Alkali-regulated high-temperature-resistant modified cyclopropene, fresh-keeping varnish and fresh-keeping packaging product

Abstract

The present invention discloses an alkali-regulated high-temperature-resistant modified cyclopropene, a fresh-keeping varnish, and a fresh-keeping packaging product. The modified cyclopropene is in a solid state and includes an active ingredient, a cyclopropene compound, a curing inclusion agent, and a high-temperature-resistant modifier; the high-temperature-resistant modifier is an organosilicon compound. The present application adopts an organosilicon compound and a curing inclusion agent to modify the cyclopropene compound, which can significantly enhance its thermal stability and antioxidant stability, and can meet the high-temperature condition of 180°C required for corrugated cardboard production; and has an alkali-regulated release characteristic, can be stably stored in a neutral system of pH 6.5 to 8.5, and is activated to release cyclopropene gas in an alkaline system of pH>8.5. Therefore, the modified MCP and other products prepared from the modified MCP, such as fresh-keeping varnish and fresh-keeping cartons, can be stored for a long time under conventional conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of fresh-keeping, and in particular relates to an alkali-regulated high-temperature-resistant modified cyclopropene, a fresh-keeping varnish and a fresh-keeping packaging product. Background Art

[0002] Existing desiccants or preservatives for fruits, vegetables, and other fresh foods are typically packaged in single-sided, breathable paper-plastic packaging and placed in fresh produce boxes. This results in a small contact area and limited preservation effectiveness. While respiration-inhibiting preservatives for fruits and vegetables offer excellent preservation effects, they are typically used for fumigation in cold storage and have yet to be applied to fresh produce transportation.

[0003] Existing technical research is mostly focused on antibacterial preservation, anti-mildew preservation coatings, or adsorption coatings. Some technologies are cumbersome to operate and cannot be applied on a large scale, while some technologies have limited effects and cannot cope with perishable fruits such as cherries, bananas, and kiwis.

[0004] 1-Methylcyclopropene (1-MCP for short) is a cyclopropene compound that exists in a gaseous state at room temperature. It is non-toxic and odorless, with a boiling point of about 10°C. It is unstable in a liquid state. Because of its similar molecular structure to ethylene, 1-MCP can competitively bind to these receptors and inhibit various biochemical reactions related to ripening. In reality, it is mostly used for warehouse fumigation and preservation.

[0005] In the prior art, in order to solve the problem of storage and transportation of cyclopropene liquid preservatives, a binding agent such as dextrin is generally used for solidification. When used, it can release 1-MCP gas by absorbing a small amount of water.

[0006] The most commonly used packaging material for transporting fruits and vegetables is cartons. Specifically, the solidified MCP inclusions can be made into bagged preservatives and placed directly in cartons for use. However, as mentioned above, this method has the problems of small contact area and limited preservation effect.

[0007] Another method is to prepare the MCP inclusion compound into a coating, which is then applied to the surface of the base paper layer by coating, and then dried at 40-60°C to obtain fresh-keeping paper. The fresh-keeping paper is then made into a carton. Before fruits and vegetables are placed in the carton, the moisture in the air is insufficient to cause the release of gaseous MCP. After the fruits and vegetables are placed directly into the carton, the water vapor generated by the respiration of the fruits and vegetables will induce the slow release of MCP gas. Or as described in patent CN201710283918.5, the cyclodextrin-coated MCP is added to monomers, porogens, cross-linking agents, initiators, etc. to make a premixed liquid. After drying, it is used in the printing ink of the packaging carton. After adding fruits and vegetables, the water vapor from the respiration of the fruits and vegetables can be used to achieve the slow release of gaseous MCP. Although this method is easy to use and has a good preservation effect. However, these two patents also have certain problems: 1. Although under normal conditions, the moisture in the air is not enough to cause the solidified MCP to release MCP gas, when the cartons are stored for a long time without being used, the storage environment is complex and changeable. In a humid environment, it is still easy to cause the release of gaseous MCP, affecting the preservation effect. 2. The carton obtained by direct coating and drying in patent CN201610637567.9 has poor coating adhesion and is easy to fall off. The carton obtained by patent CN201710283918.5 uses a printing method. During the ink printing process, high temperatures of over 120°C can be instantly generated, resulting in a large amount of gaseous MCP released. In particular, the existing carton pre-printing process is becoming more and more popular. After pre-printing, corrugated cardboard is produced on a 160-180°C flatbed line. Therefore, the solidified MCP is required to withstand high temperatures above 180°C, which neither of the two patented products can meet. Summary of the Invention

[0008] The purpose of the present invention is to provide an alkali-regulated high-temperature-resistant modified cyclopropene, a fresh-keeping varnish and a fresh-keeping packaging product in order to solve the deficiencies of the prior art.

