Packing material with pH value response as well as preparation method and application thereof

Abstract

The invention discloses a packaging material with pH value response. The color of the packaging material with pH value response changes in a range of 3-9 along with the change of an environmental pH value. The invention relates to a preparation method and application of the aviation packaging material. According to the packaging material with the pH value response function, accurate, real-time and visual response to the pH value within the range of 3-9 is achieved.

Description

Technical Field

[0001] This invention belongs to the field of intelligent packaging technology, specifically relating to a visually responsive packaging material, its preparation method, and its uses. Background Technology

[0002] In the food, pharmaceutical, and chemical industries, product quality is closely related to the pH value of the storage environment. For example, during the spoilage process, fresh foods such as meat and seafood produce acidic substances (such as lactic acid) or alkaline substances (such as amines) due to microbial metabolism, causing significant changes in the pH value of the environment. In the pharmaceutical field, biological agents (such as vaccines and protein drugs) are extremely sensitive to pH fluctuations; excessively acidic or alkaline environments can lead to the degradation of active ingredients. In the chemical industry, certain chemicals (such as adhesives and coatings) may deteriorate or lose performance if the pH becomes unbalanced during storage.

[0003] Traditional packaging materials only provide physical barriers and cannot provide real-time feedback on pH changes in the internal environment. This makes it difficult to detect product spoilage in a timely manner, resulting in not only economic losses but also potential food safety incidents or medical risks. Existing pH monitoring technologies (such as pH test strips and electronic sensors) have drawbacks such as complex operation, high cost, and inability to be integrated into packaging. Therefore, developing a packaging material that can respond to changes in pH in real time and with visualization is of great significance for improving product safety and reducing spoilage.

[0004] This invention is proposed for this purpose. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned defects in the prior art and to provide a visually responsive packaging material, its preparation method and uses.

[0006] The technical solution of the present invention is as follows:

[0007] The first aspect of this invention discloses an acid-base responsive packaging material, wherein the color of the acid-base responsive packaging material changes in various ways as the ambient pH value changes within the range of 3 to 9.

[0008] Preferably, the packaging material includes a substrate layer and an acid-base responsive layer; the acid-base responsive layer includes a polymer matrix, a pH-sensitive colorant, and a compatibility additive; the acid-base responsive layer is laminated onto the surface of the substrate layer, typically by coating or other lamination methods.

[0009] Preferably, the thickness of the substrate layer is 60 - 180 μm; the thickness of the acid-base responsive layer is 8 - 18 μm, the light transmittance ≥ 88% (at a wavelength of 450 nm), the color change ΔE ≥ 18 (CIE LAB color difference standard) within the pH range of 3 - 9, and there are four color states that can be visually recognized and distinguished within the pH range of 3 - 9.

[0010] Preferably, the four distinguishable color states within the pH range of 3 - 9 are as follows: when pH ≤ 4, it presents a magenta color; when 4 < pH ≤ 5.5, it presents a pink color; when 5.5 < pH ≤ 7.5, it presents a yellow-green color; when pH > 7.5, it presents a blue-green color.

[0011] Preferably, the material of the substrate layer is polyhydroxyalkanoate (PHA) or poly(butylene adipate-co-terephthalate) (PBAT), the tensile strength ≥ 18 MPa, the number-average molecular weight of PHA or PBAT is 50,000 - 80,000 g / mol; the polymer matrix material is a modified polyurethane, the pH-sensitive chromogenic agent is purple cabbage extract, gardenia blue or naphthol purple, and the compatibility aid is epoxidized soybean oil.

[0012] Preferably, the number-average molecular weight of the polyurethane is 30,000 - 60,000 g / mol; the polyurethane modifier is a copolymer of polylactic acid and polyethylene glycol.

[0013] Preferably, the mass ratio of the polymer matrix to the pH-sensitive chromogenic agent is 12:1 - 25:1; the addition amount of the compatibility aid is 6 wt% - 12 wt% of the total amount of the polymer matrix and the pH-sensitive chromogenic agent.

