Solvent type medium-resistant functional polyurethane curing agent and preparation method thereof

Abstract

The invention discloses a solvent type medium-resistant functional polyurethane curing agent and a preparation method thereof, and belongs to the field of polyurethane adhesives for composite flexible packages. The polyurethane curing agent is obtained by modifying a polyurethane prepolymer with dianhydride at a high temperature. The preparation method comprises the following steps: adding dianhydride and a polyurethane prepolymer into a reaction kettle, heating to 150 DEG C, adding a catalyst, reacting for 5 hours, cooling to 50 DEG C, and adding ethyl acetate to obtain the polyurethane curing agent. The curing agent is matched with a conventional polyurethane main agent for use, and can resist strong acid, chemicals and other caustic contents.

Description

Technical Field

[0001] This invention relates to the field of polyurethane adhesives for composite flexible packaging, and more particularly to a method for preparing a solvent-based, media-resistant functional polyurethane curing agent. Background Technology

[0002] Around the 1990s, the domestic demand for printed materials increased rapidly. Lamination, as an important process for improving the abrasion resistance, gloss, and water resistance of printed materials, also saw a surge in demand, driving the development of laminating adhesives. At that time, laminating adhesives were mainly oil-based, using toluene and xylene as solvents. Two-component polyurethane laminating adhesives, due to their strong adhesion and excellent low-temperature resistance, were widely used in bonding various materials such as plastics, films, metals, and wood. For example, in the food packaging, printing, plastic color printing, and bookbinding industries, two-component polyurethane laminating adhesives can give laminated products high transparency, strong initial tack, firm adhesion, good aging resistance, and excellent water resistance, meeting the performance requirements of different industries.

[0003] Domestically and internationally, the main categories are food packaging, pharmaceutical packaging, and chemical packaging. In food packaging, stricter food safety requirements have driven the application of media-resistant adhesives in high-temperature sterilization and oil-resistant packaging, such as for juice and condiment packaging. In pharmaceutical packaging, stringent safety standards require packaging materials to be resistant to chemical corrosion, primarily used for packaging some traditional Chinese medicines and pharmaceutical granules. In the chemical industry, chemical product packaging requires corrosion and solvent resistance, leading to its widespread use in sealant packaging and pesticide packaging. Currently, the curing agent in two-component polyurethane adhesives used for composite flexible packaging is typically L75 type curing agent, which is a TDI chain extender TMP with a high degree of crosslinking, but its media resistance is insufficient, making it difficult to meet the requirements of composite flexible packaging resistant to harsh media such as acids and chemicals.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a solvent-based, media-resistant functional polyurethane curing agent, which can improve the performance of polyurethane adhesives using this curing agent in resisting harsh media such as acids and chemicals, thereby solving the above-mentioned technical problems existing in the prior art.

[0006] The objective of this invention is achieved through the following technical solution: A solvent-based, media-resistant functional polyurethane curing agent, wherein the polyurethane curing agent is obtained by modifying a polyurethane prepolymer at high temperature with dianhydride.

[0007] A method for preparing the solvent-based, media-resistant functional polyurethane curing agent of the present invention, characterized in that it comprises: Dihydride and polyurethane prepolymer are added to a reactor, heated to 150°C, and then a catalyst is added and reacted for 5 hours. The temperature is then lowered to 50°C and ethyl acetate is added to obtain the polyurethane curing agent.

[0008] Compared with the prior art, the solvent-based media-resistant functional polyurethane curing agent and its preparation method provided by the present invention have the following beneficial effects: Modifying polyurethane prepolymers with dianhydrides at high temperatures can accelerate the reaction between dianhydrides and urethane bonds in the prepolymer to generate urethane and polyimide. Urea-formaldehyde has high strength, which can improve the weather resistance and density of the film, while polyimide can improve the film's resistance to high and low temperatures, high strength, and chemical corrosion resistance. Incorporating these two substances into polyurethane films can enhance the polyurethane packaging adhesive's resistance to acids and chemicals. Detailed Implementation

[0009] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the specific content of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments, which do not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0010] First, the following explanations are provided for the terms that may be used in this article: The term "and / or" means that either or both can be achieved simultaneously. For example, X and / or Y means that it includes both "X" or "Y" as well as the three cases of "X and Y".

[0011] The terms "comprising," "including," "containing," "having," or other similar semantic descriptions should be interpreted as non-exclusive inclusion. For example, including a technical feature element (such as raw material, component, ingredient, carrier, dosage form, material, size, part, component, mechanism, device, step, process, method, reaction conditions, processing conditions, parameter, algorithm, signal, data, product or article of manufacture, etc.) should be interpreted as including not only the expressly listed technical feature element, but also other technical feature elements that are not expressly listed and are well-known in the art.

