Production method of high-curing-efficiency formaldehyde-free high-strength recombined decorative material

Abstract

The present application relates to a kind of high curing efficiency formaldehyde-free high-strength recombination decorative material production method, belong to the field of decorative veneer processing and manufacturing.The preparation method of the present application, using organic formaldehyde-free adhesive and the curing agent of the inorganic glue containing organic formaldehyde-free adhesive respectively to the single board of being divided into two groups is glued, the two kinds of single board after being glued are alternately stacked and are combined with the method of pre-pressing, solve the problem that the adding amount of curing agent is increased and lead to the short pot life, to allow the curing agent of 30% of the weight of formaldehyde-free water-based emulsion to be added at most, accelerate the colloid curing, shorten the wood square curing cycle;Also solve the problem that the veneer is too soft and leads to planing deformation, veneer is torn, and form the problem of loose and insufficient meat phenomenon.In addition, the adhesive raw material used does not contain formaldehyde, avoid the harm to the environment and human health in the production process, and the formaldehyde emission of the obtained product can reach E NF Class, and more flexible than the veneer produced by urea-formaldehyde resin.

Description

Technical Field

[0001] This invention relates to a method for producing formaldehyde-free, high-strength reconstituted decorative materials with high curing efficiency, belonging to the field of decorative material processing and manufacturing. Background Technology

[0002] Reconstituted decorative materials, also known as engineered wood, are made by laminating and gluing veneers into timber blocks, which are then slicing. They possess the texture, grain, and color characteristics of natural precious wood species. Compared to natural wood veneers, engineered wood veneers have significant advantages in utilization rate, processing difficulty, cost, and grain and color stability. Currently, the global annual production value of engineered wood is approximately 1.5 billion yuan, with 90% of production capacity in China. The adhesives used are mainly urea-formaldehyde resin (including modified versions), and the environmental protection level remains at E2 to E1, with formaldehyde-free products accounting for less than 1%.

[0003] There are two existing solutions for improving the environmental protection level of engineered wood veneer: First, by optimizing the urea-formaldehyde resin synthesis formula and adding formaldehyde scavengers to reduce formaldehyde emissions, but this method cannot fundamentally solve the formaldehyde problem. Second, by replacing urea-formaldehyde resin with formaldehyde-free adhesives, which can achieve formaldehyde-free production and allow the veneer to directly meet E5 standards. NF While it is formaldehyde-free, several problems remain: 1) The cold curing requirements of adhesives for engineered wood limit the range of formaldehyde-free adhesives available. Currently, water-based emulsions are the main type, and their curing depends on drainage, resulting in slow drying and a long curing period for the wood, typically more than 1.5 times that of urea-formaldehyde resin; 2) Wood made with this adhesive lacks overall rigidity, and the veneer deforms severely during planing, tearing and resulting in a loose and underdeveloped appearance; 3) Most emulsions are two-component, using PMDI (polyisocyanate) as a curing agent. For example, the invention patent with authorization announcement number CN111826112B discloses a method for preparing an anti-cracking engineered wood veneer layer. The preparation method includes the following steps: coating the veneer with modified waterborne polyurethane adhesive, assembling the preform, cold pressing, and planing; the preparation method of the modified waterborne polyurethane adhesive is as follows: 100 parts by weight of waterborne polyurethane adhesive, 1-10 parts of thickener, 15-50 parts by weight of humectant, and 2-25 parts by weight of latent isocyanate compound. However, the process of applying adhesive to engineered wood is relatively long, and the adhesive needs to have a sufficient pot life after preparation, which limits the amount of curing agent to be added, thus affecting the bonding strength and curing speed. Summary of the Invention

[0004] This invention aims to solve the above-mentioned problems by providing a method for producing formaldehyde-free, high-strength reconstituted decorative materials with high curing efficiency. The preparation method of this invention involves applying an organic formaldehyde-free adhesive and an inorganic adhesive containing a curing agent of the organic formaldehyde-free adhesive to two groups of veneers, and then alternately stacking the two types of veneers after adhesive application to assemble the material. This approach solves both the problem of limited curing agent addition and the problem of thin and weak wood veneer.

