Special partially-closed pur hot melt adhesive for veneering decorative paper and preparation method of special partially-closed pur hot melt adhesive

Abstract

The invention discloses a preparation method of a special partially-closed type pur hot melt adhesive for veneering decorative paper, which comprises the following steps: by taking crystalline polyester polyol, polyether polyol, acrylic resin, isocyanate and the like as raw materials, setting parameters such as reaction material ratio, reaction time length, reaction temperature and the like, and closing a part of NCO groups by utilizing an isocyanate sealing agent, thereby obtaining the partially-closed type pur hot melt adhesive for veneering decorative paper. After the pur glue is coated on the facing paper, the unclosed NCO group and water vapor on the facing paper form crosslinking and effective bonding, and after long-term storage and transportation, the closed-NCO group is unclosed through high temperature when the facing paper and a plate are hot-pressed, and the bonding effect with the plate is formed. The solid content of the pur hot melt adhesive prepared by the scheme is 100%, the pur hot melt adhesive is high in initial adhesion and final adhesion strength, good in stripping resistance and dense in adhesion, can be exposed in air for a long time after being coated into an adhesive film, and can be widely applied to veneering decoration of furniture and decorative plates.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a partially blocked PUR hot melt adhesive for veneer decorative paper and a preparation method thereof. Background Art

[0002] At present, veneered wood-based panels have been widely used in the fields of interior decoration, furniture, etc. Veneer decorative paper is an important veneer material for wood-based panels, which plays a role in protecting and beautifying wood-based panels. In the prior art, veneer decorative paper and wood-based panels are generally adhered by a flat pasting process, and the adhesives used in the pasting process are basically solvent-based adhesives or water-based adhesives. In recent years, due to environmental protection requirements, one-component moisture-curing polyurethane adhesives have also begun to be used for the bonding of veneered wood-based panels.

[0003] The one-component moisture-curing polyurethane adhesive (PUR) is coated on the surface of the substrate, the adherend is attached, and after cooling and curing, it cross-links and cures through the reaction of isocyanate groups with water molecules in the air to achieve the bonding purpose. Due to the characteristic that isocyanate groups are easy to react with water, if exposed to air for too long, the PUR glue will lose its viscosity, resulting in bonding failure. In the production process of veneering wood-based panels, after the veneer decorative paper is applied with glue, it should be immediately pressed against the wood-based panel to ensure the activity of the glue, which requires that the gluing of the veneer decorative paper and the pressing against the wood-based panel must be continuous processes. In order to enable the manufacturer of veneer decorative paper to provide a customer with a veneer decorative paper with glue applied on the back, therefore, it is necessary to invent a partially blocked PUR hot melt adhesive for veneer decorative paper. Summary of the Invention

[0004] Object of the Invention: In view of the deficiencies of the above prior art, the object of the present invention is to provide a moisture-curing polyurethane hot melt adhesive with a solid content of 100%, high initial and final adhesion strengths, good anti-peeling property, dense adhesion, and can be exposed to air for a long time after being coated into a glue film, which can be widely used for the veneer decoration of furniture and decorative wood-based panels.

[0005] Technical Solution: The preparation method of the partially blocked PUR hot melt adhesive for veneer decorative paper according to the present invention, the reaction raw materials include the following components:

[0006] 10-40 parts of crystalline polyester polyol;

[0007] 15-60 parts of polyether polyol;

[0008] 20-50 parts of acrylic resin;

[0009] 15-40 parts of isocyanate;

[0010] 5-30 parts of blocking agent;

[0011] 0.1-1 part of other auxiliaries;

[0012] The above components are all based on the mass fraction of the system;

[0013] The specific preparation method includes the following steps:

[0014] Step (1): Add crystalline polyester polyol, polyether polyol and acrylic resin into the reaction kettle, heat up to 120 - 140 °C, and stir for at least 20 - 40 min after the solid melts to fully mix each component;

[0015] Step (2): Heat up to 110 - 130 °C under nitrogen protection to dehydrate for 1 - 3 h;

[0016] Step (3): Cool down to 70 - 80 °C, add isocyanate into the reaction kettle. After the system heats up naturally due to exothermic reaction, react at 80 - 100 °C for 1 - 3 h under nitrogen protection;

[0017] Step (4): When the system temperature drops to 70 - 90 °C, slowly drop the capping agent into the reaction kettle, and the reaction time is 3 - 6 h; then add other additives, stir for 10 - 30 min and then discharge to obtain a partially blocked PUR hot melt adhesive for veneer decorative paper.

