A solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing and a preparation method thereof

Abstract

A solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing, comprising component A and component B; component A is made of the following raw materials in a weight ratio: 10-20% isophorone diisocyanate, 20-50% hexamethylene diisocyanate, 0-50% 1,4-cyclohexane diisocyanate, 0-40% cyclohexane dimethylene diisocyanate, and 0-30% norbornane diisocyanate; component B is made of the following raw materials in a weight ratio: 30-60% dimer acid polyester diol, 15-30% polyetheramine, 15-30% polyaspartic acid ester, 1-5% dihydroxy polydimethylsiloxane, and 1-5% silane coupling agent; the ratio of component A to component B is determined based on an R value of 1.02-1.10. The present invention also provides a preparation method for the solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing. The solvent-free polyurethane coating of the present invention can form a heat-sealable release layer with heat-sealability and easy peelability after coating and curing, and has no VOCs emission during the manufacturing and use process, which is more environmentally friendly.

Description

Technical Field

[0001] The present invention relates to a coating composition, in particular to a solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing, and a preparation method thereof. Background Art

[0002] Internationally, oxygen permeability is less than 3.8cm 3 / (m 2 Coating materials with a pressure drop of 0.1 MPa (·24h·0.1MPa) are considered high-barrier materials. High-barrier materials block oxygen, water vapor, oil, and odors. They effectively preserve the taste and odor of packaged food, prevent product spoilage, and extend shelf life and expiration. In the global packaging industry, especially in food and pharmaceutical packaging, an increasing number of manufacturers are turning to packaging materials with high barrier properties. Traditionally, high-barrier materials have primarily been plastic packaging. However, with growing global awareness of environmental protection and resource conservation, recyclable paper-based high-barrier packaging materials are gaining increasing attention.

[0003] To create paper packaging materials with high oxygen and water barrier properties, the traditional method involves vapor-depositing a layer of high-barrier silicon oxide or aluminum oxide onto plastic film, then laminating the film with paper to create a high-barrier paper-plastic composite packaging material. However, this method produces barrier paper and plastic products that are non-recyclable and non-biodegradable, which is detrimental to environmental protection and resource conservation. Some also combine paper with aluminum foil, leveraging the foil's high barrier properties to achieve high-barrier packaging material requirements. However, this packaging material wastes a large amount of aluminum foil and is also detrimental to resource conservation. Another method involves coating paper with a high-barrier polyvinylidene chloride (PVDC) coating, which effectively blocks oxygen and water vapor. However, the barrier paper produced by this method contains a PVDC coating, and polyvinylidene chloride and its decomposition products are highly toxic, resulting in poor safety and sanitation properties, making it unsuitable for packaging materials such as food and pharmaceuticals. Others use PVA, a highly barrier polymer, as a barrier coating. However, PVA is a highly hydrophilic polymer that not only lacks water barrier properties but also readily absorbs moisture from the air, completely eliminating its oxygen barrier properties.

[0004] While solvent-free polyurethane coatings are predicted to be a key growth area, existing polyurethane systems still face technical bottlenecks such as high viscosity and poor coating uniformity, making it difficult to achieve both heat-sealing and peelability. Introducing polar groups improves heat-sealing properties but weakens peelability. Silicone modification reduces peel force but can lead to contamination of the coating contents. Cross-linking enhances peelability but compromises the coating's heat-sealing and flexibility. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a solvent-free polyurethane coating that can form a heat-sealable release layer after coating and curing, and a preparation method thereof. This solvent-free polyurethane coating can form a heat-sealable release layer with heat-sealability and easy peelability after coating and curing. The manufacturing and use processes of this solvent-free polyurethane coating are free of VOCs emissions, making it more environmentally friendly. The technical solution adopted is as follows:

[0006] A solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing, comprising component A and component B, characterized in that:

[0007] Component A is made of the following raw materials in the following weight ratios: 10-20% of isophorone diisocyanate, 20-50% of hexamethylene diisocyanate, 0-50% of 1,4-cyclohexane diisocyanate, 0-40% of cyclohexane dimethylene diisocyanate, and 0-30% of norbornane diisocyanate;

[0008] Component B is made of the following raw materials in the following weight ratios: dimer acid polyester diol 30-60%, polyether amine 15-30%, polyaspartic acid ester 15-30%, dihydroxy polydimethylsiloxane 1-5%, and silane coupling agent 1-5%;

[0009] The ratio of component A to component B is determined according to an R value of 1.02-1.10, wherein the R value is the molar ratio of the total isocyanate groups (-NCO) to the total hydroxyl groups (-OH) of components A and B.

[0010] Preferably, component A is made of the following raw materials in the following weight ratio: 10-20% isophorone diisocyanate, 20-50% hexamethylene diisocyanate, 0.2-20% 1,4-cyclohexane diisocyanate, 0.2-20% cyclohexane dimethylene diisocyanate, and 0.2-20% norbornane diisocyanate.

[0011] Preferably, the molecular weight of the dimer acid polyester diol is 2000-2500 and the hydroxyl value is 35-45. In a specific embodiment, the dimer acid polyester diol is a dimer acid polyester diol polymerized from oleic acid and 1,6-hexanediol (eg, Baiyuan BY3026).

[0012] The molecular weight of the polyetheramine is preferably 400-1000. In a specific embodiment, the molecular weight of the polyetheramine is 400 (such as Huntsman T-403).

