Environmentally friendly degradable adhesive sticker and preparation method therefor

Abstract

Disclosed in the present invention are an environmentally friendly degradable adhesive sticker and a preparation method therefor. In the present application, the use of gancaonin R as an anti-aging agent of a polyvinyl alcohol adhesive is disclosed for the first time. Further disclosed is a polyvinyl alcohol adhesive. The adhesive takes gancaonin R as an anti-aging agent, such that the durability of the polyvinyl alcohol adhesive can be significantly enhanced. In addition, it is unexpected to find that the biodegradation performance of an adhesive sticker label taking the adhesive as a back adhesive is also slightly improved.

Description

Environmentally friendly degradable self-adhesive sticker and preparation method thereof Technical Field

[0001] The invention belongs to the technical field of self-adhesive stickers, and particularly relates to an environmentally friendly degradable self-adhesive sticker and a preparation method thereof. Background Art

[0002] The word "label" originally referred to a band or ribbon attached to a Christian bishop's hat, a symbol of power and identification. As early as 1700, the first labels were printed in Europe for use on medicines and cloth to identify goods. Following the advent of labels, as society continued to evolve, certain applications required the attachment of labels to items. This was achieved by coating the back of the label with a substance to provide adhesion. Initially, people applied a layer of adhesive to the back of the label, either by dipping it in water or using rice paste. However, this method lacked durability, leading to the use of wet glue. However, wet glue suffers from its storage limitations and is easily oxidized by air, losing its stickiness. It wasn't until the invention of self-adhesive labels that labels achieved the desired long-term adhesion and durability. Labels using this type of glue are known as self-adhesive labels.

[0003] Self-adhesive labels were invented by American Stanton Avery in the 1930s. Initially, they were made by hand. Later, Mr. Avery invented the first coating machine and label production equipment and established a company to initiate mechanized production. In 1994, he established China's first professional self-adhesive label manufacturer. Subsequently, the company rapidly developed into Avery Dennison, a Fortune 500 company with global sales exceeding US$6 billion this year. Self-adhesive materials posed a significant challenge to traditional label materials and marked a revolution in the labeling industry. Since the 1990s, self-adhesive material technology has rapidly spread around the world. Many countries have established factories and researched and developed a wide variety of label materials.

[0004] Adhesive (glue) acts as a medium between the label material and the adhesive substrate, acting as a link. Research has shown that the bonding process of pressure-sensitive adhesives (PSAs) is a low-speed process that can be described by rheological parameters at low frequencies (0.1 Hz), while the debonding process is a high-speed process that corresponds well to rheological parameters at high frequencies (100 Hz). Adhesives are available in a variety of formulations, suitable for different surface materials and applications. Adhesives are the most important component in self-adhesive labels and are key to label application technology. Research on glue modification has advanced rapidly in recent years, including modified tackifying resins, blending with silicone latex, and increasing solids content with reactive emulsifiers.

[0005] Self-adhesive adhesives can be broadly categorized by their composition and physical form: solvent-based, water-soluble (latex), and hot-melt adhesives. Emulsion-based acrylic PSA modifications primarily involve the introduction of tackifying resins, reactive emulsifiers, silicones (to improve surface properties), and cross-linking. While research on tackifying resins has been relatively widespread, issues such as poor compatibility between tackifying resins and acrylic emulsions persist. Reactive emulsifier modification is also gaining momentum, while silicone modification has achieved significant results on specialized substrates. Cross-linked emulsions can be categorized by packaging format as either two-component or one-component (self-crosslinking). The former requires mixing the two components before use, resulting in a shorter shelf life, while the latter is easier to use, though research on self-crosslinking emulsions is relatively limited. A comparison of the properties of these three adhesive types is shown in Table 1. Durable self-adhesive adhesives primarily utilize solvent-based adhesives, with a smaller percentage using water-based adhesives. These adhesives are primarily designed for harsh environments and excellent durability.

