Hot melt adhesive capable of developing color when encountering water as well as preparation method and application of hot melt adhesive

Abstract

The invention relates to the technical field of hot melt adhesives, in particular to a hot melt adhesive capable of developing color when encountering water as well as a preparation method and application thereof. The hot melt adhesive capable of developing color when encountering water is prepared from the following components in percentage by mass: 10 to 20 percent of olefin polymer, 5 to 10 percent of indicator microcapsule, 30 to 45 percent of tackifying resin, 30 to 45 percent of saturated fatty acid and 0.1 to 1.5 percent of antioxidant, the indicator microcapsule is composed of a capsule core and a capsule wall wrapping the surface of the capsule core; the capsule core comprises an indicator, and the capsule wall comprises polyvinylpyrrolidone and nano silicon dioxide. The hot melt adhesive capable of developing color when encountering water does not contain formaldehyde, can realize melting and coating at low temperature in the processing process, effectively avoids the damage of high temperature to developing components, and has good adhesion with a non-polar base film; the hot melt adhesive can still keep stable under a high-temperature storage condition, and does not respond to failure in advance; the color can be quickly developed when meeting water-based liquid such as urine, and the color can be uniformly and stably developed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot melt adhesive, in particular to a water-induced color-changing hot melt adhesive, a preparation method and application thereof. BACKGROUND

[0002] In the application of paper diapers, the water-induced color-changing hot melt adhesive needs to meet the following performance requirements: firstly, during preparation, the hot melt adhesive needs to have appropriate adhesion to ensure that it can be accurately coated and firmly attached to the bottom film; secondly, during storage, the hot melt adhesive needs to maintain stable color-changing stability, so that the hot melt adhesive will not change color in advance even in a high-temperature environment; in addition, during the use stage, once in contact with urine, the hot melt adhesive should be able to respond quickly and achieve obvious and reliable color change in a short time.

[0003] The current water-induced color-changing hot melt adhesive mainly has the following problems: using melamine-formaldehyde resin to wrap the color-changing agent, there is a risk of formaldehyde release, which is not environmentally friendly; the melting temperature of the hot melt adhesive is about 160℃, which is not conducive to the stability of the color-changing agent during high-temperature preparation and coating; the adhesion of the hot melt adhesive to non-polar bottom films such as PE bottom films is insufficient.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The purpose of the present application is to provide a water-induced color-changing hot melt adhesive, a preparation method and application thereof. The water-induced color-changing hot melt adhesive of the present application is environmentally friendly, has no formaldehyde release, is easy to melt and coat, can quickly change color when in contact with water, and has good storage stability in a high-temperature environment.

[0006] In order to achieve the above-mentioned purpose of the present application, the first aspect of the present application provides a water-induced color-changing hot melt adhesive, which comprises the following components by mass percentage: Olefin polymer 10% to 20%, indicator microcapsule 5% to 10%, tackifying resin 30% to 45%, saturated fatty acid 30% to 45%, and antioxidant 0.1% to 1.5%; The indicator microcapsule is composed of a capsule core and a capsule wall wrapped on the surface of the capsule core; the capsule core comprises an indicator, and the capsule wall comprises polyvinylpyrrolidone and nanosilica; The viscosity of the olefin polymer at 190℃ is not more than 20000cps.

[0007] In the specific embodiment of the present application, the olefin polymer comprises at least one of polypropylene, amorphous alpha-olefin copolymer, metallocene polyolefin, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid copolymer.

[0008] In the specific embodiment of the present application, in the capsule wall, the mass ratio of the polyvinylpyrrolidone to the nanosilica is (8 to 10) to 1.

[0009] In the embodiment of the present application, the K value of the polyvinylpyrrolidone is 25-30.

[0010] In the embodiment of the present application, the indicator is a pH indicator with a color developing range of 3-8. Further, the indicator includes at least one of bromophenol blue and bromocresol green.