[0013] Preferably, the molecular weight of the polyaspartic acid ester is 400-600 (eg Feiyang F520).

[0014] The molecular weight of the dihydroxy polydimethylsiloxane is preferably 500-2000. In a specific embodiment, the molecular weight of the dihydroxy polydimethylsiloxane is about 1000 (for example, Sihai's 209 hydroxy silicone oil).

[0015] The silane coupling agent may be silane coupling agent KH-560 or silane coupling agent KH-792.

[0016] On the other hand, the present invention also provides a method for preparing the solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing, characterized by comprising the following steps:

[0017] (1a) Prepare component A

[0018] (1a-1) The following raw materials are prepared by weight: 10-20% isophorone diisocyanate, 20-50% hexamethylene diisocyanate, 0-50% 1,4-cyclohexane diisocyanate, 0-40% cyclohexane dimethylene diisocyanate, and 0-30% norbornane diisocyanate;

[0019] (1a-2) isophorone diisocyanate, hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, cyclohexane dimethylene diisocyanate, and norbornane diisocyanate prepared in step (1a-1) are mixed uniformly to obtain component A, which is set aside;

[0020] (2a) Preparation of component B

[0021] (2a-1) The following raw materials are prepared by weight: 30-60% of dimer acid polyester diol, 15-30% of polyether amine, 15-30% of polyaspartic acid ester, 1-5% of dihydroxy polydimethylsiloxane, and 1-5% of silane coupling agent;

[0022] (2a-2) uniformly mixing the dimer acid polyester diol, polyetheramine, polyaspartic acid ester, dihydroxy polydimethylsiloxane and silane coupling agent prepared in step (2a-1) to obtain component B, which is set aside;

[0023] (3a) Preparation of solvent-free polyurethane coatings

[0024] Determine the ratio of component A to component B according to the R value of 1.02-1.10, mix component A and component B evenly to obtain the required solvent-free polyurethane coating.

[0025] In the preferred step (3a), components A and B are preheated to 40-60°C (preferably 45°C) before application, and are accurately measured (i.e., the ratio of components A and B is determined according to an R value of 1.02-1.10, and components A and B are measured and fed into a pipeline mixer), and then added to the glue tank of the compounding machine using a pipeline mixer for coating by the compounding machine.

[0026] The solvent-free polyurethane coating is a two-component, solvent-free polyurethane. After curing, it exhibits high density and hardness, along with certain barrier properties, effectively blocking moisture, oil, and oxygen. Cured, it also becomes thermoplastic, offering excellent heat-sealability (capable of heat sealing at 130°C). Furthermore, it exhibits excellent transferability and peelability. After curing, the coating can be easily peeled from the cover film (such as non-corona-treated OPP film). After vacuum coating with aluminum oxide or silicon oxide, it can then be peeled from the carrier layer (such as non-corona-treated PET film), transferring the heat-sealable release layer to the paper. Conventional polyurethane coatings, however, are not peelable when applied to PET film.

[0027] The above-mentioned component A is isocyanate, which is the reactive hard segment component of the heat-sealable release layer. Its combined use can not only improve the barrier and peelability of the release layer, but also maintain a certain degree of flexibility in the coating. The functions of its various components are as follows: Isophorone diisocyanate imparts strength, heat resistance, abrasion resistance and other properties to the coating, while also improving flexibility and film-forming properties, and helping to reduce the heat-sealing temperature; Hexamethylene diisocyanate (HDI) has good crystallization properties, can reduce the heat-sealing temperature, and can improve barrier properties after curing; 1,4-cyclohexane diisocyanate (CHDI) is the reactive hard segment component of the heat-sealable release layer. It has a compact and more symmetrical molecular structure, which enables the cured heat-sealable release layer to form more precise hard segments, improve barrier properties, solvent resistance, water resistance, and have a high softening temperature and low glass transition temperature. Norbornane diisocyanate (NBDI) gives the heat-sealable release layer higher thermal stability, hardness, and heat resistance after curing, improving peelability.

[0028] The above-mentioned component B is a polymer polyol with hydroxyl or amino groups, which is the soft segment component of the heat-sealable release layer. After curing with component A, the heat-sealable release layer can have good peelability, heat sealability and certain barrier properties, and also improve the adhesion of vapor-deposited silicon oxide. The functions of its various components are as follows: dimer acid polyester diol imparts flexibility and water barrier properties to the heat-sealable release layer; polyaspartic acid ester can improve the peelability, hardness, barrier properties and curing speed of the heat-sealable release layer; dihydroxy polydimethylsiloxane can reduce the surface friction coefficient of the heat-sealable release layer, improve the flatness, reduce the generation of static electricity when the film is peeled off, and at the same time improve the adhesion between the heat-sealable release layer and the vapor-deposited layer.

[0029] The above-mentioned solvent-free polyurethane coating can be used to manufacture high-barrier paper with heat-sealing properties. The high-barrier paper includes paper, an adhesive layer, a vapor-deposited layer and a heat-sealable release layer arranged in sequence. The vapor-deposited layer is a silicon oxide or aluminum oxide barrier layer vapor-deposited on one side of the heat-sealable release layer. The vapor-deposited layer is composited on one side of the paper through an adhesive layer. The heat-sealable release layer has heat-sealability and easy peelability. Among them, the heat-sealable release layer is formed using the above-mentioned solvent-free polyurethane coating. The heat-sealable release layer in the above-mentioned high-barrier paper has heat-sealability and easy peelability. When used as a packaging material, it can be used as a heat-sealable layer. For example, when the above-mentioned high-barrier paper is used to make a paper packaging bag, the heat-sealable release layers of the papers on both sides of the bag opening are in the innermost layer. The heat-sealable release layers of the papers on both sides can be heat-sealed together by applying pressure and heating to achieve sealing.