[0005] The technical solution of the present invention to solve the above problems is as follows:

[0006] A method for producing formaldehyde-free, high-strength reconstituted decorative materials with high curing efficiency includes the following steps:

[0007] S1. Provide a plurality of single boards, divide the single boards into two groups, the first group of single boards are coated with organic formaldehyde-free adhesive on both sides, and the second group of single boards are coated with inorganic adhesive with a curing agent added to the organic formaldehyde-free adhesive on both sides.

[0008] S2. After applying glue, the two types of veneers are stacked alternately to form a blank, thus obtaining a wood blank;

[0009] S3. Cold press the wood blank to obtain timber squares;

[0010] S4. Plane the timber into reconstituted decorative material.

[0011] This invention improves the overall rigidity of the wood by uniformly distributing the inorganic adhesive in the wood, thus solving the problem of severe deformation during planing. On the other hand, the addition of a curing agent to the inorganic adhesive allows for increased dosage without affecting the pot life of the organic adhesive, thereby ensuring bonding strength.

[0012] As a preferred embodiment of the above technical solution, the organic formaldehyde-free adhesive is selected from at least one of polyvinyl acetate, ethylene-polyvinyl alcohol copolymer, ethylene-vinyl acetate copolymer, polyacrylate, and waterborne polyurethane; the curing agent is at least one of polyisocyanate and polyisocyanate oligomer.

[0013] As a preferred embodiment of the above technical solution, the inorganic adhesive comprises the following components in parts by weight: 42-54 parts magnesium oxide, 30-40 parts magnesium chloride, and 35-45 parts water.

[0014] In the above technical solution of the present invention, the magnesium chloride is magnesium chloride hexahydrate with a purity of over 98%, wherein the magnesium chloride content is higher than 45%. Too low a content or too many impurities will lead to a decrease in colloidal strength and easy moisture absorption and efflorescence. Magnesium chloride hexahydrate is low in cost and simpler to handle than anhydrous magnesium chloride, and its exothermic reaction when dissolved in water is milder.

[0015] The magnesium oxide mentioned refers to mineral powder with a magnesium oxide content higher than 85% and an activity of 60-65%. The activity of magnesium oxide refers to its ability to promote the curing reaction in a colloidal system and its role in regulating the colloidal microstructure. Essentially, it reflects the ease with which MgO participates in chemical reactions and its impact on the final colloidal properties. Insufficient purity or activity can lead to poor bonding strength and slow curing. In the above-mentioned technical solution of the present invention, the degree of activity is defined as 100% activity of active magnesium oxide. Active magnesium oxide (such as nano-sized MgO, specific surface area > 50 m² / g) has more surface defects and sufficient exposure of active sites (O²⁻). When reacting with MgCl₂, the H⁺ neutralization rate is 3 to 5 times faster than that of ordinary MgO (specific surface area < 10 m² / g), and the curing time is shortened from 24 hours to 6 hours. When active MgO (such as 50 nm particle size) is added to magnesium chloride adhesive, the porosity of the adhesive can be controlled below 15%, and the compressive strength reaches 20 MPa. However, when low-activity MgO (such as 5 μm particle size) is used, the porosity increases to 25%, and the compressive strength is only 10 MPa.

[0016] As a preferred embodiment of the above technical solution, the ratio of the inorganic adhesive to the curing agent is (3~4):1.

[0017] In the above technical solution of the present invention, the curing agent is further preferably a latent polymeric isocyanate. Latent polymeric isocyanate is a common term for polymethylene polyphenyl isocyanate, whose molecular chain consists of multiple benzene rings linked by methylene groups, with isocyanate groups at both ends. Compared to diphenylmethane diisocyanate, polymethylene polyphenyl isocyanate has a longer molecular chain structure and lower activity compared to conventional isocyanates. It reacts relatively slowly with hydroxyl and carboxyl groups in formaldehyde-free emulsions, thus extending the operating time window during coating and assembly, and facilitating production operations.

[0018] As a preferred embodiment of the above technical solution, the organic formaldehyde-free adhesive has a solid content of 45-60%, a pH of 6-8, and a viscosity of 3000-30000 MPa·s.