[0011] In the embodiment of the present application, the mass ratio of the polyvinylpyrrolidone and the nanosilica to the mass of the indicator is 1: (0.05-0.2).

[0012] In the embodiment of the present application, the tackifying resin includes a hydrogenated rosin resin. Further, the tackifying resin also includes a hydrogenated petroleum resin.

[0013] In the embodiment of the present application, the softening point of the tackifying resin is not more than 100℃.

[0014] In the embodiment of the present application, the melting point of the saturated fatty acid is 68-88℃.

[0015] In the embodiment of the present application, the saturated fatty acid includes an alkanoic acid with a carbon number of 18-24. Further, the saturated fatty acid includes at least one of stearic acid and arachidic acid.

[0016] In the embodiment of the present application, in the water-developing color hot melt adhesive, the sum of the mass percentages of the saturated fatty acid and the tackifying resin is not less than 70%.

[0017] The second aspect of the present application provides a preparation method of the water-developing color hot melt adhesive of the first aspect of the present application, including the following steps: heating and melting an olefin polymer, a saturated fatty acid, a tackifying resin and an antioxidant at 130-150℃; then cooling to 110-130℃, adding an indicator microcapsule to obtain a mixture; coating the mixture to obtain a hot melt adhesive.

[0018] In the embodiment of the present application, the preparation method of the indicator microcapsule includes: (a) dissolving an indicator in ethanol to obtain an indicator solution; dissolving polyvinylpyrrolidone in ethyl acetate, then adding nanosilica to obtain a mixed dispersion; adding the indicator solution to the mixed dispersion, stirring uniformly to obtain an oil phase; (b) adding an emulsifier in water to obtain a water phase with an emulsifier mass concentration of 0.1%-0.5%; under stirring, adding the oil phase to the water phase to obtain a water / oil emulsion; heating to remove ethyl acetate in the water / oil emulsion, then centrifuging to collect the lower precipitate to obtain the indicator microcapsule.

[0019] The third aspect of the present invention provides the application of the water-sensitive color-developing hot melt adhesive provided in the first aspect of the present invention in the preparation of disposable sanitary products.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The water-based color-developing hot melt adhesive of the present invention is formaldehyde-free. It can be melted and coated at low temperatures (such as below 130°C) during processing, effectively avoiding the damage of the color-developing components by high temperature, and has good adhesion to non-polar substrate film. Furthermore, the hot melt adhesive of the present invention can remain stable under high temperature storage conditions and will not fail prematurely. It develops color quickly when exposed to water-based liquids such as urine, and the color development is uniform and stable. (2) The preparation process of the water-sensitive color-developing hot melt adhesive of the present invention is simple, has good repeatability, and is suitable for mass production. The hot melt adhesive can be used for disposable hygiene products such as diapers, surgical pads, and pet pads. The instantaneous change in the color of the hot melt adhesive indicates the presence of urine, assists users in timely replacement, and improves the user experience and hygiene safety. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0022] The first aspect of the present invention provides a water-sensitive color-developing hot melt adhesive, comprising the following components by mass percentage: 10%–20% olefin polymer, 5%–10% indicator microcapsules, 30%–45% tackifying resin, 30%–45% saturated fatty acid, and 0.1%–1.5% antioxidant; The indicator microcapsule consists of a core and a capsule wall encapsulating the surface of the core; the core includes an indicator, and the capsule wall includes polyvinylpyrrolidone and nano-silica. The viscosity of olefin polymers at 190°C does not exceed 20,000 cps.

[0023] The water-based color-developing hot melt adhesive of the present invention is formaldehyde-free and can be melted and coated at temperatures below 130°C during processing, effectively avoiding damage to the color-developing components caused by high temperatures. Furthermore, the hot melt adhesive of the present invention can maintain color stability under high-temperature storage conditions without pre-discoloration and develops color rapidly when exposed to water-based liquids such as urine.