[0006] Table 1 Comparison of self-adhesive glue properties

[0007] Self-adhesive label adhesives are pressure-sensitive. During label processing, the adhesive is applied to a release material (silicone oil backing paper), dried at high temperature, and then laminated with the surface material to transfer the adhesive film to the surface material. At room temperature, the adhesive is dry and always sticky. During use, it can be peeled from the release material and firmly adhered to the surface with a light pressure. The more the pressure-sensitive adhesive "likes" the adherend, the more secure it adheres. Different surface materials, labeling speeds, and adherend surface properties dictate different performance requirements for labels. For example, beer bottle labels require high initial tack, sustained tack, and peel strength, as well as good water resistance, while labels for frozen foods must be resistant to low temperatures. However, regardless of the type of water-based pressure-sensitive adhesive for self-adhesive labels, in addition to being non-toxic and environmentally friendly, generally require good initial tack, sustained tack, high peel strength, fast drying speed, stable performance, and good processability. Because water-based adhesives are easy to modify, come in many varieties, have different properties, and have a wide range of label uses, different adhesives are suitable for different objects and labeling requirements.

[0008] Water-based pressure-sensitive adhesives are made of polymers that can disperse or dissolve in water. They dry by evaporation of water or penetration of water into the label material. They have low preparation costs, are non-flammable, non-toxic, and non-polluting, have a wide range of viscosity and solid content distribution, are tolerant to other substances, can accept a variety of additives, have large formula variability, are easy to use, and do not require solvents or heat for labeling. Gentle pressure can produce a strong bond on the adhered material. However, they generally have poor water resistance, are prone to freezing, dry slowly, are selective for adhered materials, and are more suitable for porous materials or materials whose contact surfaces are wetted by water. However, with the growing call for environmental protection, scientific researchers have adopted various modification studies on water-based pressure-sensitive adhesives, gradually overcoming their shortcomings and developing various types of water-based pressure-sensitive adhesives with superior performance. For example, when preparing emulsion acrylic pressure-sensitive adhesives, several tackifier resins are added to the blend to improve the pressure-sensitive adhesive's wettability and adhesion to non-polar adherends. The addition of cross-linking agents to form cross-linked copolymers also improves the water resistance and physical properties of emulsion acrylic pressure-sensitive adhesives. Currently, there are two main types of water-based pressure-sensitive adhesives: aqueous solution adhesives formed by dissolving polymers in water, and emulsion pressure-sensitive adhesives formed by dispersing polymers into a suspension. The characteristics and common types of these two adhesives are shown in Table 2.

[0009] Label adhesives have various final uses and a wide range of performance requirements. Therefore, relevant staff have developed various types of special adhesives, such as beer high-speed labeling adhesives, high-temperature and low-temperature adhesives, conductive adhesives, standard pressure-sensitive label adhesives (with a wide range of performance, more labeling solutions and a wider range of surface materials and adherends), etc. When using, be sure to select the appropriate adhesive based on the performance characteristics of the adhesive itself.

[0010] Table 2 Types and characteristics of water-based adhesives

[0011] Polyvinyl alcohol (PVA) is a water-soluble organic compound with a wide range of applications due to its remarkable properties. As early as 1924, German chemists Professor W.O. Herrmann and Dr. W.W. Heinrich Heinrich, using caustic potash, hydrolyzed polyvinyl acetate in alcohol, resulting in the first production of PVA (Kim et al., 2004). Industrial production began in 1926, and in 1950, Kuraray, a Japanese company, pioneered the production of PVA fibers, subsequently achieving large-scale production. According to literature, PVA is primarily produced through three methods: the ethylene process, the natural gas acetylene process, and the calcium carbide acetylene process (Qiu Tianrong, 2009). It possesses environmentally friendly properties, high thermal stability, high film strength and surface tension, and excellent adhesive properties. First widely used as a raw material for PVA fibers, PVA has since evolved into an important polymer chemical raw material with applications in textiles, gasoline-resistant pipes, vinylon synthetic fibers, emulsifiers, construction, and pharmaceuticals.