[0030] The method for preparing the high-barrier paper having heat-sealing properties comprises the following steps:

[0031] (1) Making heat-sealable release film

[0032] A non-corona-treated PET film is used as a carrier layer, and a polyurethane coating is applied on the carrier layer using a solvent-free polyurethane coating. After curing, the polyurethane coating forms a heat-sealable release layer that has heat-sealability and can be peeled off from the carrier layer.

[0033] (2) Making the vapor deposition layer

[0034] Vacuum evaporating a layer of aluminum oxide or silicon oxide on the heat-sealable release layer to form an evaporation layer, i.e., an aluminum oxide or silicon oxide barrier layer, to obtain a composite layer material;

[0035] (3) Making high barrier paper

[0036] An adhesive layer is applied to one side of the paper, and then the composite material obtained in step (2) is composited with the paper, and the vapor-deposited layer in the composite material is bonded to one side of the paper via the adhesive layer; and then the carrier layer is peeled off (i.e., the carrier layer is separated from the heat-sealable release layer), thereby obtaining the desired high-barrier paper with heat-sealability.

[0037] In the preferred step (1), the coating amount of the polyurethane coating is 3-8 g / m 2 .

[0038] In step (1), after applying the polyurethane coating, a covering film is laminated on the polyurethane coating to form a composite film, which is then rolled up. The composite film roll is then placed in an environment with a humidity of less than 40% and a temperature of 30-50°C for aging for 24-72 hours (preferably 48 hours). After aging, the covering film is peeled off and recovered (the recovered covering film can be reused), thereby forming a heat-sealable release layer on the carrier layer. The covering film is a non-corona-treated OPP film.

[0039] Preferably, in step (1), solvent-free compounding equipment is used in the coating and compounding process, and the coating and compounding speed is 100-400 m / min.

[0040] Preferably, each operation of the above step (1) is performed in an environment with an air humidity of less than 40%.

[0041] Preferably, in step (2), the thickness of the deposited layer is 5-50 nm. Silicon oxide is preferably used for vacuum deposition.

[0042] In the preferred step (3), the composite layer material is rolled up after being composited with the paper, and then aged for 24-72 hours (preferably 48 hours) in an environment with a humidity of 60-80% and a temperature of 30-50°C. After the ageing, the carrier layer is peeled off.

[0043] Preferably, in step (3), solvent-free compounding equipment is used in the coating and compounding process, and the coating and compounding speed is 100-400 m / min.

[0044] Preferably, in step (3), the coating amount of the adhesive layer is 2-8 g / m 2 .

[0045] The solvent-free polyurethane coating of the present invention, after coating and curing, forms a heat-sealable release layer that exhibits heat-sealability and easy peelability. When used in the manufacture of high-barrier paper, this heat-sealable release layer serves as the heat-sealable layer, imparting heat-sealability and environmentally friendly recyclability (repulpable and recyclable). When used in the manufacture of high-barrier paper, the OPP film is first peeled and recycled, with a peel strength of less than 0.5N / 25mm, leaving a clean interface with no coating residue. During transfer, the PET film can then be peeled and recycled, with a peel strength of 0.6-1.0N / 25mm, leaving a clean interface with no coating residue.

[0046] In addition, the solvent-free polyurethane coating of the present invention is a two-component solvent-free polyurethane, which has no VOC emissions during the manufacturing and use process, does not contain or release toxic substances, is more environmentally friendly, and saves energy (using a solvent-free system, the curing process does not require heating or radiation energy). DETAILED DESCRIPTION

[0047] Example 1: In this example, a method for preparing a solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing comprises the following steps:

[0048] (1a) Prepare component A

[0049] (1a-1) The following raw materials are prepared by weight: 100 g of isophorone diisocyanate (10%), 500 g of hexamethylene diisocyanate (50%), 20 g of 1,4-cyclohexane diisocyanate (2%), 350 g of cyclohexane dimethylene diisocyanate (35%), and 30 g of norbornane diisocyanate (3%);

[0050] (1a-2) isophorone diisocyanate, hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, cyclohexane dimethylene diisocyanate, and norbornane diisocyanate prepared in step (1a-1) are mixed uniformly to obtain component A, which is set aside;

[0051] (2a) Preparation of component B

[0052] (2a-1) The following raw materials are prepared by weight: 480 g (48%) of dimer acid polyester diol, 190 g (19%) of polyetheramine, 240 g (24%) of polyaspartic acid ester, 50 g (5%) of dihydroxy polydimethylsiloxane, and 40 g (4%) of silane coupling agent;

[0053] The dimer acid polyester diol is a dimer acid polyester diol obtained by polymerization of oleic acid and 1,6-hexanediol (e.g., Baiyuan BY3026, molecular weight 2500, hydroxyl value 39.4); the molecular weight of the polyetheramine is 400 (e.g., Huntsman T-403); the molecular weight of the polyaspartic acid ester is 590 (e.g., Feiyang New Materials F520); the molecular weight of the dihydroxy polydimethylsiloxane is about 1000 (e.g., Sihai's 209 hydroxy silicone oil); and the silane coupling agent is silane coupling agent KH-560.