[0014] In the second aspect of the present invention, a preparation method of the packaging material is disclosed, including the following steps:

[0015] (1) Dissolve the polymer matrix material in a mixed solvent until completely dissolved to obtain a solution with a concentration of 12 wt% - 18 wt%.

[0016] (2) Add the pH-sensitive chromogenic agent and the compatibility aid to the solution in step (1), and perform high-pressure homogenization and dispersion for a period of time to form a uniform dispersion.

[0017] (3) Perform corona pretreatment on the surface of the substrate layer to increase the surface energy to ≥ 50 mN / m.

[0018] (4) Coating the dispersion in step (2) on the surface of the substrate layer material pretreated in step (3) by microgravure coating, and the coating amount is 8 - 15 g / m 2 ; drying and then ultraviolet curing to form the acid-base responsive layer; that is, the packaging material.

[0019] Preferably, in step (1), the mixed solvent is a mixture of N,N-dimethylacetamide and ethyl acetate in a volume ratio of 3:1; in step (2), the high-pressure homogenization dispersion is carried out at a pressure of 30-50 MPa for 20-40 min; in step (3), the corona treatment is carried out at a power of 600 W for 40 s; in step (4), the drying conditions are hot air circulation at 70-90°C for 1.5-3 hours under the protection of an inert gas (such as nitrogen, with a flow rate of 10-20 L / min), and ultraviolet curing is carried out at a wavelength of 365 nm and a power of 50 W for 30-60 s.

[0020] The third aspect of this invention discloses the use of the packaging material for packaging dairy products, seafood, or cosmetics, whereby changes in color are used to monitor pH changes in the internal environment of the packaging.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. The pH-responsive packaging material of this invention can: ensure product quality and safety; monitor changes in the internal environment of the packaging in real time through a visualized pH response signal, provide timely warnings of product spoilage, and reduce food safety and medication risks; reduce resource waste; avoid blind discarding due to the inability to determine product freshness, and effectively extend product shelf life; promote the intelligent development of packaging; break through the functional limitations of traditional packaging, provide a new technological path for intelligent packaging, and promote the upgrading of the packaging industry towards high added value and multi-functionality; expand application scenarios; and can be widely used in fresh food, pharmaceutical preparations, chemical products, and other fields to meet the pH monitoring needs in different scenarios.

[0023] 2. The pH-responsive packaging material of this invention provides real-time visual feedback: pH fluctuations are intuitively reflected through color changes, allowing for determination of environmental pH levels without specialized equipment, with a response time ≤3 seconds. It exhibits high sensitivity and specificity: achieving precise response within a pH range of 3–9, with superior specificity for H+ and OH+ ions compared to existing materials, and is unaffected by environmental factors such as temperature and humidity. It demonstrates good compatibility: it can be combined with existing packaging materials (such as polyethylene, polylactic acid, and paper-based materials) without affecting the packaging's barrier properties, mechanical properties, or processing performance. It is biodegradable and environmentally friendly: using natural polymer matrices (such as chitosan and starch) and bio-based pH-sensitive materials, it can biodegrade in the natural environment after disposal, reducing white pollution. It is reusable: within a reversible pH range (e.g., pH 4–8), the color change can be repeatedly switched, making it suitable for scenarios requiring multiple monitoring sessions.

