High-barrier modified PVA / acrylic composite coating liquid and preparation method thereof

Abstract

The application relates to the field of high-barrier plastic packaging, and provides a high-barrier modified PVA / acrylic composite coating liquid and a preparation method thereof. The preparation method comprises the following components in percentage by weight: 10-30% of an aqueous acrylic emulsion, 2-10% of PVA resin, 1-5% of low-molecular-weight polyolefin resin containing a hydroxyl group, 1-5% of a crosslinking agent, 2-8% of a cosolvent, and 50-80% of deionized water. The modified PVA / acrylic composite coating liquid prepared through the method of chemical crosslinking and physical mixing can be coated on plastic film substrates such as PE, BOPP and PET, has excellent water-barrier and oxygen-barrier properties, has good substrate adhesion and storage stability, and can be widely applied to the fields of high-barrier packaging of food, medicine and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-barrier plastic packaging, in particular to a high-barrier modified PVA / acrylic composite coating solution and a preparation method thereof. BACKGROUND

[0002] High-barrier packaging is to use materials with high barrier properties to oxygen and water vapor to package products, thereby prolonging the shelf life and shelf life of food, medicine and other products. At present, the commonly used high-barrier packaging materials on the market include aluminum foil, aluminum-coated film, PVDC film, EVOH multi-layer co-extruded film, etc. Among them, although aluminum foil and aluminum-coated film have good barrier properties, they are not transparent, which affects the consumer's perception, and are difficult to recycle; PVDC film has excellent water, oxygen and oil resistance, but due to the presence of chlorine element in the film, toxic substances such as dioxin will be generated during incineration, which is harmful to the environment; EVOH co-extruded film generally needs more than 5 layers of materials to be co-extruded, which is not conducive to the development of plastic packaging reduction, and is difficult to recycle.

[0003] PVA (PVA) is a high molecular polymer containing hydroxyl groups. Due to the presence of a large number of strong polar hydroxyl groups in its molecular chain, it is easy to form intramolecular and intermolecular hydrogen bonds. A large number of hydrogen bonds make the PVA molecular structure regular and highly crystalline, thereby having excellent barrier properties to O2, CO2 and other small molecules. At the same time, PVA resin can be dissolved in water, and by coating it on plastic film as a water-based coating solution, the barrier properties of the film to O2 and CO2 can be significantly improved. However, PVA resin is easily absorbed and swollen in a high humidity environment, which destroys the intermolecular hydrogen bonds and causes a significant decrease in the barrier properties of the resin. Therefore, it is necessary to modify PVA resin to improve its water resistance and gas barrier properties.

[0004] At present, the commonly used methods for modifying PVA include chemical cross-linking and inorganic nano-material composite modification. Inorganic nano-material composite modification refers to the blending of sheet-like nano-scale montmorillonite, graphene and other inorganic materials with water-based PVA coating solution, which takes advantage of the high specific surface area and impermeability of nano-materials to achieve the purpose of improving the gas barrier properties and water resistance of the coating. Patent CN109535867A discloses a high-barrier PVA coating solution and a preparation method thereof, which adds silicate and other inorganic nano-particles to greatly improve the barrier properties of the coating solution. Patent CN112795248 A discloses a high-barrier PVA coating solution, which adds graphene nano-materials loaded with copper atoms to effectively prevent external oxygen from entering. However, inorganic nano-materials are not easy to disperse in water-based systems, and even if they are dispersed, they are prone to agglomeration and coarsening, resulting in poor storage stability and short shelf life of the modified PVA / coating solution; at the same time, the PVA coating solution has poor adhesion on PE, BOPP, PET and other plastic substrates, which also hinders its application in plastic packaging. SUMMARY

[0005] To address the shortcomings of existing technologies, this invention provides a high-barrier modified PVA / acrylic composite coating liquid and its preparation method. This high-barrier modified PVA / acrylic composite coating liquid not only has excellent oxygen and water vapor barrier properties, but also solves the problems of poor storage stability and poor substrate adhesion of existing PVA coating liquids.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: a high-barrier modified PVA / acrylic composite coating liquid, comprising the following components by weight percentage:

[0007] 10-30% aqueous acrylic emulsion;

[0008] 2-10% PVA resin;

[0009] 1-5% of low molecular weight hydroxyl-containing polyolefins;

[0010] Crosslinking agent 1-5%;

[0011] Cosolvent 2-8%;

[0012] Deionized water 50%–80%.