[0018] Furthermore, as a preferred embodiment, the number average molecular weight of the crystalline polyester polyol is 1000 - 8000, the melting point Tm is 50 °C - 75 °C, and at least one of HDPOL - 4410, HDPOL - 6630, HDPOL - 6650S, 7360, 7380, 7361 is selected; among them, HDPOL - 4410, HDPOL - 6630, HDPOL - 6650S are purchased from Shanghai Huide Technology Co., Ltd.; 7360, 7380, 7361 are purchased from Evonik Chemistry.

[0019] Furthermore, as a preferred embodiment, the number average molecular weight of the polyether polyol is 600 - 3000; at least one of PPG - 600, PPG - 1000, PPG - 2000, PEG - 1500 from Hai'an Petrochemical is selected.

[0020] Furthermore, as a preferred embodiment, the number average molecular weight of the acrylic resin is 30000 - 85000, the Tg is 50 °C - 100 °C, and at least one of BR - 103, BR - 106, BR - 113, BR - 116 from Mitsubishi of Japan is selected.

[0021] Furthermore, as a preferred embodiment, the isocyanate is selected from one or more of MDI - 50, MDI - 100, MDI - 100LL.

[0022] Further, as a preferred embodiment, the sealant is liquid at room temperature, and one of methyl ethyl ketoxime, diethyl malonate, and Cardolite NX-2026 is selected.

[0023] Further, as a preferred embodiment, the other auxiliary agent is an antioxidant, and one or more of 1010, 168, and 626 from Rianlon Corporation are selected.

[0024] The present invention also provides a partially blocked PUR hot melt adhesive for veneer decorative paper prepared by the above method.

[0025] Beneficial effects: (1) In the solution of the present invention, by setting parameters such as the reaction material ratio, reaction duration, and reaction temperature, and using an isocyanate sealant to block a part of the NCO groups, after the PUR glue is applied to the veneer paper, the unblocked NCO groups crosslink with the water vapor on the veneer paper to form an effective bond. After long-term storage and transportation, when the veneer paper and the board are hot-pressed, the blocked -NCO groups are unblocked by high temperature to form a bonding effect with the board; (2) The partially blocked PUR hot melt adhesive prepared by the solution of the present invention enables the two originally continuous processes of veneer paper gluing and hot-pressing to the board to be separated in different times and spaces, making the production of artificial boards more efficient and convenient; the partially blocked PUR glue is exposed to the air after the first heating and coating, and can still be hot-pressed to the board after transportation and storage. The use of the partially blocked PUR glue overcomes the drawback of poor bonding strength of thermoplastic glue. Description of the Drawings

[0026] Figure 1 It is the infrared spectrum of the partially blocked PUR hot melt adhesive for veneer decorative paper prepared in Example 3. Detailed Embodiments

[0027] In order to better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with embodiments. The purpose is to understand the content of the present invention in detail, rather than to limit the present invention.

[0028] Unless otherwise specified, the reagents and raw materials used in the embodiments and comparative examples of the present invention are all commercially available.

[0029] Example 1:

[0030] (1) Add 20 parts of Evonik Chemical 7380, 20 parts of Evonik Chemical 7361, 60 parts of PPG2000 from Hai'an Petrochemical, and 33.6 parts of acrylic resin BR-113 with a molecular weight of 30,000 and a tg of 75°C into the reaction kettle, heat up to 130°C, and stir for at least 30 minutes after the solids are melted to fully mix each component;

[0031] (2) Cool down to 120 °C and dehydrate for 2 h; cool down to below 75 °C, add 26.2 parts of MDI-100. After the natural temperature rise ends, under nitrogen protection, react at 90 °C for 2 h. At this time, the measured NCO content is about 2.6%;

[0032] (3) When the temperature drops to 80 °C, slowly drip 9.8 parts of methyl ethyl ketoxime into the reaction kettle, and the reaction time is about 4 h until the reaction is complete. The measured NCO content is 0;

[0033] (4) Add 0.5 part of antioxidant 1010, stir for 20 min and then discharge to obtain a partially blocked PUR hot melt adhesive for veneer decorative paper.

