Damping type hot melt adhesive for protecting surface of brittle object

Abstract

The invention relates to the field of adhesives, and particularly discloses a damping type hot melt adhesive for protecting the surface of a brittle object. The damping type hot melt adhesive for protecting the surface of the brittle object is prepared from the following raw materials: polyester polyol, polyether polyol, aliphatic isocyanate, hydroxyethyl acrylate, a fluorine-containing composite active monomer, modified nano zinc oxide, a photoinitiator and a chain extender. Wherein the lactic acid, the citric acid and the catalyst are used for modifying the nano-zinc oxide, the compatibility of the nano-zinc oxide and a hot melt adhesive system can be remarkably improved, and the roughness between the hot melt adhesive and an adhered object is increased after the modified nano-zinc oxide is added, so that the hot melt adhesive can be easily stripped from the surface of a protected object; and a protected object cannot be damaged.

Description

Technical Field

[0001] The present invention relates to the field of adhesives, and in particular, to a shock-absorbing hot melt adhesive for protecting the surface of brittle objects. Background Art

[0002] With the continuous progress of technology and the increasing demand for item protection by people, as an efficient and environmentally friendly adhesive, hot melt adhesive is more and more widely used in the field of protecting fragile items. In the molten state, hot melt adhesive can quickly penetrate into the surface of the adherend, form a strong adhesion force, and achieve rapid curing. Moreover, after curing, hot melt adhesive has a certain flexibility, which can effectively relieve external impacts and reduce the breakage risk of fragile items.

[0003] Although the strong adhesiveness of hot melt adhesive makes it very effective in protecting fragile items, it also brings difficulties to the cleaning work. Since hot melt adhesive becomes very hard after cooling and has a high adhesion force, certain force and skills are required to peel it off from the protected item. However, even with certain force and skills, it is still very difficult to completely clean hot melt adhesive from the protected item. On the one hand, during the adhesion process, hot melt adhesive may form some tiny connection points with the surface of the protected item, which are easily overlooked during peeling, resulting in part of the hot melt adhesive remaining on the protected item and affecting the appearance of the item. On the other hand, since hot melt adhesive will generate a certain frictional force on the surface of the protected item during peeling, it is easy to cause secondary damage to the protected item. Summary of the Invention

[0004] In order to make the hot melt adhesive form a relatively weak adhesion force after curing, be easier to clean from the protected item, and reduce the damage to the surface of the protected item, so as to better protect fragile items, the present application provides a shock-absorbing hot melt adhesive for protecting the surface of brittle objects.

[0005] In the first aspect, a shock-absorbing hot melt adhesive for protecting the surface of brittle objects provided by the present application adopts the following technical solution: A shock-absorbing hot melt adhesive for protecting the surface of brittle objects is prepared from the following raw materials by weight: 20 - 30 parts of polyester polyol, 28 - 36 parts of polyether polyol, 16 - 20 parts of aliphatic isocyanate, 6 - 10 parts of hydroxyethyl acrylate, 7 - 9 parts of fluorine-containing composite active monomer, 15 - 20 parts of modified nano-zinc oxide, 0.3 - 0.5 part of photoinitiator, 2 - 4 parts of chain extender; The preparation raw materials of the modified nano-zinc oxide include nano-zinc oxide, lactic acid, citric acid and a catalyst, and the weight ratio of the nano-zinc oxide, lactic acid, citric acid and the catalyst is 10:(4 - 6):(2.8 - 3.2):(0.3 - 0.5).

[0006] By adopting the above technical solution, the hot melt adhesive of the present application adopts a UV / moisture dual-curing method, which can effectively improve the flexibility and adhesion performance of the hot melt adhesive, so that the hot melt adhesive has good shock absorption effect after curing, thereby better protecting the surface of brittle objects from external impacts. Polyester polyol, polyether polyol, aliphatic isocyanate and hydroxyethyl acrylate are synthesized to produce a polyurethane acrylate prepolymer containing both carbon-carbon double bonds and -NCO in the molecular structure. By introducing a fluorine-containing composite active monomer, the release force is increased. Since the fluorine-containing composite active monomer contains C-F bonds and has a low surface energy, when spreading the adhesive, the fluorine-containing active monomer forms a thin isolation layer between the hot melt adhesive and the surface of the protected article, achieving a release effect. In addition, lactic acid, citric acid and a catalyst are used to modify nano-zinc oxide. The -OH in the lactic acid molecule reacts with the -COOH in the citric acid molecule to form a carboxyl-terminated polylactic acid-citric acid copolymer, or the -OH in the citric acid combines with the -COOH in the lactic acid molecule to form a hydroxyl-terminated polylactic acid-citric acid copolymer. The hydroxyl groups on the surface of zinc oxide react with the carboxyl groups of the carboxyl-terminated polylactic acid-citric acid copolymer to form a polymer coating layer. The carboxyl-terminated polylactic acid-citric acid copolymer further reacts with the -NCO in the polyurethane to promote the uniform dispersion of nano-zinc oxide in the organic phase, increase the roughness during film spreading, and assist the easy peeling of the hot melt adhesive.

