Gradient curing type formaldehyde-free adhesive for impregnated paper as well as preparation method and application of gradient curing type formaldehyde-free adhesive

Abstract

The invention discloses a gradient curing type formaldehyde-free adhesive for impregnated paper as well as a preparation method and application thereof. The preparation method comprises the following steps: 1) uniformly mixing an acrylate monomer and a functional acrylic acid or ester monomer; dispersing the emulsifier and the acid catalyst into water, uniformly stirring, heating to 55-65 DEG C, adding the persulfate initiator, continuously heating to 70-90 DEG C, dropwise adding into the mixed solution, cooling the emulsion to room temperature, filtering and discharging to obtain the gradient curing type formaldehyde-free adhesive for impregnated paper. The acrylate monomer and the functional acrylate monomer are used as mixed monomers, the catalyst and the initiator are added, and polymerization is carried out in water to finally obtain the special gradient curing type formaldehyde-free adhesive emulsion for impregnated paper, which is excellent in comprehensive performance, non-toxic and environment-friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of adhesives, and in particular relates to a gradient-curing formaldehyde-free adhesive for impregnated paper, and a preparation method and application thereof. Background Art

[0002] Impregnated paper (abbreviated as impregnated paper) is a kind of paper with a certain resin and volatile content obtained by impregnating plain paper or printed decorative paper with resin and drying to a certain degree. It can be glued with the artificial board substrate after hot pressing. Impregnated paper is mainly obtained by impregnating and drying melamine formaldehyde resin (i.e. melamine resin) and some additives, so it is also called melamine paper. Melamine resin can give decorative boards excellent heat resistance, water resistance, wear resistance and appearance quality. At present, the biggest problem of impregnated paper is that formaldehyde is one of the main raw materials for the production of trialdehyde glue, and there is inevitably a problem of formaldehyde release. In the list of carcinogens published by the International Agency for Research on Cancer of the World Health Organization in 2017, formaldehyde is a Class 1 carcinogen. At present, the first problem of decorative materials is formaldehyde release. Decorative materials can be free of formaldehyde except for decorative film paper. Therefore, whether the problem of free formaldehyde of decorative film paper can be solved is the only way to determine whether the decorative artificial board and even the entire furniture industry can be green. With the implementation of the new environmental protection law in 2015, formaldehyde-free is the inevitable development direction of the furniture industry.

[0003] Emulsion acrylic adhesive is a common formaldehyde-free adhesive with excellent performance, especially excellent color retention, light resistance and weather resistance, not easy to oxidize, insensitive to ultraviolet degradation, widely used in packaging, coatings, construction, textiles and leather and other industries, and emulsion adhesive products are environmentally friendly and non-toxic. As the country and consumers have higher and higher requirements for environmental protection, as one of the formaldehyde-free adhesives, the performance of emulsion adhesives can fully meet the requirements of the decorative paper industry. However, conventional acrylic adhesives cannot meet the current production process requirements of impregnated paper impregnation-drying (partial curing of resin)-hot pressing (complete curing of resin) and cannot give decorative panels excellent wear resistance. Only acrylic adhesives with gradient curing can be used for impregnated paper. In addition, because there is a layer of ink on the surface of plain paper or printed decorative paper, the pore size of the paper becomes smaller and the permeability becomes worse. Only adhesives with smaller particle size, i.e. good permeability and highly transparent film formation can be used for impregnated paper adhesives. Summary of the invention

[0004] Technical problem to be solved: The present invention provides a non-aldehyde adhesive for preparing impregnated paper with excellent comprehensive performance, non-toxicity and environmental friendliness and with gradient curing, as well as a preparation method and application thereof.

[0005] Technical solution: A method for preparing a gradient-curing formaldehyde-free adhesive for impregnated paper, the preparation steps are: 1) uniformly mixing acrylate monomers accounting for 10% to 50% of the total weight of the emulsion and functional acrylic acid or ester monomers accounting for 0.5% to 5% of the total weight of the emulsion; 2) dispersing 0.1% to 5% of the emulsion by weight of the emulsion and 0.01% to 1% of the acid catalyst accounting for the total weight of the emulsion into water accounting for 50% to 90% of the total weight of the emulsion, stirring evenly, heating to 55 to 65° C., adding a persulfate initiator, continuing to heat to 70 to 90° C., and dripping the mixed solution obtained in step 1) for 2 to 6 hours, and keeping warm for 0.5 to 2 hours, cooling the emulsion to room temperature, filtering the material, and obtaining a gradient-curing formaldehyde-free adhesive for impregnated paper.