[0024] In some embodiments, the olefin polymer in the hot melt adhesive is 10% to 20% by mass, for example, it can be 10%, 12%, 15%, 18%, 20% or any combination thereof; in the hot melt adhesive of the present invention, the use of olefin polymer can improve the adhesion effect of the hot melt adhesive to non-polar substrates such as PE base film.

[0025] In some embodiments, the viscosity of the olefin polymer at 190°C does not exceed 20,000 cps, for example, it can be a range of 20,000 cps, 18,000 cps, 15,000 cps, 14,000 cps, 13,000 cps, 12,000 cps, 11,000 cps, 10,000 cps, 9,000 cps, 8,000 cps, 5,000 cps, or any combination thereof. Meeting the above viscosity condition ensures that the olefin polymer has good flowability, which is beneficial for the low-temperature preparation and low-temperature coating of hot melt adhesives.

[0026] In some embodiments, the olefin polymer includes at least one of olefin copolymers and olefin homopolymers, such as at least one of polypropylene (PP), amorphous α-olefin copolymer (APAO), metallocene polyolefin (MPO), ethylene-vinyl acetate copolymer (EVA), and ethylene-acrylic acid copolymer (EAA).

[0027] In some embodiments, the mass ratio of polyvinylpyrrolidone (PVP) to nano-silica in the capsule wall is (8-10):1, for example, it can be within the range of 8:1, 8.5:1, 9:1, 9.5:1, 10:1, or any combination thereof. Using a composite of PPV and nano-silica as the capsule wall material gives the capsule wall an organic-inorganic composite structure, resulting in better mechanical strength, temperature resistance, and chemical inertness. This protects the capsule core indicator from oxidation, high temperatures, and other adverse effects. Furthermore, the porous structure of nano-silica helps the indicator to develop color rapidly upon contact with water. However, if the amount of PPV in the capsule wall material is too high, the mechanical properties and chemical inertness of the capsule wall are limited, which is detrimental to the storage stability of the hot melt adhesive. If the amount of PPV is too low, it is not conducive to the coating of the indicator and the control of the color development time, and it also affects its adhesive properties.

[0028] In some embodiments, the K value of polyvinylpyrrolidone is 25–30. Regulating the K value of polyvinylpyrrolidone within this range is more beneficial for balancing the strength and dispersion uniformity of the microcapsules. When the K value is too low, film-forming properties are poor, and the mechanical strength and stability of the microcapsules are insufficient; when the K value is too high, the solubility in water deteriorates, leading to poor dispersion uniformity of the microcapsules and prolonged color development time.

[0029] In some embodiments, the particle size of the nano-silica is 10 to 40 nm, for example, it can be a range of 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm or any combination thereof.

[0030] In some embodiments, the nano-silica includes at least one of untreated nano-silica and silane-pretreated nano-silica. The silane pretreatment of the nano-silica can be performed using conventional pretreatment methods, which will not be elaborated here.

[0031] In some embodiments, the indicator is a pH indicator with a colorimetric range of 3 to 8. Further, the indicator includes at least one of bromophenol blue and bromocresol green.

[0032] In some embodiments, the mass ratio of polyvinylpyrrolidone and nano-silica to the mass of the indicator is 1:(0.05 to 0.2), such as 1:0.05, 1:0.08, 1:0.1, 1:0.12, 1:0.15, 1:0.18, 1:0.2, or any combination thereof.

[0033] In some embodiments, the tackifying resin includes hydrogenated rosin resin. Further, the tackifying resin also includes hydrogenated petroleum resin. The tackifying resin is primarily hydrogenated rosin resin; specifically, the proportion of hydrogenated rosin resin in the tackifying resin may be no less than 80 wt%. Using hydrogenated rosin resin and hydrogenated petroleum resin is more beneficial for improving the heat resistance and weather resistance stability of the hot melt adhesive, and can also reduce the odor of the hot melt adhesive.