[0012] Polyvinyl alcohol (PVA) is a water-soluble polymer material with excellent properties. Its molecular structure and single-molecule chain contain multiple hydroxyl groups and strong hydrogen bonds. It is inexpensive, exhibits good bonding strength, and is environmentally friendly. Polyvinyl alcohol can be categorized into flake (including granular) and flocculent forms, as shown in the figure below.

[0013] Excellent adhesives must possess not only good mechanical properties and mildew resistance but also exceptional durability to meet the reliability requirements of bonded components during storage. Humidity and temperature are the primary factors influencing adhesive aging and degradation, while moisture adsorption and diffusion within the adhesive layer are the primary characteristics of adhesive aging. Moisture can penetrate most polymers, causing a plasticizing effect that disrupts the interactions between them and degrades their physical properties. Furthermore, the increased presence of moisture increases the degree of hydrolysis, accelerating adhesive aging and leading to a decrease in durability.

[0014] The physical and chemical properties of polyvinyl alcohol (PVA) vary depending on its chemical structure, degree of alcoholysis, and degree of polymerization. There are numerous types of PVA, and domestic and international grades vary significantly (Zhang Yu, 2010). Naturally, their properties and uses also differ. This distinction is primarily based on the degree of polymerization and alcoholysis (Su Ling, 2015). Domestic grades typically include 17-88, 17-99, 20-88, and 20-99. The first two digits of the grade represent the degree of polymerization, while the last two represent the degree of alcoholysis. For example, in 17-99, the 17 represents a degree of polymerization of 1700, and the 99 represents a degree of alcoholysis of 99%.

[0015] The higher the degree of polymerization and alcoholysis of PVA molecules, the lower its solubility in water, or the less soluble it is. Generally speaking, compared to the effect of polymerization on solubility, alcoholysis has a greater effect (Wang Baolin, 2014). A higher alcoholysis degree means more hydrophilic hydroxyl groups and more hydrogen bonds between hydroxyl groups (Xu Jun, 2012), making it more difficult for water molecules to enter the crystalline portion, resulting in less solubility in water. However, increasing the temperature can accelerate its dissolution. However, not all PVAs can be accelerated by increasing the temperature. For example, PVA with an alcoholysis degree of over 99% has more stringent solubility requirements and can only be dissolved in hot water at 95°C. PVA with an alcoholysis degree between 89-90% has better solubility at 60-70°C. PVA with an alcoholysis degree between 75-80% can be dissolved only in cold water. PVA with an alcoholysis degree between 87% and 89% has relatively good water solubility and can be dissolved in both hot and cold water.

[0016] Generally speaking, PVA with a lower alcoholysis degree has relatively poor water solubility. This is because PVA with a low alcoholysis degree has more -OCOCH3 groups, which are hydrophobic in nature. Therefore, the presence of more -OCOCH3 groups reduces PVA's solubility in water. PVA with an alcoholysis degree below 66% is already poorly soluble, and at 50% or below, it is difficult to dissolve. A lower alcoholysis degree indicates a decrease in the number of hydroxyl groups in the molecule, resulting in fewer hydrogen-bonding groups and a weakening of hydrogen bonding capacity. -OCOCH3 groups weaken hydrogen bonding, and as the number of -OCOCH3 groups increases, the number of hydrophobic groups gradually increases, weakening PVA's solubility. Therefore, PVA with an alcoholysis degree of around 85%-88% has the best water solubility. Increasing the alcoholysis degree and degree of polymerization of polyvinyl alcohol increases PVA's adhesive strength, water resistance, and film stability, but its viscosity and rheological properties deteriorate. Of course, PVA is also slightly soluble in some organic solvents, such as dimethyl sulfoxide (DMSO).

