retardant of the adhesive, it has a certain flame retardancy.

Among them, the methacrylate monomer can be methyl methacrylate; the acrylate monomer can be butyl acrylate or ethyl acrylate; the vinyl monomer can be acrylonitrile; the acrylic ester monomer can be hydroxyethyl acrylate or hydroxyethyl methacrylate; the silicon-containing monomer can be vinyl triethoxysilane (VTES). Each type of monomer can also select other specific monomers of the same series.

The present invention will be further described below in conjunction with the embodiments.

Example 1

100 parts of ethyl acetate were added to a reaction kettle equipped with a mechanical stirrer, a thermometer, a condenser and a constant pressure titration funnel, and heated to 80°C. 15 parts of methyl methacrylate, 40 parts of butyl acrylate, 10 parts of acrylonitrile, 5 parts of hydroxyethyl acrylate, 30 parts of vinyltriethoxysilane and 2 parts of azobisisobutyronitrile were mixed evenly and then continuously added dropwise to the reaction system through a constant pressure titration funnel within 2 hours. The mixture was kept warm for 4 hours until it was cooled to room temperature to obtain a hydroxyl-containing silicon-containing acrylic polyol prepolymer solution with a solid content of 50% (Mn=38,000, hydroxyl value 5 mgKOH/g).

The hydroxyl-containing silicone acrylic polyol prepolymer synthesized above was mixed with an isocyanate curing agent (Wanhua PM200) in a ratio of 5:1, and a catalyst of 0.1% dibutyltin dilaurate (DBTDL) and 1% 1000 mesh heavy calcium were added and mixed evenly to obtain a flame retardant adhesive.

Example 2

The synthesis of the hydroxyl-containing silicone-containing acrylic polyol prepolymer solution is the same as in Example 1.

The hydroxy acrylate prepolymer synthesized above was mixed with an isocyanate curing agent (Covestro N3300) in a ratio of 10:1, and a catalyst of 0.1% dibutyltin dilaurate (DBTDL) and 5% 1000 mesh heavy calcium were added and mixed evenly to obtain a flame retardant adhesive.

Example 3

100 parts of ethyl acetate were added to a reaction kettle equipped with a mechanical stirrer, a thermometer, a condenser and a constant pressure titration funnel, and heated to 80°C. 20 parts of methyl methacrylate, 35 parts of butyl acrylate, 5 parts of acrylonitrile, 15 parts of hydroxyethyl acrylate, 25 parts of vinyltriethoxysilane and 1.5 parts of azobisisobutyronitrile were uniformly mixed and then continuously added dropwise to the reaction system through a constant pressure titration funnel within 2 hours. The mixture was kept warm for 4 hours until it was cooled to room temperature to obtain a hydroxyl-containing silicon-containing acrylic polyol prepolymer solution with a solid content of 50% (Mn=45,000, hydroxyl value 15 mgKOH/g).

The hydroxy acrylate prepolymer A2 synthesized above was mixed with the isocyanate curing agent B (Wanhua PM200) in a ratio of 10:1, and 0.3% of the catalyst C dibutyltin dilaurate (DBTDL) and 5% of 3000 mesh heavy calcium were added and mixed evenly to obtain a flame retardant adhesive.

Example 4

The synthesis of the hydroxyl-containing silicon-containing acrylic polyol prepolymer solution is the same as in Example 3.

The hydroxy acrylate prepolymer synthesized above was mixed with the isocyanate curing agent (Covestro N3300) in a ratio of 20:1, and 0.3% of stannous octoate as a catalyst and 5% of 5000 mesh heavy calcium were added and mixed evenly to obtain a flame retardant adhesive.

Example 5

100 parts of ethyl acetate were added to a reaction kettle equipped with a mechanical stirrer, a thermometer, a condenser and a constant pressure titration funnel, and the mixture was heated to 80°C. 10 parts of methyl methacrylate, 30 parts of butyl acrylate, 15 parts of acrylonitrile, 10 parts of hydroxyethyl acrylate, 35 parts of vinyltriethoxysilane and 1 part of azobisisobutyronitrile were uniformly mixed and then continuously added dropwise to the reaction system through a constant pressure titration funnel within 2 hours. The mixture was kept warm for 4 hours until it was cooled to room temperature to obtain a hydroxyl-containing silicon-containing acrylic polyol prepolymer solution having a solid content of 50% (Mn=62,000, hydroxyl value 10 mgKOH/g).

The synthesized hydroxyl-containing silicone acrylic polyol prepolymer was mixed with an isocyanate curing agent (Wanhua PM200) at a ratio of 10:1, and 0.2% of diethylenetriamine as a catalyst and 10% of 3000 mesh heavy calcium were added and mixed evenly to obtain a flame retardant adhesive.

Example 6

The synthesis of the hydroxyl-containing silicon-containing acrylic polyol prepolymer is the same as in Example 5.

The hydroxy acrylate prepolymer synthesized above was mixed with an isocyanate curing agent (Covestro N3300) in a ratio of 20:1, and 0.2% of a catalyst triethylamine and 10% of 5000 mesh nano-calcium were added and mixed evenly to obtain a flame retardant adhesive.

Comparative Example 1

The synthesis of the hydroxyl-containing silicon-containing acrylic polyol prepolymer is the same as in Example 1.

The hydroxy acrylate prepolymer synthesized above was mixed with the isocyanate curing agent (Wanhua PM200) at a ratio of 50:1, and 0.1% of the catalyst dibutyltin dilaurate (DBTDL) and 1% of 1000 mesh heavy calcium were added and mixed evenly to obtain a flame retardant adhesive.

Comparative Example 2

The synthesis of the hydroxyl-containing silicon-containing acrylic polyol prepolymer is the same as in Example 3.