[0054] (2a-2) uniformly mixing the dimer acid polyester diol, polyetheramine, polyaspartic acid ester, dihydroxy polydimethylsiloxane and silane coupling agent prepared in step (2a-1) to obtain component B, which is set aside;

[0055] (3a) Preparation of solvent-free polyurethane coatings

[0056] The ratio of component A to component B is determined according to the R value of 1.077 (the mass ratio of component A to component B is A:B=1:3.5), and component A and component B are mixed evenly to obtain the required solvent-free polyurethane coating.

[0057] In the above step (3a), component A and component B are preheated to 45°C before application, and are accurately measured (i.e., the ratio of component A to component B is determined according to an R value of 1.077, and component A and component B are measured and sent to a pipeline mixer). They are then added to the glue tank of the solvent-free laminating machine using a pipeline mixer for coating by the solvent-free laminating machine.

[0058] The solvent-free polyurethane coating can be used to manufacture high-barrier paper with heat-sealing properties. The method for preparing the high-barrier paper with heat-sealing properties comprises the following steps:

[0059] (1) Making heat-sealable release film

[0060] The PET film without corona discharge is used as the carrier layer, and the polyurethane coating is coated on the carrier layer using solvent-free polyurethane coating (the coating amount of the polyurethane coating is 4g / m 2 After the polyurethane coating is applied, a covering film is laminated on the polyurethane coating (the covering film is an OPP film without corona treatment) to form a composite film, which is then rolled up. The composite film roll is then placed in an environment with a humidity of less than 40% and a temperature of 40°C for aging for 48 hours. After aging, the covering film is peeled off and recovered (the recovered covering film can be reused), thereby forming a heat-sealable release layer on the carrier layer that has heat-sealability and can be peeled off from the carrier layer.

[0061] In step (1), a solvent-free laminating machine is used in the coating and laminating process, and the coating and laminating speed is 200 m / min; the glue tank and transfer roller of the solvent-free laminating machine are preheated to 45°C;

[0062] The various operations of step (1) are performed in an environment where the air humidity is less than 40%;

[0063] (2) Making the vapor deposition layer

[0064] Vacuum evaporating a layer of aluminum oxide on the heat-sealable release layer to form an evaporation layer (the thickness of the evaporation layer is 40 nm), namely, an aluminum oxide barrier layer, to obtain a composite layer material;

[0065] (3) Making high barrier paper

[0066] Apply an adhesive layer on one side of the paper (the adhesive is the above-mentioned solvent-free moisture-curing transfer adhesive, and the solvent-free moisture-curing transfer adhesive is heated to 90°C when used; the coating amount of the adhesive layer is 5g / m 2 ), then compounding the composite layer material obtained in step (2) with paper, and bonding the vapor-deposited layer in the composite layer material to one side of the paper via the adhesive layer; then peeling off the supporting layer (i.e., separating the supporting layer from the heat-sealable release layer) to obtain the desired high-barrier paper with heat-sealability.

[0067] In step (3), the composite layer material is rolled up after being composited with the paper, and then aged for 48 hours in an environment with a humidity of 70% and a temperature of 45°C. After the ageing, the carrier layer is peeled off.

[0068] In step (3), a solvent-free laminating machine is used for coating and laminating, and the coating and laminating speed is 150 m / min. The glue tank and transfer roller of the solvent-free laminating machine are preheated to 90°C.

[0069] The obtained high-barrier paper with heat-sealing properties includes paper, an adhesive layer, a vapor-deposited layer and a heat-sealable release layer arranged in sequence. The vapor-deposited layer is an aluminum oxide barrier layer vapor-deposited on one side of the heat-sealable release layer. The vapor-deposited layer is compounded on one side of the paper through the adhesive layer. The heat-sealable release layer has heat-sealability and easy peelability.

[0070] The preparation method of the solvent-free moisture-curing transfer adhesive (used for coating an adhesive layer on one side of paper) used in the above step (3) comprises the following steps in sequence:

[0071] (1b) The following raw materials are prepared by weight: 400g (40%) of dimer acid polyester diol, 190g (19%) of pentaerythritol polyoxypropylene tetraol, 155g (15.5%) of polyneopentyl terephthalate diol, 250g (25%) of diphenylmethane diisocyanate, and 5g (0.5%) of bismorpholino diethyl ether;

[0072] The dimer acid polyester diol is a dimer acid polyester diol polymerized from oleic acid and 1,6-hexanediol (e.g., Baiyuan BY3026, molecular weight 2500, hydroxyl value 39.4); pentaerythritol polyoxypropylene tetraol has a molecular weight of 856 (e.g., Yinuowei 380); and polyneopentyl terephthalate diol has a molecular weight of 2000 (e.g., Huiyuan Technology P320).

[0073] (2b) Add the dimer acid polyester diol, pentaerythritol polyoxypropylene tetraol and poly (neopentyl terephthalate) diol prepared in step (1b) into a reactor, and then heat the contents of the reactor to 110°C and place them under vacuum at -8×10 -4 MPa for 1.5 hours;

[0074] (3b) The contents of the reactor were cooled to 45°C, diphenylmethane diisocyanate was added, and the mixture was reacted at 80°C for 3 hours;

[0075] (4b) The contents of the reactor were cooled to 50°C, and then bismorpholinyl diethyl ether was added and stirred to obtain a solvent-free moisture-curing transfer adhesive, which was then sealed for later use.

