Moisture-proof polyurethane glue for self-adhesive label and preparation method of moisture-proof polyurethane glue

Abstract

The invention discloses moisture-proof polyurethane glue for a self-adhesive label and a preparation method of the moisture-proof polyurethane glue, and belongs to the technical field of polyurethane glue, the moisture-proof polyurethane glue comprises the following raw materials by mass: 15-20 parts of polyether polyol; 10 to 15 parts of MDI (diphenylmethane diisocyanate); 25 to 62 parts of ethyl acetate; 0.5 to 2 parts of a catalyst; and 0.5 to 1 part of an organic silicon defoaming agent. The preparation method comprises the following steps: uniformly distributing ethyl acetate at the bottom of a reaction kettle; slowly adding MDI into the ethyl acetate solution; adding a mixture of MDI and ethyl acetate into polyether polyol, and adding the diluted catalyst solution; and directly adding the organic silicon defoaming agent into the reaction kettle, and stirring to eliminate bubbles, thereby obtaining the moisture-proof polyurethane glue. The polyurethane glue provided by the invention not only can meet the requirement of self-adhesive labels in the electronic industry on viscosity, so that the self-adhesive labels can be firmly attached to the surfaces of devices, but also can achieve a certain moisture-proof effect in the transportation and storage processes.

Description

Technical Field

[0001] The invention mainly relates to the technical field of polyurethane glue, and specifically relates to moisture-proof polyurethane glue for self-adhesive labels and a preparation method thereof. Background Art

[0002] From the basic structure, the self-adhesive label is mainly composed of three parts, including the surface material, glue, and backing paper. In terms of moisture resistance of self-adhesive labels, PET (polyethylene terephthalate) surface material has good moisture resistance because its molecular structure is tight and water molecules are difficult to penetrate; some paper release papers may have a certain degree of air permeability, while plastic release films coated with silicone oil can better block external air and moisture. Therefore, the research and development of moisture-proof glue has become the top priority of the research on moisture-proof performance of self-adhesive labels.

[0003] In the electronics industry, there are certain requirements for the moisture resistance of self-adhesive labels. The humidity of the storage environment for self-adhesive materials is usually required to be 45%-55%. If the humidity is too high, the surface material performance of film materials may decline in a humid environment, resulting in poor ink adhesion during printing. Therefore, self-adhesive labels need to have good moisture resistance to ensure that the information on the label is still clearly readable in a humid environment, and the label will not lose its stickiness or deform due to moisture. This requires that the polyurethane glue used in self-adhesive labels also needs to have certain moisture resistance.

[0004] However, there is no polyurethane glue with suitable viscosity for self-adhesive labels and certain moisture-proof performance in the prior art. Summary of the invention

[0005] The technical solution of the present invention aims at the technical problem that the existing technical solutions are too single, and provides a solution that is significantly different from the existing technology. It mainly provides a moisture-proof polyurethane glue for self-adhesive labels and a preparation method thereof, so as to meet the viscosity requirements of self-adhesive labels in the electronics industry, so that they can be firmly attached to the surface of the device, and can also play a certain moisture-proof effect during its transportation and storage.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: A moisture-proof polyurethane glue for self-adhesive labels is made from the following raw materials in parts by weight: Polyether polyol: 15-20 parts; Diphenylmethane diisocyanate: 10-15 parts; Ethyl acetate: 25-62 parts; Catalyst: 0.5-2 parts; Silicone defoamer: 0.5-1 part.

[0007] Preferably, the catalyst is dibutyltin dilaurate.

[0008] Further, the purity of the polyether polyol is 98%; And / or, the purity of the diphenylmethane diisocyanate is 98%.

[0009] Further, the purity of the ethyl acetate is 99%; And / or, the purity of the catalyst is 98%; And / or, the purity of the organosilicon defoamer is 95%.