[0019] As a preferred embodiment of the above technical solution, the glue application amount of the first group of veneers is 90~120 g / m², and the glue application amount of the second group of veneers is 110~140 g / m².

[0020] In the above technical solution of the present invention, the amount of adhesive applied is the amount of adhesive applied on both sides, that is, calculated based on the area of ​​a single board. Since double-sided adhesive is used, if calculated based on a single side (since the single board is very thin, the side is negligible), the amount of adhesive (organic formaldehyde-free adhesive) applied to each single board in the first group is about 45~60 g / m²; similarly, the amount of adhesive (inorganic adhesive, curing agent containing organic formaldehyde-free adhesive) applied to each single board in the second group is about 55~70 g / m².

[0021] As a preferred embodiment of the above technical solution, in step S3, the cold pressing of the wood blank specifically involves first pre-pressing to 1~1.5 MPa and holding the pressure for at least 30 minutes, then increasing the pressure to 2~2.5 MPa and holding the pressure for 7~9 days.

[0022] In the above technical solution of the present invention, during the specific process of stacking and cold pressing, when the stacking reaches 80 to 150 layers, the wood blank is placed into the press for pre-pressing to prevent the early-applied veneer from being left for too long, which would affect the bonding performance.

[0023] As a preferred embodiment of the above technical solution, the thickness of the single board is 0.5~1 mm.

[0024] In the above technical solution of the present invention, if the thickness of the veneer is less than 0.5 mm, it is difficult to rotary cut the veneer, and the veneer is easily damaged after bleaching, dyeing and drying, resulting in downgrading; if the thickness of the veneer is greater than 1 mm, the adhesive is difficult to penetrate into the interior of the veneer, affecting the bonding performance.

[0025] As a preferred embodiment of the above technical solution, step S2 specifically involves using two opposing glue-applying machines to apply glue to the first group of single boards and the second group of single boards respectively, and then alternately stacking the two types of glued single boards onto a moving platform located between the two glue-applying machines.

[0026] As a preferred embodiment of the above technical solution, the pressure holding specifically involves placing pressure-bearing steel plates on the upper and lower sides of the timber, applying pressure together with the timber, and then fixing the upper and lower steel plates with fasteners to maintain pressure.

[0027] In summary, the present invention has the following beneficial effects:

[0028] 1. The adhesive raw materials used in the method of this invention do not contain formaldehyde, thus avoiding harm to the environment and human health during the production process. Simultaneously, the formaldehyde release of the resulting product can reach E... NF It is of a higher grade and is more flexible than engineered wood veneer made with urea-formaldehyde resin.

[0029] 2. This invention uses an organic formaldehyde-free adhesive and an inorganic adhesive containing a curing agent of the organic formaldehyde-free adhesive to apply adhesive to two groups of veneers. The two types of veneers are then stacked alternately to form a blank, and a pre-pressing method is used. This solves the problem of excessively short service life caused by increasing the amount of curing agent added. Thus, a maximum of 30% of the weight of the formaldehyde-free water-based emulsion can be added as curing agent, which accelerates the curing of the adhesive and shortens the curing cycle of the wood.

[0030] 3. This invention uses isocyanate curing agent mixed with magnesium oxychloride inorganic adhesive, which solves the problems of small amount of polymeric isocyanate added, difficulty in uniform coating when applying adhesive alone, easy penetration, and fast drying.

[0031] 4. This invention improves the rigidity of the wood after the adhesive has cured by uniformly distributing an inorganic adhesive layer in the wood, thereby solving the problem of severe deformation and tearing of the veneer during the planing process, resulting in a loose and underdeveloped wood.

[0032] 5. By adjusting the ratio of inorganic adhesive and curing agent and the amount of adhesive applied, the hardness of the adhesive can be adjusted to adapt to tree species with different hardness and density, thus making it widely applicable. Detailed Implementation

[0033] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. Any changes made by those skilled in the art after reading the specification of the present invention, as long as they are within the scope of the claims, will be protected by patent law.