[0034] In some embodiments, the softening point of the tackifying resin does not exceed 100°C, and may be, for example, a range of 100°C, 95°C, 90°C, 85°C, 80°C, 75°C, 70°C, or any combination thereof. Using a tackifying resin with a lower softening point is beneficial for the low-temperature melting of the hot melt adhesive.

[0035] In some embodiments, the melting point of the saturated fatty acid is 68–88°C, for example, it can be a range of 68°C, 70°C, 72°C, 75°C, 78°C, 80°C, 82°C, 85°C, 88°C, or any combination thereof. Saturated fatty acids can reduce the viscosity of the hot melt adhesive system, improve coating performance, and facilitate the uniform dispersion of indicator microcapsules in the hot melt adhesive system. Furthermore, the carboxyl groups in the saturated fatty acid have better compatibility with the indicator microcapsules and hydrogenated rosin resin, which is beneficial for the dispersion and water release of the indicator in the hot melt adhesive system, ensuring uniform color development and stability.

[0036] In some embodiments, the saturated fatty acid includes alkyl acids with 18 to 24 carbon atoms. Further, the saturated fatty acid includes at least one of stearic acid and arachidic acid. Saturated fatty acids with the above-mentioned carbon number are more conducive to improving the thermal stability of the hot melt adhesive and preventing oxidation and degradation.

[0037] In some embodiments, the sum of the mass percentages of saturated fatty acids and tackifying resins in the water-reactive color-developing hot melt adhesive is not less than 70%, for example, it can be 70%, 72%, 74%, 76%, 78%, 80%, or any combination thereof. When the ratio of the two is less than 70%, the viscosity of the hot melt adhesive system increases, which is not conducive to low-temperature coating.

[0038] In some embodiments, the antioxidants include hindered phenolic antioxidants and phosphite antioxidants, such as, but not limited to, a combination of antioxidant 1010 and antioxidant 168.

[0039] The second aspect of the present invention provides a method for preparing the water-sensitive color-developing hot melt adhesive of the first aspect of the present invention, comprising the following steps: heating and melting an olefin polymer, a saturated fatty acid, a tackifying resin and an antioxidant at 130-150°C; then cooling to 110-130°C, adding indicator microcapsules to obtain a mixture; and coating the mixture to obtain a hot melt adhesive.

[0040] In some embodiments, the heating and melting time at 130–150°C can be 30–40 minutes. Furthermore, the heating and melting process is accompanied by vacuuming.

[0041] In some embodiments, after adding the indicator microcapsules, the mixture is vacuumed and stirred for 30–40 minutes.

[0042] In some embodiments, the coating temperature is 110–130°C, for example, a range of 110°C, 115°C, 120°C, 125°C, 130°C, or any combination thereof. Furthermore, the coating basis weight can be conventionally adjusted according to actual needs, for example, including but not limited to 7–10 gsm.

[0043] In some embodiments, the method for preparing indicator microcapsules includes: (a) Dissolve the indicator in ethanol to obtain an indicator solution; dissolve polyvinylpyrrolidone in ethyl acetate, then add nano-silica to obtain a mixed dispersion; add the indicator solution to the mixed dispersion and stir until homogeneous to obtain an oil phase; (b) Add an emulsifier to water to obtain an aqueous phase with an emulsifier mass concentration of 0.1% to 0.5%; under stirring conditions, add the oil phase to the aqueous phase to obtain a water / oil emulsion; heat to remove ethyl acetate from the water / oil emulsion, and then centrifuge to collect the lower precipitate to obtain indicator microcapsules.

[0044] In some embodiments, in step (a), the mass concentration of the indicator in the indicator solution is 1% to 2%.

[0045] In some embodiments, in step (a), polyvinylpyrrolidone is dissolved in ethyl acetate to achieve a polyvinylpyrrolidone mass concentration of 8% to 12%.