[0010] The present invention also provides a method for preparing the moisture-proof polyurethane glue, comprising the following steps: S1. Turn on the stirring device of the reactor and slowly pour ethyl acetate into the reactor to ensure that the ethyl acetate is evenly distributed at the bottom of the reactor; S2, diphenylmethane diisocyanate is slowly added into the ethyl acetate solution in the reaction kettle in a thin stream; during this process, the temperature is controlled at 20-40°C; S3, adding the mixture of diphenylmethane diisocyanate and ethyl acetate obtained in step S2 to a reactor containing polyether polyol, turning on the stirring device of the reactor, and slowly adding the diluted catalyst solution to the reactor; after adding, continue stirring for 10-30 minutes to allow the catalyst to fully dissolve and be evenly distributed in the glue system; S4, directly adding the organosilicon defoamer into the reaction kettle of step S3, stirring, so that the defoamer can effectively eliminate bubbles, and obtaining moisture-proof polyurethane glue.

[0011] Furthermore, in step S1, the stirring speed of the stirring device is set to 100-300 rpm.

[0012] Furthermore, in step S2, when the ambient temperature is higher than 25°C, the diphenylmethane diisocyanate is pre-cooled, that is, the sealed container containing diphenylmethane diisocyanate is placed in a cold water bath or a low-temperature thermostatic bath, and the temperature is adjusted to 10-20°C.

[0013] Furthermore, in step S2, the addition rate of diphenylmethane diisocyanate is controlled within a range that can steadily increase the temperature in the reaction kettle, and the dropwise addition time is not less than 30 minutes.

[0014] Furthermore, in step S3, the catalyst dilution operation is: diluting the catalyst with ethyl acetate, stirring evenly to form a uniform solution; the mass ratio of the catalyst to ethyl acetate is 1:5.

[0015] Further, in step S4, after adding the organosilicon defoamer, the stirring speed is reduced to 100-200 rpm and stirred for 10-20 minutes.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention is aimed at the PET material of the self-adhesive label in the electronics industry. Considering the affinity and water absorption of the polyurethane glue to water, the present invention selects polyether polyol, catalyst (dibutyltin dilaurate), silicon defoamer, MDI (diphenylmethane diisocyanate), and ethyl acetate as the formula raw materials, and by limiting the mass ratio of the raw materials, the polyurethane glue with suitable viscosity for the self-adhesive label and certain moisture-proof performance is prepared. The polyurethane glue under this formula can not only meet the viscosity requirements of the self-adhesive label in the electronics industry, so that it can be firmly attached to the surface of the device, but also play a certain moisture-proof effect during its transportation and storage.

[0017] (2) The MDI in the present invention is a polyurethane hard segment raw material, which contains an aromatic ring structure, which helps to improve the chemical resistance and water resistance of polyurethane; and the polyurethane hard segment formed by the reaction of MDI and polyether polyol can increase the crosslinking density of the glue, thereby reducing the penetration of water molecules; polyether polyol contains a polyether segment with good hydrophobicity, which helps to reduce the overall water absorption of the polyurethane glue, thereby improving its moisture resistance; silicon defoaming agent is usually hydrophobic, which can reduce the surface tension of the glue, help eliminate foam, and form a hydrophobic film on the surface of the glue, which can prevent the penetration of water molecules. Therefore, the polyurethane glue prepared by the present invention with a few simple ingredients can meet the requirements of good moisture resistance. It can be seen from the experiment that although the viscosity and bonding strength of the polyurethane glue provided by the present invention in a humid environment are reduced, they can still be maintained at a good level.

[0018] (3) The mass ratio of MDI (diphenylmethane diisocyanate) to polyether polyol in the formula provided by the present invention is between 1:2 and 1:1. By forming a closed-cell foam structure, controlling the density and cross-linking density, and utilizing the thermophysical properties of polyurethane itself, the final polyurethane glue has good thermal insulation performance. In some low-temperature environments, the initial viscosity of ordinary glue will decrease. For example, in provinces with warm climates, the temperature change is small and the initial viscosity of glue changes little. When the PET self-adhesive label is in a low-temperature atmosphere, the initial viscosity will decrease. In the long run, temperature fluctuations will also cause the glue to age and reduce viscosity. Glue with thermal insulation function can reduce this effect and keep the label firmly attached for a long time. For some temperature-sensitive products, such as medicines and biological products, labels with thermal insulation function can also avoid adverse effects on products caused by glue temperature problems during the pasting process. Glue with thermal insulation function can enable PET self-adhesive labels to be used in more complex and changing environments, whether in summer or cold winter, they can maintain their good adhesion.

