PREPARATION METHOD FOR VENEER MANUFACTURED BOARD

Abstract

Disclosed herein is a method for efficiently producing formaldehyde-free veneer manufactured boards, comprising steps of: using wood or non-wood veneer as a raw material; controlling the moisture content of the veneer to within an appropriate range; first applying an accelerant and then applying an isocyanate adhesive; then assembling the veneer into a slab according to a certain rule; carrying out microwave preheating on the slab; and feeding the slab into a hot pressing mechanism to obtain aldehyde-free veneer manufactured boards. In the present method, the process for producing aldehyde-free veneer manufactured boards is simple and easy to implement, hot-pressing production efficiency is high, and the mechanical properties of the boards are excellent.

Claims

1. A preparation method for a veneer-based panel, comprising the following steps: (1) applying an accelerator onto the surface of a veneer; (2) applying an isocyanate adhesive onto the surface of the veneer treated in step (1); (3) combining veneers treated in step (2) into a panel blank; (4) preheating the panel blank obtained in step (3) by using microwave; and (5) transferring the panel blank after the microwave preheating in step (4) into a heat press within 200 s, and subjecting the panel blank to hot-pressing molding.

2. The preparation method according to claim 1, wherein the veneer is a wooden veneer or a non-wooden veneer, comprising a eucalyptus veneer, a pine veneer, a poplar veneer, a birch veneer and a bamboo veneer, and a moisture content of the veneer is controlled at 5-35%.

3. The preparation method according to claim 1, wherein the accelerator is polyether containing polyethylene oxide segment.

4. The preparation method according to claim 3, wherein the polyether is one or a combination of at least two of ethylene oxide-based polyether or ethylene oxide-co-propylene oxide-based polyether.

5. The preparation method according to claim 3, wherein the polyether has a functionality of more than or equal to 3, and a molecular mass of 200-6000, preferably 600-3000, and the polyether is ethylene oxide-capped polyether, and the polyethylene oxide segment has a mass content of more than or equal to 50%, preferably more than 70%.

6. The preparation method according to claim 3, wherein the polyether has an unsaturation degree of 0.0005-0.002 mol/kg, preferably 0.0005-0.001 mol/kg.

7. The preparation method according to claim 1, wherein the accelerator has an applied amount of 5-300 g/m.sup.2.

8. The preparation method according to claim 3, wherein a polyhydroxy compound and/or an amine compound is used as an initiator for the polyether.

9. The preparation method according to claim 3, wherein an amine compound is used as an initiator for the polyether.

10. The preparation method according to claim 1, wherein the isocyanate adhesive comprises one or more of aromatic polyisocyanate and aliphatic polyisocyanate, preferably aromatic polyisocyanate, and further preferably one or more of toluene diisocyanate, methylene diphenyl diisocyanate and polymethylene polyphenyl polyisocyanate; preferably, the isocyanate adhesive contains methylene diphenyl diisocyanate with a mass content of 40-100 wt %.

11. The preparation method according to claim 1, wherein the isocyanate adhesive has a NCO content of 20-34 wt %.

12. The preparation method according to claim 1, wherein the isocyanate adhesive has an applied amount of 10-80 g/m.sup.2.

13. The preparation method according to claim 1, wherein the veneers treated in step (2) are combined into a plywood blank according to an odd-numbered layer principle wherein adjacent veneers are oriented with their grain directions perpendicular to each other, or a plurality of veneers are combined into a laminated veneer lumber blank in the same grain direction.

14. The preparation method according to claim 1, wherein in step (4), the microwave preheating is performed for a period of 10-300 s, and a center temperature of the panel blank after the microwave preheating is less than or equal to 90 C.

15. The preparation method according to claim 1, wherein a hot pressing factor in step (5) is controlled at 5-30 s/mm.

16. The preparation method according to claim 1, wherein the hot pressing in step (5) is performed at a temperature of 120-250 C. with panel pressure of 0-1 MPa.