[0046] In some embodiments, in step (a), after adding nano-silica, the mixture is stirred and dispersed at a speed of not less than 500 r / min to form a uniformly dispersed mixed dispersion.

[0047] In some embodiments, in step (a), after adding the indicator solution to the mixed dispersion, the mixture is stirred for 10 to 15 minutes to obtain the oil phase.

[0048] In some embodiments, in step (b), under stirring conditions, the stirring speed is not less than 500 r / min, the temperature is 30-35°C, and the stirring time is 30-40 min.

[0049] In some embodiments, the heating temperature for removing ethyl acetate from the water / oil emulsion can be 35–45°C.

[0050] In some embodiments, the emulsifier includes a nonionic emulsifier. Further, the emulsifier includes, but is not limited to, at least one of polyoxyethylene sorbitan fatty acid ester, sorbitan monolaurate, sorbitan monostearate, and sorbitan monooleate.

[0051] In some embodiments, the mass ratio of the oil phase to the water phase is 1:(10-20), such as 1:10, 1:12, 1:15, 1:18, 1:20, or any combination thereof.

[0052] The third aspect of the present invention provides the application of the water-sensitive color-developing hot melt adhesive provided in the first aspect of the present invention in the preparation of disposable sanitary products.

[0053] The raw material information used in the following specific embodiments of the present invention may be as follows, but is not limited thereto: APAO TB1320, viscosity at 190℃ is 10000cps, Qida Chemical; APAO TB9005, viscosity at 190℃ is 130,000 cps, Qida Chemical; APAO E1200, viscosity at 190℃ is 20000cps, EASTMAN, USA; Hydrogenated rosin resin KHR75, softening point 80℃, produced by Guangdong Kemao Forestry Chemical Co., Ltd. Stearic acid, melting point 67-72℃, Shandong Zhongwang Oils Co., Ltd.; Myristic acid, melting point 52-55℃, Shanghai Yiyan Biotechnology; Polyvinylpyrrolidone (PVP), K value 30, K value 90, BASF, Germany; A200 nano-silica, with an average particle size of 12nm, is manufactured by Evonik Degussa, Germany. Bromocresol green indicator, Shenyang Shisan Biochemical Technology Co., Ltd. Emulsifier, polyoxyethylene sorbitan fatty acid ester Tween 80, Guangdong Huana Chemical Co., Ltd.; Fischer-Tropsch wax SX70, Shell Netherlands.

[0054] Example 1 This embodiment provides a water-sensitive color-developing hot melt adhesive, which comprises the following raw materials by mass percentage: 15% olefin polymer APAO TB1320, 8% indicator microcapsules, 36% hydrogenated rosin resin KHR75, 40% stearic acid, 0.5% antioxidant 1010 and 0.5% antioxidant 168.

[0055] The method for preparing the indicator microcapsules in this embodiment includes: (1) Dissolve bromocresol green in ethanol to prepare a bromocresol green ethanol solution with a mass concentration of 2%.

[0056] (2) Dissolve PVP (K value 30) in ethyl acetate to prepare a solution with a PVP mass concentration of 10%; then add nano silica A200 and stir at 500 r / min for about 30 min to obtain a mixed dispersion; wherein, the mass ratio of PVP to nano silica is 9:1.

[0057] (3) Slowly add the bromocresol green ethanol solution from step (1) to the mixed dispersion from step (2), stir for 10 min, and obtain the oil phase; wherein the mass ratio of the mixed dispersion to the bromocresol green ethanol solution is 2.5:1.

[0058] (4) Add the emulsifier polyoxyethylene sorbitan fatty acid ester Tween 80 to water and stir to dissolve to obtain an aqueous phase with an emulsifier mass concentration of 0.3%; then slowly add the oil phase from step (3) to the aqueous phase, control the system temperature at 30°C, and stir at a stirring speed of 500 r / min while adding. After adding, stir for 30 min to obtain a water / oil mixed emulsion; wherein, the mass ratio of the oil phase to the water phase is 1:15.