[0019] (4) The chemical structure and molecular weight of polyether polyols and MDI in polyurethane glue will affect the reactivity of the glue. MDI reacts with polyols to form a cross-linked structure. As the number of cross-linking points increases, the viscosity of the system will also increase. Long-chain polyether polyols can increase the elasticity of the glue, so that the bonding interface can better adapt to deformation when subjected to external forces, thereby improving the bonding strength. MDI provides cross-linking points to form hard segments, which increase the rigidity and strength of the glue through hydrogen bonds and van der Waals forces, thereby improving the bonding strength. The catalyst accelerates the cross-linking reaction and forms a more uniform and dense cross-linked network. A more uniform and dense cross-linked network helps to improve the cohesion and bonding strength of the glue. The solvent can dissolve the solid components in the glue and reduce the viscosity of the system. The evaporation rate and amount of the solvent will affect the final viscosity of the glue. Ethyl acetate helps the glue to better penetrate and wet the bonding surface. Good wettability helps the glue and the bonding material form a closer intermolecular force, thereby improving the bonding strength. Silicone defoamer ensures that there are no bubbles in the glue during mixing and coating, and ensures the integrity of the bonding surface. The bubble-free bonding surface means that the contact area between the glue and the bonding material is larger, thereby improving the bonding strength. The present invention is aimed at the self-adhesive labels in the electronics industry, and defines the ratio of polyether polyol, MDI, catalyst, silicon defoamer and ethyl acetate, so that the final polyurethane glue product can provide suitable viscosity and bonding strength. It can be seen from the experiment that a lower content of polyether polyol / MDI / catalyst / silicon defoamer / ethyl acetate will lead to a decrease in the viscosity, adhesion, holding force and release force of the final polyurethane glue product; a higher content of polyether polyol can only slightly increase the viscosity but not the bonding strength; a higher content of ethyl acetate does not significantly increase the viscosity; a higher content of MDI, catalyst and silicon defoamer will instead lead to a decrease in the viscosity, adhesion, holding force and release force of the final polyurethane glue product.

[0020] (5) Ethyl acetate in the present invention is used as a diluent and solvent to dilute the catalyst and reactants, and as a solvent for the reaction of MDI and polyether polyol, so that the types of auxiliary agents in the present invention are relatively small, the formulation and preparation method can be simplified, which is conducive to reducing costs and facilitating product quality control.

[0021] (6) The raw materials of the moisture-proof polyurethane glue provided by the present invention mainly include polyether polyol, diphenylmethane diisocyanate, ethyl acetate, a catalyst and a silicone defoaming agent. Compared with other polyurethane glues, the ingredients are simple, which is conducive to reducing costs.

[0022] (7) The polyurethane glue preparation method provided by the present invention is economical and practical, and the preparation process is simple and the cost is low.

[0023] The present invention will be explained in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention provides a flow chart of the preparation method. DETAILED DESCRIPTION

[0025] To facilitate understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are given in the drawings, but the present invention can be implemented in different forms and is not limited to the embodiments described in the text. On the contrary, these embodiments are provided to make the content disclosed in the present invention more thorough and comprehensive.

[0026] Example 1: A moisture-proof polyurethane glue formula for bonding PET (polyethylene terephthalate) surface material is as follows: Polyether polyol: 150 g; MDI (diphenylmethane diisocyanate): 100 g; Ethyl acetate: 250 g; Dibutyltin dilaurate: 5 g; Silicone defoamer: 5 g.