[0012] The term "composed of" excludes any technical features not expressly listed. When used in a claim, it closes the claim to exclude all technical features other than those expressly listed, except for associated conventional impurities. If the term appears only in a clause of a claim, it limits the claim to the elements expressly listed in that clause; elements recited in other clauses are not excluded from the overall claim.

[0013] The term "parts by mass" indicates the mass ratio between multiple components. For example, if component X is described as x parts by mass and component Y as y parts by mass, then the mass ratio of component X to component Y is x:y. One part by mass can represent any mass; for example, one part by mass can be expressed as 1 kg or 3.1415926 kg, etc. The sum of the parts by mass of all components is not necessarily 100 parts; it can be greater than 100 parts, less than 100 parts, or equal to 100 parts. Unless otherwise stated, parts, proportions, and percentages mentioned herein are all measured by mass.

[0014] When concentration, temperature, pressure, size, or other parameters are expressed as numerical ranges, such ranges should be understood to specifically disclose all ranges formed by any pairing of upper limits, lower limits, or preferred values ​​within that range, regardless of whether the range is explicitly stated; for example, if the numerical range "2 to 8" is stated, then that range should be interpreted to include ranges such as "2 to 7", "2 to 6", "5 to 7", "3 to 4 and 6 to 7", "3 to 5 and 7", "2 and 5 to 7", etc. Unless otherwise stated, the numerical ranges described herein include both their endpoints and all integers and fractions within that range.

[0015] The solution provided by this invention will be described in detail below. Contents not described in detail in the embodiments of this invention are prior art known to those skilled in the art. Where specific conditions are not specified in the embodiments of this invention, they shall be performed according to conventional conditions in the art or conditions recommended by the manufacturer. Reagents or instruments used in the embodiments of this invention whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0016] This invention provides a solvent-based, media-resistant functional polyurethane curing agent, which is a polyurethane curing agent obtained by modifying a polyurethane prepolymer at high temperature with dianhydride.

[0017] Preferably, in the above-mentioned curing agent, the polyurethane curing agent is prepared by reacting 5 parts by weight of dianhydride and 55 parts by weight of polyurethane prepolymer in a reactor at 150°C with a catalyst for 5 hours, then cooling to 50°C and adding 40 parts by weight of solvent, resulting in a polyurethane curing agent with a solid content of 60% and an NCO value of 5-10.

[0018] Preferably, in the above-mentioned curing agent, the dianhydride is one or more of bisphenol A type diether dianhydride, hexafluorodianhydride, 1,4,5,8-naphthalenetetracarboxylic anhydride, 3,3′,4,4′-benzophenonetetracarboxylic anhydride, and 2,3,3',4'-biphenyltetracarboxylic anhydride. Using fluorinated dianhydrides or alicyclic dianhydrides can improve the transparency of the adhesive. Because conventional polyimides are yellowish, the curing agent adhesive will also have a yellowish color. However, dianhydrides with strongly electronegative groups can reduce the packing of polyimide molecular chains, increase the free volume between chains, thereby reducing intramolecular charge transfer interactions and improving transparency. Furthermore, dianhydrides with alicyclic structures can disrupt the conjugated structure on aromatic polyimide segments, reduce intermolecular forces, thereby reducing the formation of charge transfer complexes, which can also improve the transparency of polyimides, ultimately increasing the transparency of the curing agent adhesive.

[0019] Preferably, in the above-mentioned curing agent, the polyurethane prepolymer is an isocyanate-terminated polyurethane prepolymer obtained by reacting a polyhydroxy resin with a diisocyanate at a molar ratio of 8 to 12:1, where the total NCO groups in the diisocyanate are equal to the total hydroxyl groups in the polyhydroxy resin. This polyurethane prepolymer, by introducing a greater number of trifunctional small-molecule alcohols into the polyester polyol used in the polyhydroxy resin, can increase the crosslinking degree of the polyester polyol, resulting in a prepolymer with more hard segments. This leads to a harder film obtained after reacting with the main agent, making it more difficult for caustic substances to precipitate.

[0020] Preferably, in the above-mentioned curing agent, the polyhydroxy resin used in the polyurethane prepolymer is: One or more of polyester polyols, polycaprolactone, acrylates, and polycarbonates. The polyester polyol used in the polyhydroxy resin can be prepared by a condensation polymerization method commonly used in the art. The small molecule dicarboxylic acid required for the polyester polyol is one or more of adipic acid, terephthalic acid, or isophthalic acid. The small molecule diol contains a diol or triol, wherein the small molecule diol is one or more of diethylene glycol, methyl propylene glycol, and dipropylene glycol; and the triol is one or more of glycerol and 1,2,6-hexanetriol.