[0013] Preferably, the glass transition temperature (Tg) of the aqueous acrylic emulsion is 40–60°C.

[0014] Preferably, the aqueous acrylic emulsion includes acrylic acid, acrylates, and other additives (such as defoamers, surfactants, etc.).

[0015] Preferably, the degree of alcoholysis of the PVA resin is 87-99%.

[0016] The low molecular weight hydroxyl-containing polyolefin is characterized by the following molecular structure:

[0017]

[0018] Wherein, X = 10 to 40, Y = 2 to 10, and the number-average molecular weight of the polyolefin is Mn = 2000 to 3000.

[0019] Preferably, the low molecular weight hydroxyl-containing polyolefin is Mitsubishi Chemical's POLYTAIL H.

[0020] Preferably, the crosslinking agent is an aqueous isocyanate crosslinking agent, such as at least one of Bayhydur 304, Bayhydur 305, and Bayhydur XP 2655.

[0021] Preferably, the co-solvent is one or more of toluene, butanone, ethyl acetate, methylcyclohexane, and N-methylpyrrolidone.

[0022] This invention also provides a method for preparing the aforementioned high-barrier modified PVA / acrylic composite coating liquid:

[0023] (a) First, add deionized water to a container, then add PVA resin and stir continuously, and heat to completely dissolve the PVA; (b) Add low molecular weight hydroxyl-containing polyolefin resin to a cosolvent and stir to dissolve, add a crosslinking agent and react at 70-80℃, then add the dissolved PVA solution and continue the reaction, and then cool to room temperature to obtain a modified PVA resin solution; (c) Add water-based acrylic emulsion to the modified PVA resin solution and mix evenly to obtain a high-barrier modified PVA / acrylic composite coating solution.

[0024] Preferably, in step (a), deionized water is heated to 90-100°C to dissolve PVA, and after the PVA is completely dissolved, it is cooled to room temperature before adding low molecular weight hydroxyl-containing polyolefin resin.

[0025] Preferably, in step (b), the crosslinking agent is added and the reaction is carried out for 1-2 hours.

[0026] Preferably, in step (b), the reaction is carried out for 2-3 hours after the PVA solution is added.

[0027] The present invention also provides the application fields of the high-barrier modified PVA / acrylic composite coating liquid, which can be applied to the fields of high-barrier plastic packaging such as food and pharmaceuticals.

[0028] The present invention has the following beneficial effects:

[0029] (1) In the modified PVA / acrylic composite coating liquid provided by the present invention, the water-based acrylic resin has a high glass transition temperature and regular molecular arrangement, which can effectively prevent the passage of small gas molecules and improve the water and oxygen barrier capabilities of the coating.

[0030] (2) In the preparation of the modified PVA / acrylic composite coating liquid provided by the present invention, the low molecular weight hydroxyl-containing water-based isocyanate crosslinking agent is used to graft the low molecular weight polyolefin onto the PVA resin through chemical crosslinking. The network structure formed by the crosslinking of isocyanate and PVA can improve the density of the resin, and the special non-polar structure of polyolefin gives it excellent adhesion to substrates such as PE and BOPP. Thus, the barrier coating can adhere well to the substrate surface without the need for a primer, reducing the packaging process.

[0031] (3) The modified PVA / acrylic composite coating liquid provided by the present invention does not contain inorganic nanomaterials, and there is no problem of nanomaterials being dispersed and agglomerated in water, and it has good storage stability. Detailed implementation method:

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0033] Example 1

[0034] A high-barrier modified PVA / acrylic composite coating liquid: comprising the following components by weight percentage: 10% aqueous acrylic emulsion;

[0035] 10% PVA resin;

[0036] 5% low molecular weight hydroxyl-containing polyolefin;

[0037] 5% crosslinking agent;

[0038] 8% cosolvent;

[0039] 62% deionized water.

[0040] The aqueous acrylic emulsion is DSM's Neocryl FL-715, with a glass transition temperature (Tg) of 55°C.

[0041] The degree of alcoholysis of the PVA resin is 99%.