[0009] The purpose of the present invention is achieved by the following technical solutions:

[0010] A alkali-regulated high-temperature-resistant modified cyclopropene is in a solid state and comprises an active ingredient, a cyclopropene compound, a curing inclusion agent, and a high-temperature-resistant modifier; the high-temperature-resistant modifier is an organosilicon compound; and the content of the organosilicon compound is 1 to 50% by mass of the cyclopropene compound.

[0011] Preferably, the modified cyclopropene can withstand high temperatures of ≥180° C. and can be stably stored in a neutral system with a pH of 6.5 to 8.5 without releasing cyclopropene-like gases, and can be activated to release cyclopropene-like gases in an alkaline system with a pH of >8.5.

[0012] Preferably, the cyclopropene compound is 1-methylcyclopropene;

[0013] Preferably, the organosilicon compound is selected from tetraethyl orthosilicate, and / or silicic acid hydrogel obtained by hydrolysis of tetraethyl orthosilicate;

[0014] Preferably, the solidifying inclusion agent is one or more combinations selected from β-cyclodextrin, yellow dextrin, and white dextrin.

[0015] Preferably, in the modified cyclopropene, the content of the curing inclusion agent is 8 to 12 times the mass of the cyclopropene compound.

[0016] The method for preparing the high-temperature-resistant modified cyclopropene regulated by alkali as described above comprises the following steps:

[0017] S1. First, the ratio of the amount of the cyclopropene compound solution and the organosilicon compound is mixed to obtain a first mixture; the curing agent and the quantitative water are mixed to obtain a second mixture;

[0018] S2. Then the first mixture and the second mixture are mixed and reacted;

[0019] S3. The reaction mixture is separated into solid and liquid to obtain the modified cyclopropene;

[0020] Step S1 and step S2 are performed at a temperature lower than the boiling point of the cyclopropene compound.

[0021] A fresh-keeping varnish having a pH of 6.5 to 8.5, comprising a water-based resin and the modified cyclopropene as described above; the modified cyclopropene in the fresh-keeping varnish having a mass percentage of 0.1 to 5%;

[0022] The resin type in the water-based resin system is selected from resins that can withstand high temperatures of ≥180° C. without decomposition and are stable under pH conditions of ≥6.5.

[0023] Preferably, the resin is selected from one or more combinations of styrene acrylic emulsion, sulfonated polyester, and sulfonic acid type waterborne polyurethane.

[0024] Preferably, the resin is a mixture selected from high hardness styrene acrylic emulsion, medium hardness styrene acrylic emulsion and low hardness styrene acrylic soft emulsion; the amounts of the high hardness styrene acrylic emulsion, the medium hardness styrene acrylic emulsion and the low hardness styrene acrylic soft emulsion are 10-35%, 30-70% and 10-35% of the total mass of the resin respectively.

[0025] Preferably, the fresh-keeping varnish further comprises a defoaming agent and water;

[0026] The mass percentage of the water in the fresh-keeping varnish is 0.5-12%, the mass percentage of the defoaming agent is 0.3-0.5%, and the rest is the resin.

[0027] A fresh-keeping packaging product, comprising a packaging material body layer and a fresh-keeping varnish layer located on at least one side of the packaging material body layer;

[0028] The fresh-keeping varnish layer is formed by solidifying the fresh-keeping varnish mentioned above by adding alkali; the amount of the alkali used is 2-6% of the mass of the fresh-keeping varnish.

[0029] Preferably, the packaging material is paper; the fresh-keeping packaging product is prepared by any of the following processes:

[0030] A. Pre-printing process: First, neutral fresh-keeping varnish and alkali are evenly mixed as printing ink, and then immediately printed on a pre-printing machine to obtain a fresh-keeping varnish paper roll. Then, a flat-plate line is used to prepare a paperboard containing a fresh-keeping varnish layer.

[0031] B. Ordinary process: Ordinary paper is first used to pass through a flatbed line to obtain ordinary cardboard. Then, neutral preservative varnish and alkali are evenly mixed with the ordinary cardboard as printing ink, and immediately printed with a watermark printer to obtain a cardboard containing a preservative varnish layer.