[0027] The preparation steps of the above-mentioned moisture-proof polyurethane glue are as follows: 1. Raw materials and equipment preparation 1. Raw materials Table 1 raw material purity effect Polyether polyols 98% The main reactive component provides the hydroxyl (-OH) functional group Ethyl acetate 99% Dilute isocyanate, adjust the viscosity of glue, and mix all ingredients evenly Dibutyltin dilaurate 98% Used to adjust the curing speed of glue MDI 98% It undergoes addition polymerization reaction with hydroxyl (-OH) to form polyurethane segments Silicone defoamer 95% Used to eliminate bubbles generated during glue mixing 2. Equipment Reactor: Stainless steel reactor with stirring device, thermometer, condenser and heating / cooling jacket. 5L reactor, stirring device can achieve variable speed stirring, speed range is 0-1000 rpm.

[0028] Raw material storage container: dry, well-sealed plastic or stainless steel barrels, used to store MDI, polyether polyols, ethyl acetate, additives and other raw materials to prevent them from moisture and contamination.

[0029] Weighing equipment: High-precision electronic balance, used to accurately weigh raw materials. The accuracy of the balance is determined by the amount of raw materials used, and is required to be accurate to 0.01g.

[0030] Protective equipment: chemical-resistant gloves (such as nitrile gloves), goggles, and gas masks to protect operators from the irritation and toxicity of MDI. At the same time, prepare protective work clothes and work shoes to ensure full body protection for operators.

[0031] 2. Safety protection measures 1. Ventilation of operating environment Install an effective ventilation system, such as a fume hood or comprehensive ventilation equipment, in the glue preparation operation area. The wind speed of the fume hood should be no less than 0.5m / s to ensure that the MDI volatile gas generated during the operation can be discharged in time, so that the concentration of isocyanate in the working environment is lower than the safety limit (generally 0.02ppm).

[0032] 2. Inspection of personal protective equipment Operators must wear protective gear before entering the work area. Check whether gloves are damaged, whether goggles are clear and well sealed, and whether the gas mask canister is effective and installed correctly. Ensure that the collar, cuffs and trouser legs of protective work clothes are sealed, and work shoes are not damaged.

[0033] 3. Configuration process 1. Precooling When the ambient temperature is high (above 25°C), pre-cooling MDI can help control the reaction rate when it is mixed with ethyl acetate and reduce heat accumulation and side reactions caused by violent reactions.

[0034] Operation method: Place the sealed container containing MDI in a cold water bath or a low-temperature thermostatic bath and adjust the temperature to 10-20°C. The precooling time depends on the amount of MDI and the thermal conductivity of the container, and is generally 30-60 minutes.

[0035] (II) Mixing process, please refer to the attached Figure 1 .

[0036] 1. Add ethyl acetate into the reactor Turn on the stirring device of the reactor and set the stirring speed to 100-300 rpm. Slowly pour the measured ethyl acetate (as the solvent of MDI, its amount can be calculated based on the amount of MDI) into the reactor to ensure that the ethyl acetate is evenly distributed at the bottom of the reactor.

[0037] 2.MDI added to ethyl acetate Slowly open the valve of the MDI container and slowly add MDI to the ethyl acetate solution in the reactor in a thin stream. The rate of MDI addition should be controlled within a range that can steadily increase the temperature in the reactor, and the general addition time should be no less than 30 minutes. During the addition process, closely observe the thermometer reading in the reactor to ensure that the temperature is controlled at 20-40 ℃. If the temperature rises too quickly and exceeds 40 ℃, stop adding MDI immediately and cool it with water through the reactor jacket. Continue adding after the temperature drops to a suitable range.