[0007] Preferably, the fluorine-containing composite active monomer includes trifluoroethyl acrylate and perfluorooctylethyl acrylate, and the weight ratio of trifluoroethyl acrylate to perfluorooctylethyl acrylate is 1:(0.8 - 1.2).

[0008] By adopting the above technical solution, trifluoroethyl acrylate and perfluorooctylethyl acrylate are used as fluorine-containing composite active monomers. During the copolymerization process, they induce in-situ phase separation, enabling the trifluoroethyl acrylate rich in short side chains and the perfluorooctylethyl acrylate rich in long side chains to interact synergistically to form a dynamic microphase separation structure, enhancing the internal intermolecular friction and improving the shock absorption performance. Among them, trifluoroethyl acrylate has a short side chain structure and is easy to form a highly entangled matrix, providing good elastic properties for the hot melt adhesive; while perfluorooctylethyl acrylate, due to its long side chain structure, forms high-dissipation regions rich in liquid nanophases in the matrix. These regions have short-range lamellar liquid crystal order and can accompany the strain-enhanced liquid crystal assembly during the stretching process, significantly increasing the intermolecular friction force. In addition, the combination of trifluoroethyl acrylate and perfluorooctylethyl acrylate makes the hot melt adhesive obtain a lower surface energy, achieving an extremely light release force when peeling the hot melt adhesive, and having significant advantages in protecting the surface of brittle objects.

[0009] Preferably, the preparation method of the modified nano-zinc oxide includes the following steps: (1) Dehydrate lactic acid using a dehydration reactor, mix the dehydrated lactic acid with citric acid and a part of the catalyst, and directly carry out a melting reaction at 150 - 160 °C and 0.09 - 0.1 MPa for 3 - 5 h to obtain a carboxyl - terminated polylactic acid - citric acid copolymer; (2) Dissolve the carboxyl - terminated polylactic acid - citric acid copolymer in toluene, stir evenly, add nano - zinc oxide and the remaining catalyst, react at 60 - 70 °C for 2 - 3 h, after the reaction is completed, wash it alternately with absolute ethanol and distilled water for 2 - 3 times, filter by suction, and obtain modified nano - zinc oxide after vacuum drying.

[0010] By adopting the above - mentioned technical solution, through dehydrating lactic acid and carrying out a melting reaction with citric acid and a part of the catalyst, a carboxyl - terminated polylactic acid - citric acid copolymer is generated. This copolymer can react with nano - zinc oxide under specific conditions, thereby realizing the surface modification of nano - zinc oxide, effectively improving the dispersibility and compatibility of nano - zinc oxide in the hot - melt adhesive system. When spreading the adhesive, it plays a role in increasing the roughness of the contact surface, assisting the easy peeling of the hot - melt adhesive. Moreover, the modified nano - zinc oxide also endows the hot - melt adhesive with better flexibility and impact resistance, and can reduce the risk of damage caused by external impact while protecting the surface of brittle objects.

[0011] Preferably, the conditions for the dehydration treatment in step (1) are: dehydration temperature 100 - 105 °C, dehydration pressure 0.1 - 0.3 MPa, and dehydration time 1 - 2 h.

[0012] By adopting the above - mentioned technical solution, dehydrating lactic acid reduces or even removes the free water in the raw material lactic acid, promotes the forward progress of the reaction, and thus improves the purity of the raw material lactic acid.

[0013] Preferably, the catalyst is compounded by stannous octoate and p - toluenesulfonic acid according to a weight ratio of 1:(0.8 - 1.2).

[0014] By adopting the above - mentioned technical solution, the catalyst is compounded by stannous octoate and p - toluenesulfonic acid according to a specific weight ratio, which can significantly improve the reaction efficiency and product stability in the preparation process of modified nano - zinc oxide. The compounded catalyst shows a synergistic effect in the reaction system, promotes the efficient combination of the carboxyl - terminated polylactic acid - citric acid copolymer and nano - zinc oxide, and enhances the surface activity of the modified nano - zinc oxide.