[0032] The present application uses an organic silicon compound and a curing agent to modify the cyclopropene compound, which can significantly enhance its thermal stability and antioxidant stability, and can meet the high temperature conditions of 180°C required for printing (pre-printing); and has an alkali-regulated release property, can be stably stored in a neutral system of pH 6.5 to 8.5, and is activated to release cyclopropene gas in an alkaline system of pH>8.5. Therefore, the modified MCP and other products prepared from the modified MCP, such as fresh-keeping varnish and fresh-keeping cartons, can be stored for a long time under conventional conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 1 is the gas release curve of the modified MCP solid powder obtained in Example 1 and the conventional dextrin-modified MCP when heated;

[0034] Figure 2 1 is a graph showing the stability test results of the neutral fresh-keeping varnish obtained in Example 1 and the fresh-keeping varnish with a pH of 11 after adding sodium hydroxide;

[0035] Figure 3 This is a diagram of the fresh-keeping carton preservation test process;

[0036] Figure 4 This is a graph showing the hardness changes of kiwifruit stored in fresh-keeping cartons and ordinary cartons;

[0037] Figure 5 This is a graph showing the weight changes of kiwifruit stored in fresh-keeping cartons and ordinary cartons. DETAILED DESCRIPTION

[0038] The present application provides an alkali-regulated high-temperature-resistant modified cyclopropene, which is in a solid state and includes an active ingredient cyclopropene compound, a curing inclusion agent, and a high-temperature-resistant modifier; the high-temperature-resistant modifier is an organosilicon compound; the content of the organosilicon compound is 1 to 50% of the mass of the cyclopropene compound.

[0039] In existing technologies, MCP cured by inclusion with substances such as dextrin releases gaseous MCP in a neutral medium. Consequently, subsequent applications, such as fresh-keeping cartons (as described in Patents 201710283918.5 and 201610637567.9), may absorb excessive moisture during normal storage and release MCP prematurely, limiting the application of cured MCP. Furthermore, conventional inclusion-cured MCP has poor high-temperature resistance and cannot withstand the high temperatures required for conventional printing, such as watermark printing and pre-printing.

[0040] Through in-depth research, the present application has found that the use of organosilicon compounds and curing agents to modify cyclopropene compounds (such as 1-MCP) can significantly enhance their thermal stability and antioxidant stability based on the strong thermal stability and oxidative stability of the silicon-oxygen bond in the organosilicon molecule. The thermal release curve shows that the modified gas MCP is almost not released at 180°C, and a large amount of release temperature is between 250 and 350°C, which can meet the high temperature of 180°C required for corrugated cardboard production. In addition, it has alkali-regulated release characteristics and can be stably stored in a neutral system of pH 6.5 to 8.5. It is activated and releases cyclopropene gas in an alkaline system with a pH greater than 8.5. Therefore, the modified MCP and other products prepared from the modified MCP, such as fresh-keeping varnish and fresh-keeping cartons, can be stored for a long time under normal conditions. Regarding the alkali-regulated release mechanism, the applicant speculates that the modified cyclopropene has certain Lewis base characteristics, and strong alkali can destroy this structural characteristic, resulting in the release of the encapsulated gas. However, in the absence of water vapor, the strong base is solid and has limited destructive power on the coating structure. Therefore, it is relatively stable in a dry state and does not release cyclopropene gas.

[0041] The heat release curve can be adjusted by adjusting the amount of the organosilicon compound. Generally, within a limited range, when the amount of the organosilicon compound is large, the heat release temperature is relatively high.

[0042] Preferably, the cyclopropene compound is the widely used 1-methylcyclopropene, or a cyclopropene derivative having similar properties to 1-methylcyclopropene.

[0043] Preferably, the organosilicon compound is selected from tetraethyl orthosilicate and / or silicic acid hydrogel obtained by hydrolysis of tetraethyl orthosilicate.

[0044] Preferably, the curing inclusion agent is one or more combinations selected from β-cyclodextrin, yellow dextrin, and white dextrin, and more preferably β-cyclodextrin is the most common and widely used.

[0045] Preferably, in the modified cyclopropene, the content of the curing inclusion agent is 8 to 12 times the mass of the cyclopropene compound.

[0046] The method for preparing the high-temperature-resistant modified cyclopropene regulated by alkali as described above comprises the following steps:

[0047] S1. First, the ratio of the amount of the cyclopropene compound solution and the organosilicon compound is mixed to obtain a first mixture; the curing agent and the quantitative water are mixed to obtain a second mixture;

[0048] S2. Then the first mixture and the second mixture are mixed and reacted;

[0049] S3. Separating the reaction mixture into solid and liquid to obtain modified cyclopropene.

[0050] The proportions are as follows: the amount of the organosilicon compound is 1 to 50% of the mass of the cyclopropene compound, and the amount of the curing inclusion agent is 8 to 12 times of the mass of the cyclopropene compound.

[0051] Step S1 and step S2 are performed at a temperature lower than the boiling point of the cyclopropene compound to prevent the freshness-preserving gas from being released prematurely under high temperature conditions.