[0006] The acrylic acid ester monomer in step 1) is a mixture of at least three of methyl methacrylate, butyl acrylate, isooctyl acrylate, butyl methacrylate, tert-butyl methacrylate or isobornyl acrylate.

[0007] The functional acrylic (ester) monomer in step 1) is a mixture of at least two of acrylic acid, methacrylic acid, hydroxyethyl acrylate, acrylamide, diallyl phthalate, ditrimethylolpropane acrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, ethylene glycol dimethacrylate, hexanediol dimethacrylate, butanediol dimethacrylate or glycidyl methacrylate.

[0008] The emulsifier in step 2) is a mixture of at least two of sodium dodecyl sulfate (SLS), polyoxyethylene nonylphenol ether (OP), sodium octylphenol polyoxyethylene ether maleate (OS), and alkylphenol polyoxyethylene ether ammonium sulfate (CO436).

[0009] The persulfate in step 2) is sodium persulfate, potassium persulfate or ammonium persulfate, and its usage amount accounts for 0.01% to 1% of the total weight of the emulsion.

[0010] The acidic catalyst in step 2) is disodium hydrogen phosphate, sodium dihydrogen phosphate or phosphoric acid.

[0011] The preferred preparation method is as follows: 100 g of methyl methylpropionate, 100 g of butyl methacrylate, 5 g of tert-butyl methacrylate, 3 g of ditrimethylolpropane acrylate, 2 g of acrylic acid and 3 g of acrylamide are weighed and mixed into a monomer solution; 300 g of water is prepared, 3 g of SLS, 2 g of OP and 3 g of CO436 are added while stirring, and after uniform mixing, 0.3 g of disodium hydrogen phosphate is added, the temperature is raised to 60° C., 0.5 g of ammonium persulfate is added, the temperature is raised to 86° C., the monomer solution is added dropwise for 4 hours, the temperature is kept for 1 hour, the mixture is cooled to room temperature, and the material is filtered to obtain a gradient-curing formaldehyde-free adhesive for impregnated paper.

[0012] The gradient curing formaldehyde-free adhesive is prepared by the above preparation method.

[0013] Application of the above-mentioned gradient curing formaldehyde-free adhesive in the preparation of impregnated paper.

[0014] An impregnated paper is prepared from the above-mentioned gradient curing formaldehyde-free adhesive.

[0015] Beneficial effects: 1. The functional acrylate monomers with heterocyclic rings, methyl groups, tert-butyl groups and multiple double bonds are introduced, and cross-linked copolymerization is carried out during the emulsion polymerization process to achieve partial curing of the polymer, which can give the acrylate polymer good wear resistance, water resistance and other properties, and can maintain good permeability and polymer retention rate in the paper during the impregnation process of the impregnated paper.

[0016] 2. Introduce functional acrylate monomers with amide, hydroxyl, carboxyl and epoxy groups. These groups do not participate in the reaction during emulsion polymerization and impregnation, but can be cross-linked and cured during high temperature. This can give the impregnated paper prepared with acrylate adhesives both bonding and heat curing properties during high temperature hot pressing.

[0017] 3. It is easy to mass produce, can be used for impregnating film paper, and has gradient curing properties, can meet the existing impregnated paper production process requirements, and has a good storage period (the storage period of ordinary melamine formaldehyde impregnated resin is only 3-5 days).

[0018] 4. The present invention can directly obtain products with high solid content, low viscosity and small particle size, and the reaction process is simple and easy to control.

[0019] The present invention is centered around the major needs of green development of the artificial board industry and improvement of the human living environment. Aiming at the problems of formaldehyde release, easy breakage and short storage period of impregnated decorative paper for artificial board decoration, the present invention adopts emulsion polymerization technology and gradient curing molding technology to prepare an acrylate adhesive emulsion for impregnated paper without formaldehyde, with a high solid content and a long storage period through cross-linking copolymerization of cross-linked functional monomers and acrylate monomers. There are no research reports on an acrylate adhesive emulsion for impregnated paper with high solid content, small particle size and gradient curing properties in China. The technology of the present invention fully meets the requirements of sustainable development and has important significance and far-reaching impact on reducing environmental pollution, maintaining ecological balance and saving energy. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with embodiments:

[0021] Example 1

[0022] A method for preparing a gradient curing formaldehyde-free adhesive emulsion for impregnated paper is prepared by emulsion polymerization and is achieved by the following steps:

[0023] 1) 10% to 50% of the total amount of the emulsion is uniformly mixed with 0.5% to 5% of the functional acrylate monomer; wherein the percentage of the acrylate monomer can be selected from 10%, 20%, 30%, 40%, 50%, and can be selected from a mixture of at least three of methyl methacrylate, butyl acrylate, isooctyl acrylate, butyl methacrylate, tert-butyl methacrylate or isobornyl acrylate; the percentage of the functional acrylic (ester) monomer can be selected from 0.5%, 0.9%, 1.8%, 2.5%, 3.8%, 4.3%, 4.9%, and can be selected from a mixture of at least two of acrylic acid, methacrylic acid, hydroxyethyl acrylate, acrylamide, diallyl phthalate, ditrimethylolpropane acrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, ethylene glycol dimethacrylate, hexanediol dimethacrylate, butanediol dimethacrylate or glycidyl methacrylate.

[0024] 2) Dispersing 0.1% to 5% of the total weight of the emulsion with an emulsifier and 0.01% to 1% of the total weight of the emulsion with an acidic catalyst into 50% to 90% of the total weight of the emulsion, wherein the emulsifier may account for 0.9%, 1.6%, 3%, 5%, and the acidic catalyst may account for 0.05%, 0.1%, 0.3%, 0.5%, 0.85%, stirring evenly, heating to 55 to 65°C, the temperature may be selected to be 58°C, 62°C, and stirring to Persulfate is added as an initiator, and the temperature is continuously raised to 70-90° C., and the temperature can be selected as 78° C. or 84° C., and the mixed solution obtained in step 1) is added dropwise, preferably in a uniform dropping manner, and the dropping time is 2-6 hours, for example, 3.5 hours or 4.9 hours, and the mixture is kept warm for 0.5-2 hours, for example, 2.8 hours, 3.9 hours or 5.2 hours. The emulsion is cooled to room temperature, and the material is filtered to obtain a gradient curing formaldehyde-free adhesive emulsion for impregnated paper.

[0025] The persulfate initiator described in the above step 2) can be sodium persulfate, potassium persulfate or ammonium persulfate, and its usage amount accounts for 0.01-1% of the total weight of the emulsion, such as: 0.1%, 0.3%, 0.5%, 0.7%, 0.85%, 1%; the acid catalyst is disodium hydrogen phosphate, sodium dihydrogen phosphate or phosphoric acid, and the emulsifier is a mixture of at least two of sodium dodecyl sulfate (SLS), polyoxyethylene nonylphenol ether (OP), sodium octylphenol polyoxyethylene ether maleate (OS), and alkylphenol polyoxyethylene ether ammonium sulfate (CO436).

[0026] The invention uses cross-linking functional monomers and acrylate monomers for cross-linking copolymerization to obtain an acrylate adhesive emulsion for impregnated paper which has excellent performance, single dispersion, clean surface, no formaldehyde, high solid content and long storage period.

[0027] Example 2

[0028] Weigh 100g of methyl methylpropionate, 100g of butyl methacrylate, 5g of tert-butyl methacrylate, 3g of ditrimethylolpropane acrylate, 2g of acrylic acid and 3g of acrylamide to form a monomer solution, add 300g of water into a 1000mL four-necked flask, add 3g of SLS, 2g of OP and 3g of CO436 while stirring, mix well, add 0.3g of disodium hydrogen phosphate, heat to 60°C, add 0.5g of ammonium persulfate, heat to 86°C, add the monomer solution dropwise for 4 hours, keep warm for 1 hour, cool to room temperature, filter and obtain a gradient-curing formaldehyde-free adhesive emulsion for impregnated paper. The emulsion performance results are shown in the table in the specification.

[0029] Example 3

[0030] A gradient-curing formaldehyde-free adhesive emulsion for impregnated paper was prepared using the same formula and process as in Example 2, except that tert-butyl methacrylate was replaced with isobornyl acrylate, and ditrimethylolpropane acrylate, acrylic acid and acrylamide were replaced with pentaerythritol tetraacrylate, methacrylic acid and glycidyl methacrylate to obtain a gradient-curing formaldehyde-free adhesive emulsion for impregnated paper. The emulsion performance results are shown in the table in the specification.