[0015] Preferably, the photo - initiator is one or more of BAPO, 1 - hydroxycyclohexyl phenyl ketone, and hydroxy - dimethyl phenyl ethyl ketone.

[0016] By adopting the above technical solution, the photoinitiator can absorb ultraviolet light of a specific wavelength in the hot melt adhesive, generating active free radicals or cations, thereby initiating the polymerization reaction of hydroxyethyl acrylate and fluorine-containing composite active monomers to achieve rapid curing. This application adopts the UV / moisture dual-curing method, combining the rapidity of UV curing and the deep penetration of moisture curing, effectively reducing the residue of unreacted monomers, increasing the curing speed, and enabling the hot melt adhesive to have more excellent shock-absorbing performance and peeling characteristics when protecting brittle objects.

[0017] Preferably, the aliphatic isocyanate includes one or more of dicyclohexylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

[0018] Preferably, the polyester polyol adopts one or more of polyethylene adipate glycol, polyneopentyl adipate glycol, polycaprolactone glycol, poly(1,4-butylene adipate) glycol, poly(castor oil adipate) polyol, and poly(1,6-hexanediol carbonate) glycol; the polyether polyol is polytetrahydrofuran ether glycol.

[0019] By adopting the above technical solution, the aliphatic isocyanate has excellent yellowing resistance due to the absence of an aromatic ring in its molecular structure, and can effectively avoid color changes of the hot melt adhesive caused by light or oxidation during long-term use, thereby maintaining the appearance quality of the product. At the same time, the aliphatic isocyanate has a moderate reaction activity and can stably react with polyols at a lower temperature to form a polyurethane structure with good mechanical properties and adhesion.

[0020] Preferably, the chain extender includes one or more of dioxazoline, 1,4-butanediol, neopentyl glycol, sorbitol, ethylenediamine, and N,N-dihydroxy(diisopropyl)aniline.

[0021] By adopting the above technical solution, adding a chain extender effectively adjusts the crosslinking density and mechanical properties of the hot melt adhesive, enabling it to have better flexibility and peeling performance while ensuring strong adhesion, thereby reducing secondary damage to the surface of the protected article.

[0022] In the second aspect, a preparation method of a shock-absorbing hot melt adhesive for protecting the surface of a brittle object provided by this application adopts the following technical solution: A preparation method of a shock-absorbing hot melt adhesive for protecting the surface of a brittle object includes the following steps: Weigh the raw materials according to the component ratio, mix the polyester polyol and the polyether polyol in a vacuum environment, stir and react at 120 - 130 °C for 30 - 40 min, and under the protection of nitrogen, cool down to 60 - 70 °C and add the aliphatic isocyanate and the chain extender, and react for 1 - 2 h to obtain a polyurethane prepolymer; Using dibutyltin dilaurate as a catalyst, a polyurethane prepolymer is mixed with hydroxyethyl acrylate, a fluorine-containing composite active monomer, and a photoinitiator, and stirred at 60-70 °C for 1.5-2.5 h to obtain a polyurethane acrylate prepolymer; Nanometer zinc oxide is added to the polyurethane acrylate prepolymer, and stirring is continued for 30-45 min, and then the product is discharged to obtain a shock-absorbing hot melt adhesive for protecting the surface of a brittle object, which is stored in vacuum-sealed and light-shielded manner.

[0023] By adopting the above technical solution, polyester polyol and polyether polyol are mixed in a vacuum environment, and after adding an aliphatic isocyanate and a chain extender, a uniform and stable polyurethane prepolymer is formed. Subsequently, hydroxyethyl acrylate, a fluorine-containing composite active monomer, and a photoinitiator are introduced and mixed to synthesize a polyurethane acrylate prepolymer containing both carbon-carbon double bonds and -NCO groups in the molecular structure, which not only further improves the adhesion of the hot melt adhesive, but also endows it with the ability of rapid curing. Among them, the introduction of the fluorine-containing composite active monomer significantly improves the release performance of the hot melt adhesive. Because it contains C-F bonds with low surface energy, it can form an isolation layer between the hot melt adhesive and the surface of the protected article during the gluing process, effectively reducing the damage to the article surface during peeling. After adding modified nanometer zinc oxide, the roughness between the hot melt adhesive and the adhered article is increased, so that the hot melt adhesive can be easily peeled off from the surface of the protected article without damaging the protected article.