[0076] Example 2: In this example, a method for preparing a solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing comprises the following steps:

[0077] (1a) Prepare component A

[0078] (1a-1) The following raw materials are prepared by weight: 150 g of isophorone diisocyanate (15%), 400 g of hexamethylene diisocyanate (40%), 400 g of 1,4-cyclohexane diisocyanate (40%), 20 g of cyclohexane dimethylene diisocyanate (2%), and 30 g of norbornane diisocyanate (3%);

[0079] (1a-2) isophorone diisocyanate, hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, cyclohexane dimethylene diisocyanate, and norbornane diisocyanate prepared in step (1a-1) are mixed uniformly to obtain component A, which is set aside;

[0080] (2a) Preparation of component B

[0081] (2a-1) The following raw materials are prepared by weight: 590 g (59%) of dimer acid polyester diol, 200 g (20%) of polyetheramine, 160 g (16%) of polyaspartic acid ester, 30 g (3%) of dihydroxy polydimethylsiloxane, and 20 g (2%) of silane coupling agent;

[0082] The dimer acid polyester diol is a dimer acid polyester diol obtained by polymerization of oleic acid and 1,6-hexanediol (e.g., Baiyuan BY3026, molecular weight 2500, hydroxyl value 39.4); the molecular weight of the polyetheramine is 400 (e.g., Huntsman T-403); the molecular weight of the polyaspartic acid ester is 590 (e.g., Feiyang New Materials F520); the molecular weight of the dihydroxy polydimethylsiloxane is about 1000 (e.g., Sihai's 209 hydroxy silicone oil); and the silane coupling agent is silane coupling agent KH-560.

[0083] (2a-2) uniformly mixing the dimer acid polyester diol, polyetheramine, polyaspartic acid ester, dihydroxy polydimethylsiloxane and silane coupling agent prepared in step (2a-1) to obtain component B, which is set aside;

[0084] (3a) Preparation of solvent-free polyurethane coatings

[0085] The ratio of component A to component B is determined according to the R value of 1.064 (the mass ratio of component A to component B is A:B=1:3.9), and component A and component B are mixed evenly to obtain the required solvent-free polyurethane coating.

[0086] In the above step (3a), component A and component B are preheated to 45°C before application, and are added to the glue tank of the solvent-free laminating machine through precise measurement (i.e., the ratio of component A and component B is determined according to the R value of 1.064, and component A and component B are measured and sent to the pipeline mixer) through the pipeline mixer for coating by the solvent-free laminating machine.

[0087] The solvent-free polyurethane coating can be used to manufacture high-barrier paper with heat-sealing properties. The method for preparing the high-barrier paper with heat-sealing properties comprises the following steps:

[0088] (1) Making heat-sealable release film

[0089] The PET film without corona discharge is used as the carrier layer, and the polyurethane coating is coated on the carrier layer using solvent-free polyurethane coating (the coating amount of the polyurethane coating is 5g / m 2 After the polyurethane coating is applied, a covering film is laminated on the polyurethane coating (the covering film is an OPP film without corona treatment) to form a composite film, which is then rolled up. The composite film roll is then placed in an environment with a humidity of less than 40% and a temperature of 35°C for aging for 72 hours. After aging, the covering film is peeled off and recovered (the recovered covering film can be reused), thereby forming a heat-sealable release layer on the carrier layer that has heat-sealability and can be peeled off from the carrier layer.

[0090] In step (1), a solvent-free laminating machine is used in the coating and laminating process, and the coating and laminating speed is 400 m / min; the glue tank and transfer roller of the solvent-free laminating machine are preheated to 45°C;

[0091] The various operations of step (1) are performed in an environment where the air humidity is less than 40%;

[0092] (2) Making the vapor deposition layer

[0093] Vacuum evaporating a layer of silicon oxide on the heat-sealable release layer to form an evaporation layer (the thickness of the evaporation layer is 10 nm), namely, a silicon oxide barrier layer, to obtain a composite layer material;

[0094] (3) Making high barrier paper

[0095] Apply an adhesive layer on one side of the paper (the adhesive is the above-mentioned solvent-free moisture-curing transfer adhesive, and the solvent-free moisture-curing transfer adhesive is heated to 85°C when used; the coating amount of the adhesive layer is 4g / m 2 ), then compounding the composite layer material obtained in step (2) with paper, and bonding the vapor-deposited layer in the composite layer material to one side of the paper via the adhesive layer; then peeling off the supporting layer (i.e., separating the supporting layer from the heat-sealable release layer) to obtain the desired high-barrier paper with heat-sealability.

[0096] In step (3), the composite layer material is rolled up after being compounded with the paper, and then aged for 48 hours in an environment of 70% humidity and 40°C. After the ageing, the supporting layer is peeled off.

[0097] In step (3), a solvent-free laminating machine is used for coating and laminating, and the coating and laminating speed is 150 m / min. The glue tank and transfer roller of the solvent-free laminating machine are preheated to 85°C.

[0098] The obtained high-barrier paper with heat-sealing properties includes paper, an adhesive layer, a vapor-deposited layer and a heat-sealable release layer arranged in sequence. The vapor-deposited layer is a silicon oxide barrier layer vapor-deposited on one side of the heat-sealable release layer. The vapor-deposited layer is compounded on one side of the paper through the adhesive layer. The heat-sealable release layer has heat-sealability and easy peelability.