Description

DETAILED DESCRIPTION

[0038] The technical solutions of the present application are further described below in terms of the examples, but the present application is not limited to the examples; any other change known in the art shall be included within the scope to which protection is sought in the present application. [0039] Polymethylene polyphenyl polyisocyanate (PMDI): CW20, a proportion of methylene diphenyl diisocyanate is 40 wt %, Wanhua Chemical Group Co., LTD.; [0040] Coarse M: a proportion of methylene diphenyl diisocyanate is 55-60 wt %, Wanhua Chemical Group Co., LTD.; [0041] MDI100: a proportion of methylene diphenyl diisocyanate is 100 wt %, Wanhua Chemical Group Co., LTD.; [0042] MDI50: a proportion of methylene diphenyl diisocyanate is 100 wt %, Wanhua Chemical Group Co., LTD.; [0043] PM700: a proportion of methylene diphenyl diisocyanate is 25-30 wt %, Wanhua Chemical Group Co., LTD.; [0044] ethylene oxide-based polyether polyol A: a molecular mass of 1000, a functionality of 3, an EO unit end-capping, a mass fraction of an EO unit of 90.8% and an unsaturation degree of 0.0005 mol/kg; [0045] ethylene oxide-based polyether polyol B: a molecular mass of 6000, a functionality of 8, an EO unit end-capping, a mass fraction of an EO unit of 94.3% and an unsaturation degree of 0.0007 mol/kg; [0046] ethylene oxide-based polyether polyol C: a molecular mass of 200, a functionality of 3, an EO unit end-capping, a mass fraction of an EO unit of 54.5% and an unsaturation degree of 0.001 mol/kg; [0047] ethylene oxide-co-propylene oxide-based polyether D: a molecular mass of 3000, a functionality of 4, an EO unit end-capping, a mass fraction of an EO unit of 77.9% and an unsaturation degree of 0.0006 mol/kg; [0048] ethylene oxide-co-propylene oxide-based polyether E: a molecular mass of 1000, a functionality of 3, an EO unit end-capping, a mass fraction of an EO unit of 79.3% and an unsaturation degree of 0.002 mol/kg; [0049] ethylene oxide-based polyether polyol F: a molecular mass of 3000, a functionality of 3, an EO unit end-capping, a mass fraction of an EO unit of 96.9% and an unsaturation degree of 0.004 mol/kg; [0050] ethylene oxide-co-propylene oxide-based polyether polyol G: a molecular mass of 1000, a functionality of 3, an EO unit end-capping, a mass fraction of an EO unit of 44.2% and an unsaturation degree of 0.002 mol/kg; [0051] a metal-porphyrin complex catalyst TPPH.sub.2-Et.sub.2AlCl, Xi'an Qiyue Biotechnology Co., LTD.; [0052] an alkaline earth metal catalyst Ba(OH).sub.2*8H.sub.2O, Shenyang Shisan Biochemical Technology Development Co., LTD.; [0053] diethylene glycol, Tianjin Kermel Chemical Reagent Co., LTD; [0054] potassium hydroxide, Shanghai Aladdin Biochemical Technology Co., LTD; [0055] an eucalyptus veneer with a moisture content of 20% and a thickness of 1.7 mm; [0056] an eucalyptus veneer with a moisture content of 5% and a thickness of 1.7 mm; [0057] an eucalyptus veneer with a moisture content of 35% and a thickness of 1.7 mm.

Example 1

[0058] Preparation of ethylene oxide-based polyether polyol A: glycerol, which was used as an initiator, and ethylene oxide were fed according to a molar ratio of 1:20.6, added with a metal-porphyrin complex catalyst of TPPH.sub.2-Et.sub.2AlCl whose mass fraction was 0.01% of the above raw materials, and reacted at 90 C. for 105 h to prepare the ethylene oxide-based polyether polyol A.

[0059] An eucalyptus veneer with a moisture content of 20% was used as a base material; the accelerator of polyether polyol A and water were prepared into an aqueous solution according to a mass ratio of 1:4, and the accelerator aqueous solution was applied to the surface of the veneer by spraying, and an applied amount of the polyether polyol aqueous solution was 40 g/m.sup.2; CW20 was applied to the surface of the veneer by spraying with an applied amount of 40 g/m.sup.2; treated veneers were combined into a plywood panel blank having 9 layers according to an odd-numbered layer principle wherein adjacent veneers were oriented with their grain directions perpendicular to each other; the panel blank was preheated by microwave for 30 s, and a center temperature of the preheated panel blank was 70 C.; the panel blank was put into a hot press within 10 s and pressed with a hot pressing temperature of 160 C., a hot pressing pressure of 1 MPa in a high-pressure section, a hot pressing pressure of 0.1 MPa in a low-pressure section and a hot pressing factor of 15 s/mm, and a no-added formaldehyde plywood was obtained.