[0024] 3. The acid-base responsive packaging material of this invention, through the rational design of the composition and ratio of the substrate layer and the acid-base responsive layer, achieves precise, real-time, and visual response to pH values ​​within the range of 3 to 9. The packaging material of this invention not only possesses excellent mechanical properties, aging resistance, and environmental friendliness, but also allows for adjustment of the response range according to different application scenarios, meeting the monitoring needs of fresh food, pharmaceutical preparations, chemical products, and other fields. The acid-base responsive packaging material of this invention has a simple preparation process, controllable cost, and is easy to industrialize, possessing broad market application prospects. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0026] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," "fixing," "adhesion," etc., should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0027] In this specification, the illustrative expressions of the terms used above should not be construed as necessarily referring to the same embodiments or examples. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0028] The present invention discloses an acid-base responsive packaging material, wherein the color of the acid-base responsive packaging material changes in various ways as the ambient pH value changes within the range of 3 to 9.

[0029] The packaging material includes a substrate layer and an acid-base responsive layer; the acid-base responsive layer includes a polymer matrix, a pH-sensitive colorant, and a compatibility additive; the acid-base responsive layer is laminated onto the surface of the substrate layer.

[0030] The thickness of the substrate layer is 60–180 μm; the thickness of the acid-base responsive layer is 8–18 μm, the transmittance is ≥88% (450 nm wavelength), the color change ΔE is ≥18 (CIE LAB color difference standard) in the pH range of 3–9, and it has four color states that can be distinguished by the naked eye in the pH range of 3–9.

[0031] Among them, there are four distinguishable color states within the pH range of 3 to 9: when pH ≤ 4, it presents a magenta color; when 4 < pH ≤ 5.5, it presents a pink color; when 5.5 < pH ≤ 7.5, it presents a yellowish-green color; when pH > 7.5, it presents a blue-green color.

[0032] Among them, the substrate layer material is polyhydroxyalkanoate (PHA) or poly(butylene adipate-co-terephthalate) (PBAT), the tensile strength ≥ 18 MPa, and the number-average molecular weight of PHA or PBAT is 50,000 - 80,000 g / mol; the polymer matrix material is modified polyurethane, the pH-sensitive colorant is red cabbage extract, gardenia blue or naphthol violet, and the compatibility aid is epoxidized soybean oil.

[0033] Among them, the number-average molecular weight of polyurethane is 30,000 - 60,000 g / mol; the polyurethane modifier is a copolymer of polylactic acid and polyethylene glycol.

[0034] Among them, the mass ratio of the polymer matrix to the pH-sensitive colorant is 12:1 - 25:1; the addition amount of the compatibility aid is 6 wt% - 12 wt% of the total amount of the polymer matrix and the pH-sensitive colorant.

[0035] The preparation method of the pH-responsive packaging material of the present invention includes the following steps:

[0036] (1) Dissolve the polymer matrix material in a mixed solvent until completely dissolved to obtain a solution with a concentration of 12 wt% - 18 wt%.

[0037] (2) Add the pH-sensitive colorant and the compatibility aid to the solution in step (1), and perform high-pressure homogenization and dispersion for a period of time to form a uniform dispersion.

[0038] (3) Perform corona pretreatment on the surface of the substrate layer to increase the surface energy to ≥ 50 mN / m. [[ID=…]]

[0039] (4) Coating the dispersion in step (2) on the surface of the substrate layer material pretreated in step (3) by microgravure coating, and the coating amount is 8 - 15 g / m 2 ; drying, and then ultraviolet curing to form an acid-base response layer; that is, the packaging material.

[0040] In step (1), the mixed solvent is a mixture of N,N-dimethylacetamide and ethyl acetate in a volume ratio of 3:1; in step (2), the high-pressure homogenization dispersion is carried out at a pressure of 30-50 MPa for 20-40 min; in step (3), the corona treatment is carried out at a power of 600 W for 40 s; in step (4), the drying conditions are hot air circulation at 70-90℃ for 1.5-3 hours under the protection of inert gas (such as nitrogen, with a flow rate of 10-20 L / min), and ultraviolet curing is carried out at a wavelength of 365 nm and a power of 50 W for 30-60 s.

[0041] pH-responsive packaging materials are used for packaging dairy products, seafood, or cosmetics, and monitor changes in pH levels within the packaging environment through color changes.