[0038] Reasons for temperature control in this step: MDI (methylene diphenyl diisocyanate) is a highly active chemical substance, and its -NCO (isocyanate) group easily reacts with many compounds containing active hydrogen. Although ethyl acetate is relatively stable, it may also react with MDI under certain conditions. When the temperature rises, the movement speed of the molecules increases, the collision frequency of MDI and ethyl acetate molecules increases, and the reaction activity also increases. If the temperature is not controlled, some undesirable side reactions may occur; The chemical stability of ethyl acetate itself will change with temperature. At higher temperatures, ethyl acetate may undergo decomposition reactions. Its decomposition products may interact with MDI, changing the chemical composition of the reaction system. The polyurethane glue may have problems such as incomplete curing, reduced bonding strength, and poor flexibility. MDI and ethyl acetate are both dangerous chemicals. MDI is a toxic isocyanate that may cause harm to the human body if inhaled or in contact with the skin. At the same time, in a high temperature environment, the reaction system may get out of control due to overheating, causing safety accidents such as fire or explosion.

[0039] 3. Catalyst dilution Dilute the measured dibutyltin dilaurate with a small amount of ethyl acetate and stir evenly in a small beaker to form a uniform solution; the mass ratio of the catalyst to ethyl acetate is 1:5.

[0040] The dilution with ethyl acetate can reduce the viscosity of dibutyltin dilaurate, making it easier to disperse in the reaction system, which can ensure that the catalyst is evenly distributed in the entire polyurethane reaction system, thereby ensuring that the reaction can proceed at a relatively consistent rate in all parts; by diluting with ethyl acetate, the concentration of dibutyltin dilaurate in the reaction system can be more accurately controlled. If it is added directly without dilution, it is difficult to accurately control the amount added, which can easily lead to a reaction rate that is too fast or too slow.

[0041] 4. Polyether polyol reaction Add the mixture of MDI and ethyl acetate to the reactor containing polyether polyol, turn on the stirring device of the reactor, and slowly add the diluted catalyst solution into the reactor. During the addition process, pay attention to uniform dispersion to avoid excessive local concentration. After adding, continue stirring for 10-30 minutes to fully dissolve the catalyst and evenly distribute it in the glue system to play its role in regulating the curing speed.

[0042] 5. Defoaming treatment Defoamer addition method: If a lot of bubbles are generated during the glue mixing process, add the measured silicone defoamer directly into the reactor. After adding, reduce the stirring speed to 100-200 rpm and stir for 10-20 minutes to allow the defoamer to effectively eliminate the bubbles.

[0043] 6. Glue quality inspection 1. Viscosity test Use a rotational viscometer to measure the viscosity of the glue. Pour the glue sample into the measuring container of the viscometer, select a suitable rotor and speed, and measure according to the operating instructions of the viscometer.

[0044] (II) Bond strength test Prepare PET adhesive material, apply glue evenly on the surface of release paper, and bond with PET, and cure at a certain temperature. After a certain curing time, use a tensile testing machine to perform a tensile test to measure the bonding strength, including initial adhesion, adhesion, holding force, and release force. The bonding strength should meet the expected application requirements of the glue.

[0045] The functions of the raw materials in the formula of the present invention are: The chemical structure and molecular weight of polyether polyols will affect the reactivity of glue. Its hydroxyl (-OH) group can react with isocyanate (-NCO) group to form polyurethane. Selecting the appropriate content of polyether polyol can adjust the curing speed of glue. It is very important to control the curing speed of glue. The appropriate curing speed can ensure production efficiency and bonding quality. For PET self-adhesive labels, it has a 7 to 9-section oven during the coating process. The appropriate curing speed is matched with the length and temperature of the oven. When the glue comes out of the oven, it has a certain degree of curing. There will be no residual glue when winding, and the viscosity will reach the required viscosity. Such a curing speed is appropriate, otherwise it is necessary to adjust the curing speed.

