Curing agent for formaldehyde-free substrate and preparation method and application thereof

Abstract

The present invention belongs to the technical field of artificial boards, and relates to a curing agent for a formaldehyde-free substrate, which is composed of 5-10wt% of methyl ethyl ketone oxime, 20-30wt% of polyacrylamide, and the balance of water by weight percentage. A preparation method and application of the curing agent for the formaldehyde-free substrate are also disclosed. The curing agent for the formaldehyde-free substrate disclosed by the present invention has good sealing property, can reduce the viscosity of isocyanate, extend the application period, and improve the fluidity and dispersibility of spray glue. By sealing the free isocyanate group, the pre-curing during drying is reduced, and the isocyanate is unsealed during high-temperature hot pressing, and the isocyanate is cured quickly, the hot pressing efficiency is improved, the hot pressing time is shortened, and the water loss is reduced; more active isocyanate groups are retained in the adhesive, the bonding performance and water resistance are improved, the amount of isocyanate glue applied is reduced, and the reaction with water is reduced. The present invention can also effectively improve the production capacity of the formaldehyde-free floor substrate and reduce the cost; by increasing the moisture content, the expansion or contraction degree caused by the change of humidity in the external environment is reduced, and the dimensional stability is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of artificial boards and relates to a curing agent, in particular to a curing agent for an aldehyde-free substrate and a preparation method and application thereof. Background Art

[0002] Impregnated paper laminated wood flooring, also known as laminate flooring in the market, has the advantages of wear resistance, easy installation, moderate price, easy cleaning, beautiful patterns and comfortable feeling, etc., and occupies most of the market of wood flooring in my country. Laminate flooring generally uses high-density fiberboard as the base material. The urea-formaldehyde resin adhesive used in the manufacture of the base material has problems such as poor water resistance, easy aging of the glue layer, and formaldehyde pollution during production and use, which cannot meet people's requirements for green and environmentally friendly home concepts.

[0003] The base material of formaldehyde-free flooring usually uses polyisocyanate (pMDI) as an adhesive. Its bonding mechanism is that the active group -N=C=O directly forms a chemical bond with the active hydrogen in the plant cellulose to bond. No other additives containing formaldehyde are added during production. It is a green, healthy and environmentally friendly board. When the formaldehyde-free flooring base material slab is hot-pressed, pMDI reacts with water to produce polyurea, which fills the gaps in the wood fiber like a foaming material, making the upper and lower surfaces of the flooring base material denser and making it more difficult for the temperature to transfer from the surface to the core layer. In order to ensure that the core layer temperature can reach the solidified state, the hot pressing time of the slab needs to be extended, which also causes the slab to lose more water. Therefore, the formaldehyde-free flooring base material has the problems of low production capacity and low moisture content, especially low moisture content. After being processed into laminate flooring, it is easy to deform due to changes in the humidity of the external environment, resulting in arching or separation, which affects the consumer's experience.

[0004] In response to the defects of formaldehyde-free floor substrates, industry technicians generally reduce the amount of pMDI and then add other formaldehyde-free adhesives, but this method has the problem of reduced mechanical properties; some manufacturers add formaldehyde-free modification additives such as polyvinyl alcohol, but these can only improve plasticity but cannot increase moisture content. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a curing agent for an aldehyde-free substrate.

[0006] Technical Solution

[0007] A curing agent for a formaldehyde-free substrate consists of the following components by weight percentage: 5-10wt% of methyl ethyl ketone oxime, 20-30wt% of polyacrylamide, and the balance of water.

[0008] Preferably, the curing agent for the formaldehyde-free substrate is composed of the following components by weight percentage: 7wt% methyl ethyl ketone oxime, 25wt% polyacrylamide, and the balance water.

[0009] Preferably, the curing agent for the formaldehyde-free substrate is composed of the following components by weight percentage: 8wt% methyl ethyl ketone oxime, 25wt% polyacrylamide, and the balance water.

[0010] The present invention also discloses a method for preparing the above-mentioned curing agent for the formaldehyde-free substrate, comprising the following steps:

[0011] (1) Add water to the reaction kettle, use 30% by mass of H2SO4 or NaOH solution, adjust the pH to 2.0-4.0, preferably 3.0, and keep the liquid in the reaction kettle at 30-40°C;

[0012] (2) Add methyl ethyl ketone oxime and polyacrylamide evenly in proportion, slowly stir at a speed of 400-600 r / min, and cool naturally to obtain the product.