[0042] This invention relates to an acid-base responsive packaging material. Through a visualized pH response signal, it monitors changes in the internal environment of the packaging in real time, providing timely warnings of product spoilage and reducing food safety and medication risks. It avoids indiscriminate discarding due to the inability to determine product freshness, effectively extending product shelf life. Breaking through the functional limitations of traditional packaging, it provides a new technological path for intelligent packaging, promoting the upgrading of the packaging industry towards high added value and multi-functionality. It can be widely applied in fresh food, pharmaceutical preparations, chemical products, and other fields, meeting pH monitoring needs in different scenarios.

[0043] The pH-responsive packaging material of this invention visually reflects pH fluctuations through color changes, allowing for the determination of environmental pH levels without specialized equipment, with a response time of ≤3 seconds. High sensitivity and specificity: It achieves precise response within a pH range of 3–9, exhibiting superior specificity for H+ and OH- ions compared to existing similar materials, and is unaffected by environmental factors such as temperature and humidity. It can be combined with existing packaging materials (such as polyethylene, polylactic acid, and paper-based materials) without affecting the packaging's barrier properties, mechanical properties, or processing performance. Utilizing natural polymer matrices (such as chitosan and starch) and bio-based pH-sensitive materials, it degrades naturally after disposal, reducing white pollution. Reusability: Within a reversible pH range (e.g., pH 4–8), the color change can be repeatedly switched, making it suitable for scenarios requiring multiple monitoring sessions.

[0044] The acid-base responsive packaging material of this invention achieves precise, real-time, and visual response to pH values ​​within the range of 3 to 9 through a rationally designed composition and ratio of the substrate layer and the acid-base responsive layer. This packaging material not only possesses excellent mechanical properties, aging resistance, and environmental friendliness, but also allows for adjustment of the response range according to different application scenarios, meeting the monitoring needs of fresh food, pharmaceutical preparations, chemical products, and other fields. The preparation process of this acid-base responsive packaging material is simple, cost-controllable, and easy to industrialize, possessing broad market application prospects.

[0045] Example 1: Visualization material for pH response of dairy product packaging based on purple cabbage extract.

[0046] 1. Material formula (by mass parts):

[0047] Substrate layer: PHA, number average molecular weight 60,000 g / mol, thickness 120 μm, tensile strength 22 MPa;

[0048] Acid-base responsive layer; Polymer matrix: 100 parts of polylactic acid-polyethylene glycol copolymer (PLA-PEG) modified polyurethane (number average molecular weight 45,000 g / mol); pH-sensitive colorant: 8 parts of purple cabbage extract (purified by ethanol extraction, color value ≥50); Compatibility additive: 10 parts of epoxidized soybean oil.

[0049] 2. Preparation steps:

[0050] (1) Solution preparation: Dissolve 100 parts of polymer matrix in a mixed solvent (N,N-dimethylacetamide: ethyl acetate = 3:1, volume ratio), stir until completely dissolved, and prepare a solution with a concentration of 15wt%;

[0051] (2) Add 8 parts of purple cabbage extract and 10 parts of epoxidized soybean oil to the above solution, and homogenize under high pressure at 40 MPa for about 30 minutes to obtain a uniform dispersion acid-base responsive coating.

[0052] (3) Substrate pretreatment: The PHA substrate layer is subjected to corona treatment to increase the surface energy to 52mN / m; conditions: power 600W, time about 40 seconds;

[0053] (4) The acid-base responsive dispersion coating from step (2) is applied to the pretreated substrate surface using a microgravure coating method, with a coating amount of 12 g / m². 2 The material is dried in hot air circulation at 80°C for about 2 hours with nitrogen gas (flow rate 15L / min); then cured with 365nm ultraviolet light (50W) for about 45 seconds to form an acid-base responsive layer with a thickness of 12μm.