[0046] MDI: During the synthesis of polyurethane glue, it reacts with hydroxyl groups (-OH) in polyols (such as polyester polyols or polyether polyols) to form carbamate bonds (-NH - COO -). These bonds have a certain polarity and can produce strong interactions between molecular chains. This reaction is the core reaction of polyurethane synthesis. Through this reaction, MDI and polyols are alternately connected to construct the polymer skeleton of polyurethane. At the same time, polyurethane molecular chains can also be connected to each other through hydrogen bonds and other means to form a tight three-dimensional network structure. This three-dimensional network structure is like a dense "net bag" that can effectively prevent the passage of water molecules. It is difficult for water molecules to penetrate this structure because the size of water molecules is relatively large, while the pores of the polyurethane network structure are small, and its internal chemical bonds and intermolecular forces can resist the invasion of water molecules.

[0047] The role of dibutyltin dilaurate in polyurethane reaction: In the synthesis process of polyurethane, the main reaction is the reaction between isocyanate (-NCO) group and hydroxyl (-OH) group to form urethane bond. Dibutyltin dilaurate can significantly increase the rate of this reaction. The catalyst accelerates the cross-linking reaction and forms a more uniform and dense cross-linking network; a more uniform and dense cross-linking network helps to improve the cohesion and bonding strength of the glue.

[0048] Ethyl acetate is used as a diluent and solvent to dilute the catalyst and reactants, and as a solvent for the polyether polyol reaction. The amount used is mainly in combination with other reagents. An appropriate amount of ethyl acetate can improve the wettability of the glue. When the glue is applied to the surface of the adherend, ethyl acetate can help the glue spread better, so that the glue and the adherend surface are fully in contact, thereby improving the bonding performance. However, if excessive ethyl acetate is added and remains in the glue layer after volatilization or volatilization is incomplete, gaps may be formed inside the glue layer, reducing the bonding strength and water resistance of the glue. Too little ethyl acetate will result in insufficient wettability of the glue, which will have an adverse effect on its bonding performance.

[0049] Silicone defoamer: In the production process of polyurethane glue, air is easily drawn in to form bubbles due to various factors such as stirring and adding additives. Silicone defoamer can reduce the surface tension of the glue system, making the surface tension of the bubble film uneven, thereby destroying the stability of the bubbles and preventing new bubbles from being generated. If too much is added, it may affect other properties of the glue, such as reducing the surface tension of the glue, which in turn affects the wettability and adhesion of the glue to the adherend. If too little is added, the bubbles cannot be completely eliminated, resulting in a poor appearance of the polyurethane glue.

[0050] The proportion of each ingredient is determined by the addition amount when testing the self-adhesive label for the best effect.

[0051] Embodiment 2: This embodiment differs from Embodiment 1 in that: A moisture-proof polyurethane glue formula for bonding PET (polyethylene terephthalate) surface materials is as follows: Polyether polyol: 200 g; MDI (diphenylmethane diisocyanate): 120 g; Ethyl acetate: 300 g; Dibutyltin dilaurate: 10 g; Silicone defoamer: 8 g.

[0052] The rest is the same as the first embodiment.

[0053] Embodiment 3: This embodiment differs from Embodiment 1 in that: A moisture-proof polyurethane glue formula for bonding PET (polyethylene terephthalate) surface materials is as follows: Polyether polyol: 160 g; MDI (diphenylmethane diisocyanate): 150 g; Ethyl acetate: 500 g; Dibutyltin dilaurate: 20 g; Silicone defoamer: 10 g.

[0054] The rest is the same as the first embodiment.

[0055] Embodiment 4: This embodiment differs from Embodiment 1 in that: A moisture-proof polyurethane glue formula for bonding PET (polyethylene terephthalate) surface materials is as follows: Polyether polyol: 200 g; MDI (diphenylmethane diisocyanate): 150 g; Ethyl acetate: 620 g; Dibutyltin dilaurate: 15 g; Silicone defoamer: 10 g.

[0056] The rest is the same as the first embodiment.

[0057] Comparative Example 1: The difference from Example 1 is that the content of polyether polyol is lower, and the amount of polyether polyol used is 100 g; The rest is the same as the first embodiment.

[0058] Comparative Example 2: The difference from Example 1 is that the content of polyether polyol is higher, and the amount of polyether polyol used is 250 g.

[0059] The rest is the same as the first embodiment.