[0052] Preferably, when the cyclopropene compound is 1-MCP, in step S1, the cyclopropene compound stock solution and the organosilicon compound are stirred and mixed at -5°C to -10°C for 60 to 90 minutes, and the curing agent and a certain amount of water are ground and mixed at 1 to 5°C, and the amount of water is 1.5 to 2.5 times the mass of the curing agent; in step S2, the first mixture is poured into the second mixture and the grinding and mixing is continued for 90 to 120 minutes.

[0053] Step S3: The ground solid mixture is filtered, the filter cake is rinsed with ethanol for more than two times, and then placed in a vacuum drying oven at 40-60° C. for vacuum drying for 18-30 hours, and then taken out and ground to obtain the modified cyclopropene.

[0054] This modified cyclopropene can be used in the same ways as conventional cyclopropene preservatives, such as in fresh-keeping bags. Benefiting from its excellent high-temperature resistance, these bags can be stored for long periods in a hot, dry environment. For use, they can be placed directly in fruit and vegetable transport boxes and then moistened with alkali to release cyclopropene gases. Alternatively, fresh-keeping bags can be made by mixing the modified cyclopropene with solid alkali powder. These bags can then be placed directly in fruit and vegetable transport boxes and moistened with water.

[0055] In order to fully utilize the advantages of the modified cyclopropene in this application, such as its high-temperature resistance and alkali-controlled release, this application provides a fresh-keeping varnish that is stable under neutral conditions and can withstand temperatures above 180°C. This fresh-keeping varnish can be used as an ink for direct printing in the production of fruit and vegetable packaging boxes. Specifically, the fresh-keeping varnish has a pH of 6.5 to 8.5 and includes a water-based resin and the modified cyclopropene described above; the weight percentage of the modified cyclopropene in the fresh-keeping varnish is 0.1 to 5%. When the amount of modified cyclopropene in the varnish is too small, the corresponding fresh-keeping effect is not achieved. When the amount is too large, the cost is high.

[0056] This preservative varnish resin system can utilize a conventional water-based resin system. Using a water-based coating not only offers enhanced safety, making it suitable for preserving fresh fruits and vegetables, but also facilitates moisture absorption and release of preservative gases during subsequent use. However, the resin must be able to withstand temperatures exceeding 180°C without decomposition and be stable under neutral or alkaline conditions of pH 6.5 or higher. Preferably, the resin is a combination of styrene-acrylic emulsions, sulfonated polyesters, and sulfonic acid-based waterborne polyurethanes. Styrene-acrylic emulsions are particularly preferred, as they are inexpensive and suitable for large-scale production.

[0057] There are many styrene-acrylic emulsion products in the prior art. By adjusting the ratio of styrene and other acrylic functional monomers, styrene-acrylic emulsions of different hardness can be obtained respectively. The styrene-acrylic emulsion of the present application preferably adopts a mixture of high-hardness styrene-acrylic emulsion, medium-hardness styrene-acrylic emulsion and low-hardness styrene-acrylic soft emulsion, wherein the usage of high-hardness styrene-acrylic emulsion, medium-hardness styrene-acrylic emulsion and low-hardness styrene-acrylic soft emulsion is 10-35%, 30-70% and 10-35% of the total resin mass respectively. The technical characteristics of the high-hardness styrene-acrylic emulsion, medium-hardness styrene-acrylic emulsion and low-hardness styrene-acrylic soft emulsion in the present application are shown in Table 1 (hardness is mainly referenced by Tg value; the higher the Tg value, the greater the emulsion hardness).

[0058] Table 1

[0059]

[0060] The higher the hardness of the styrene acrylic emulsion, the worse the film-forming property. After printing and curing, tiny cracks will be generated, which will help the entry of water vapor and the release of fresh-keeping gas. However, the printing process has certain requirements for the hardness of the ink. If the hardness is too high, the printability will be poor. Therefore, on the basis of taking into account printability, stability and release properties, this application preferably uses a mixture of styrene acrylic emulsions of different hardnesses, which has better technical effects than using a styrene acrylic emulsion of a single hardness.

[0061] As those skilled in the art will appreciate, when other resin systems are used, the principle is similar to that of styrene acrylic emulsion, and it is also preferred to use a mixture of resins of different hardnesses.

[0062] Preferably, the preservative varnish also includes a defoamer and water. The water content of the preservative varnish is 0.5-12% by weight, the defoamer content is 0.3-0.5% by weight, and the remainder is resin. BYK-019 is preferably used as the defoamer. The amount of water can be adjusted according to the water content of the resin to maintain the viscosity of the preservative varnish within the printing range. Generally, the total water content of the varnish is maintained between 30% and 60%.

[0063] This preservative varnish can be directly applied to the surface of packaging materials, as described in Patent 201610637567.9. Because the modified MCP in this application's preservative varnish uses an alkali to regulate the release of preservative gases, a certain amount of alkali must be added to the preservative varnish before application. To reduce excessive release of preservative gases during the coating and drying process, the varnish must be applied immediately after mixing and dried quickly. The packaging material, such as paper or foam, needs to be able to quickly absorb moisture from the coating and cure it quickly.