[0017] Gancaonin R, Gancaonin R, is an extract of the aerial part of licorice, chemical name: 5-[2-(3,4-dihydroxyphenyl)ethyl]-4,6-bis(3-methylbut-2-enyl)benzene-1,3-diol, molecular formula C 24 H3O4, relative molecular mass 382.5, chemical structure is as follows:

[0018] It is known that Licorice R has a strong inhibitory activity against Bacillus subtilis H17, slightly lower than that of kanamycin. However, there are no reports of other applications of Licorice R in the prior art.

[0019] Summary of the Invention

[0020] The present invention aims to overcome the aforementioned deficiencies in the prior art. The applicant conducted in-depth research on polyvinyl alcohol adhesives used as adhesives for self-adhesive labels and unexpectedly discovered that glycyrrhizin R, a natural licorice extract, can be used as an anti-aging agent for polyvinyl alcohol adhesives, improving their durability. Furthermore, polyvinyl alcohol adhesives containing glycyrrhizin R as an anti-aging agent maintain excellent environmental and biodegradability, with slightly improved performance.

[0021] The present application provides a rationally designed environmentally friendly degradable self-adhesive sticker and a preparation method thereof.

[0022] The technical solutions adopted by the present invention to solve the above problems are as follows:

[0023] The present application first discloses the use of Glycyrrhizin R as an anti-aging agent for polyvinyl alcohol adhesives to improve their durability.

[0024] The chemical structure of Licorice R is as follows:

[0025] The mass fraction of the glycyrrhizin R added to the polyvinyl alcohol adhesive is 0.2%-5.0%.

[0026] The mass fraction of the glycyrrhizin R added to the polyvinyl alcohol adhesive is 2.0%.

[0027] This application also discloses a polyvinyl alcohol adhesive and a preparation method thereof. The polyvinyl alcohol adhesive is composed of the following components:

[0028] Polyvinyl alcohol: 5-10%

[0029] Glutaraldehyde: 0.1-0.5%

[0030] Starch: 20-40%

[0031] Licorice R: 0.2-2.0%

[0032] Potassium persulfate: 0.2-1.0%

[0033] Sodium hydroxide: 1%-4%

[0034] Deionized water: solvent

[0035] The preparation method of the polyvinyl alcohol adhesive is as follows:

[0036] (1) Add an appropriate amount of sodium hydroxide to a beaker, then add deionized water and stir to dissolve it. Then add corn starch and stir continuously to dissolve it faster. Set aside for later use.

[0037] (2) Place a four-necked round-bottom flask in a water bath, then install a mechanical stirrer, reflux condenser, and thermometer. Add deionized water and polyvinyl alcohol to the flask and stir at room temperature for a while. Once the polyvinyl alcohol is evenly dispersed, heat the mixture and maintain the temperature until the polyvinyl alcohol is completely dissolved. Then cool the mixture to a desired temperature. Once the temperature stabilizes, add an oxidant and oxidize the mixture.

[0038] (3) Add the prepared corn starch solution to a four-necked round-bottom flask, heat the water bath to a certain temperature, add the crosslinking agent, and react for one hour. After the reaction is complete, cool it, add the antioxidant, stir, and dissolve it to obtain the adhesive.

[0039] The polyvinyl alcohol is a polyvinyl alcohol with a high alcoholysis degree, specifically PVA1788 or PVA1799.

[0040] The polyvinyl alcohol adhesive can be used alone as a liquid self-adhesive sticker, or as the backing adhesive of a self-adhesive label.

[0041] Finally, this application discloses a self-adhesive sticker using the aforementioned polyvinyl alcohol adhesive as a backing adhesive. The preparation method thereof is as follows:

[0042] The polyvinyl alcohol adhesive obtained above is used as the backing adhesive, which is coated on pure wood pulp paper, dried in the shade, pressed with release paper, and cut into appropriate sizes to make self-adhesive labels.