[0060] According to LYT 1738-2020 Veneer-based Panel for Parquet, the obtained panels were subjected to Class I veneer-based panel performance test; according to GBT 17657-2013 Test Methods of Evaluating the Properties of Wood-Based Panels and Surface Decorated Wood-Based Panels, the obtained panels were subjected to the formaldehyde emission test by climatic chamber method. The results are shown in Table 1.

Example 2

[0061] Preparation of ethylene oxide-based polyether polyol C: glycerol, which was used as an initiator, and ethylene oxide were fed according to a molar ratio of 1:2.5, added with an alkaline earth metal catalyst of Ba (OH).sub.2*8H.sub.2O whose mass fraction was 0.01% of the above raw materials and a co-catalyst diethylene glycol whose mass fraction was 0.01% of the above raw materials, and reacted at 80 C. for 105 h to prepare the ethylene oxide-based polyether polyol C.

[0062] An eucalyptus veneer with a moisture content of 35% was used as a base material; the accelerator of polyether polyol C was applied to the surface of the veneer by spraying with an applied amount of 5 g/m.sup.2; CW20 was applied to the surface of the veneer by curtain coating with an applied amount of 80 g/m.sup.2; treated veneers were combined into a plywood panel blank having 9 layers according to an odd-numbered layer principle wherein adjacent veneers were oriented with their grain directions perpendicular to each other; the panel blank was preheated by microwave for 90 s, and a center temperature of the preheated panel blank was 90 C.; the panel blank was immediately put into a hot press within 5 s and pressed with a hot pressing temperature of 250 C., a hot pressing pressure of 1 MPa in a high-pressure section, a hot pressing pressure of 0.1 MPa in a low-pressure section and a hot pressing factor of 5 s/mm, and a no-added formaldehyde plywood was obtained.

[0063] Test methods for panel performance and formaldehyde emission are the same as those of Example 1. The results are shown in Table 1.

Example 3

[0064] Preparation of ethylene oxide-based polyether polyol B: sucrose, which was used as an initiator, and ethylene oxide were fed according to a molar ratio of 1:128.3, added with TPPH.sub.2-Et.sub.2AlCl whose mass fraction was 0.02% of the above raw materials, and reacted at 90 C. for 100 h to prepare the ethylene oxide-based polyether polyol B.

[0065] An eucalyptus veneer with a moisture content of 5% was used as a base material; the accelerator of polyether polyol B and water were prepared into an aqueous solution according to a mass ratio of 1:10, and the accelerator aqueous solution was applied to the surface of the veneer by curtain coating, and an applied amount of the polyether polyol aqueous solution was 300 g/m.sup.2; CW20 was applied to the surface of the veneer by roll coating with an applied amount of 10 g/m.sup.2; treated veneers were combined into a plywood panel blank having 9 layers according to an odd-numbered layer principle wherein adjacent veneers were oriented with their grain directions perpendicular to each other; the panel blank was preheated by microwave for 300 s, and a center temperature of the preheated panel blank was 60 C.; the panel blank was put into a hot press within 180-200 s and pressed with a hot pressing temperature of 120 C., a hot pressing pressure of 1 MPa in a high-pressure section, a hot pressing pressure of 0 MPa in a low-pressure section and a hot pressing factor of 30 s/mm, and a no-added formaldehyde plywood was obtained.

[0066] Test methods for panel performance and formaldehyde emission are the same as those of Example 1. The results are shown in Table 1.

Example 4

[0067] Preparation of ethylene oxide-co-propylene oxide-based polyether D: ethylenediamin, which was used as an initiator, and propylene oxide were fed according to a molar ratio of 1:10.4, added with catalyst TPPH.sub.2-Et.sub.2AlCl whose mass fraction was 0.02% of the above raw materials, and reacted at 90 C. for 65 h, then added with ethylene oxide according to a molar ratio of ethylenediamine to ethylene oxide of 1:53, and continued to react at 90 C. for 40 h to prepare the ethylene oxide-co-propylene oxide-based polyether D.