[0054] 3. Performance Testing:

[0055] Light transmittance: 91% at a wavelength of 450nm, meeting the transparency requirements for dairy product packaging.

[0056] pH response performance: pH=3.0 (simulating the early stage of yogurt spoilage): purplish-red (ΔE=22); pH=5.0 (normal dairy product environment): pink (ΔE=20); pH=7.0 (neutral environment): yellow-green (ΔE=19); pH=8.0 (slightly alkaline spoilage): blue-green (ΔE=21).

[0057] Response time: Color change can be observed within 2 seconds of contact with the target environment. After 10 cycles of repeatability testing (pH 4.0→7.0→4.0), ΔE remains ≥18.

[0058] Example 2: Visualization material for the acid-base response of seafood packaging based on naphthol purple.

[0059] 1. Material formula (by mass parts):

[0060] Substrate layer: Polybutylene adipate-butylene terephthalate (PBAT), thickness 150μm, tensile strength 19MPa;

[0061] Acid-base responsive layer: Polymer matrix: 100 parts PLA-PEG modified polyurethane (number average molecular weight 50,000 g / mol); pH sensitive colorant: 5 parts naphthol purple (analytical grade); Compatibility additive: 8 parts epoxidized soybean oil.

[0062] 2. Preparation steps:

[0063] (1) Solution preparation: Dissolve 100 parts of polymer matrix in a mixed solvent (N,N-dimethylacetamide: ethyl acetate = 3:1, volume ratio), stir until completely dissolved, and prepare a solution with a concentration of 16wt%;

[0064] (2) Add 5 parts naphthol purple and 8 parts epoxidized soybean oil to the above solution, and homogenize under high pressure at 35 MPa for about 25 minutes to obtain a uniform dispersion, acid and alkali responsive coating.

[0065] (3) Substrate pretreatment: The PBAT substrate layer is subjected to corona treatment to increase the surface energy to about 51mN / m; conditions: power 600W, time about 40 seconds;

[0066] (4) Apply the acid-base responsive dispersion coating from step (2) to the pretreated substrate surface using a microgravure coating method, with a coating amount of 10 g / m². 2 The material was dried in a hot air circulation system at 75°C for 1.8 hours with nitrogen gas (flow rate 12L / min); then cured with 365nm ultraviolet light (50W) for about 50 seconds to form an acid-base responsive layer with a thickness of 10μm.

[0067] 3. Performance Testing:

[0068] Light transmittance: 89% at a wavelength of 450nm, allowing for clear observation of the seafood's condition.

[0069] pH response performance: pH=3.5 (acidic environment in the early stage of seafood spoilage): purplish-red (ΔE=20); pH=5.2 (fresh seafood environment): pink (ΔE=19); pH=7.2 (neutral preservation environment): yellow-green (ΔE=18); pH=8.5 (alkaline environment in severe spoilage): blue-green (ΔE=23).

[0070] Mechanical compatibility: The tensile strength of the composite film is 18.5 MPa and the elongation at break is 350%, which meets the tear resistance requirements of seafood packaging; after being stored at 4℃ for 30 days, the response performance shows no significant degradation.

[0071] Examples 1 and 2, respectively, address packaging for dairy products and seafood. By adjusting the type of pH-sensitive colorant (natural extract or synthetic reagent) and coating thickness, precise responses to different pH ranges were achieved. The high-pressure homogenization dispersion and UV curing processes employed during preparation ensured uniform distribution of the colorant and stability of the acid-base responsive layer, meeting the requirements of industrial production. Performance testing showed that the material outperformed existing technologies in terms of transmittance, response speed, and repeatability, effectively enabling visualized monitoring of the internal environment of the packaging.

[0072] Example 3: Visualization of acid-base response of cigarette packaging based on gardenia blue.