[0042] The low molecular weight hydroxyl-containing polyolefin mentioned is POLYTAIL H from Mitsubishi Chemical.

[0043] The crosslinking agent is the water-based isocyanate crosslinking agent Bayhydur 304.

[0044] The co-solvent is toluene.

[0045] Preparation method of the high-barrier modified PVA / acrylic composite coating liquid:

[0046] (a) First, add 620g of deionized water to a container, then add 100g of PVA resin and stir continuously. Then, while stirring, slowly raise the temperature to 90℃. After the PVA is completely dissolved, cool to 25℃. (b) Add 50g of low molecular weight hydroxyl-containing polyolefin resin POLYTAIL H to 80g of cosolvent toluene and stir to dissolve. Add 50g of waterborne isocyanate crosslinking agent Bayhydur 304 and heat to 80℃ for 1h. Then add the dissolved PVA solution and continue to react for 2h to obtain modified PVA resin solution. (c) Add 100g of waterborne acrylic emulsion to the modified PVA resin solution and mix evenly to obtain a high-barrier modified PVA / acrylic composite coating solution.

[0047] Example 2

[0048] A high-barrier modified PVA / acrylic composite coating liquid: comprising the following components by weight percentage: 30% aqueous acrylic emulsion;

[0049] 2% PVA resin;

[0050] 1% low molecular weight hydroxyl-containing polyolefin;

[0051] 1% crosslinking agent;

[0052] 3% cosolvent;

[0053] 63% deionized water.

[0054] The aqueous acrylic emulsion is BASF's Joncryl 95, with a glass transition temperature (Tg) of 43°C.

[0055] The degree of alcoholysis of the PVA resin is 87%.

[0056] The low molecular weight hydroxyl-containing polyolefin mentioned is POLYTAIL H from Mitsubishi Chemical.

[0057] The crosslinking agents are water-based isocyanate crosslinking agents Bayhydur 304 and Bayhydur 305, with a weight ratio of 1:1.

[0058] The co-solvent is toluene and butanone in a weight ratio of 1:1.

[0059] The preparation method of the high-barrier modified PVA / acrylic composite coating liquid is as follows:

[0060] (a) First, add 63 kg of deionized water to a container, then add 2 kg of PVA resin and stir continuously. Then, while stirring, slowly raise the temperature to 98°C. After the PVA is completely dissolved, cool it down. (b) Add 1 kg of low molecular weight hydroxyl-containing polyolefin resin to a mixed cosolvent of 1.5 kg toluene and 1.5 kg butanone and stir to dissolve. Add 0.5 kg of waterborne isocyanate crosslinking agent Bayhydur 304 and 0.5 kg of Bayhydur 305 and raise the temperature to 75°C and react for 1 h. Then add the dissolved PVA solution and continue to react for 2 h to obtain the modified PVA resin solution. (c) Add 30 kg of waterborne acrylic emulsion to the modified PVA resin solution and mix evenly to obtain a high-barrier modified PVA / acrylic composite coating solution.

[0061] Example 3

[0062] A high-barrier modified PVA / acrylic composite coating liquid: comprising the following components by weight percentage:

[0063] 20% aqueous acrylic emulsion;

[0064] 5% PVA resin;

[0065] 3% low molecular weight hydroxyl-containing polyolefins;

[0066] Crosslinking agent 2%;

[0067] 6% cosolvent;

[0068] 64% deionized water.

[0069] The aqueous acrylic emulsion is DSM's Neocryl XK-160, with a glass transition temperature (Tg) of 50°C.

[0070] The degree of alcoholysis of the PVA resin is 98%.

[0071] The low molecular weight hydroxyl-containing polyolefin mentioned is POLYTAIL H from Mitsubishi Chemical.

[0072] The crosslinking agent is the water-based isocyanate crosslinking agent Bayhydur XP 2655.

[0073] The co-solvent is toluene and N-methylpyrrolidone in a weight ratio of 1:1.