[0034] Example 2

[0035] (1) Add 20 parts of Evonik Chemical 7380, 20 parts of Evonik Chemical 7361, 60 parts of PPG2000 from Hai'an Petrochemical, and 33.6 parts of acrylic resin BR-113 with a molecular weight of 30,000 and a tg of 75 °C into the reaction kettle. Heat up to 130 °C. After the solids melt, stir for at least 30 min to fully mix the components;

[0036] (2) Cool down to 120 °C and dehydrate for 2 h; cool down to below 75 °C, add 26.2 parts of MDI-100. After the natural temperature rise ends, under nitrogen protection, react at 90 °C for 2 h. At this time, the measured NCO content is about 2.5%;

[0037] (3) When the temperature drops to 80 °C, slowly drip 5.5 parts of methyl ethyl ketoxime into the reaction kettle, and the reaction time is about 4 h until the reaction is complete. The measured NCO content is 1.11%;

[0038] (4) Add 0.5 part of antioxidant 1010, stir for 20 min and then discharge to obtain a partially blocked PUR hot melt adhesive for veneer decorative paper.

[0039] Example 3

[0040] (1) Add 20 parts of Evonik Chemical 7380, 20 parts of Evonik Chemical 7361, 60 parts of PPG1000 from Hai'an Petrochemical, and 46 parts of acrylic resin BR-113 with a molecular weight of 30,000 and a tg of 75 °C into the reaction kettle. Heat up to 130 °C. After the solids melt, stir for at least 30 min to fully mix the components;

[0041] (2) Cool down to 120 °C and dehydrate for 2 h; cool down to below 75 °C, add 64 parts of MDI-100. After the natural temperature rise ends, under nitrogen protection, react at 90 °C for 2 h. The measured NCO content is 6.4%;

[0042] (3) When the temperature drops to 80 °C, slowly drip 15.5 parts of methyl ethyl ketoxime into the reaction kettle, and the reaction time is about 4 h until the reaction is complete. The measured NCO content is about 2.3%;

[0043] (4) Add 0.5 part of antioxidant 1010, stir for 20 min and then discharge to obtain a partially blocked PUR hot melt adhesive special for veneered decorative paper.

[0044] As Figure 1 shown, the infrared spectrum of the partially blocked PUR hot melt adhesive special for veneered decorative paper prepared in this example. In the infrared spectrum, there is a strong and sharp absorption peak at 2263.29 cm-1, which is the characteristic peak of the -NCO group of isocyanate. 2.3% -NCO groups are exposed in the formula.

[0045] The carbamate bond formed by the reaction has a strong carbonyl (C=O) absorption peak at 1732.78 cm-1; at 1512.03 is the absorption peak of N-H bending vibration (the absorption peak of N-H bending vibration is generally at 1530 - 1550 cm-1. There are a large number of polar groups in the PUR molecule, which are easy to form hydrogen bonds. When the NH group participates in the formation of hydrogen bonds, the electron cloud density of the N-H bond will change, and the force constant of the bond will decrease, resulting in the NH peak shifting to the low wavenumber direction), and there is a C-O-C stretching vibration absorption peak at 1241.92 cm-1. The appearance of these peaks indicates the formation of PUR.

[0046] Example 4

[0047] (1) Add 20 parts of Evonik Chemistry 7380, 20 parts of Evonik Chemistry 7361, 60 parts of PPG1000 from Hai'an Petrochemical, and 46 parts of acrylic resin BR-113 with a molecular weight of 30000 and a tg of 75 °C into the reaction kettle, heat up to 130 °C, and stir for at least 30 min after the solid melts to fully mix each component;

[0048] (2) Cool down to 120 °C and dehydrate for 2 h; cool down to below 75 °C and add 64 parts of MDI-100. After the natural temperature rise ends, react at 90 °C for 2 h under nitrogen protection, and the measured NCO content is 6.2%;

[0049] (3) When the temperature drops to 80 °C, slowly drip 19.0 parts of methyl ethyl ketoxime into the reaction kettle, and the reaction time is about 4 h until the reaction is complete. The measured NCO content is about 1.5%;

[0050] (4) Add 0.5 part of antioxidant 1010, stir for 20 min and then discharge to obtain a partially blocked PUR hot melt adhesive special for veneered decorative paper.