[0024] The present application has the following beneficial effects: The hot melt adhesive of the present application adopts a UV / moisture dual-curing method, which can effectively improve the flexibility and adhesion performance of the hot melt adhesive, so that the hot melt adhesive has a good shock-absorbing effect after curing, thereby better protecting the surface of the brittle object from external impacts. Polyester polyol, polyether polyol, aliphatic isocyanate and hydroxyethyl acrylate are synthesized into a polyurethane acrylate prepolymer containing both carbon-carbon double bonds and -NCO in the molecular structure. By introducing a fluorine-containing composite active monomer, the release force is increased. Because the fluorine-containing composite active monomer contains C-F bonds and has low surface energy, during gluing, the fluorine-containing active monomer forms a thin isolation layer between the hot melt adhesive and the surface of the protected article to achieve the release effect. In addition, lactic acid, citric acid and a catalyst are used to modify nanometer zinc oxide. The -OH in the lactic acid molecule reacts with the -COOH in the citric acid molecule to form a terminal carboxyl poly(lactic acid-citric acid) copolymer. The hydroxyl group on the surface of zinc oxide reacts with the carboxyl group of the terminal carboxyl poly(lactic acid-citric acid) copolymer to form a polymer coating layer. The terminal carboxyl poly(lactic acid-citric acid) copolymer further reacts with -NCO in the polyurethane to promote the uniform dispersion of nanometer zinc oxide in the organic phase, increase the roughness during film laying, and assist the hot melt adhesive to be easily peeled off. Specific embodiments

[0025] Preparation examples Preparation example 1 Preparation method of modified nano-zinc oxide: (1) Dehydrate lactic acid using a dehydration reactor. Mix 6 kg of dehydrated lactic acid with 4.2 kg of citric acid, 0.11 kg of stannous octoate, and 0.12 kg of p-toluenesulfonic acid, and directly carry out a melting reaction at 150 °C and 0.09 MPa for 3 h to obtain a carboxyl-terminated poly(lactic acid)-citric acid copolymer; (2) Dissolve the carboxyl-terminated poly(lactic acid)-citric acid copolymer in toluene, stir evenly, add 15 kg of nano-zinc oxide, 0.11 kg of stannous octoate, and 0.11 kg of p-toluenesulfonic acid, react at 60 °C for 2 h, after the reaction is completed, wash twice alternately with absolute ethanol and distilled water, filter by suction, and obtain modified nano-zinc oxide after vacuum drying.

[0026] Preparation Example 2 Preparation method of modified nano-zinc oxide: (1) Dehydrate lactic acid using a dehydration reactor. Mix 9 kg of dehydrated lactic acid with 5.4 kg of citric acid, 0.18 kg of stannous octoate, and 0.18 kg of p-toluenesulfonic acid, and directly carry out a melting reaction at 155 °C and 0.095 MPa for 4 h to obtain a carboxyl-terminated poly(lactic acid)-citric acid copolymer; (2) Dissolve the carboxyl-terminated poly(lactic acid)-citric acid copolymer in toluene, stir evenly, add 18 kg of nano-zinc oxide, 0.18 kg of stannous octoate, and 0.18 kg of p-toluenesulfonic acid, react at 65 °C for 2.5 h, after the reaction is completed, wash three times alternately with absolute ethanol and distilled water, filter by suction, and obtain modified nano-zinc oxide after vacuum drying.

[0027] Preparation Example 3 Preparation method of modified nano-zinc oxide: (1) Dehydrate lactic acid using a dehydration reactor. Mix 12 kg of dehydrated lactic acid with 6.4 kg of citric acid, 0.23 kg of stannous octoate, and 0.27 kg of p-toluenesulfonic acid, and directly carry out a melting reaction at 160 °C and 0.1 MPa for 5 h to obtain a carboxyl-terminated poly(lactic acid)-citric acid copolymer; (2) Dissolve the carboxyl-terminated poly(lactic acid)-citric acid copolymer in toluene, stir evenly, add 20 kg of nano-zinc oxide, 0.23 kg of stannous octoate, and 0.27 kg of p-toluenesulfonic acid, react at 70 °C for 3 h, after the reaction is completed, wash three times alternately with absolute ethanol and distilled water, filter by suction, and obtain modified nano-zinc oxide after vacuum drying.

[0028] Preparation Example 4 The difference between this preparation example and Preparation Example 2 is that an equal amount of stearic acid is used to replace citric acid.