[0034] Example 1

[0035] A method for producing formaldehyde-free, high-strength reconstituted decorative materials with high curing efficiency includes the following steps:

[0036] Preparation of magnesium oxychloride inorganic adhesive:

[0037] Weigh out 35 parts magnesium chloride, 50 parts magnesium oxide, and 40 parts water by weight. Dissolve magnesium chloride in water and cool to room temperature. Add magnesium oxide and stir for 10 minutes until uniform to obtain magnesium oxychloride inorganic adhesive.

[0038] Preparation of component B:

[0039] The inorganic adhesive and the isocyanate curing agent (polymethylene polyphenyl isocyanate) are mixed in a weight ratio of 3:1 and stirred for 10 minutes until homogeneous to obtain component B.

[0040] Preparation of Component A:

[0041] Component A is ethylene-polyvinyl acetate;

[0042] Sizing and preform assembly:

[0043] Divide the required veneer into two equal parts, and use two glue application machines to simultaneously apply component A and component B respectively. The glue application amount of component A is 120 g / m2 on both sides, and the glue application amount of component B is 140 g / m2 on both sides. The veneers coated with the two glues are stacked alternately to form a blank, with each pair of veneers being a composite of two glue layers.

[0044] Cold pressing:

[0045] After each stack reaches 1 / 10 of the load capacity of the press in a single operation, it is placed into the press for pre-pressing at a unit pressure of 1 MPa. Once all the veneers have been glued, the press is increased to 2 MPa after loading, and the pressure is maintained continuously through a pressure holding device. After 8 days of cold pressing, formaldehyde-free engineered wood squares are obtained.

[0046] Slicing wood veneer:

[0047] The reconstituted decorative material of this invention is obtained by slicing the engineered wood into 0.40 mm thick veneers.

[0048] According to GB / T 12914 "Determination of tensile strength of paper and paperboard", the transverse tensile strength of the prepared crack-resistant engineered wood veneer was tested. The specimen size was 100 mm * 15 mm, and the number of specimens was 10. All specimens were taken in the transverse direction. The test result was 0.12 N / mm.

[0049] The transverse dimensional shrinkage rate was tested according to method 4.36 of GB / T 17657-2022 (treatment in a 70℃ forced-air drying oven for 24 hours), and the result was 1.5%. The formaldehyde emission was tested according to method 4.59 of GB / T 17657-2022 (desiccant method), and the result was not detected.

[0050] Example 2

[0051] The remaining implementation steps remain unchanged, the difference from Example 1 is as follows:

[0052] Preparation of magnesium oxychloride inorganic adhesive:

[0053] Weigh out 40 parts magnesium chloride, 45 parts magnesium oxide, and 40 parts water by weight. Dissolve magnesium chloride in water and cool to room temperature. Add magnesium oxide and stir for 10 minutes until uniform to obtain magnesium oxychloride inorganic adhesive.

[0054] Cold pressing:

[0055] The cold pressing time has been changed to 7 days.

[0056] According to GB / T 12914 "Determination of Tensile Strength of Paper and Paperboard", the transverse tensile strength of the prepared crack-resistant engineered wood veneer was tested. Ten specimens, each 100 mm x 15 mm in size, were used, with all specimens tested transversely. The result was 0.10 N / mm. The transverse dimensional shrinkage rate was tested according to method 4.36 of GB / T 17657-2022 (treatment in a 70℃ forced-air drying oven for 24 hours), and the result was 0.9%. Formaldehyde emission was tested according to method 4.59 of GB / T 17657-2022 (desiccant method), and the result was not detected.

[0057] Example 3

[0058] The remaining implementation steps remain unchanged, the difference from Example 1 is as follows:

[0059] Step (3) Apply adhesive to form the preform: Component A is changed to water-based polyurethane, and the amount of adhesive applied to Component A is changed to 100g / m2 on both sides;

[0060] Step (4) Cold pressing: The cold pressing time is changed to 7 days;

[0061] According to GB / T 12914 "Determination of Tensile Strength of Paper and Paperboard", the transverse tensile strength of the prepared crack-resistant engineered wood veneer was tested. Ten specimens, each 100 mm x 15 mm in size, were used, with all specimens tested transversely. The result was 0.22 N / mm. The transverse dimensional shrinkage rate was tested according to method 4.36 of GB / T 17657-2022 (treatment in a 70℃ forced-air drying oven for 24 hours), and the result was 1.3%. Formaldehyde emission was tested according to method 4.59 of GB / T 17657-2022 (desiccant method), and the result was not detected.