The hydroxy acrylate prepolymer synthesized above was added with 0.1% of dibutyltin dilaurate (DBTDL) as a catalyst and 1% of 3000 mesh heavy calcium carbonate, and mixed evenly to obtain a flame retardant adhesive.

Comparative Example 3

First, a silicon-free hydroxy acrylate prepolymer is synthesized. 100 parts of ethyl acetate are added to a reaction kettle equipped with a mechanical stirrer, a thermometer, a condenser and a constant pressure titration funnel, and heated to 80°C. 25 parts of methyl methacrylate, 50 parts of butyl acrylate, 15 parts of acrylonitrile, 10 parts of hydroxyethyl acrylate and 2 parts of azobisisobutyronitrile are uniformly mixed and continuously added dropwise to the reaction system through a constant pressure titration funnel within 2 hours, and the mixture is kept warm for 4 hours and cooled to room temperature to obtain a hydroxyl-free silicon-free acrylate polyol prepolymer solution with a solid content of 50% (Mn=41,000, hydroxyl value 10 mgKOH/g).

The hydroxy acrylate polyol prepolymer synthesized above was mixed with an isocyanate curing agent (Wanhua PM200) at a ratio of 10:1, and 0.2% of diethylenetriamine as a catalyst was added and mixed evenly to obtain an adhesive.

The flame retardant board and veneer are bonded by the adhesive prepared in each embodiment and comparative example of the present invention, and the specific process is as follows:

Applying adhesive on the surface of the flame retardant board;

The adhesive is also applied on the surface of the veneer;

The glue-coated surface of the veneer is composited with the flame-retardant board coated with glue, and the non-glue-coated surface of the veneer is hot-pressed at a temperature of 100 to 200°C, a pressure of 30 to 200N, and a time of 10 to 20 minutes;

The other side of the flame retardant board is also subjected to the same composite treatment;

The edges of the flame retardant board are also subjected to the same composite treatment to complete the edge sealing;

Place the entire flame retardant board in a 30-40°C environment for 2-3 days.

The flame retardant board is a commercially available flame retardant density board, the thickness of which can be 3 to 25 mm, and the fire protection grade is B1.

The bonding strength of the finished flame retardant board after bonding was tested. 100 squares were drawn on the veneer on each board, as shown in Figure 1. The veneer was scraped with a flat shovel, and the scraping situation was observed and recorded. The wood breakage rate was recorded, as shown in Table 1. From Table 1, it can be seen that the wood breakage rate of the flame retardant board bonded by the adhesive of the present invention is less than that of the comparative example, indicating that the bonding strength of the adhesive of the present invention is higher.

At the same time, the flame retardant properties of the prepared flame retardant board were tested, and the flame retardant properties test reference standard GB/T8625-2005; and the tensile shear strength of the adhesive was tested, and the reference standard GB/T 7124 2008. The test results are shown in Table 1.

Table 1 Performance test results

Claims (8)

1. The adhesive for sticking the veneer of the flame-retardant density board is characterized in that: the adhesive comprises a component A, a component B, a component C and a component D, wherein the component A is a silicon-containing acrylate polyol prepolymer with hydroxyl, the component B is a polyisocyanate curing agent, the component C is a catalyst, the component D is a flame-retardant filler, the mass content of the component A is 60-90%, the mass content of the component B is 5-30%, the mass content of the component C is 0.05-0.5%, and the mass content of the component D is 1-10%.

2. The adhesive for fire retardant density board veneering of claim 1, wherein: the hydroxyl-containing silicon-containing acrylate polyol prepolymer is prepared by free radical polymerization of methacrylate monomer, acrylate monomer, vinyl monomer, hydroxyl acrylate monomer and silicon-containing monomer, and the number average molecular weight M of the hydroxyl-containing silicon-containing acrylate polyol prepolymer _n 30000-70000 and a hydroxyl value of 5-15 mgKOH/g.

3. The adhesive for fire retardant density board veneering of claim 2, wherein: the addition ratio of the methacrylate monomer, the acrylate monomer, the vinyl monomer, the hydroxyl acrylate monomer and the silicon-containing monomer is 10-20: 30 to 40:5 to 15:5 to 15:25 to 35.

4. The adhesive for fire retardant density board veneering of claim 3, wherein: the ester group of the silicon-containing acrylate polyol prepolymer with hydroxyl is positioned on a molecular chain side chain, and the preparation process comprises the following steps: adding ethyl acetate into a three-mouth bottle provided with a stirrer, a condenser pipe and a constant pressure titration funnel, heating to 80 ℃, dropwise adding a mixture of a methacrylate monomer, an acrylate monomer, a vinyl monomer, a hydroxyl acrylate monomer, a silicon-containing monomer and an initiator azobisisobutyronitrile through the constant pressure titration funnel, stirring while dropwise adding, and rotating at the speed of 90-120 rpm.

5. The adhesive for fire retardant density board veneering veneer facing of claim 1, wherein: the polyisocyanate curing agent comprises at least one of toluene diisocyanate trimer, diphenylmethane diisocyanate trimer, hexamethylene diisocyanate trimer, isophorone diisocyanate trimer and m-xylylene isocyanate.

6. The adhesive for fire retardant density board veneering veneer facing of claim 1, wherein: the adding proportion of the polyisocyanate curing agent to the silicon-containing acrylate polyol prepolymer with hydroxyl is 1:5 to 1:20.

7. the adhesive for fire retardant density board veneering veneer facing of claim 1, wherein: the catalyst is at least one of organic metal catalyst and organic amine catalyst.

8. The adhesive for fire retardant density board veneering of claim 1, wherein: the flame-retardant filler is one or more of calcium carbonate, magnesium hydroxide and aluminum hydroxide powder, and the particle size of the powder is 0.1-30 mu m.

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