[0064] Therefore, the present application also provides a fresh-keeping packaging product, comprising a packaging material body layer, and a fresh-keeping varnish layer located on at least one side surface of the packaging material body layer;

[0065] The fresh-keeping varnish layer is formed by solidifying the fresh-keeping varnish mentioned above by adding alkali; the amount of alkali used is 2-6% of the mass of the fresh-keeping varnish.

[0066] Cardboard boxes are the most widely used fruit and vegetable packaging boxes. They are inexpensive and have excellent water absorption properties. Therefore, paper is the preferred packaging material. This application proposes for the first time that a small amount of alkali, preferably sodium hydroxide / potassium hydroxide, is artificially added before printing, and then used immediately for printing. When the cardboard box is in a dry state at room temperature, the active ingredient 1-MCP is slowly released and can be stably stored for several months. When in use, only the coating needs to be wetted with a sprayer, and then the 1-MCP can be activated and released after packaging fruits and vegetables. Specifically, any of the following processes can be used to prepare fresh-keeping cartons:

[0067] A. Pre-printing process: First, a neutral preservative varnish is evenly mixed with an alkali to form a printing ink. This is immediately printed on a pre-printing machine to produce a preservative varnish paper roll. This roll is then processed on a flatbed line to produce a paperboard containing a preservative varnish layer. As will be understood by those skilled in the art, this preservative varnish layer is located on the inner layer of the paperboard. Conventional surface printing can also be performed on the outer surface of the paperboard using a watermark printer.

[0068] B. Conventional Process: First, ordinary base paper is processed through a flat-sheeting line to produce ordinary paperboard. Then, a neutral preservative varnish is mixed with an alkali solution to form the printing ink, which is then immediately printed using a watermark printer to produce a paperboard layer containing a preservative varnish. As those skilled in the art will appreciate, the preservative varnish layer is located on the inner layer of the paperboard, and the substrate can be ordinary paperboard printed with a conventional top layer.

[0069] In order to ensure that the fresh-keeping varnish and alkali are fully mixed, the solid alkali can be diluted with a small amount of water and then added to the fresh-keeping varnish. In order to reduce the release of MCP gas, printing should be done immediately after mixing.

[0070] The pre-printing process offers high production efficiency and uniform printing. The conventional process is simpler and slightly less uniform, but due to its complex steps, it is inefficient and relatively costly. The process can be selected for printing production based on actual production conditions. Both the pre-printing process and the conventional process can be used with conventional corrugated cardboard production and printing processes, and will not be described in detail in this application.

[0071] Dry fresh-keeping cartons can be stored for a long time in a dry room temperature environment. When in use, spray the inside of the carton with water to moisten it, and then put fruits and vegetables in it to achieve the fresh-keeping effect. The length of the fresh-keeping period can be adjusted by adjusting the alkali content and the amount of coating printed. In addition, the fresh-keeping period is also related to the ambient temperature and air humidity of the carton.

[0072] Example 1

[0073] (1) Preparation of modified MCP solid

[0074] (a) Set the low-temperature reactor temperature to -10°C, pour 10 g of 1-MCP stock solution and 0.5 g of ethyl orthosilicate into a split four-necked flask, and maintain low-temperature stirring at 360 rpm for 60 min.

[0075] (b) The temperature of the low-temperature dispersion device was set to 3°C. After the dispersion device was fully cooled, 100g of β-cyclodextrin and 200g of distilled water were added in sequence and ground into a paste. The mixed solution obtained in step (1) was then added and grinding was continued for 120min.

[0076] (c) The ground solid mixture was filtered, and the filter cake was rinsed three times with 30 ml of ethanol and placed in a 50° C. vacuum drying oven (vacuum degree -0.09 MPa). After 24 hours, it was taken out and ground to obtain a modified MCP solid powder.

[0077] (2) Preparation of fresh-keeping varnish

[0078] At room temperature, add 15g of high-hardness styrene-acrylic emulsion, 60g of medium-hardness styrene-acrylic emulsion, 15g of low-hardness styrene-acrylic soft emulsion, 9.5g of deionized water, 0.1g of modified MCP, and 0.4g of BYK-019 defoamer to a high-speed disperser. Disperse at high speed for 60 minutes to obtain a fresh-keeping varnish with a pH of 7.8. (The 0590 and 1207 emulsions are from Tianlong Ink, and the BYK-019 is from BYK Chemical.)