[0029] Preparation method of modified nano-zinc oxide: (1) Use a dehydration reactor to dehydrate lactic acid. Mix 9 kg of dehydrated lactic acid with 5.4 kg of stearic acid, 0.18 kg of stannous octoate, and 0.18 kg of p-toluenesulfonic acid, and directly carry out a melting reaction at 155 °C and 0.095 MPa for 4 h to obtain a carboxyl-terminated polylactic acid-stearic acid copolymer; (2) Dissolve the carboxyl-terminated polylactic acid-stearic acid copolymer in toluene, stir evenly, add 18 kg of nano-zinc oxide, 0.18 kg of stannous octoate, and 0.18 kg of p-toluenesulfonic acid, and react at 65 °C for 2.5 h. After the reaction is completed, wash it alternately with anhydrous ethanol and distilled water 3 times, filter by suction, and obtain modified nano-zinc oxide after vacuum drying. Example

[0030] Example 1 A shock-absorbing hot-melt adhesive for protecting the surface of brittle objects, comprising 20 kg of poly(hexamethylene adipate) glycol (Prolite 25212-06-0), 28 kg of polytetrahydrofuran ether glycol (De Yitai 25190-06-1), 16 kg of dicyclohexylmethane diisocyanate (Mingyu 5124-30-1), 6 kg of hydroxyethyl acrylate, 3.8 kg of trifluoroethyl acrylate (Koji Bio 407-47-6), and 3.2 kg of perfluorooctylethyl acrylate (Lanabai 27905-45-9), 15 kg of modified nano-zinc oxide (prepared in Preparation Example 1), 0.3 kg of 1-hydroxycyclohexyl phenyl ketone, and 2 kg of ethylenediamine.

[0031] Among them, the preparation method of the shock-absorbing hot-melt adhesive for protecting the surface of brittle objects in this example includes the following steps: Weigh the raw materials according to the above component ratios. Mix poly(hexamethylene adipate) glycol and polytetrahydrofuran ether glycol in a vacuum environment, stir and react at 120 °C for 30 min. Under the protection of nitrogen, cool down to 60 °C and add dicyclohexylmethane diisocyanate and ethylenediamine, and react for 1 h to obtain a polyurethane prepolymer; Using dibutyltin dilaurate as a catalyst, mix the polyurethane prepolymer with hydroxyethyl acrylate, trifluoroethyl acrylate, perfluorooctylethyl acrylate, and 1-hydroxycyclohexyl phenyl ketone, and stir and react at 60 °C for 1.5 h to obtain a polyurethane acrylate prepolymer; Add nano-zinc oxide to the polyurethane acrylate prepolymer, continue to stir for 30 min and then discharge to obtain a shock-absorbing hot-melt adhesive for protecting the surface of brittle objects, and store it in a vacuum-sealed and light-proof manner.

[0032] Example 2 A shock-absorbing hot-melt adhesive for protecting the surface of brittle objects, comprising 25 kg of neopentyl glycol adipate diol (Xinyuhong 27925-07-1), 32 kg of polytetrahydrofuran ether diol (Deyitai 25190-06-1), 18 kg of isophorone diisocyanate (Kanos 4098-71-9), 8 kg of hydroxyethyl acrylate, 4 kg of trifluoroethyl acrylate (Koji Biotech 407-47-6) and 4 kg of perfluorooctylethyl acrylate (Lanabai 27905-45-9), 18 kg of modified nano-zinc oxide (prepared in Preparation Example 2), 0.4 kg of BAPO, and 3 kg of dioxazoline.

[0033] Among them, the preparation method of the shock-absorbing hot-melt adhesive for protecting the surface of brittle objects in this embodiment includes the following steps: Weigh the raw materials according to the above-mentioned component ratios. Mix neopentyl glycol adipate diol and polytetrahydrofuran ether diol in a vacuum environment, stir and react at 125 °C for 35 min. Under the protection of nitrogen, cool down to 65 °C and add isophorone diisocyanate and dioxazoline, and react for 1.5 h to obtain a polyurethane prepolymer. Using dibutyltin dilaurate as a catalyst, mix the polyurethane prepolymer with hydroxyethyl acrylate, trifluoroethyl acrylate, perfluorooctylethyl acrylate and BAPO, stir and react at 65 °C for 2 h to obtain a polyurethane acrylate prepolymer; add nano-zinc oxide to the polyurethane acrylate prepolymer, continue to stir for 40 min and then discharge to obtain a shock-absorbing hot-melt adhesive for protecting the surface of brittle objects, and store it in a vacuum-sealed and light-proof manner.