[0068] An eucalyptus veneer with a moisture content of 20% was used as a base material; the accelerator D and water were prepared into an aqueous solution according to a mass ratio of 1:4, and the accelerator aqueous solution was applied to the surface of the veneer by spraying, and an applied amount of the polyether polyol aqueous solution was 70 g/m.sup.2; CW20 was applied to the surface of the veneer by spraying with an applied amount of 30 g/m.sup.2; treated veneers were combined into a plywood panel blank having 9 layers according to an odd-numbered layer principle wherein adjacent veneers were oriented with their grain directions perpendicular to each other; the panel blank was preheated by microwave for 10 s, and a center temperature of the preheated panel blank was 50 C.; the panel blank was put into a hot press within 60-70 s and pressed with a hot pressing temperature of 160 C., a hot pressing pressure of 1 MPa in a high-pressure section, a hot pressing pressure of 0.1 MPa in a low-pressure section and a hot pressing factor of 10 s/mm, and a no-added formaldehyde plywood was obtained.

[0069] Test methods for panel performance and formaldehyde emission are the same as those of Example 1. The results are shown in Table 1.

Example 5

[0070] Preparation of ethylene oxide-co-propylene oxide-based polyether E: triethanolamine, which was used as an initiator, and propylene oxide were fed according to a molar ratio of 1:1, added with TPPH.sub.2-Et.sub.2AlCl whose mass fraction was 0.02% of the above raw materials, and reacted at 120 C. for 8 h, then added with ethylene oxide according to a molar ratio of triethanolamine to ethylene oxide of 1:18, and continued to react at 120 C. for 15 h to prepare the ethylene oxide-co-propylene oxide-based polyether E.

[0071] A no-added formaldehyde plywood was prepared by the same method as in Example 1 except that in this example, ethylene oxide-co-propylene oxide-based polyether E was used.

Example 6

[0072] Preparation of polyether polyol F: glycerol, which was used as an initiator, and ethylene oxide were fed according to a molar ratio of 1:66, added with KOH whose mass fraction was 0.02% of the above raw materials, and reacted at 120 C. for 25 h to prepare the polyether polyol F.

[0073] A no-added formaldehyde plywood was prepared by the same method as in Example 1 except that in this example, polyether polyol F was used.

Example 7

[0074] A no-added formaldehyde plywood was prepared by the same method as in Example 1 except that in this example, CW20 was replaced by coarse M.

Example 8

[0075] Preparation of low-viscosity isocyanate: CW20 and MDI100 were prepared into the low-viscosity isocyanate according to a mass ratio of 60:40, and a proportion of methylene diphenyl diisocyanate was 64 wt %.

[0076] A no-added formaldehyde plywood was prepared by the same method as in Example 1 except that in this example, CW20 was replaced by low-viscosity isocyanate.

Example 9

[0077] A no-added formaldehyde plywood was prepared by the same method as in Example 1 except that in this example, CW20 was replaced by MDI50.

Example 10

[0078] A no-added formaldehyde plywood was prepared by the same method as in Example 1 except that in this example, CW20 was replaced by PM700.

Comparative Example 1

[0079] No accelerator was applied; no microwave preheating was performed; a hot pressing factor was 30 s/mm, and other process conditions are the same as in Example 1.

[0080] Test methods for panel performance and formaldehyde emission are the same as those of Example 1. The results are shown in Table 1.

Comparative Example 2

[0081] No accelerator was applied; the microwave preheating was performed, and other process conditions are the same as in Example 1.

[0082] Test methods for panel performance and formaldehyde emission are the same as those of Example 1. The results are shown in Table 1.

Comparative Example 3

[0083] The accelerator was applied; no microwave preheating was performed, and other process conditions are the same as in Example 1.

[0084] Test methods for panel performance and formaldehyde emission are the same as those of Example 1. The results are shown in Table 1.

Comparative Example 4

[0085] CW20 was first applied and then the accelerator was applied, and other process conditions are the same as in Example 1.

[0086] Test methods for panel performance and formaldehyde emission are the same as those of Example 1. The results are shown in Table 1.

Comparative Example 5

[0087] Preparation of polyether polyol G: glycerol, which was used as an initiator, and propylene oxide were fed according to a molar ratio of 1:8, added with TPPH.sub.2-Et.sub.2AlCl whose mass fraction was 0.02% of the above raw materials, and reacted at 90 C. for 75 h, then added with ethylene oxide according to a molar ratio of glycerol to ethylene oxide of 1:10, and continued to react at 90 C. for 30 h to prepare the polyether polyol G.

[0088] In this comparative example, polyether polyol G was used as an accelerator, and other process conditions are the same as in Example 1.

[0089] Test methods for panel performance and formaldehyde emission are the same as those of Example 1. The results are shown in Table 1.