[0060] Comparative Example 3: The difference from Example 1 is that the MDI content is lower and the amount of MDI used is 80 g.

[0061] The rest is the same as the first embodiment.

[0062] Comparative Example 4: The difference from Example 1 is that the MDI content is higher, and the amount of MDI used is 180 g.

[0063] The rest is the same as the first embodiment.

[0064] Comparative Example 5: The difference from Example 1 is that the ethyl acetate content is lower and the amount of ethyl acetate used is 200g.

[0065] The rest is the same as the first embodiment.

[0066] Comparative Example 6: The difference from Example 1 is that the ethyl acetate content is higher, and the amount of ethyl acetate used is 650g.

[0067] The rest is the same as the first embodiment.

[0068] Comparative Example 7: The difference from Example 1 is that the content of dibutyltin dilaurate is lower, and the amount of dibutyltin dilaurate used is 3 g.

[0069] The rest is the same as the first embodiment.

[0070] Comparative Example 8: The difference from Example 1 is that the content of dibutyltin dilaurate is higher, and the amount of dibutyltin dilaurate used is 30 g.

[0071] Comparative Example 9: The difference from Example 1 is that the content of the organosilicon defoamer is lower, and the amount of the organosilicon defoamer used is 3 g.

[0072] The rest is the same as the first embodiment.

[0073] Comparative Example 10: The difference from Example 1 is that the content of the organosilicon defoamer is higher, and the amount of the organosilicon defoamer used is 20 g.

[0074] The final viscosity test and bonding strength test results of the polyurethane glue prepared in Example 1 and Comparative Examples 1 to 10 are shown in Table 2.

[0075] Table 2 Glue quality test data table Example / Comparative Example Test Items Viscosity (cps) Initial adhesion (ball size) Adhesion (kg / 25mm) Hour Release force (g / 25mm) Embodiment 1 11000 10 1.3 >9 20 Comparative Example 1 10500 7 0.98 >8 17 Comparative Example 2 11100 10 0.97 >8 16 Comparative Example 3 10600 7 0.98 >7 15 Comparative Example 4 10600 8 0.97 >8 15 Comparative Example 5 9300 10 0.97 >7 16 Comparative Example 6 11000 7 0.96 >7 15 Comparative Example 7 10700 10 0.98 >8 15 Comparative Example 8 10800 10 0.96 >8 16 Comparative Example 9 10700 10 0.97 >8 16 Comparative Example 10 10700 10 0.97 >8 15 It can be seen from the data in Table 2 that the polyurethane adhesive provided in Example 1 has excellent viscosity and bonding strength. In comparison, a lower content of polyether polyol / MDI / catalyst / silicon defoamer / ethyl acetate will lead to a decrease in the viscosity, adhesion, holding force and release force of the final polyurethane adhesive product; a higher content of polyether polyol can only slightly increase the viscosity but cannot increase the bonding strength; a higher content of ethyl acetate has no obvious effect on viscosity improvement; a higher content of MDI, catalyst and silicon defoamer will instead lead to a decrease in the viscosity, adhesion, holding force and release force of the final polyurethane adhesive product.

[0076] In a humid environment, the final viscosity test and bonding strength test of the polyurethane glue prepared in Example 1 and Comparative Examples 1 to 10 were tested again, and the results are shown in Table 3.

[0077] Table 3 Glue quality test data in humid environment Example / Comparative Example Test Items Viscosity (cps) Initial adhesion (ball size) Adhesion (kg / 25mm) Hour Release force (g / 25mm) Embodiment 1 10700 9 1.3 >9 19 Comparative Example 1 10300 7 0.95 >7 15 Comparative Example 2 10700 8 0.93 >7 14 Comparative Example 3 10500 7 0.88 >7 14 Comparative Example 4 10300 8 0.91 >7 13 Comparative Example 5 9200 8 0.93 >7 14 Comparative Example 6 10600 7 0.91 >7 13 Comparative Example 7 10600 8 0.95 >7 14 Comparative Example 8 10600 8 0.96 >7 15 Comparative Example 9 10300 8 0.97 >7 14 Comparative Example 10 10300 8 0.96 >7 13 By comparing Table 2 and Table 3, it can be seen that although the viscosity and bonding strength of the polyurethane glue provided by the present invention are reduced in a humid environment, they can still be maintained at a good level, indicating that the polyurethane glue provided by the present invention has good moisture-proof performance.