[0059] (5) Heat the water / oil mixed emulsion obtained in step (4) to 40°C and stir at 200 r / min for about 50 min until the solvent ethyl acetate evaporates and a suspension is formed. Transfer the suspension to a centrifuge tube and centrifuge at 3000 r / min for 10 to 20 min (e.g., 20 min). Clear stratification will occur, with the upper layer being a clear liquid and the lower layer being the precipitated microcapsules. Remove the upper clear liquid, wash the wet microcapsule material, and dry it at 40 to 50°C for 6 h to obtain solid indicator microcapsules.

[0060] The preparation method of the water-sensitive color-developing hot melt adhesive in this embodiment includes the following steps: The olefin polymer APAO TB1320, stearic acid, hydrogenated rosin resin KHR75, antioxidant 1010, and antioxidant 168 were heated to 140°C and melted under vacuum for 30 minutes. Then, the temperature was lowered to 120°C, and indicator microcapsules were added. The mixture was stirred under vacuum for 30 minutes to obtain the coating mixture. The coating mixture was then coated onto the surface of a PET film at 140°C with a coating basis weight of 8 gsm and allowed to cool naturally to room temperature.

[0061] Example 2 This embodiment refers to the water-sensitive color-developing hot melt adhesive and its preparation method in Example 1, with the only difference being the amount of some raw materials used.

[0062] The water-reactive color-developing hot melt adhesive of this embodiment comprises the following raw materials by mass percentage: 19% olefin polymer APAO TB1320, 5% indicator microcapsules, 30% hydrogenated rosin resin KHR75, 45% stearic acid, 0.5% antioxidant 1010 and 0.5% antioxidant 168.

[0063] Example 3 This embodiment refers to the water-sensitive color-developing hot melt adhesive and its preparation method in Example 1, with the only difference being the amount of some raw materials used.

[0064] The water-reactive color-developing hot melt adhesive of this embodiment comprises the following raw materials by mass percentage: 10% olefin polymer APAO TB1320, 10% indicator microcapsules, 45% hydrogenated rosin resin KHR75, 34% stearic acid, 0.5% antioxidant 1010 and 0.5% antioxidant 168.

[0065] Example 4 This embodiment refers to the water-reactive color-developing hot melt adhesive and its preparation method in Example 1, the only difference being the type of olefin polymer.

[0066] In this embodiment, the water-reactive color-developing hot melt adhesive uses an equal weight of olefin polymer APAO E1200 to replace the olefin polymer APAO TB1320 in Example 1.

[0067] Example 5 This embodiment refers to the water-reactive color-developing hot melt adhesive and its preparation method in Example 1, the only difference being that the type of PVP used to prepare indicator microcapsules is different.

[0068] In this embodiment, an equal weight of PVP with a K value of 90 is used instead of PVP with a K value of 30 in Example 1.

[0069] Example 6 This embodiment refers to the water-soluble color-developing hot melt adhesive and its preparation method in Example 1. The only difference is that in step (2) of preparing indicator microcapsules, the mass ratio of PVP to nano silica is different.

[0070] In the preparation of the indicator microcapsules in this embodiment, in step (2), the mass ratio of PVP to nano-silica is 5:5.

[0071] Example 7 This embodiment refers to the water-reactive color-developing hot melt adhesive and its preparation method in Example 1, with the only difference being that: in this embodiment, myristic acid of equal weight is used instead of stearic acid in Example 1.

[0072] Comparative Example 1 Comparative Example 1 refers to the water-reactive color-developing hot melt adhesive and its preparation method of Example 1, the only difference being that: in Comparative Example 1, an equal weight of Fischer-Tropsch wax SX70 is used to replace stearic acid in Example 1.

[0073] Comparative Example 2 Comparative Example 2 refers to the water-reactive color-developing hot melt adhesive and its preparation method in Example 1, the only difference being that steps (2) and (3) for preparing indicator microcapsules are different.