Comparative Example 6

[0090] The accelerator was mixed with CW20 and then applied, and other process conditions are the same as in Example 1.

[0091] Test methods for panel performance and formaldehyde emission are the same as those of Example 1. The results are shown in Table 1.

Comparative Example 7

[0092] The microwave preheating was performed for 400 s, and a center temperature of the preheated 5 panel blank was 95 C., and other process conditions are the same as in Example 1.

[0093] Test methods for panel performance and formaldehyde emission are the same as in Example 1. The results are shown in Table 1.

Comparative Example 8

[0094] The veneer used was tested for formaldehyde emission by climate chamber method, and the method is the same as in Example 1. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Summary of test results of veneer-based panel performance Class I Class I Formaldehyde bonding impregnation Dimensional emission strength MPa peeling stability % mg/m.sup.3 Example 1 1.36 No peeling 0.04 0.01 Example 2 1.33 No peeling 0.03 0.01 Example 3 1.34 No peeling 0.03 0.01 Example 4 1.35 No peeling 0.04 0.01 Example 5 1.31 No peeling 0.03 0.01 Example 6 1.10 No peeling 0.06 0.01 Example 7 1.25 No peeling 0.03 0.01 Example 8 1.23 No peeling 0.04 0.01 Example 9 1.22 No peeling 0.03 0.01 Example 10 1.19 No peeling 0.03 0.01 Comparative 0.88 No peeling 0.09 0.01 Example 1 Comparative 0.65 Peeling 0.09 0.01 Example 2 Comparative 0.62 Peeling 0.10 0.01 Example 3 Comparative 0.71 Peeling 0.09 0.01 Example 4 Comparative 0.74 Peeling 0.09 0.01 Example 5 Comparative 0.40 Peeling 0.09 0.01 Example 6 Comparative 0.60 Peeling 0.09 0.01 Example 7 Comparative 0.01 Example 8

[0095] The test results of the panel performance in Examples 1-10 show that the mode of combining accelerator and microwave preheating can significantly improve the hot pressing production efficiency of the panel, and the panel performance is excellent; compared with the formaldehyde emission of the wood veneer in Comparative Example 8, the formaldehyde emission of the panel obtained by using the technical solution provided in the present application is comparable to that of the raw material veneer.

[0096] The results of Example 2 and Comparative Example 1 show that the mode of combining accelerator and microwave preheating can reduce the hot pressing factor of the plywood to 5 s/mm, and the production efficiency of the panel is 83% higher than that of Comparative Example 1 (the hot pressing factor is 30 s/mm, compared with the highest hot pressing efficiency in the present application).

[0097] The results of Example 1 and Comparative Examples 2-3 show that the effect of the technical solutions of the present application cannot be achieved by adopting either the accelerator or microwave preheating alone. The results of Example 1 and Comparative Example 4 show that the sequence of applying the accelerator and PMDI has a great impact on the bonding strength of the adhesive and the panel performance, and the panel performance is higher by applying the accelerator first and then PMDI. It can be seen from the comparison between Example 1 and Example 6 that the reduction of the unsaturation degree of polyether polyol is conducive to improving the strength of the adhesive and enhancing the dimensional stability. The results of Example 1 and Comparative Example 5 show that when the proportion of the EO segment in polyether is relatively low, the obtained panel performance is poor, because when the proportion of the EO segment is too low, the polyether will have inadequate hydrophilicity, which leads to a weak promotion effect on the reaction between water and isocyanate. The results of Example 1 and Comparative Example 6 show that the accelerator cannot be mixed with PMDI for microwave preheating because the adhesive can be pre-cured. The results of Example 1 and Comparative Example 7 show that the temperature of microwave preheating should not exceed 90 C., which otherwise will also cause the pre-curing of the adhesive.

[0098] Compared with the Example 10, Examples 7-9 has a high proportion of methylene diphenyl diisocyanate in the isocyanate adhesive, and compared with Example 10, the adhesive of Examples 7-9 has a lower viscosity, which is more conducive to spraying coating, and the reaction speed is fast, and the hot pressing curing speed is faster.

[0099] Finally, it is to be noted that the preceding examples are merely used for illustrating the preferred embodiments of the present application and are not to limit the scope of the present application. Although the present application has been described in detail with reference to preferred examples, it is to be understood by those of ordinary skill in the art that all variations or improvements made to the technical solutions of the present application because of modifications or equivalent substitutions shall fall within the protection scope defined by the claims of the present application.