[0062] Comparative Example 1

[0063] Preparation of reconstituted decorative materials using conventional urea-formaldehyde resin:

[0064] Mixing adhesive:

[0065] By weight, add 3 parts flour and 2 parts 20% ammonium chloride solution to 100 parts urea-formaldehyde resin;

[0066] Sizing and preform assembly:

[0067] The veneer is coated with urea-formaldehyde resin using a glue applicator, with a glue application rate of 140 g / m2 on both sides, to obtain glued veneer.

[0068] Cold pressing:

[0069] After being stacked to a predetermined height, cold pressing begins at a unit pressure of 2 MPa for 7 days to obtain wood squares prepared from urea-formaldehyde resin.

[0070] Planing: Planing engineered wood into 0.40 mm thick reconstituted decorative materials.

[0071] According to GB / T 12914 "Determination of tensile strength of paper and paperboard", the transverse tensile strength of the prepared crack-resistant engineered wood veneer was tested. The specimen size was 100 mm*15 mm, and the number of specimens was 10. All specimens were taken in the transverse direction. The test result was 0.09 N / mm.

[0072] The transverse dimensional shrinkage rate was tested according to method 4.36 of GB / T 17657-2022 (treatment in a 70℃ forced-air drying oven for 24 hours), and the result was 2.5%. The formaldehyde emission was tested according to method 4.59 of GB / T 17657-2022 (desiccant method), and the result was 1.4 mg / L.

[0073] Comparative Example 2

[0074] Conventional polyvinyl acetate preparation of engineered wood veneer:

[0075] The remaining implementation steps remain unchanged, the difference from Comparative Example 1 is:

[0076] Replace urea-formaldehyde resin with polyvinyl acetate, do not add flour and ammonium chloride solution, apply adhesive at 100 g / m² on both sides, and cold press for 12 days.

[0077] According to GB / T 12914 "Determination of tensile strength of paper and paperboard", the transverse tensile strength of the prepared crack-resistant engineered wood veneer was tested. The specimen size was 100 mm * 15 mm, and the number of specimens was 10. All specimens were taken in the transverse direction. The test result was 0.07 N / mm.

[0078] The transverse dimensional shrinkage rate was tested according to method 4.36 of GB / T 17657-2022 (treatment in a 70℃ forced-air drying oven for 24 hours), and the result was 3.1%. The formaldehyde emission was tested according to method 4.59 of GB / T 17657-2022 (desiccant method), and the result was not detected.

[0079] Comparative Example 3

[0080] Waterborne polyurethane for engineered wood veneer preparation:

[0081] The remaining implementation steps remain unchanged, the difference from Comparative Example 1 is:

[0082] Replace urea-formaldehyde resin with water-based polyurethane, do not add flour and ammonium chloride solution, apply adhesive at 100 g / m² on both sides, and cold press for 8 days.

[0083] According to GB / T 12914 "Determination of tensile strength of paper and paperboard", the transverse tensile strength of the prepared crack-resistant engineered wood veneer was tested. The specimen size was 100 mm*15 mm, and the number of specimens was 10. All specimens were taken in the transverse direction. The test result was 0.09 N / mm.

[0084] The transverse dimensional shrinkage rate was tested according to method 4.36 of GB / T 17657-2022 (treatment in a 70℃ forced-air drying oven for 24 hours), and the result was 2.2%. The formaldehyde emission was tested according to method 4.59 of GB / T 17657-2022 (desiccant method), and the result was not detected.