[0034] Example 3 A shock-absorbing hot-melt adhesive for protecting the surface of brittle objects, comprising 30 kg of polycarbonate-1,6-hexanediol ester diol (Kemike 29862-10-0), 36 kg of polytetrahydrofuran ether diol (Deyitai 25190-06-1), 20 kg of hexamethylene diisocyanate (Wanhua HT-100), 10 kg of hydroxyethyl acrylate, 4 kg of trifluoroethyl acrylate (Koji Biotech 407-47-6) and 5 kg of perfluorooctylethyl acrylate (Lanabai 27905-45-9), 20 kg of modified nano-zinc oxide (prepared in Preparation Example 3), 0.5 kg of hydroxydimethylacetophenone, and 4 kg of 1,4-butanediol.

[0035] Among them, the preparation method of the shock-absorbing hot-melt adhesive for protecting the surface of brittle objects in this embodiment includes the following steps: Weigh the raw materials according to the above-mentioned component ratios. Mix polycarbonate-1,6-hexanediol ester diol and polytetrahydrofuran ether diol in a vacuum environment, stir and react at 130 °C for 40 min. Under the protection of nitrogen, cool down to 70 °C and add hexamethylene diisocyanate and 1,4-butanediol, and react for 2 h to obtain a polyurethane prepolymer. Using dibutyltin dilaurate as a catalyst, a polyurethane prepolymer was mixed with hydroxyethyl acrylate, trifluoroethyl acrylate, perfluorooctylethyl acrylate and hydroxydimethylacetophenone, and stirred at 70 °C for 2.5 h to obtain a polyurethane acrylate prepolymer; Nanometer zinc oxide was added to the polyurethane acrylate prepolymer, and after stirring for another 45 min, the mixture was discharged to obtain a shock-absorbing hot melt adhesive for protecting the surface of brittle objects, which was stored in vacuum-sealed and light-proof manner.

[0036] Example 4 A shock-absorbing hot melt adhesive for protecting the surface of brittle objects, which is different from Example 2 in that tetrafluoropropyl methacrylate is used to replace trifluoroethyl acrylate in equal amount.

[0037] Example 5 A shock-absorbing hot melt adhesive for protecting the surface of brittle objects, which is different from Example 2 in that dodecafluoroheptyl methacrylate is used to replace perfluorooctylethyl acrylate.

[0038] Comparative Example Comparative Example 1 A shock-absorbing hot melt adhesive for protecting the surface of brittle objects, which is different from Example 2 in that an equal amount of nanometer zinc oxide is used to replace the modified nanometer zinc oxide.

[0039] Comparative Example 2 A shock-absorbing hot melt adhesive for protecting the surface of brittle objects, which is different from Example 2 in that the modified nanometer zinc oxide prepared in Preparation Example 4 is used.

[0040] Comparative Example 3 A shock-absorbing hot melt adhesive for protecting the surface of brittle objects, which is different from Example 2 in that an equal amount of modified kaolin is used to replace the modified nanometer zinc oxide.

[0041] Among them, the preparation method of the modified kaolin is as follows: (1) Using a dehydration reactor to dehydrate lactic acid, 9 kg of dehydrated lactic acid was mixed with 5.4 kg of citric acid and 0.36 kg of catalyst, and directly melted and reacted at 155 °C and 0.095 MPa for 4 h to obtain a carboxyl-terminated polylactic acid-citric acid copolymer; (2) The carboxyl-terminated polylactic acid-citric acid copolymer was dissolved in toluene, stirred evenly, 18 kg of kaolin and 0.36 kg of catalyst were added, and reacted at 65 °C for 2.5 h. After the reaction was completed, it was washed alternately with anhydrous ethanol and distilled water 3 times, filtered by suction, and dried in vacuum to obtain modified nanometer kaolin.

[0042] Comparative Example 4 A shock-absorbing hot melt adhesive for protecting the surface of brittle objects, which is different from Example 2 in that an equal amount of 2,2,2-trifluoroethyl acrylate is used to replace perfluorooctylethyl acrylate.

[0043] Comparative Example 5 A shock-absorbing hot melt adhesive for protecting the surface of brittle objects, which is different from Example 2 in that an equal amount of perfluorooctylethyl acrylate is used to replace 2,2,2-trifluoroethyl acrylate.

[0044] Comparative Example 6 A shock-absorbing hot melt adhesive for protecting the surface of brittle objects, which is different from Example 2 in that 2,2,2-trifluoroethyl acrylate and perfluorooctylethyl acrylate are not added.

[0045] Comparative Example 7 A shock-absorbing hot melt adhesive for protecting the surface of brittle objects, which is different from Example 2 in that an equal amount of ethyl acrylate is used to replace 2-hydroxyethyl acrylate.