[0043] Compared with the prior art, the present invention has the following advantages and effects:

[0044] This application discloses for the first time the use of glycyrrhizin R as an anti-aging agent for polyvinyl alcohol adhesives. It also discloses a polyvinyl alcohol adhesive in which glycyrrhizin R is used as an anti-aging agent, significantly enhancing the durability of the polyvinyl alcohol adhesive and, unexpectedly, slightly improving the biodegradability of the polyvinyl alcohol adhesive. DETAILED DESCRIPTION

[0045] The present invention will be further described in detail below with reference to the accompanying drawings and through examples. The following examples are intended to explain the present invention but the present invention is not limited to the following examples.

[0046] Example 1: Preparation of polyvinyl alcohol adhesive (unit: g)

[0047] formula:

[0048] The preparation method is as follows:

[0049] (1) Weigh 2 g of sodium hydroxide in a beaker, add 30 ml of deionized water, stir to dissolve, then add the prescribed amount of corn starch, stir continuously to accelerate dissolution, and set aside;

[0050] (2) Place a 500ml four-necked round-bottom flask in a water bath and install a mechanical stirrer, reflux condenser, and thermometer. Add 60ml of deionized water and a certain amount of polyvinyl alcohol (PVA-1788) to the round-bottom flask and stir at room temperature for a period of time. Once the polyvinyl alcohol is evenly dispersed, heat to 90°C and maintain the temperature until the polyvinyl alcohol is completely dissolved. Then cool to a certain temperature. Once the temperature stabilizes, add potassium persulfate, an oxidant, and oxidize for one hour.

[0051] (3) The prepared corn starch solution was added to a four-necked round-bottom flask, and a water bath was heated to a certain temperature. The prescribed amount of glutaraldehyde was added and the mixture was allowed to react for one hour. After the reaction was completed, the mixture was cooled to 40°C, and the prescribed amount of Licorice R was added as an antioxidant. The mixture was stirred and dissolved to obtain an adhesive.

[0052] Example 2 Preparation of self-adhesive labels

[0053] The polyvinyl alcohol adhesive obtained in formula 1-6 of Example 1 was used as the backing adhesive, coated on pure wood pulp paper, dried in the shade, pressed with release paper, and cut into appropriate sizes to obtain a self-adhesive label.

[0054] Example 3 Test of the anti-aging performance of the adhesive in the self-adhesive label samples of various formulas in Example 2

[0055] Place the adhesive tape in a high temperature and high humidity test environment for a sufficient period of time, and then measure the changes in the physical or chemical properties of the adhesive tape to obtain the performance parameters of the adhesive tape's resistance to high temperature and high humidity aging.

[0056] 3.1 Prepare the moisturizing solution according to GB / T 32368-2015 (Test method for high temperature and high humidity aging resistance of adhesive tape):

[0057] The moisturizing solution is a glycerin-water solution containing the following ingredients:

[0058] 46 g of glycerol is diluted to 100 ml with deionized water to obtain a glycerol solution. At 23°C, its relative density (specific gravity) is about 1.17 and its refractive index (D line in the sodium spectrum) is about 1.392.

[0059] Add 0.1% (by weight) copper sulfate to the aqueous solution containing glycerol to prevent mold growth (e.g., add 4 drops of saturated copper sulfate solution to every 100 mL of glycerol aqueous solution).

[0060] 3.2 Sample preparation

[0061] The self-adhesive labels of formulations 1-6 obtained in Example 2 were cut into appropriate sizes according to the test requirements, and the release paper was peeled off to expose the adhesive backing to prepare the test specimens. The self-adhesive labels were divided into four parts and tested for their performance before and after aging at (40±2)°C and (65±2)°C.

[0062] 3.3 Test conditions and time

[0063] The test temperatures were (40±2)°C and (65±2)°C, respectively, and the relative humidity was (85±2)%. The test lasted for 7 days.

[0064] 3.4 Operation steps

[0065] Place the desiccator containing the moisturizing solution in an air-circulating oven at the test temperature shown in 3.3. Place the specimens horizontally on the perforated plate in the desiccator, preventing them from touching each other. When the oven temperature reaches equilibrium, close the desiccator cover.