[0085] Table 1 Performance test results of reconstituted decorative materials

[0086] sample Transverse tensile strength N / mm Lateral dimensional shrinkage rate % Formaldehyde release (mg / L) Pressure holding time / day Example 1 0.12 1.5 Not detected 8 Example 2 0.1 0.9 Not detected 7 Example 3 0.22 1.3 Not detected 7 Comparative Example 1 0.09 2.5 1.4 7 Comparative Example 2 0.07 3.1 Not detected 12 Comparative Example 3 0.09 2.2 Not detected 8

[0087] As can be seen from the data in Table 1, the transverse tensile strength of the engineered wood veneer prepared using the process of this invention is significantly superior to that of conventional urea-formaldehyde resin or formaldehyde-free engineered wood veneer. A comparison between Example 1 and Comparative Example 2 shows that this invention can shorten the pressure holding time of the wood blocks, solving the problem of long curing cycles for formaldehyde-free engineered wood. The transverse dimensional shrinkage rate of ordinary engineered wood veneer is higher than that of the engineered wood veneer prepared by this invention, indicating that the increased proportion of curing agent and the introduction of inorganic adhesives make the colloidal structure more compact, improving the dimensional stability of the veneer. Furthermore, the formaldehyde release of the engineered wood veneer prepared by this invention is undetectable, meeting E... NF The environmental protection level.

Claims

1. A method for producing formaldehyde-free, high-strength reconstituted decorative materials with high curing efficiency, comprising the following steps: S1. Provide a plurality of single boards, divide the single boards into two groups, the first group of single boards are coated with organic formaldehyde-free adhesive on both sides, and the second group of single boards are coated with inorganic adhesive with a curing agent added to the organic formaldehyde-free adhesive on both sides. S2. After applying glue, the two types of veneers are stacked alternately to form a blank, thus obtaining a wood blank; S3. Cold press the wood blank to obtain timber squares; S4. Plane the timber into reconstituted decorative material; The organic formaldehyde-free adhesive is selected from at least one of polyvinyl acetate, ethylene-polyvinyl alcohol copolymer, ethylene-vinyl acetate copolymer, polyacrylate, and waterborne polyurethane; the curing agent is at least one of polyisocyanate and polyisocyanate oligomer. The inorganic adhesive comprises the following components in parts by weight: 42-54 parts magnesium oxide, 30-40 parts magnesium chloride, and 35-45 parts water.

2. The method for producing a formaldehyde-free, high-strength reconstituted decorative material with high curing efficiency according to claim 1, characterized in that: The ratio of the inorganic adhesive to the curing agent is (3~4):

1.

3. The method for producing a formaldehyde-free, high-strength reconstituted decorative material with high curing efficiency according to claim 1, characterized in that: The organic formaldehyde-free adhesive has a solid content of 45-60%, a pH of 6-8, and a viscosity of 3000-30000 MPa·s.

4. The method for producing a formaldehyde-free, high-strength reconstituted decorative material with high curing efficiency according to claim 1, characterized in that: The glue application rate for the first group of veneers is 90 ~ 120 g / m². 2 The glue application rate for the second group of veneers is 110 ~ 140 g / m². 2 .

5. The method for producing a formaldehyde-free, high-strength reconstituted decorative material with high curing efficiency according to claim 1, characterized in that: In step S3, the cold pressing of the wood blank specifically involves first pre-pressing it to 1~1.5 MPa and holding the pressure for at least 30 minutes, then increasing the pressure to 2~2.5 MPa and holding the pressure for 7~9 days.

6. The method for producing a formaldehyde-free, high-strength reconstituted decorative material with high curing efficiency according to claim 1, characterized in that: The thickness of the single board is 0.5~1 mm.

7. The method for producing a formaldehyde-free, high-strength reconstituted decorative material with high curing efficiency according to claim 1, characterized in that: Step S2 specifically involves using two opposing glue-applying machines to apply glue to the first group of veneers and the second group of veneers respectively, and then alternately stacking the two types of glued veneers onto a moving platform located between the two glue-applying machines.

8. The method for producing a formaldehyde-free, high-strength reconstituted decorative material with high curing efficiency according to claim 5, characterized in that: The pressure holding process involves placing pressure-bearing steel plates on the top and bottom of the timber, applying pressure together with the timber, and then fixing the upper and lower steel plates with fasteners to maintain the pressure.