[0078] In summary, the formula of the polyurethane glue is configured according to the viscosity requirements of the PET self-adhesive label, and has strong pertinence. The prepared polyurethane glue has a suitable viscosity for the self-adhesive label and has good moisture-proof performance.

[0079] The above is an exemplary description of the present invention in combination with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as such non-substantial improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A moisture-proof polyurethane glue for self-adhesive labels, characterized in that: Made from the following raw materials in parts by weight: Polyether polyol: 15-20 parts; Diphenylmethane diisocyanate: 10-15 parts; Ethyl acetate: 25-62 parts; Catalyst: 0.5-2 parts; Silicone defoamer: 0.5-1 part.

2. The moisture-proof polyurethane glue for self-adhesive labels according to claim 1, characterized in that: The catalyst is dibutyltin dilaurate.

3. The moisture-proof polyurethane glue for self-adhesive labels according to claim 1, characterized in that: The purity of the polyether polyol is 98%; And / or, the purity of the diphenylmethane diisocyanate is 98%.

4. The moisture-proof polyurethane glue for self-adhesive labels according to claim 1, characterized in that: The purity of the ethyl acetate is 99%; And / or, the purity of the catalyst is 98%; And / or, the purity of the organosilicon defoamer is 95%.

5. A method for preparing the moisture-proof polyurethane glue according to any one of claims 1 to 4, characterized in that: The steps include: S1. Turn on the stirring device of the reactor and slowly pour ethyl acetate into the reactor to ensure that the ethyl acetate is evenly distributed at the bottom of the reactor; S2, diphenylmethane diisocyanate is slowly added into the ethyl acetate solution in the reaction kettle in a thin stream; during this process, the temperature is controlled at 20-40°C; S3, adding the mixture of diphenylmethane diisocyanate and ethyl acetate obtained in step S2 to a reactor containing polyether polyol, turning on the stirring device of the reactor, and slowly adding the diluted catalyst solution to the reactor; after adding, continue stirring for 10-30 minutes to allow the catalyst to fully dissolve and be evenly distributed in the glue system; S4, directly adding the organosilicon defoamer into the reaction kettle of step S3, stirring, so that the defoamer can effectively eliminate bubbles, and obtaining moisture-proof polyurethane glue.

6. The method for preparing a moisture-proof polyurethane glue according to claim 5, characterized in that: In step S1, the stirring speed of the stirring device is set to 100-300 rpm.

7. The method for preparing a moisture-proof polyurethane glue according to claim 5, characterized in that: In step S2, when the ambient temperature is higher than 25°C, the diphenylmethane diisocyanate is pre-cooled in advance, that is, the sealed container containing diphenylmethane diisocyanate is placed in a cold water bath or a low-temperature thermostatic bath, and the temperature is adjusted to 10-20°C.

8. The method for preparing a moisture-proof polyurethane glue according to claim 5, characterized in that: In step S2, the addition rate of diphenylmethane diisocyanate is controlled within a range that can steadily increase the temperature in the reactor, and the dropwise addition time is not less than 30 minutes.

9. The method for preparing a moisture-proof polyurethane glue according to claim 5, characterized in that: In step S3, the catalyst dilution operation is: diluting the catalyst with ethyl acetate, stirring evenly to form a uniform solution; the mass ratio of the catalyst to ethyl acetate is 1:

5.

10. The method for preparing moisture-proof polyurethane glue according to claim 5, characterized in that: In step S4, after adding the organosilicon defoamer, the stirring speed is reduced to 100-200 rpm and stirred for 10-20 minutes.

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