[0073] Application Background: During the storage of cigarette products, if the ambient humidity is abnormal or mold develops, the tobacco will produce organic acids (such as oxalic acid and propionic acid) due to microbial metabolism, causing the pH value inside the packaging to drop (the normal storage environment for cigarettes has a pH of about 6.5 to 7.5, which can drop below 4.0 after mold growth). The material prepared in this embodiment can monitor the pH changes inside the cigarette packaging in real time through color changes, providing early warning of mold risk.

[0074] 1. Material formula (by mass parts):

[0075] Substrate layer: Polybutylene adipate-butylene terephthalate (PBAT), 100μm thick, tensile strength 20MPa (meets the stiffness requirements of cigarette packaging);

[0076] Acid-base responsive layer: Polymer matrix: 100 parts of polylactic acid-polyethylene glycol copolymer (PLA-PEG) modified polyurethane (number average molecular weight 40,000 g / mol); pH sensitive colorant: 6 parts of gardenia blue (food grade, purified by water extraction and alcohol precipitation); Compatibility additive: 9 parts of epoxidized soybean oil.

[0077] 2. Preparation steps:

[0078] (1) Solution preparation: Dissolve 100 parts of polymer matrix (A) in a mixed solvent (N,N-dimethylacetamide: ethyl acetate = 3:1, volume ratio), stir until completely dissolved, and prepare a 14% concentration solution (reduce the concentration to meet the thin coating requirements of cigarette packaging).

[0079] (2) Add 6 parts of gardenia blue and 9 parts of epoxidized soybean oil to the above solution, and homogenize under high pressure at 38MPa for about 28 minutes to obtain a uniform dispersion acid-base responsive coating; avoid particles clogging the coating mesh.

[0080] (3) Substrate pretreatment: The PBAT substrate layer is subjected to corona treatment to increase the surface energy to about 53mN / m, so as to enhance the adhesion to the cigarette packaging printing layer; conditions: power 600W, time about 40 seconds;

[0081] (4) Apply the acid-base responsive coating dispersion from step (2) to the pretreated substrate surface using a microgravure coating method, with a coating amount of 9 g / m². 2 The purpose is to control the coating thickness so as not to affect the appearance of the packaging; the coating is dried by circulating nitrogen gas (flow rate 13L / min) for about 1.6 hours at 72℃; then it is cured by 365nm ultraviolet light (50W) for about 40 seconds to form an acid-base responsive layer with a thickness of 9μm, in order to meet the requirements of thinness in cigarette packaging.

[0082] 3. Performance Testing:

[0083] Light transmittance: 89% at a wavelength of 450nm, which does not affect the clarity of the printed patterns on cigarette packaging.

[0084] pH response performance (simulating cigarette storage scenarios): pH=7.0 (normal storage environment): yellow-green (ΔE=19); pH=5.5 (slightly damp, organic acids begin to form): pink (ΔE=18); pH=4.0 (early stage of mold growth, increased acidity): purplish-red (ΔE=21); pH=8.0 (abnormally alkaline environment, such as contact with alkaline desiccants): blue-green (ΔE=20).

[0085] Suitability verification: Compatible with aluminum foil composite layers commonly used in cigarette packaging; the bonding does not affect the packaging's airtightness (oxygen permeability ≤ 0.5 cm). 3 / (m 2 (24h, 0.1MPa) Under standard storage conditions of 25℃ and 60% relative humidity for 6 months, the coating did not peel off, and the pH response sensitivity remained stable (response time ≤3 seconds). It did not adsorb common components in mainstream cigarette smoke (such as nicotine and tar) and did not affect the taste of cigarettes.

[0086] The packaging material in this embodiment can be directly laminated to the inner lining of cigarette cartons or individual packs. Consumers or warehouse personnel can visually determine whether cigarettes are damp or moldy by observing color changes: when the color changes from yellowish-green to pink, it indicates the need for enhanced moisture protection; when it turns purplish-red, it indicates mold has occurred and the cigarettes should be discontinued. Its environmental friendliness (PBAT substrate is biodegradable) and safety (gardenia blue is a food-grade pigment) meet the health requirements of the tobacco industry.