[0079] (3) Printing of fresh-keeping cartons

[0080] Add 2wt% sodium hydroxide solid powder to the fresh-keeping varnish (a small amount of water can be used to dilute and mix it evenly with the fresh-keeping varnish), stir it thoroughly, pour it into the pre-printing machine for printing, and reel it up to obtain a fresh-keeping varnish layer paper roll. The fresh-keeping varnish layer paper roll passes through a 180℃ flatbed line to obtain a paperboard with a fresh-keeping varnish layer on the inner layer (the printing amount of the fresh-keeping varnish layer is 3g / m 2 The cardboard is printed on the surface by a watermark printing machine to obtain a fresh-keeping paper box.

[0081] Example 2

[0082] (1) Preparation of modified MCP solid

[0083] (a) Set the low-temperature reactor temperature to -5°C, pour 10 g of 1-MCP liquid and 5 g of silicic acid hydrogel into a split four-necked flask, and stir at 800 rpm for 90 min.

[0084] (b) The temperature of the low-temperature dispersion device was set at 3°C. After the dispersion device was fully cooled, 80g of yellow dextrin and 160g of distilled water were added in sequence and ground into a paste. The mixed solution obtained in step (1) was then added and the grinding was continued for 90min.

[0085] (c) The ground solid mixture was filtered, and the filter cake was rinsed three times with 30 ml of ethanol and placed in a 50° C. vacuum drying oven (vacuum degree -0.09 MPa). After 24 hours, it was taken out and ground to obtain a modified MCP solid powder.

[0086] (2) Preparation of fresh-keeping varnish

[0087] Under room temperature conditions, 30 g each of high hardness styrene acrylic emulsion, medium hardness styrene acrylic emulsion, and styrene acrylic soft emulsion, 9.3 g of deionized water, 0.3 g of modified MCP, and 0.4 g of BYK-019 defoamer were added to a high-speed disperser in sequence. The mixture was dispersed at high speed for 90 minutes to obtain a fresh-keeping varnish having a pH of 7.6.

[0088] (3) Printing of fresh-keeping cartons:

[0089] (a) Ordinary corrugated cardboard was made by using ordinary base paper through a 180℃ flatbed line, and the surface layer was printed by a watermark printing machine.

[0090] (b) Add 3 wt% of sodium hydroxide solid powder to the fresh-keeping varnish and stir thoroughly.

[0091] (c) Pour the watermark printing machine into the back of the cardboard with the surface layer printed as the base, and print the inner layer of fresh-keeping varnish to obtain a fresh-keeping carton (the printing amount of the fresh-keeping varnish layer is 3g / m 2 ).

[0092] Example 3

[0093] (1) Preparation of modified MCP solid

[0094] (a) Set the low-temperature reactor temperature to -3°C, pour 10 g of 1-MCP stock solution and 0.1 g of ethyl orthosilicate into a split four-necked flask, and stir at 720 rpm for 30 min.

[0095] (b) Set the temperature of the low-temperature dispersion device to 3°C. After the dispersion device is fully cooled, add 100g of dextrin and 200g of distilled water in sequence and grind into a paste. Then add the mixed solution obtained in step (1) and continue grinding for 120min.

[0096] (c) The ground solid mixture was filtered, and the filter cake was rinsed three times with 30 ml of ethanol and placed in a 50° C. vacuum drying oven (vacuum degree -0.09 MPa). After 24 hours, it was taken out and ground to obtain a modified MCP solid powder.

[0097] (2) Preparation of fresh-keeping varnish

[0098] At room temperature, add 10g of high-hardness styrene-acrylic emulsion, 60g of medium-hardness styrene-acrylic emulsion, 20g of low-hardness styrene-acrylic soft emulsion, 9.1g of deionized water, 0.5g of modified MCP, and 0.4g of BYK-019 defoamer to a high-speed disperser. Disperse at high speed for 120 minutes to obtain a fresh-keeping varnish with a pH of 7.9. (The 0590 and 1207 emulsions are from Tianlong Ink, and BYK-019 is from BYK Chemical.)

[0099] (3) Printing of fresh-keeping cartons

[0100] Add 2wt% sodium hydroxide solid powder to the fresh-keeping varnish and stir thoroughly. Pour the mixture into the pre-printing machine for printing and then roll up to obtain a fresh-keeping varnish layer paper roll. The fresh-keeping varnish layer paper roll passes through a 180℃ flatbed line to obtain a paperboard with a fresh-keeping varnish layer on the inner layer (the printing amount of the fresh-keeping varnish layer is 3g / m 2 The cardboard is printed on the surface by a watermark printing machine to obtain a fresh-keeping paper box.

[0101] Example 4

[0102] (1) Preparation of modified MCP solid

[0103] (a) Set the low-temperature reactor temperature to -5°C, pour 10 g of 1-MCP liquid and 1 g of silicic acid hydrogel into a split four-necked flask, and stir at 800 rpm for 90 min.