[0074] The preparation of indicator microcapsules in Comparative Example 2 includes step (2): dissolving PVP (K value 30) in ethyl acetate to prepare a solution with a PVP mass concentration of 10%; step (3) includes: slowly adding the bromocresol green ethanol solution from step (1) to the bromocresol green ethanol solution from step (2) and stirring for 10 min to obtain an oil phase; wherein the mass ratio of the bromocresol green ethanol solution with a PVP mass concentration of 10% to the bromocresol green ethanol solution is 2.5:1.

[0075] Comparative Example 3 Comparative Example 3 refers to the water-soluble color-developing hot melt adhesive and its preparation method in Example 1, with the only difference being the amount of some raw materials used.

[0076] The water-soluble color-developing hot melt adhesive of Comparative Example 3 comprises the following raw materials by mass percentage: 25% olefin polymer APAO TB1320, 8% indicator microcapsules, 37% hydrogenated rosin resin KHR75, 30% stearic acid, 0.5% antioxidant 1010 and 0.5% antioxidant 168.

[0077] Comparative Example 4 Comparative Example 4 refers to the water-soluble color-developing hot melt adhesive and its preparation method in Example 1, the only difference being the type of olefin polymer.

[0078] In the water-soluble color-developing hot melt adhesive of Comparative Example 4, an equal weight of olefin polymer APAO TB9005 was used to replace the olefin polymer APAO TB1320 in Example 1.

[0079] Experimental Example The hot melt adhesives of different embodiments and comparative examples were tested as follows, and the test results are shown in Table 1.

[0080] (1) Viscosity at 120℃: The viscosity at 120℃ of the mixtures to be coated prepared in different embodiments and comparative examples was tested with reference to GB / T 2794-2022.

[0081] (2) Peel strength of PE board: According to GB / T 2792-2014, hot melt adhesives prepared in different embodiments and comparative examples were applied to the surface of PET film and then bonded to PE boards to test the 180° peel strength.

[0082] (3) Color Response Time: The hot melt adhesives prepared in different examples and comparative examples were cut into 1cm*3cm strips, laid flat on the table, and 1.0mL of simulated urine was drawn up with a pipette and dropped vertically onto the center of the strip. The stopwatch was started immediately. The color change of the strip was observed. When the color changed and basically stabilized, the stopwatch was stopped immediately. The simulated urine was prepared as follows: 2g of urea, 5g of sodium chloride, and 1.5g of disodium hydrogen phosphate were dissolved in an appropriate amount of water, and then water was added to make up to 1L. The pH was then adjusted to 6.5 with 3% hydrochloric acid.

[0083] (4) Color stability at 160℃: The initial yellow value of the hot melt adhesive prepared in different examples and comparative examples was tested. Then the hot melt adhesive was placed in a 160℃ oven for 3 days, and then the yellow value of the hot melt adhesive was tested. The difference between the yellow value of the aging and the initial yellow value was calculated to evaluate the color stability at 160℃.

[0084] (5) Color stability at 40℃: The initial yellow value of the hot melt adhesives prepared in different examples and comparative examples was tested. Then the hot melt adhesives were placed in a 40℃ oven for 6 months. The aged yellow value of the hot melt adhesives was then taken out and the difference between the aged yellow value and the initial yellow value was calculated to evaluate the color stability at 40℃.

[0085] (6) Coating performance at 120°C: Prepare the mixture to be coated according to each example and comparative example, and then coat it at 120°C; a smooth coating surface and uniform adhesive application are preferred; an uneven coating surface or obvious unevenness on the left and right sides is preferred.

[0086] Table 1. Test results of hot melt adhesives in different embodiments and comparative examples.