[0046] Performance detection test 1. Rebound performance test: The hot melt adhesives of Examples 1-5 and Comparative Examples 1-8 are produced into films with a thickness of 0.05 mm through a single-screw extruder, and made into films with a width of 10 mm × a length of 50 mm. At a stretching speed of 100 mm / min, they are stretched to three times the original length, that is, a length of 150 mm, and maintained at this length for 30 min. Then, the stress on the film is released, and the length L is measured 12 hours later. The calculation of the rebound rate adopts the following formula: 2. Melting point: The melting point temperature of the polyurethane hot melt adhesive is tested by DSC differential scanning.

[0047] 3. Peel strength test: The polyurethane hot melt adhesive is cast onto the base fabric by a casting machine and thermally bonded to another base fabric through a laminating machine to obtain a sample. The sample is placed in a constant temperature oven at 23 °C for 12 hours, and then cut into strips with a width of 25 mm. With a stretching rate of 100 mm / min and a peeling angle of 180°, the test results are the average values of 3 parallel strips to obtain the peel strength, and the test results are recorded in Table 1.

[0048] 4. Residual situation of the hot melt adhesive after peeling: The bonded sample is subjected to a peeling test to observe the residual situation of the hot melt adhesive on the sample after peeling.

[0049] Table 1 According to the comparison between Example 1 and Comparative Example 1 and the data in Table 1, it can be seen that the modified nano-zinc oxide of the present application is uniformly dispersed in the organic phase, increasing the roughness during film laying, assisting the hot melt adhesive to be easily peeled off. Moreover, the modified nano-zinc oxide endows the hot melt adhesive with better flexibility and impact resistance, which can protect the surface of brittle objects while reducing the risk of breakage caused by external impacts. In contrast, the nano-zinc oxide in the comparative example is not modified and is prone to agglomeration, thus affecting the performance of the hot melt adhesive.

[0050] According to the comparison between Example 1 and Comparative Example 2 and the data in Table 1, it can be seen that in Comparative Example 2, lactic acid and stearic acid were used to modify nano-zinc oxide. The stearic acid molecule only contains a carboxyl group and no hydroxyl group, and cannot bind well with lactic acid or the hydroxyl groups on the surface of nano-zinc oxide, thus affecting the performance of the hot melt adhesive. In the present application, lactic acid, citric acid and a catalyst are used to modify nano-zinc oxide to form a polymer coating layer on the nano-zinc oxide, and then further combined with polyurethane to promote the uniform dispersion of nano-zinc oxide in the organic phase and make the nano-zinc oxide firmly adhere to the surface of the hot melt adhesive, increasing the roughness during film laying and assisting the hot melt adhesive to be easily peeled off.

[0051] According to the comparison between Example 1 and Comparative Example 3 and the data in Table 1, it can be seen that kaolin has a layered structure and is not as effective as nano-zinc oxide in increasing the roughness of the hot melt adhesive film layer.

[0052] According to the comparison between Example 1 and Comparative Examples 4-5 and the data in Table 1, it can be seen that Comparative Examples 4 and 5 only contain one fluorinated active monomer, while in the present application, trifluoroethyl acrylate rich in short side chains and perfluorooctylethyl acrylate rich in long side chains interact synergistically to form a dynamic microphase separation structure, enhancing the friction between internal molecules, improving the shock absorption performance, and the combination of the two makes the hot melt adhesive obtain a lower surface energy, achieving an extremely light release force when peeling off the hot melt adhesive, and having significant advantages in protecting the surface of brittle objects.

[0053] According to the comparison between Example 1 and Comparative Example 6 and the data in Table 1, it can be seen that Comparative Example 6 did not add a fluorinated composite active monomer, resulting in a high adhesion of the hot melt adhesive after curing, making it difficult to be removed, and the hot melt adhesive is likely to remain on the protected article. In the present application, the combination of trifluoroethyl acrylate and perfluorooctylethyl acrylate makes the hot melt adhesive obtain a lower surface energy, forming a weak bond with the protected article, which is convenient to be quickly torn off after the protection is completed without leaving residual glue.

[0054] From the comparison between Example 1 and Comparative Example 7 and the data in Table 1, it can be seen that the molecular structure of ethyl acrylate contains only one ethyl ester group and no hydroxyl group, so its hydrophilicity and reactivity are relatively weak. The synergistic effect of hydroxyethyl acrylate and fluorine-containing composite active monomers in this application endows the hot melt adhesive with excellent stain resistance and anti-peeling performance, reduces the residue problem and lowers the risk of secondary damage to the protected article.