[0074] This invention also provides a method for preparing a high-barrier modified PVA / acrylic composite coating liquid as described in the above technical solution:

[0075] (a) First, add 64g of deionized water to a container, then add 5g of PVA resin and stir continuously. Then, while stirring, slowly raise the temperature to 95℃. After the PVA is completely dissolved, cool to 25℃. (b) Add 3g of low molecular weight hydroxyl-containing polyolefin resin to a mixed cosolvent of 3g methyl ethyl ketone and 3g N-methylpyrrolidone and stir to dissolve. Add 2g of waterborne isocyanate crosslinking agent Bayhydur XP 2655 and heat to 80℃ for 1h. Then add the dissolved PVA solution and continue to react for 2h to obtain modified PVA resin solution. (c) Add 20g of waterborne acrylic emulsion to the modified PVA resin solution and mix evenly to obtain a high-barrier modified PVA / acrylic composite coating solution.

[0076] Comparative Example 4

[0077] To investigate the chemical modification effect of low molecular weight hydroxyl-containing polyolefins on PVA resin, Comparative Example 4 provides an unmodified PVA / acrylic composite coating solution and its preparation method, comprising the following components by weight percentage:

[0078] 20% aqueous acrylic emulsion;

[0079] 5% PVA resin;

[0080] 6% cosolvent;

[0081] 69% deionized water.

[0082] Preferably, the aqueous acrylic emulsion, PVA resin, and co-solvent are the same as in Example 3.

[0083] This invention also provides a method for preparing an unmodified PVA / acrylic composite coating liquid as described in the above technical solution:

[0084] (a) First, add 69g of deionized water to a container, then add 5g of PVA resin and stir continuously. Then, while stirring, slowly raise the temperature to 95°C. After the PVA is completely dissolved, cool it to 25°C. (b) Add 3g of a mixed co-solvent of butanone and 3g of N-methylpyrrolidone, and 20g of water-based acrylic emulsion to the unmodified PVA resin solution. After mixing evenly, an unmodified PVA / acrylic composite coating solution is obtained.

[0085] Comparative Example 5

[0086] To investigate the chemical modification effect of low molecular weight hydroxyl-containing polyolefins on PVA resin, Comparative Example 5 provides an aqueous isocyanate-modified PVA / acrylic composite coating liquid and its preparation method, comprising the following components by weight percentage:

[0087] 20% aqueous acrylic emulsion;

[0088] 5% PVA resin;

[0089] Crosslinking agent 2%;

[0090] 6% cosolvent;

[0091] 67% deionized water.

[0092] Preferably, the aqueous acrylic emulsion, PVA resin, crosslinking agent, and cosolvent are the same as in Example 3.

[0093] This invention also provides a method for preparing an aqueous isocyanate-modified PVA / acrylic composite coating liquid as described in the above technical solution:

[0094] (a) First, add 67g of deionized water to a container, then add 5g of PVA resin and stir continuously. Then, while stirring, slowly raise the temperature to 95℃. After the PVA is completely dissolved, cool to 25℃. (b) Stir 3g of methyl ethyl ketone and 3g of N-methylpyrrolidone mixed cosolvent evenly, add 2g of waterborne isocyanate crosslinking agent Bayhydur XP 2655 and raise the temperature to 80℃. Then add the dissolved PVA solution and react for 2 hours to obtain isocyanate modified PVA resin liquid. (c) Add 20g of waterborne acrylic emulsion to the modified PVA resin liquid and mix evenly to obtain a waterborne isocyanate modified PVA / acrylic composite coating liquid.

[0095] Comparative Example 6

[0096] To investigate the storage stability of the high-barrier modified PVA / acrylic composite coating solution of the present invention, Comparative Example 6 provides a commercially available high-barrier inorganic nanomaterial modified PVA coating solution: the coating solution contains component A, PVA resin liquid, and component B, inorganic nanomaterial dispersion. Before use, component A and component B are mixed and stirred evenly at a weight ratio of 1:2 to obtain a high-barrier inorganic nanomaterial modified PVA coating solution.

[0097] Performance testing:

[0098] To investigate the beneficial effects of the high-barrier modified PVA / acrylic composite coating liquid and its preparation method described in this invention, we tested the storage stability, substrate adhesion and barrier properties of the high-barrier modified PVA / acrylic composite coating liquids obtained in Examples 1-3 and the coating liquids obtained in Comparative Examples 4-6, respectively.