[0087] The test results above show that the hot melt adhesive of the present invention can be melted and coated at low temperatures during processing, effectively avoiding damage to the color-developing components and the PE film substrate caused by high temperatures. Furthermore, the hot melt adhesive of the present invention exhibits good adhesion to non-polar substrates such as PE. Simultaneously, the hot melt adhesive of the present invention remains stable under high-temperature storage conditions and does not prematurely fail; it develops color rapidly, uniformly, and stably when exposed to aqueous liquids such as urine.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A water-sensitive color-changing hot melt adhesive, characterized in that, Includes the following components by mass percentage: The composition includes 10%–20% olefin polymer, 5%–10% indicator microcapsules, 30%–45% tackifying resin, 30%–45% saturated fatty acids, and 0.1%–1.5% antioxidant. The indicator microcapsule consists of a core and a capsule wall encapsulating the surface of the core; the core includes an indicator, and the capsule wall includes polyvinylpyrrolidone and nano-silica. The viscosity of the olefin polymer at 190°C does not exceed 20,000 cps.

2. The water-sensitive color-developing hot melt adhesive according to claim 1, characterized in that, The olefin polymer includes at least one of polypropylene, amorphous α-olefin copolymer, metallocene polyolefin, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid copolymer.

3. The water-sensitive color-developing hot melt adhesive according to claim 1, characterized in that, The capsule wall has at least one of the following characteristics: (1) In the capsule wall, the mass ratio of the polyvinylpyrrolidone to the nano-silica is (8-10):1; (2) The K value of the polyvinylpyrrolidone is 25 to 30.

4. The water-sensitive color-developing hot melt adhesive according to claim 1, characterized in that, It has at least one of the following characteristics: (1) The indicator is a pH indicator with a colorimetric range of 3 to 8; (2) The mass ratio of the polyvinylpyrrolidone and the nano silica to the mass of the indicator is 1: (0.05 to 0.2).

5. The water-sensitive color-developing hot melt adhesive according to claim 1, characterized in that, The tackifying resin has at least one of the following characteristics: (1) The tackifying resin includes hydrogenated rosin resin; (2) The softening point of the tackifying resin does not exceed 100℃.

6. The water-sensitive color-developing hot melt adhesive according to claim 1, characterized in that, The saturated fatty acid has at least one of the following characteristics: (1) The melting point of the saturated fatty acid is 68-88℃; (2) The saturated fatty acids include alkyl acids with 18 to 24 carbon atoms.

7. The water-sensitive color-developing hot melt adhesive according to claim 1, characterized in that, In the water-reactive color-developing hot melt adhesive, the sum of the mass percentages of the saturated fatty acid and the tackifying resin is not less than 70%.

8. The method for preparing the water-sensitive color-developing hot melt adhesive according to any one of claims 1 to 7, characterized in that, The process includes the following steps: heating and melting an olefin polymer, saturated fatty acid, tackifying resin, and antioxidant at 130–150°C; then cooling to 110–130°C and adding indicator microcapsules to obtain a mixture; and then coating the mixture to obtain a hot melt adhesive.

9. The preparation method according to claim 8, characterized in that, The method for preparing the indicator microcapsules includes: (a) Dissolve the indicator in ethanol to obtain an indicator solution; dissolve polyvinylpyrrolidone in ethyl acetate, then add nano-silica to obtain a mixed dispersion; add the indicator solution to the mixed dispersion and stir until homogeneous to obtain an oil phase; (b) Add an emulsifier to water to obtain an aqueous phase with an emulsifier mass concentration of 0.1% to 0.5%; under stirring conditions, add the oil phase to the aqueous phase to obtain a water / oil emulsion; heat to remove ethyl acetate from the water / oil emulsion, and then centrifuge to collect the lower precipitate to obtain the indicator microcapsules.

10. The use of the water-reactive color-developing hot melt adhesive according to any one of claims 1 to 7 or the water-reactive color-developing hot melt adhesive prepared by the preparation method according to any one of claims 8 to 9 in the preparation of disposable sanitary products.

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