[0031] Example 4

[0032] A gradient-curing formaldehyde-free adhesive emulsion for impregnated paper was prepared using the same formula and process as in Example 2, except that methyl methpropionate, butyl methacrylate, tert-butyl methacrylate, ditrimethylolpropane acrylate, acrylic acid and acrylamide were added in amounts of 150 g, 115 g, 10 g, 10 g, 5 g and 10 g, respectively, CO436 was changed to OS, ammonium persulfate was changed to potassium persulfate, and disodium hydrogen phosphate was changed to phosphoric acid. The dropping time was 2 hours, and the insulation time was 2 hours to obtain a gradient-curing formaldehyde-free adhesive emulsion for impregnated paper. The emulsion performance results are shown in the table in the specification.

[0033] Example 5

[0034] A gradient-curing formaldehyde-free adhesive emulsion for impregnated paper was prepared using the same formula and process as in Example 2, except that methyl methpropionate, butyl methacrylate, tert-butyl methacrylate, ditrimethylolpropane acrylate, acrylic acid and acrylamide were used in amounts of 10 g, 20 g, 5 g, 1 g, 1 g and 1 g, ammonium persulfate was replaced by sodium persulfate in an amount of 3 g, and disodium hydrogen phosphate was replaced by sodium dihydrogen phosphate in an amount of 3 g to obtain a gradient-curing formaldehyde-free adhesive emulsion for impregnated paper. The emulsion performance results are shown in the table in the specification.

[0035] Comparative Example 1

[0036] A gradient-curing formaldehyde-free adhesive emulsion for impregnated paper was prepared using the same formula and process as in Example 2, but ditrimethylolpropane acrylate, acrylic acid and acrylamide were not used. The amount of disodium hydrogen phosphate used was 0.05 g, and the amount of water used was 200 g. A gradient-curing formaldehyde-free adhesive emulsion for impregnated paper was obtained. The emulsion performance results are shown in the table in the specification.

[0037] Comparative Example 2

[0038] A gradient-curing formaldehyde-free adhesive emulsion for impregnated paper was prepared using the same formula and process as in Example 2, but SLS and CO436 were not used, the amount of ammonium persulfate used was 2 g, and the reaction temperature when the monomer solution was added was 90°C to obtain a gradient-curing formaldehyde-free adhesive emulsion for impregnated paper. The emulsion performance results are shown in the table in the specification.

[0039] Comparative Example 3

[0040] A gradient-curing formaldehyde-free adhesive emulsion for impregnated paper was prepared using the same formula and process as in Example 2, but acrylic acid and acrylamide were not used. The amount of ditrimethylolpropane acrylate used was 25 g, the amount of ammonium persulfate used was 0.05 g, the amount of disodium hydrogen phosphate used was 2 g, the dropping time was 6 hours, the reaction temperature when the monomer solution was added was 70°C, and the insulation time was 0.5 hour to obtain a gradient-curing formaldehyde-free adhesive emulsion for impregnated paper. The emulsion performance results are shown in the table in the specification.

[0041] Comparative Example 4

[0042] A gradient-curing formaldehyde-free adhesive emulsion for impregnated paper was prepared by the same formula and process as in Example 1, but ditrimethylolpropane acrylate was not used and acrylamide was replaced by hydroxyethyl acrylate to obtain a gradient-curing formaldehyde-free adhesive emulsion for impregnated paper. The emulsion performance results are shown in the table in the specification.

[0043] Table 1: Test results of gradient curing formaldehyde-free adhesive emulsion for impregnated paper

[0044] Emulsion solid content (%) Viscosity (cps) Particle size (nm) Emulsion appearance Filter residue Monomer conversion rate (%) Example 2 40.6 105 96 Translucent homogeneous liquid none 99.5 Example 3 40.5 150 109 Translucent homogeneous liquid none 99.4 Example 4 43.1 487 242 Milky white uniform liquid many 86.7 Example 5 10.8 12 85 Translucent homogeneous liquid none 99.6 Comparative Example 1 46.8 358 223 Milky white uniform liquid many 94.4 Comparative Example 2 40.7 204 416 White homogeneous liquid Small amount 98.6 Comparative Example 3 ― － - Inhomogeneous liquid Full gel - Comparative Example 4 40.1 97 94 Translucent homogeneous liquid Small amount 99.1