[0066] 3.5 Changes in adhesive tape properties before and after high temperature and high humidity aging

[0067] First, the performance of each formula of self-adhesive adhesive before aging test was tested.

[0068] After the aging test, the sample is placed in a standard environment of (23±1)℃ and relative humidity of (50±5)% for 2h.

[0069] Test the performance of adhesive tape samples after aging.

[0070] According to GB / T 2792-2014, the peel strength of adhesive tape is tested, including the 180° peel strength with stainless steel and the 180° peel strength with anti-adhesive material, with the unit of N / 25mm;

[0071] According to GB / T 4851-2014, the adhesive tape's holding power is tested, i.e., the holding power to a vertical standard steel plate (unit: h).

[0072] According to GB / T 4852-2002, the initial tack of adhesive tapes is tested using the inclined ball rolling method, with the unit being N / 25mm.

[0073] Table 3 Performance changes of adhesives of formula 1-6 of Example 1 as back glue before and after aging test at (40±2)℃

[0074] Table 4 Performance changes of adhesives of formula 1-6 of Example 1 as back glue before and after aging test at (65±2)℃

[0075] The following conclusions can be drawn from the data in Tables 3 and 4:

[0076] Conclusion 1: The self-adhesive labels prepared with the polyvinyl alcohol adhesives of formulations 1-6 in Example 1 as the backing adhesive all had good performance before the aging test, specifically in terms of peel strength, persistent adhesion and initial adhesion.

[0077] Conclusion 2: After aging test at (40±2)℃

[0078] Compared to the performance of samples before aging, all performance parameters of the samples decreased after aging at (40±2)°C. The performance decline was particularly significant for the formulation without the antioxidant (Formula 1), with its 180° peel strength against stainless steel decreasing by approximately 30%. When the antioxidant Glycyrrhizin R was added to the adhesive formulations (Formulas 2-6), compared to Formula 1, various performance indicators increased with the amount of Glycyrrhizin R added, and this remained the case even after changes in the degree of PVA alcoholysis. However, increasing the amount of Glycyrrhizin R from 2% to 5% did not enhance the anti-aging performance. Specifically, after aging, the decline in various performance indicators for Formulation 4 was still smaller than that for Formulation 5.

[0079] Conclusion 3: After the aging test at (65±2)℃, the performance changes of the samples of formulas 1-6 are the same as those in Conclusion 2. However, the performance degradation rate is larger before and after the aging test.

[0080] In summary, the above experiments demonstrate that the polyvinyl alcohol adhesives prepared according to formulations 1-6 of Example 1, after adding Glycyrrhizin R, showed some decline in various performance indicators before and after aging testing, but the magnitude of the decline was less than that observed in formulation 1 without Glycyrrhizin R. This demonstrates that Glycyrrhizin R can effectively prevent aging of PVA adhesives.

[0081] Example 4 Degradability test of the self-adhesive labels obtained from formulations 1-6 of Example 2

[0082] The self-adhesive labels obtained in Formulations 1-6 of Example 2 were removed from the release paper as a sample and mixed with soil planted with corn at a mass ratio of 1:20. The samples were then placed at a temperature of 37°C, a relative humidity of 50%, an oxygen volume concentration of 20%, and natural light for 1 month, 2 months, 3 months, 4 months, 5 months, and 6 months. The degradation rate of the film corresponding to each month was weighed (for example, the degradation rate at 3 months (%) = (initial mass of the sample - the remaining mass of the sample at 3 months) / initial mass of the sample * 100%). The results are shown in Table 5.

[0083] Table 5: Test results of membrane degradation performance (%)

[0084] As can be seen from Table 5, the self-adhesive labels backed with polyvinyl alcohol adhesives from Formulas 1-6 of Example 1 of the present invention showed a degradation rate of 7% at one month, 55% at four months, and over 90% at six months. This demonstrates that the self-adhesive labels prepared according to the present invention, despite the addition of the antioxidant Licorice R, still exhibit good degradation properties and do not pollute the soil or air when degraded in the natural environment. Furthermore, compared to Formula 1, which does not contain the antioxidant Licorice R, the degradation rate at six months was surprisingly slightly higher.