[0104] (b) The temperature of the low-temperature dispersion device was set to 3°C. After the dispersion device was fully cooled, 120g of β-cyclodextrin and 200g of distilled water were added in sequence and ground into a paste. The mixed solution obtained in step (1) was then added and the grinding was continued for 90min.

[0105] (c) The ground solid mixture was filtered, and the filter cake was rinsed three times with 30 ml of ethanol and placed in a 50° C. vacuum drying oven (vacuum degree -0.09 MPa). After 24 hours, it was taken out and ground to obtain a modified MCP solid powder.

[0106] (2) Preparation of fresh-keeping varnish

[0107] At room temperature, 30 g of high-hardness styrene-acrylic emulsion, 40 g of medium-hardness styrene-acrylic emulsion, 20 g of styrene-acrylic soft emulsion, 8.6 g of deionized water, 1 g of modified MCP, and 0.4 g of BYK-019 defoamer were added to a high-speed disperser in sequence. The mixture was dispersed at high speed for 90 minutes to obtain a fresh-keeping varnish having a pH of 8.2.

[0108] (3) Printing of fresh-keeping cartons:

[0109] (a) Ordinary corrugated cardboard was made by using ordinary base paper through a 180℃ flatbed line, and the surface layer was printed by a watermark printing machine.

[0110] (b) Add 6 wt% of sodium hydroxide solid powder to the fresh-keeping varnish and stir thoroughly.

[0111] (c) Pour the watermark printing machine into the back of the cardboard with the surface layer printed as the base, and print the inner layer of fresh-keeping varnish to obtain a fresh-keeping carton (the printing amount of the fresh-keeping varnish layer is 3g / m 2 ).

[0112] Experimental example

[0113] 1. Modified MCP solid thermal stability test

[0114] The modified MCP solid powder obtained in Example 1 was taken, and the conventional dextrin-modified MCP solid powder (without silicone modification) was used as a control. The gas release curves thereof were tested under the following test conditions. The results are shown in FIG. Figure 1 As shown (the x-axis is temperature, unit is ° C; the y-axis is the weight residual percentage).

[0115] Test conditions: thermal gravimetric test, 5 mg sample, 30-800°C, N2 atmosphere, heating rate 10°C / min.

[0116] from Figure 1It can be seen that when the temperature reaches 200°C, more than 10% of the gas is released from the conventional dextrin-modified MCP, while the gas released by the modified cyclopropene in the present application is less than 5%, and the gas release only reaches 10% at around 250°C. Therefore, it can be proved that the modified MCP obtained in the present application can fully withstand the high temperature of 180°C printing.

[0117] 2. Stability test of fresh-keeping varnish

[0118] Separately, several cans of 100g of the neutral fresh-keeping varnish obtained in Example 1 (to improve the test accuracy, the amount of preservative added was increased from 0.1wt% to 5wt%, and the amount of water was reduced accordingly) and the fresh-keeping varnish with 2wt% sodium hydroxide added (pH 11) were placed in metal cans and sealed. The sealed cans were placed in a 60℃ oven for hot storage. Every 24 hours, one can was taken out and cooled, the seal was opened, and the weight was weighed after slight stirring. The weight change was recorded. Figure 2 shown.

[0119] from Figure 2 It can be seen that the fresh-keeping varnish prepared in the present application can be stably stored under neutral conditions with almost no loss in quality, and slowly releases fresh-keeping gas under alkaline conditions.

[0120] 3. Fresh-keeping carton fresh-keeping test

[0121] Test conditions: Kiwifruits of the same weight and from the same batch were stored in cartons with a fresh-keeping varnish layer (the fresh-keeping cartons obtained in Example 1) and cartons without a fresh-keeping varnish layer (ordinary cartons obtained under the same production process without a printed fresh-keeping varnish layer). The kiwifruits were stored at 25°C and 70% RH for 6 days. The changes in hardness and weight of the kiwifruits were compared. The test process is shown in the figure. Figure 3 As shown, the results are Figures 4-5 shown.

[0122] from Figure 4 It can be seen that the hardness of kiwifruit stored in cartons with a layer of fresh-keeping varnish is higher than that in uncoated cartons during the test time. Therefore, cartons with a layer of fresh-keeping varnish can delay the ripening of kiwifruit and play a role in preserving freshness.

[0123] from Figure 5 It can be seen that after 4-5 days of storage, the weight loss of the kiwifruit in the carton with the preservative varnish begins to approach that of the uncoated carton. During this period, the preservative varnish begins to lose its effectiveness, and the kiwifruit consumes organic matter at a faster rate. Therefore, the ethylene-inhibiting water-based coating inhibits kiwifruit respiration for approximately 4-5 days, and the carton maintains the kiwifruit's freshness for approximately 4-5 days.