[0099] The preparation method of the solvent-free moisture-curing transfer adhesive (used for coating an adhesive layer on one side of paper) used in the above step (3) comprises the following steps in sequence:

[0100] (1b) The following raw materials are prepared by weight: 520g of dimer acid polyester diol (52%), 92g of pentaerythritol polyoxypropylene tetraol (9.2%), 200g of polyneopentyl terephthalate diol (20%), 180g of diphenylmethane diisocyanate (18%), and 8g of bismorpholino diethyl ether (0.8%);

[0101] The dimer acid polyester diol is a dimer acid polyester diol polymerized from oleic acid and 1,6-hexanediol (e.g., Baiyuan BY3026, molecular weight 2500, hydroxyl value 39.4); pentaerythritol polyoxypropylene tetraol has a molecular weight of 856 (e.g., Yinuowei 380); and polyneopentyl terephthalate diol has a molecular weight of 2000 (e.g., Huiyuan Technology P320).

[0102] (2b) Add the dimer acid polyester diol, pentaerythritol polyoxypropylene tetraol and poly (neopentyl terephthalate) diol prepared in step (1b) into a reactor, and then heat the contents of the reactor to 115°C and place them under vacuum at -6×10 -4 MPa for 2 hours;

[0103] (3b) The contents of the reactor were cooled to 50°C, diphenylmethane diisocyanate was added, and the mixture was reacted at 80°C for 3 hours;

[0104] (4b) The contents of the reactor were cooled to 50°C, and then bismorpholinyl diethyl ether was added and stirred to obtain a solvent-free moisture-curing transfer adhesive, which was then sealed for later use.

[0105] Example 3: In this example, a method for preparing a solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing comprises the following steps:

[0106] (1a) Prepare component A

[0107] (1a-1) The following raw materials are prepared by weight: 200 g of isophorone diisocyanate (20%), 250 g of hexamethylene diisocyanate (25%), 250 g of 1,4-cyclohexane diisocyanate (25%), 20 g of cyclohexane dimethylene diisocyanate (2%), and 280 g of norbornane diisocyanate (28%);

[0108] (1a-2) isophorone diisocyanate, hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, cyclohexane dimethylene diisocyanate, and norbornane diisocyanate prepared in step (1a-1) are mixed uniformly to obtain component A, which is set aside;

[0109] (2a) Preparation of component B

[0110] (2a-1) The following raw materials are prepared by weight: 380 g (38%) of dimer acid polyester diol, 300 g (30%) of polyetheramine, 260 g (26%) of polyaspartic acid ester, 20 g (2%) of dihydroxy polydimethylsiloxane, and 40 g (4%) of silane coupling agent;

[0111] The dimer acid polyester diol is a dimer acid polyester diol obtained by polymerization of oleic acid and 1,6-hexanediol (e.g., Baiyuan BY3026, molecular weight 2500, hydroxyl value 39.4); the molecular weight of the polyetheramine is 400 (e.g., Huntsman T-403); the molecular weight of the polyaspartic acid ester is 590 (e.g., Feiyang New Materials F520); the molecular weight of the dihydroxy polydimethylsiloxane is about 1000 (e.g., Sihai's 209 hydroxy silicone oil); and the silane coupling agent is silane coupling agent KH-560.

[0112] (2a-2) uniformly mixing the dimer acid polyester diol, polyetheramine, polyaspartic acid ester, dihydroxy polydimethylsiloxane and silane coupling agent prepared in step (2a-1) to obtain component B, which is set aside;

[0113] (3a) Preparation of solvent-free polyurethane coatings

[0114] The ratio of component A to component B is determined according to the R value of 1.047 (the mass ratio of component A to component B is A:B=1:2.9), and component A and component B are mixed evenly to obtain the required solvent-free polyurethane coating.

[0115] In the above step (3a), component A and component B are preheated to 45°C before application, and are accurately measured (i.e., the ratio of component A to component B is determined according to an R value of 1.047, and component A and component B are measured and sent to a pipeline mixer), and then added to the glue tank of the solvent-free laminating machine using a pipeline mixer for coating by the solvent-free laminating machine.

[0116] The solvent-free polyurethane coating can be used to manufacture high-barrier paper with heat-sealing properties. The method for preparing the high-barrier paper with heat-sealing properties comprises the following steps:

[0117] (1) Making heat-sealable release film

[0118] The PET film without corona discharge is used as the carrier layer, and the polyurethane coating is coated on the carrier layer using solvent-free polyurethane coating (the coating amount of the polyurethane coating is 6g / m 2 After the polyurethane coating is applied, a covering film is laminated on the polyurethane coating (the covering film is an OPP film without corona treatment) to form a composite film, which is then rolled up. The composite film roll is then placed in an environment with a humidity of less than 40% and a temperature of 50°C for aging for 48 hours. After aging, the covering film is peeled off and recovered (the recovered covering film can be reused), thereby forming a heat-sealable release layer on the carrier layer that has heat-sealability and can be peeled off from the carrier layer.