[0099] Storage stability test:

[0100] After sealing the coating solutions obtained in Examples 1-3 and Comparative Examples 4-6, they were placed in a constant temperature drying oven at 50°C for 7 days to observe whether the coating solutions exhibited stratification or precipitation.

[0101] Substrate adhesion test:

[0102] The coating solutions obtained in Examples 1-3 and Comparative Examples 4-6 were applied to BOPP and PET substrates. After drying, the substrate adhesion of the coating was tested according to GB / T 13217.7-2009.

[0103] Barrier performance test:

[0104] The coating solutions obtained in Examples 1-3 and Comparative Examples 4-6 were coated onto 12 μm PET films, with a coating thickness of 1.5 μm. Their barrier properties against oxygen and water vapor were tested according to GB / T 1038-2000 and GB / T 1037-1988.

[0105] Table 1. Comparison of Performance Tests for Different Types of Coating Liquids

[0106]

[0107] As shown in Table 1, the high-barrier modified PVA / acrylic composite coating liquids described in Examples 1-3 exhibit better adhesion to BOPP and PET substrates than the unmodified PVA / acrylic composite coating liquids and isocyanate-modified PVA / acrylic composite coating liquids described in Comparative Examples 4-5. This indicates that the high-barrier modified PVA / acrylic composite coating liquid obtained by modifying PVA with low-molecular-weight hydroxyl-containing polyolefins in this invention has a significant advantage in substrate adhesion performance. Furthermore, the high-barrier modified PVA / acrylic composite coating liquids described in Examples 1-3 show better storage stability than the commercially available high-barrier inorganic nanomaterial modified PVA coating liquid described in Comparative Example 6. In addition, comparisons reveal that the high-barrier film prepared by the high-barrier modified PVA / acrylic composite coating liquid described in this invention also exhibits excellent barrier effects against oxygen and water vapor, and can be widely used in food, pharmaceutical, and other packaging fields.

Claims

1. A high-barrier modified PVA / acrylic composite coating solution, characterized by, Comprising the following components by weight percentage: Water-based acrylic emulsion 10-30%; PVA resin 2-10%; Low molecular weight hydroxyl-containing polyolefin 1-5%; Crosslinking agent 1-5%; Co-solvent 2-8%; Deionized water 50%-80%; The crosslinking agent is a water-based isocyanate crosslinking agent; The low molecular weight hydroxyl-containing polyolefin has the following molecular structure: Wherein, X=10-40, Y=2-10, the number average molecular weight of the polyolefin is Mn=2000-3000; The preparation method of the coating liquid comprises the following steps: (a) first add deionized water into the container, then add PVA resin and continuously stir, heat to completely dissolve the PVA; (b) add the low molecular weight hydroxyl-containing polyolefin resin into the co-solvent and stir to dissolve, add the crosslinking agent and react at 70-80℃, then add the dissolved PVA solution and continue to react, and then cool to room temperature to obtain the modified PVA resin liquid; (c) add the water-based acrylic emulsion into the modified PVA resin liquid, mix uniformly to obtain a high-barrier modified PVA / acrylic composite coating liquid.

2. The coating liquid according to claim 1, characterized by The glass transition temperature of the water-based acrylic emulsion is 40-60℃.

3. The coating liquid according to claim 1, characterized by The alcoholysis degree of the PVA resin is 87-99%.

4. The coating liquid according to claim 1, characterized by The co-solvent is one or more of toluene, butanone, ethyl acetate, methylcyclohexane, and N-methylpyrrolidone.

5. The coating liquid according to claim 1, characterized by The low molecular weight hydroxyl-containing polyolefin is POLYTAIL H from Mitsubishi Chemical.

6. The coating liquid according to claim 1, characterized by In step (a), the deionized water is heated to 90-100℃ to dissolve the PVA, and after the PVA is completely dissolved, the low molecular weight hydroxyl-containing polyolefin resin is added and cooled to room temperature.

7. The coating liquid according to claim 1, characterized by In step (b), the crosslinking agent is added and reacted for 1-2h.

8. The coating liquid according to claim 1, characterized by In step (b), the PVA solution is added and reacted for 2-3h.

9. The use of the coating liquid according to any one of claims 1-8 in the field of high-barrier plastic packaging for food and pharmaceuticals.

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