[0124] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the invention. Thus, the present invention is intended to include such changes and modifications as fall within the scope of the claims and their equivalents.

Claims

1. A method for preparing high-temperature resistant modified cyclopropene regulated by alkali, characterized in that: The base regulates the high-temperature resistant modified cyclopropene to be in a solid state, comprising an active ingredient cyclopropene compound, a curing inclusion agent, and a high-temperature resistant modifier; the high-temperature resistant modifier is an organosilicon compound; the content of the organosilicon compound is 1 to 50% of the mass of the cyclopropene compound; The preparation method comprises the following steps: S1. First, the ratio of the amount of the cyclopropene compound solution and the organosilicon compound is mixed to obtain a first mixture; the curing agent and the quantitative water are mixed to obtain a second mixture; S2. Then the first mixture and the second mixture are mixed and reacted; S3. The reaction mixture is separated into solid and liquid to obtain the modified cyclopropene; Step S1 and step S2 are performed at a temperature lower than the boiling point of the cyclopropene compound.

2. The method for preparing high temperature resistant modified cyclopropene regulated by alkali as claimed in claim 1, wherein: The modified cyclopropene can withstand high temperatures of ≥180° C. and can be stably stored in a neutral system with a pH of 6.5 to 8.5 without releasing cyclopropene-like gases, and can be activated to release cyclopropene-like gases in an alkaline system with a pH of >8.

5.

3. The method for preparing high temperature resistant modified cyclopropene regulated by alkali as claimed in claim 1, wherein: The cyclopropene compound is 1-methylcyclopropene; The organosilicon compound is selected from ethyl orthosilicate and / or silicic acid hydrogel obtained by hydrolysis of ethyl orthosilicate; The solidifying inclusion agent is one or more combinations selected from β-cyclodextrin, yellow dextrin, and white dextrin.

4. The method for preparing high temperature resistant modified cyclopropene regulated by alkali as claimed in claim 1, wherein: In the modified cyclopropene, the content of the curing inclusion agent is 8 to 12 times the mass of the cyclopropene compound.

5. A fresh-keeping varnish, characterized in that: The pH of the fresh-keeping varnish is 6.5 to 8.5, and the varnish comprises a water-based resin and a modified cyclopropene prepared by the preparation method according to any one of claims 1 to 4; the mass percentage of the modified cyclopropene in the fresh-keeping varnish is 0.1 to 5%; The resin type in the water-based resin system is selected from resins that can withstand high temperatures of ≥180° C. without decomposition and are stable under pH conditions of ≥6.

5.

6. The fresh-keeping varnish according to claim 5, characterized in that: The resin is selected from one or more combinations of styrene acrylic emulsion, sulfonated polyester, and sulfonic acid type waterborne polyurethane.

7. The fresh-keeping varnish according to claim 6, characterized in that: The resin is a mixture of high-hardness styrene-acrylic emulsion, medium-hardness styrene-acrylic emulsion and low-hardness styrene-acrylic soft emulsion; the amounts of the high-hardness styrene-acrylic emulsion, the medium-hardness styrene-acrylic emulsion and the low-hardness styrene-acrylic soft emulsion are 10-35%, 30-70% and 10-35% of the total mass of the resin respectively.

8. The fresh-keeping varnish according to claim 6, characterized in that: The fresh-keeping varnish also includes a defoaming agent and water; The mass percentage of the water in the fresh-keeping varnish is 0.5-12%, the mass percentage of the defoaming agent is 0.3-0.5%, and the rest is the resin.

9. A fresh-keeping packaging product, characterized by: The packaging material comprises a main body layer of the packaging material and a fresh-keeping varnish layer located on at least one side surface of the main body layer of the packaging material; The fresh-keeping varnish layer is formed by solidifying the fresh-keeping varnish according to any one of claims 5 to 8 by adding alkali; the amount of the alkali used is 2 to 6% of the mass of the fresh-keeping varnish.

10. The fresh-keeping packaging product according to claim 9, characterized in that: The packaging material is paper; the fresh-keeping packaging product is prepared by any of the following processes: A. Pre-printing process: First, neutral fresh-keeping varnish and alkali are evenly mixed as printing ink, and then immediately printed on a pre-printing machine to obtain a fresh-keeping varnish paper roll. Then, a flat-plate line is used to prepare a paperboard containing a fresh-keeping varnish layer. B. Ordinary process: Ordinary paper is first used to pass through a flatbed line to obtain ordinary cardboard. Then, neutral preservative varnish and alkali are evenly mixed with the ordinary cardboard as printing ink, and immediately printed with a watermark printer to obtain a cardboard containing a preservative varnish layer.

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