[0055] This specific embodiment is only an interpretation of the present application, and it does not limit the present application. After reading this specification, those skilled in the art can make modifications to this specific embodiment without creative contributions as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A shock-absorbing hot-melt adhesive for protecting the surface of brittle objects, characterized in that, It is prepared from the following raw materials by weight parts: 20 - 30 parts of polyester polyol, 28 - 36 parts of polyether polyol, 16 - 20 parts of aliphatic isocyanate, 6 - 10 parts of hydroxyethyl acrylate, 7 - 9 parts of fluorine - containing composite active monomer, 15 - 20 parts of modified nano - zinc oxide, 0.3 - 0.5 parts of photoinitiator, 2 - 4 parts of chain extender; The preparation raw materials of the modified nano - zinc oxide include nano - zinc oxide, lactic acid, citric acid and a catalyst, and the weight ratio of the nano - zinc oxide, lactic acid, citric acid and the catalyst is 10:(4 - 6):(2.8 - 3.2):(0.3 - 0.5).

2. The shock-absorbing hot melt adhesive for protecting the surface of a brittle object according to claim 1, wherein The fluorine - containing composite active monomer includes trifluoroethyl acrylate and perfluorooctylethyl acrylate, and the weight ratio of the trifluoroethyl acrylate and perfluorooctylethyl acrylate is 1:(0.8 - 1.2).

3. A shock-absorbing hot melt adhesive for protecting the surface of brittle objects according to claim 1, characterized in that, The preparation method of the modified nano - zinc oxide includes the following steps: (1) Use a dehydration reactor to dehydrate lactic acid, mix the dehydrated lactic acid with citric acid and part of the catalyst, and directly carry out a melting reaction at 150 - 160 °C and 0.09 - 0.1 MPa for 3 - 5 h to obtain a carboxyl - terminated polylactic acid - citric acid copolymer; (2) Dissolve the carboxyl - terminated polylactic acid - citric acid copolymer in toluene, stir evenly, add nano - zinc oxide and the remaining catalyst, react at 60 - 70 °C for 2 - 3 h, after the reaction is completed, wash it alternately with anhydrous ethanol and distilled water for 2 - 3 times, carry out suction filtration, and obtain the modified nano - zinc oxide after vacuum drying.

4. The shock-absorbing hot-melt adhesive for protecting the surface of a brittle object according to claim 3, characterized in that, The conditions for the dehydration treatment in step (1) are: dehydration temperature 100 - 105 °C, dehydration pressure 0.1 - 0.3 MPa, dehydration time 1 - 2 h.

5. The shock-absorbing hot-melt adhesive for protecting the surface of brittle objects according to claim 1, characterized in that, The catalyst is compounded by stannous octoate and p - toluenesulfonic acid according to a weight ratio of 1:(0.8 - 1.2).

6. The shock-absorbing hot melt adhesive for protecting the surface of a brittle object according to claim 1, wherein, The photoinitiator uses one or more of BAPO, 1 - hydroxycyclohexyl phenyl ketone, and hydroxy - dimethyl phenylacetone.

7. The shock-absorbing hot-melt adhesive for protecting the surface of brittle objects according to claim 1, wherein, The aliphatic isocyanate includes one or more of dicyclohexylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

8. A shock-absorbing hot melt adhesive for protecting the surface of a brittle object according to claim 1, characterized in that, The chain extender includes one or more of dioxazoline, 1,4 - butanediol, neopentyl glycol, sorbitol, ethylenediamine, and N,N - dihydroxy(diisopropyl)aniline.

9. The preparation method of a shock-absorbing hot-melt adhesive for protecting the surface of brittle objects according to any one of claims 1-8, characterized in that, It includes the following steps: Weigh the raw materials according to the above - mentioned component ratio, mix the polyester polyol and the polyether polyol in a vacuum environment, stir and react at 120 - 130 °C for 30 - 40 min, under the protection of nitrogen, cool down to 60 - 70 °C, add the aliphatic isocyanate and the chain extender, and react for 1 - 2 h to obtain a polyurethane prepolymer; Using dibutyltin dilaurate as a catalyst, mix the polyurethane prepolymer with hydroxyethyl acrylate, the fluorine - containing composite active monomer and the photoinitiator, and stir and react at 60 - 70 °C for 1.5 - 2.5 h to obtain a polyurethane acrylate prepolymer; Add nano - zinc oxide to the polyurethane acrylate prepolymer, continue to stir for 30 - 45 min and then discharge to obtain a shock - absorbing hot - melt adhesive for protecting the surface of brittle objects, and store it in a vacuum - sealed and light - proof manner.

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