[0051] Comparative Example 1

[0052] (1) Add 20 parts of Evonik Chemical 7380, 20 parts of Evonik Chemical 7361, 60 parts of PPG2000 from Hai'an Petrochemical, and 33.6 parts of acrylic resin BR-113 with a molecular weight of 30,000 and a tg of 75°C into the reaction kettle. Heat up to 130°C. After the solids are melted, stir for at least 30 minutes to fully mix all components;

[0053] (2) Cool down to 120°C and dehydrate for 2 hours; cool down to below 75°C and add 26.2 parts of MDI-100. After the natural temperature rise ends, react at 90°C for 2 hours under nitrogen protection. At this time, the measured NCO content is about 2.6%;

[0054] (3) Add 0.5 part of antioxidant 1010, stir for 20 minutes and then discharge to obtain the product of Comparative Example 1.

[0055] Comparative Example 2

[0056] (1) Add 20 parts of Evonik Chemical 7380, 20 parts of Evonik Chemical 7361, 60 parts of PPG1000 from Hai'an Petrochemical, and 46 parts of acrylic resin BR-113 with a molecular weight of 30,000 and a tg of 75°C into the reaction kettle. Heat up to 130°C. After the solids are melted, stir for at least 30 minutes to fully mix all components;

[0057] (2) Cool down to 120°C and dehydrate for 2 hours; cool down to below 75°C and add 64 parts of MDI-100. After the natural temperature rise ends, react at 90°C for 2 hours under nitrogen protection. At this time, the measured NCO content is about 6.2%;

[0058] (3) Add 0.5 part of antioxidant 1010, stir for 20 minutes and then discharge to obtain the product of Comparative Example 2.

[0059] To verify the performance of the product of the present invention, the following performance tests are carried out:

[0060] (1) Adhesion test

[0061] Heat the PUR hot melt adhesives obtained from Examples 1-4 and Comparative Examples 1-2 at 90°C respectively, and then coat them on the PET film with a 5μm four-sided wet film applicator, and cut into test pieces with an effective test area of 2.5 cm × 10 cm. The coated PET film is completely exposed to the air. After standing for a certain time, it is compounded with the steel plate. After compounding, it is hot-pressed (140°C, 50 Kg / sq.cm pressure, 30 s) with a hot press, and placed in a constant temperature and humidity environment of 18°C and 80% humidity for 48 hours. Referring to the adhesive tape peel strength test environment of GB / T2792-2014, measure its peel strength (unit: N / 25mm), and take the average value of 3 times. The test results are shown in Table 1.

[0062] Table 1 Test results of product adhesion for Examples 1-4 and Comparative Examples 1-2

[0063] Exposure period Closed NCO% 0 3d 5d 10d 20d 30d Example 1 2.6％ 7.22 7.03 6.99 6.75 6.40 6.01 Example 2 1.4％ 6.98 1.53 ＜0.5 - - - Example 3 4.1％ 11.86 8.00 7.88 7.57 7.16 6.62 Example 4 4.7％ 11.32 9.02 8.82 8.53 8.01 7.79 Comparative example 1 0％ 7.51 ＜0.5 - - - - Comparative example 2 0％ 11.95 ＜0.5 - - - -

[0064] From the results in Table 1, it can be seen that since no excessive amount of MEKO blocking agent was added to fully block the isocyanate groups, the peel strength of the PUR glue exposed to air would decrease over time. However, compared with Comparative Example 1 and Comparative Example 2, Examples (1)(2)(3)(4) with MEKO added to block the isocyanate groups could delay the loss of adhesion of the PUR glue to a certain extent. The decrease in the peel strength of the PUR glue in Example 2 was relatively obvious because the NCO content in the formulation was low, and the blocked NCO content was also low. In addition, over time, the blocked isocyanate groups were gradually released and reacted with the moisture in the air, causing the PUR glue in Example 2 to gradually lose its adhesion. Therefore, it is necessary to block enough -NCO% to avoid losing adhesion after long-term exposure. The designed blocked NCO content in Examples (1)(3)(4) was above 2.6%, and it still had a certain viscosity after being completely exposed to air for 30 days.

[0065] (2) Peel strength test

[0066] The PUR hot melt adhesives obtained from the above Examples (1)(2)(3)(4) were heated at a temperature of 90°C respectively, and then coated on 90 g / m 2 EB facing paper with a 5-μm four-sided wet film applicator, and cut into test pieces with an effective test area of 2.5 cm × 10 cm. The coated EB facing paper was completely exposed to air, and after being placed at 50°C for 30 days, it was laminated with particle board. After lamination, it was hot-pressed at a certain temperature with a hot press (pressure: 50 Kg / sq.cm, time: 30 s), and placed in a constant temperature and humidity environment of 18°C and 80% humidity for 48 h. Referring to the test environment for adhesive tape peel strength in GB / T 2792-2014, the peel strength (unit: N / 25 mm) was measured, and the average value of 3 measurements was taken. The test results are shown in Table 2.