[0013] Another object of the present invention is to apply the above-mentioned curing agent for formaldehyde-free substrate to the manufacture of formaldehyde-free floor substrate, comprising the following steps:

[0014] (a) pMDI glue application amount 20~40kg / m 3 , heat pMDI to 40±1°C, add the above curing agent at a weight ratio of 2-5% of pMDI, stir and mix evenly, add from a position 50-80cm away from the end of the fiber spraying pipe, and mix evenly with the fiber;

[0015] (b) drying the moisture content of the fibers after sizing to 10-12%, and forming a formaldehyde-free slab after sorting, laying and pre-pressing;

[0016] (c) hot pressing the formaldehyde-free slab at a hot pressing temperature of 160 to 230° C., a hot pressing pressure of 0.6 to 3.0 MPa, and a hot pressing factor of 7 to 9 s / mm to promote slab forming and obtain a formaldehyde-free floor substrate.

[0017] The curing agent for the formaldehyde-free substrate disclosed in the present invention has the following advantages:

[0018] 1. Use methyl ethyl ketone oxime as a blocking agent to react with pMDI to obtain blocked isocyanate. By blocking the free isocyanate in the system, the pre-curing caused by the reaction between isocyanate and moisture in wood fiber after sizing is reduced. When the formaldehyde-free slab is hot-pressed, methyl ethyl ketone oxime is unblocked at high temperature, accompanied by a self-polymerization reaction. The unblocked product can react with pMDI for a rapid curing reaction, improving the hot-pressing efficiency, shortening the hot-pressing time, and thus increasing the moisture content of the formaldehyde-free floor substrate.

[0019] 2. Under acidic conditions, the amino groups on the polyacrylamide molecules are neutralized by acid, which weakens the alkalinity of polyacrylamide and its catalytic activity on isocyanate, inhibits the reaction of polyacrylamide resin and water with isocyanate, and can reduce the initial viscosity of the adhesive, extend the applicability of the adhesive, slow the viscosity growth, improve fluidity, and make the adhesive disperse more evenly during spraying. It can also make the isocyanate adhesive system retain more active isocyanate groups, and more chemical bonds will occur with the hydroxyl groups on the wood during the hot pressing process, so that the formaldehyde-free floor substrate has better bonding performance and water resistance. While ensuring that the performance indicators of the formaldehyde-free floor substrate remain unchanged, the amount of glue applied can be reduced by 15-20%.

[0020] Beneficial Effects

[0021] The curing agent for the formaldehyde-free substrate disclosed in the present invention has good sealing properties, can reduce the viscosity of isocyanate, extend the application period, and improve fluidity and dispersibility during spraying. On the one hand, by sealing the free isocyanate groups, the pre-curing during drying is reduced, and the isocyanate is unsealed during high-temperature hot pressing to quickly cure with the isocyanate, thereby improving the hot pressing efficiency of the formaldehyde-free floor substrate, shortening the hot pressing time of the slab, and reducing the water loss during hot pressing; on the other hand, more active isocyanate groups are retained in the adhesive, which can improve the bonding performance and water resistance of the formaldehyde-free floor substrate, thereby reducing the amount of isocyanate glue applied and reducing the reaction with water. Through the above two aspects, it is possible to increase production capacity and reduce production costs, and to increase the moisture content of the formaldehyde-free floor substrate, reduce the degree of expansion or contraction caused by changes in the humidity of the external environment, and improve the dimensional stability of the formaldehyde-free floor substrate. DETAILED DESCRIPTION

[0022] The present invention is described in detail below in conjunction with the embodiments so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following embodiments.

[0023] Example 1

[0024] A curing agent for a formaldehyde-free substrate consists of the following components by weight: 5wt% of methyl ethyl ketone oxime, 20wt% of polyacrylamide, and 75wt% of water.

[0025] Example 2

[0026] A curing agent for a formaldehyde-free substrate consists of the following components by weight: 8wt% of methyl ethyl ketone oxime, 25wt% of polyacrylamide, and 67wt% of water.

[0027] Example 3

[0028] A curing agent for a formaldehyde-free substrate consists of the following components by weight: 10 wt % of methyl ethyl ketone oxime, 30 wt % of polyacrylamide and 60 wt % of water.

[0029] Effect test of the curing agent for the formaldehyde-free substrate prepared by the present invention:

[0030] 1. Test samples

[0031] The formaldehyde-free substrate curing agents prepared in Examples 1 to 3 were numbered as Sample 1, Sample 2, and Sample 3, respectively.