[0085] In Example 2 of the present invention, the self-adhesive labels, backed with polyvinyl alcohol adhesives in formulations 1-6, showed degradation rates exceeding 90% after 6 months, with formulations 4 and 6 exceeding 94%. Notably, formulations 2-5 showed slightly improved degradation rates compared to formulation 1, which lacked Licorice R. This indicates that the self-adhesive label formulations prepared according to the present invention do not affect the degradation performance of polyvinyl alcohol itself, but rather slightly improve this performance. This demonstrates that the self-adhesive labels prepared according to the present invention exhibit excellent degradation performance and are environmentally friendly.

[0086] The above contents described in this specification are merely examples of the present invention. Those skilled in the art may make various modifications, additions, or substitutions to the described embodiments, without departing from the contents of this specification or exceeding the scope defined by the claims, and such modifications, additions, or substitutions may be made to the described embodiments. Such modifications, additions, or substitutions may be made by persons skilled in the art. Such modifications, additions, or substitutions may be made to the described embodiments without departing from the contents of this specification or exceeding the scope defined by the claims, and such modifications shall fall within the scope of protection of the present invention.

Claims

1. Licorice R is used as an anti-aging agent for polyvinyl alcohol adhesive to improve its durability.

2. The use according to claim 1, It is characterized in that The chemical structure of Licorice R is as follows:

3. A polyvinyl alcohol adhesive, It is characterized in that The adhesive uses Licorice R as an anti-aging agent.

4. The adhesive according to claim 3, It is characterized in that The mass fraction of the glycyrrhizin R added to the polyvinyl alcohol adhesive is 0.2%-5.0%.

5. The adhesive according to claim 3, It is characterized in that The mass fraction of the glycyrrhizin R added to the polyvinyl alcohol adhesive is 2.0%.

6. An adhesive according to any one of claims 3 to 5, It is characterized in that The polyvinyl alcohol adhesive is composed of the following components composition: Polyvinyl alcohol: 5-10% Glutaraldehyde: 0.1-0.5% Starch: 20-40% Licorice R: 0.2-2.0% Potassium persulfate: 0.2-1.0% Sodium hydroxide: 1%-4% Deionized water: solvent.

7. An adhesive according to any one of claims 3 to 5, It is characterized in that The preparation method of the polyvinyl alcohol adhesive is as follows: 1) Add an appropriate amount of sodium hydroxide to a beaker, then add deionized water, stir to dissolve, then add corn starch, stir continuously to speed up the dissolution, and set aside for later use; 2) Place a four-necked round-bottom flask in a water bath, and then install a mechanical stirrer, a reflux condenser, and a thermometer. Then add deionized water and polyvinyl alcohol to the round-bottom flask and stir at room temperature for a while. After the polyvinyl alcohol is evenly dispersed, heating is started, and the temperature is maintained until the polyvinyl alcohol is completely dissolved, and then the temperature is lowered to a certain temperature. After the temperature stabilizes, an oxidant is added for oxidation; 3) Add the prepared corn starch solution into a four-necked round-bottom flask, heat the water bath to a certain temperature, add a cross-linking agent, react for one hour, cool after the reaction is complete, add an antioxidant, stir, dissolve, and obtain an adhesive.

8. An adhesive according to any one of claims 3 to 5, It is characterized in that The polyvinyl alcohol is polyvinyl alcohol with a high alcoholysis degree.

9. An adhesive according to any one of claims 3 to 5, It is characterized in that The polyvinyl alcohol model is PVA1788 or PVA1799.

10. A self-adhesive label, It is characterized in that The self-adhesive label has any one of the adhesives described in claims 3-5 as the backing adhesive.

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