[0045] Table 2: Test results of impregnating pre-painted paper and formaldehyde-free veneer fiberboard with gradient curing formaldehyde-free adhesive emulsion

[0046]

[0047] It can be seen from the impregnation conditions, wear resistance and surface bonding strength in the table that only the particle size of formaldehyde-free latex about 100 can meet the impregnation requirements; only functional acrylate monomers with heterocyclic, methyl, tert-butyl and multiple double bonds can be cross-linked and copolymerized during the emulsion polymerization process to impregnate paper and maintain good permeability and polymer retention rate in the paper during the impregnation process; functional acrylate monomers with amide, hydroxyl, carboxyl and epoxy groups can be cross-linked and cured during high-temperature hot pressing, and can give the impregnated paper prepared with acrylic adhesive the properties of bonding and heat curing during high-temperature hot pressing, as well as good wear resistance and surface bonding strength.

Claims

1. A method for preparing a gradient curing formaldehyde-free adhesive for impregnated paper, characterized in that: The preparation steps are as follows: 1) uniformly mixing 10% to 50% of an acrylate monomer accounting for the total weight of an emulsion and 0.5% to 5% of a functional acrylic acid or ester monomer accounting for the total weight of the emulsion; 2) dispersing 0.1% to 5% of an emulsifier accounting for the total weight of the emulsion and 0.01% to 1% of an acid catalyst accounting for the total weight of the emulsion into 50% to 90% of water accounting for the total weight of the emulsion, stirring uniformly, heating to 55 to 65° C., adding a persulfate initiator, continuing to heat to 70 to 90° C., and dripping the mixed solution obtained in step 1) for 2 to 6 hours, and keeping the temperature for 0.5 to 2 hours, cooling the emulsion to room temperature, filtering the material, and obtaining a gradient curing formaldehyde-free adhesive for impregnated paper.

2. The preparation method according to claim 1, characterized in that: The acrylic acid ester monomer in step 1) is a mixture of at least three of methyl methacrylate, butyl acrylate, isooctyl acrylate, butyl methacrylate, tert-butyl methacrylate or isobornyl acrylate.

3. The preparation method according to claim 1, characterized in that: The functional acrylic (ester) monomer in step 1) is a mixture of at least two of acrylic acid, methacrylic acid, hydroxyethyl acrylate, acrylamide, diallyl phthalate, ditrimethylolpropane acrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, ethylene glycol dimethacrylate, hexanediol dimethacrylate, butanediol dimethacrylate or glycidyl methacrylate.

4. The preparation method according to claim 1, characterized in that: The emulsifier in step 2) is a mixture of at least two of sodium dodecyl sulfate (SLS), polyoxyethylene nonylphenol ether (OP), octylphenol polyoxyethylene ether sodium maleate (OS), and alkylphenol polyoxyethylene ether ammonium sulfate (CO436).

5. The preparation method according to claim 1, characterized in that: The persulfate in step 2) is sodium persulfate, potassium persulfate or ammonium persulfate, and its usage amount accounts for 0.01% to 1% of the total weight of the emulsion.

6. The preparation method according to claim 1, characterized in that: The acidic catalyst in step 2) is disodium hydrogen phosphate, sodium dihydrogen phosphate or phosphoric acid.

7. The preparation method according to claim 1, characterized in that: Weigh 100g of methyl methylpropionate, 100g of butyl methacrylate, 5g of tert-butyl methacrylate, 3g of ditrimethylolpropane acrylate, 2g of acrylic acid and 3g of acrylamide to form a monomer solution; prepare 300g of water, add 3g of SLS, 2g of OP and 3g of CO436 while stirring, mix well, add 0.3g of disodium hydrogen phosphate, heat to 60°C, add 0.5g of ammonium persulfate, heat to 86°C, add the monomer solution dropwise for 4 hours, keep warm for 1 hour, cool to room temperature, filter the material, and obtain a gradient-curing formaldehyde-free adhesive for impregnated paper.

8. A gradient-curing formaldehyde-free adhesive prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the gradient curing formaldehyde-free adhesive according to claim 8 in the preparation of impregnated paper.

10. An impregnated paper, characterized in that: It is prepared from the gradient curing formaldehyde-free adhesive as described in claim 8.

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