[0032] 2. Preparation of curing agent for formaldehyde-free substrate

[0033] (1) Add water to the reactor, use 30% by mass of H2SO4 or NaOH solution, adjust the pH to 3.0, and keep the liquid in the reactor at 30-40°C;

[0034] (2) Add methyl ethyl ketone oxime and polyacrylamide evenly into the reaction kettle according to the proportion, and slowly stir at a speed of 400-600 r / min until uniform.

[0035] 3. Production of formaldehyde-free floor substrate

[0036] (1) pMDI glue application amount 35kg / m 3 , heat pMDI to about 40°C, add 3% of the pMDI weight ratio of curing agent, stir for 3 minutes, mix evenly, add from 50 to 80 cm away from the end of the fiber spray pipe, and mix evenly with the fiber;

[0037] (2) drying the moisture content of the fibers after sizing to 10-12%, and forming a formaldehyde-free slab after sorting, laying and pre-pressing;

[0038] (3) Under the conditions of hot pressing temperature of 170-225° C., hot pressing pressure of 0.8-2.8 MPa, and hot pressing factor of 7-8 s / mm, the formaldehyde-free slab is hot pressed to promote the slab forming, thereby obtaining a formaldehyde-free floor substrate with a thickness of 10 mm.

[0039] 4. Comparison of test results

[0040] The production of formaldehyde-free floor substrates was carried out in 4 groups. The above 3 test samples were used as the test group, and the control group sample 4 adopted conventional process. Except for not adding curing agent, all other conditions were the same.

[0041] According to the requirements of GB / T 17657-2022 "Test methods for physical and chemical properties of wood-based panels and veneered wood-based panels", some performance tests were carried out on the formaldehyde-free floor substrate samples prepared above, and the indicators in LY / T 1611-2023 "Fiberboard for floor substrates" (fiberboard for impregnated paper laminated wood floor substrates, nominal thickness ≥8mm) were used for judgment. The results are shown in the following table.

[0042]

[0043] It can be seen from the table that the product pressed using the curing agent for the formaldehyde-free substrate of the present invention has a higher unit production capacity and more excellent main physical and mechanical performance indicators, a higher moisture content and better dimensional stability than the product produced without adding the curing agent.

[0044] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the specification of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A curing agent for an aldehyde-free substrate, characterized in that: The invention is composed of the following components by weight percentage: 5-10wt% methyl ethyl ketone oxime, 20-30wt% polyacrylamide, and the balance water.

2. The formaldehyde-free substrate curing agent according to claim 1, characterized in that: The invention is composed of the following components by weight percentage: 7wt% methyl ethyl ketone oxime, 25wt% polyacrylamide, and the balance water.

3. The formaldehyde-free substrate curing agent according to claim 1, characterized in that: The invention is composed of the following components by weight percentage: 8wt% methyl ethyl ketone oxime, 25wt% polyacrylamide, and the balance water.

4. A method for preparing a curing agent for a formaldehyde-free substrate as claimed in any one of claims 1 to 3, characterized in that: The steps include: (1) Add water to the reactor, use 30% H2SO4 or NaOH solution by mass, adjust the pH to 2.0-4.0, and keep the liquid in the reactor at 30-40°C; (2) Add methyl ethyl ketone oxime and polyacrylamide evenly in proportion, stir slowly at a speed of 400-600 r / min, and cool naturally to obtain the product.

5. The method for preparing a curing agent for a formaldehyde-free substrate according to claim 4, characterized in that: In step (1), the pH value is adjusted to 3.

0.

6. An application of a curing agent for a formaldehyde-free substrate as claimed in any one of claims 1 to 3, characterized in that: It is used in the manufacture of formaldehyde-free floor substrates.

7. The use according to claim 6, characterized in that: The steps include: (a) pMDI glue application amount 20~40kg / m 3 , heat pMDI to 40±1℃, add the above curing agent at a weight ratio of 2~5% of pMDI, stir and mix evenly, add from a position 50~80cm away from the end of the fiber spraying pipe, and mix evenly with the fiber; (b) drying the moisture content of the fibers after sizing to 10-12%, and forming a formaldehyde-free slab after sorting, laying and pre-pressing; (c) hot pressing the formaldehyde-free slab at a hot pressing temperature of 160-230° C., a hot pressing pressure of 0.6-3.0 MPa, and a hot pressing factor of 7-9 s / mm to promote slab forming and obtain a formaldehyde-free floor substrate.

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