[0119] In step (1), a solvent-free laminating machine is used in the coating and laminating process, and the coating and laminating speed is 200 m / min; the glue tank and transfer roller of the solvent-free laminating machine are preheated to 45°C;

[0120] The various operations of step (1) are performed in an environment where the air humidity is less than 40%;

[0121] (2) Making the vapor deposition layer

[0122] Vacuum evaporating a layer of silicon oxide on the heat-sealable release layer to form an evaporation layer (the thickness of the evaporation layer is 8 nm), namely, a silicon oxide barrier layer, to obtain a composite layer material;

[0123] (3) Making high barrier paper

[0124] Apply an adhesive layer on one side of the paper (the adhesive is the above-mentioned solvent-free moisture-curing transfer adhesive, and the solvent-free moisture-curing transfer adhesive is heated to 85°C when used; the coating amount of the adhesive layer is 3g / m 2 ), then compounding the composite layer material obtained in step (2) with paper, and bonding the vapor-deposited layer in the composite layer material to one side of the paper via the adhesive layer; then peeling off the supporting layer (i.e., separating the supporting layer from the heat-sealable release layer) to obtain the desired high-barrier paper with heat-sealability.

[0125] In step (3), the composite layer material is rolled up after being compounded with the paper, and then aged for 48 hours in an environment of 70% humidity and 40°C. After the ageing, the supporting layer is peeled off.

[0126] In step (3), a solvent-free laminating machine is used for coating and laminating, and the coating and laminating speed is 150 m / min. The glue tank and transfer roller of the solvent-free laminating machine are preheated to 85°C.

[0127] The obtained high-barrier paper with heat-sealing properties includes paper, an adhesive layer, a vapor-deposited layer and a heat-sealable release layer arranged in sequence. The vapor-deposited layer is a silicon oxide barrier layer vapor-deposited on one side of the heat-sealable release layer. The vapor-deposited layer is compounded on one side of the paper through the adhesive layer. The heat-sealable release layer has heat-sealability and easy peelability.

[0128] The preparation method of the solvent-free moisture-curing transfer adhesive (used for coating an adhesive layer on one side of paper) used in the above step (3) comprises the following steps in sequence:

[0129] (1b) The following raw materials are prepared by weight: 570 g of dimer acid polyester diol (57%), 126 g of pentaerythritol polyoxypropylene tetraol (12.6%), 100 g of polyneopentyl terephthalate diol (10%), 200 g of diphenylmethane diisocyanate (20%), and 4 g of bismorpholino diethyl ether (0.4%);

[0130] The dimer acid polyester diol is a dimer acid polyester diol polymerized from oleic acid and 1,6-hexanediol (e.g., Baiyuan BY3026, molecular weight 2500, hydroxyl value 39.4); pentaerythritol polyoxypropylene tetraol has a molecular weight of 856 (e.g., Yinuowei 380); and polyneopentyl terephthalate diol has a molecular weight of 2000 (e.g., Huiyuan Technology P320).

[0131] (2b) Add the dimer acid polyester diol, pentaerythritol polyoxypropylene tetraol and poly (neopentyl terephthalate glycol) diol prepared in step (1b) into a reactor, and then heat the contents of the reactor to 120°C and place under vacuum at -9×10 -4 MPa for 1.5 hours;

[0132] (3b) The contents of the reactor were cooled to 48°C, diphenylmethane diisocyanate was added, and the mixture was reacted at 85°C for 2.5 hours;

[0133] (4b) The contents of the reactor were cooled to 48°C, and then bismorpholinyl diethyl ether was added and stirred to obtain a solvent-free moisture-curing transfer adhesive, which was then sealed for later use.

[0134] Experimental example:

[0135] 1. After the high-barrier paper of Examples 1-3 was produced, samples were taken and the oxygen permeability was measured according to the national standard GB / T19789-2021 "Plastic Film and Sheeting for Packaging Materials - Oxygen Permeability Test by Coulometer Method", the water vapor permeability was measured according to the national standard GB / T26253-2010 "Plastic Film and Sheeting - Determination of Water Vapor Permeability - Infrared Detector Method", and the heat seal strength was measured according to the standard QB T2358-1998 "Test Method for Heat Seal Strength of Plastic Film Packaging Bags".

[0136] The test results of each sample are shown in Table 1 below.

[0137] Table 1:

[0138] project Example 1 Example 2 Example 3 Heat sealing strength N / 15mm 4.8 5.1 5.6 <![CDATA[Oxygen permeability (cm 3 / (m 2 ·24 h·0.1 MPa)]]> 1.12 0.71 0.52 <![CDATA[Water vapor transmission rate g / m 2 .d]]> 3.36 0.14 0.24

[0139] As shown in Table 1, the high-barrier papers of Examples 1-3 of the present invention exhibit excellent water and oxygen barrier properties, high barrier properties, and excellent heat sealing performance. Example 1 is vapor-deposited with aluminum oxide, while Examples 2 and 3 are vapor-deposited with silicon oxide. The silicon oxide barrier layer exhibits higher barrier properties than the aluminum oxide barrier layer.

[0140] 2. Comparison of heat seal strength

[0141] The heat sealing strength of PE coated paper (whose heat sealing layer is a PE film layer) and PLA coated paper (whose heat sealing layer is a PLA film layer) were tested. The test results are shown in Table 2 below.

[0142] Table 2:

[0143] project PE coated paper PLA coated paper Heat sealing strength N / 15mm 4.2 3.8

[0144] As can be seen from Table 2, the heat-sealable release layer in the high-barrier paper of Examples 1-3 has a heat-seal performance comparable to that of a plastic film.

[0145] 3. Peeling performance of heat-sealable release layer

[0146] In the production of high-barrier paper in Examples 1-3, after the aging in step (1) is completed, the sample is taken to peel off the covering film (OPP film without corona treatment), and the peel strength between the release layer and the OPP film is tested according to the national standard GB / T 2792-2014 "Test method for peel strength of adhesive tapes", and the coating transfer (release performance) is observed.