[0067] Table 2 Test results of product peel strength for Examples 1-4 and Comparative Examples 1-2

[0068] Hot pressing conditions Example 1 Example 2 Example 3 Example 4 Hot pressing at 120°C 2.42 (50% material breakage) Loss of adhesion 2.22 (50% material breakage) 2.63 (50% material breakage) Hot pressing at 130°C EB paper material breakage Loss of adhesion EB paper material breakage EB paper material breakage Hot pressing at 140°C EB paper material breakage Loss of adhesion EB paper material breakage EB paper material breakage

[0069] According to the results in Table 2 above, for the PUR hot melt adhesives obtained from Examples (1)(3)(4), after coating the glue on the EB facing paper and completely exposing it to air at 50°C for 30 days, it could still effectively adhere to the particle board and achieve the effect of material breakage. The appropriate hot-pressing temperature was around 130°C.

[0070] As described above, this is only an implementation mode of the invention creation, and does not limit the scope of patent protection. Those skilled in the art make non-substantive changes or substitutions based on the invention creation, and still fall within the scope of patent protection.

Claims

1. A method for preparing a partially enclosed pur hot melt adhesive for veneer decorative paper, characterized in that The reaction raw materials include the following components: 10-40 parts of crystalline polyester polyol; 15-60 parts of polyether polyol; Acrylic resin 20-50 parts; Isocyanate 15-40 parts; Sealing agent 5-30 parts; Other additives 0.1-1 part; The above components are calculated by system mass fraction; The specific preparation method comprises the following steps: Step (1): adding crystalline polyester polyol, polyether polyol and acrylic resin into a reaction kettle, heating to 120-140° C., stirring for at least 20-40 minutes after the solid melts, so that the components are fully mixed; Step (2): heating to 110-130°C for dehydration for 1-3h under nitrogen protection; Step (3): cooling to 70-80°C, adding isocyanate into the reaction kettle, and reacting at 80-100°C for 1-3h under nitrogen protection after the system exotherms and naturally heats up; Step (4): the system temperature is lowered to 70-90°C, and the end-capping agent is slowly added dropwise into the reaction kettle for a reaction time of 3-6 hours; then other additives are added and stirred for 10-30 minutes before discharging the material to obtain a partially closed pur hot melt adhesive for veneer decorative paper.

2. The method for preparing the partially closed pur hot melt adhesive for veneer decorative paper according to claim 1, characterized in that: The number average molecular weight of the crystalline polyester polyol is 1000-8000, the melting point Tm is 50° C.-75° C., and at least one of HDPOL-4410, HDPOL-6630, HDPOL-6650S, 7360, 7380, and 7361 is selected.

3. The method for preparing the partially closed pur hot melt adhesive for veneer decorative paper according to claim 1, characterized in that: The number average molecular weight of the polyether polyol is 600-3000; at least one of PPG-600, PPG-1000, PPG-2000 and PEG-1500 is selected.

4. The method for preparing the partially closed pur hot melt adhesive for veneer decorative paper according to claim 1, characterized in that: The number average molecular weight of the acrylic resin is 30000-85000, Tg is 50°C-100°C, and at least one of BR-103, BR-106, BR-113 and BR-116 is selected.

5. The method for preparing the partially closed pur hot melt adhesive for veneer decorative paper according to claim 1, characterized in that: The isocyanate is selected from one or more of MDI-50, MDI-100, and MDI-100LL.

6. The method for preparing the partially closed pur hot melt adhesive for veneer decorative paper according to claim 1, characterized in that: The sealing agent is liquid at room temperature and is selected from one of methyl ethyl ketone oxime, diethyl malonate, and Cardolite NX-2026.

7. The method for preparing the partially closed pur hot melt adhesive for veneer decorative paper according to claim 1, characterized in that: The other auxiliary agents are antioxidants, and one or more of 1010, 168, and 626 are selected.

8. A partially closed pur hot melt adhesive specially used for veneer decorative paper prepared by the method according to any one of claims 1 to 7.

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