[0087] The above embodiments are not intended to limit the present invention, nor is the present invention limited to the examples described above. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the present invention are also within the protection scope of the present invention.

Claims

1. A packaging material responsive to acid and alkalinity, characterized in that, The pH-responsive packaging material undergoes various color changes as the environmental pH value varies within the range of 3 to 9.

2. The packaging material according to claim 1, characterized in that, The packaging material includes a substrate layer and a pH-responsive layer; the pH-responsive layer includes a polymer matrix, a pH-sensitive colorant, and a compatibility aid; the pH-responsive layer is laminated on the surface of the substrate layer.

3. The packaging material according to claim 2, characterized in that, The thickness of the substrate layer is 60 to 180 μm; the thickness of the pH-responsive layer is 8 to 18 μm, the light transmittance ≥ 88%, the color change ΔE ≥ 18 within the pH range of 3 to 9, and there are four distinguishable color states within the pH range of 3 to 9.

4. The packaging material according to claim 3, characterized in that, The four distinguishable color states within the pH range of 3 to 9 are: when pH ≤ 4, it呈现紫红色 (appears purplish-red); when 4 < pH ≤ 5.5, it呈现粉红色 (appears pink); when 5.5 < pH ≤ 7.5, it呈现黄绿色 (appears yellowish-green); when pH > 7.5, it呈现蓝绿色 (appears bluish-green).

5. The packaging material according to claim 2, characterized in that, The material of the substrate layer is PHA or PBAT, the tensile strength ≥ 18 MPa, and the number-average molecular weight of PHA or PBAT is 50,000 to 80,000 g / mol; the polymer matrix material is a modified polyurethane, the pH-sensitive colorant is purple cabbage extract, gardenia blue, or naphthol violet, and the compatibility aid is epoxy soybean oil.

6. The packaging material according to claim 5, characterized in that, The number-average molecular weight of the polyurethane is 30,000 to 60,000 g / mol; the polyurethane modifier is a copolymer of polylactic acid and polyethylene glycol.

7. The packaging material according to claim 5, characterized in that, The mass ratio of the polymer matrix to the pH-sensitive colorant is 12:1 to 25:1; the addition amount of the compatibility aid is 6 wt% to 12 wt% of the total amount of the polymer matrix and the pH-sensitive colorant.

8. A method for preparing a packaging material according to any one of claims 1-7, characterized in that, It includes the following steps: (1) Dissolve the polymer matrix material in a mixed solvent until completely dissolved to obtain a solution with a concentration of 12 wt% to 18 wt%. (2) Add the pH-sensitive colorant and the compatibility aid to the solution in step (1), and perform high-pressure homogenization and dispersion for a period of time to form a uniform dispersion. (3) Perform corona pretreatment on the surface of the substrate layer to increase the surface energy to ≥ 50 mN / m. (4) The dispersion from step (2) is coated onto the surface of the pretreated substrate material from step (3) using a microgravure coating method, with a coating amount of 8–15 g / m². 2 ; Dry and then ultraviolet-cure to form the pH-responsive layer; that is, the packaging material described above.

9. The preparation method according to claim 8, characterized in that, In step (1), the mixed solvent is a mixture of N,N-dimethylacetamide and ethyl acetate with a volume ratio of 3:1; in step (2), the pressure of high-pressure homogenization and dispersion is 30 to 50 MPa, and the time is 20 to 40 min; in step (3), the corona treatment conditions are 40 s at a power of 600 W; in step (4), the drying conditions are hot air circulation at 70 to 90 °C for 1.5 to 3 hours under inert gas protection, and the ultraviolet curing is at a wavelength of 365 nm and a power of 50 W for 30 to 60 s.

10. Use of the packaging material according to any one of claims 1-7 for packaging dairy products, seafood, or cosmetics.