[0147] In the production of high-barrier paper in Examples 1-3, after the composite layer material and the paper are composited in step (3), they are rolled up and aged, and then a sample is taken to peel off the carrier layer (PET film without corona treatment). The peel strength between the release layer and the PET film is tested according to the national standard GB / T 2792-2014 "Test method for peel strength of adhesive tapes", and the coating transfer (release performance) is observed.

[0148] The test results are shown in Table 3 below.

[0149] Table 3:

[0150] project Example 1 Example 2 Example 3 OPP release performance OPP has no coating residue OPP has no coating residue OPP has no coating residue OPP peel strength N / 25mm 0.35 0.41 0.37 PET release performance PET has no coating residue PET has no coating residue PET has no coating residue PET peel strength N / 25mm 0.77 0.91 0.83

[0151] The above test results show that after the coating of the heat-sealable release layer coating of the present invention is cured, the peeling force of OPP is smaller than the peeling force of PET. It is relatively easy to peel and recover the OPP film first, and then peel and recover the PET carrier layer. The heat-sealable release layer has good release performance for OPP film and PET film, and no coating residue is left.

[0152] Comparative Example 1:

[0153] In the preparation method of the barrier paper of Comparative Example 1, the adhesive layer in step (3) uses a commercially available moisture-curing transfer adhesive (Xinyuan D5-1) instead of the solvent-free moisture-curing transfer adhesive in Example 1, and other technical features are the same as those in Example 1.

[0154] The barrier properties of the barrier paper obtained in Comparative Example 1 were tested, and the test results are shown in Table 4. The adhesive layer used a commercially available moisture-curing transfer adhesive (such as Xinyuan D5-1), and the resulting barrier paper also had high barrier properties, but its barrier properties were slightly lower than those of Example 1.

[0155] Table 4:

[0156] project Comparative Example 1 <![CDATA[Oxygen permeability (cm 3 / (m 2 ·24 h·0.1 MPa)]]> 1.30 <![CDATA[Water vapor transmission rate g / m 2 .d]]> 3.89

Claims

1. A solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing, comprising component A and component B, characterized in that: Component A is made of the following raw materials in the following weight ratios: 10-20% isophorone diisocyanate, 20-50% hexamethylene diisocyanate, 0.2-50% 1,4-cyclohexane diisocyanate, 0.2-40% cyclohexane dimethylene diisocyanate, and 0.2-30% norbornane diisocyanate; Component B is made of the following raw materials in the following weight ratios: dimer acid polyester diol 30-60%, polyether amine 15-30%, polyaspartic acid ester 15-30%, dihydroxy polydimethylsiloxane 1-5%, and silane coupling agent 1-5%; The ratio of component A to component B is determined according to an R value of 1.02-1.10, wherein the R value is the molar ratio of the total isocyanate groups of component A and component B to the total hydroxyl groups.

2. The solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing according to claim 1, characterized in that The component A is prepared from the following raw materials in the following weight ratios: 10-20% of isophorone diisocyanate, 20-50% of hexamethylene diisocyanate, 0.2-20% of 1,4-cyclohexane diisocyanate, 0.2-20% of cyclohexane dimethylene diisocyanate, and 0.2-20% of norbornane diisocyanate.

3. The solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing according to claim 1 or 2, characterized in that: The molecular weight of the dimer acid polyester diol is 2000-2500 and the hydroxyl value is 35-45.

4. The solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing according to claim 1 or 2, characterized in that: The molecular weight of the polyetheramine is 400-1000.

5. The solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing according to claim 1 or 2, characterized in that: The molecular weight of the polyaspartic acid ester is 400-600.

6. The solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing according to claim 1 or 2, characterized in that: The molecular weight of the dihydroxy polydimethylsiloxane is 500-2000.

7. The solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing according to claim 1 or 2, characterized in that: The silane coupling agent is silane coupling agent KH-560 or silane coupling agent KH-792.

8. The method for preparing a solvent-free polyurethane coating capable of forming a heat-sealable release layer after coating and curing according to claim 1, characterized in that The steps include: (1a) Prepare component A (1a-1) The following raw materials are prepared by weight: 10-20% isophorone diisocyanate, 20-50% hexamethylene diisocyanate, 0.2-50% 1,4-cyclohexane diisocyanate, 0.2-40% cyclohexane dimethylene diisocyanate, and 0.2-30% norbornane diisocyanate; (1a-2) isophorone diisocyanate, hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, cyclohexane dimethylene diisocyanate, and norbornane diisocyanate prepared in step (1a-1) are mixed uniformly to obtain component A, which is set aside; (2a) Preparation of component B (2a-1) The following raw materials are prepared by weight: 30-60% of dimer acid polyester diol, 15-30% of polyether amine, 15-30% of polyaspartic acid ester, 1-5% of dihydroxy polydimethylsiloxane, and 1-5% of silane coupling agent; (2a-2) uniformly mixing the dimer acid polyester diol, polyetheramine, polyaspartic acid ester, dihydroxy polydimethylsiloxane and silane coupling agent prepared in step (2a-1) to obtain component B, which is set aside; (3a) Preparation of solvent-free polyurethane coatings Determine the ratio of component A to component B according to the R value of 1.02-1.10, mix component A and component B evenly to obtain the required solvent-free polyurethane coating.