[0021] Preferably, in the above-mentioned curing agent, the average molecular weight of the polyhydroxy resin is 500-2000, and the average functionality is 2-3.

[0022] Preferably, in the above-mentioned curing agent, the diisocyanate used in the polyurethane prepolymer is: One or more of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

[0023] Preferably, in the above-mentioned curing agent, the catalyst is an organotin catalyst or an amine catalyst; The solvent is one or more of ethyl acetate, butyl acetate, methyl acetate, and toluene.

[0024] Preferably, in the above-mentioned curing agent, the molecular weight of the polyurethane prepolymer is 2000 to 4000.

[0025] This invention also provides a method for preparing the above-mentioned solvent-based, media-resistant functional polyurethane curing agent, comprising: Dihydride and polyurethane prepolymer are added to a reactor, heated to 150°C, and a catalyst is added to react for 5 hours. Then the temperature is lowered to 50°C and a solvent is added to obtain the polyurethane curing agent.

[0026] Specifically, in the above method, the amount of dianhydride added is 5 parts by weight, the amount of polyurethane prepolymer added is 55 parts by weight, the amount of solvent added is 40 parts by weight, and the solid content of the obtained polyurethane curing agent is 60%, and the NCO value is 5 to 10.

[0027] Preferably, in the above method, the polyurethane prepolymer is prepared in the following manner: Preparation of polyester polyol: 2 parts by weight of adipic acid, 2 parts by weight of isophthalic acid, 3 parts by weight of neopentyl glycol, 2 parts by weight of glycerol, 500 ppm of antioxidant triphenyl phosphite and 50 ppm of catalyst tetrabutyl titanate are added to a polyester reactor. After condensation polymerization, a polyester polyol with a hydroxyl value of 56-224 mgKOH / g and a molecular weight of 500-2000 is obtained. Preparation of polyurethane prepolymer: 1 part by weight of the polyester polyol prepared above was added to a four-necked flask, followed by 10 parts by weight of toluene diisocyanate in a flask. The mixture was heated to 80°C and stirred for 3 hours, then cooled to below 50°C to obtain the polyurethane prepolymer.

[0028] The above-mentioned polyurethane curing agent can be prepared as follows: one or more of bisphenol A type diether dianhydride, hexafluorodianhydride, 1,4,5,8-naphthalenetetracarboxylic anhydride, 3,3′,4,4′-benzophenonetetracarboxylic anhydride, and 2,3,3',4'-biphenyltetracarboxylic anhydride are added to a reaction vessel at a mass ratio of 5% and a prepolymer mass percentage of 55%. After heating to 150°C, an organotin or amine catalyst is added for catalysis. After reacting for 5 hours, the temperature is lowered, and 40% solvent is added to obtain the curing agent of the present invention.

[0029] In summary, the solvent-based, media-resistant functional polyurethane curing agent of this invention modifies the polyurethane prepolymer with dianhydride. The addition of an organotin or amine catalyst during the high-temperature reaction accelerates the reaction between the dianhydride and urethane bonds to generate urethane and polyimide. Urea-formaldehyde has high strength, which can improve the weather resistance and density of the film, while polyimide can improve the film's resistance to high and low temperatures, high strength, and chemical corrosion resistance. The use of these two substances in polyurethane films can enhance the polyurethane packaging adhesive's resistance to acids and chemicals.

[0030] To more clearly demonstrate the technical solution and its effects provided by the present invention, the following detailed description of the solution provided by the embodiments of the present invention is provided with reference to specific examples.

[0031] Example 1 This embodiment provides a solvent-based, media-resistant functional polyurethane curing agent, the preparation method of which is as follows (the amounts of each raw material are parts by weight): Polyester polyols required for prepolymer preparation: 2 parts adipic acid, 2 parts isophthalic acid, 3 parts neopentyl glycol, 2 parts glycerol, 500 ppm triphenyl phosphite (antioxidant) and 50 ppm tetrabutyl titanate (catalyst) are added to a polyester reactor. After condensation polymerization, polyester polyols with hydroxyl values ​​of 56-224 mgKOH / g and molecular weights of 500-2000 are obtained.

[0032] Preparation of polyurethane prepolymer: 1 part of the polyester polyol prepared above was added to a four-necked flask, followed by 10 parts of toluene diisocyanate in a flask. The mixture was heated to 80°C and stirred for 3 hours, then cooled to below 50°C to obtain the polyurethane prepolymer.

[0033] Preparation of curing agent: 5 parts of hexafluorodianhydride and 55 parts of the above polyurethane prepolymer were added to the reactor, heated to 150°C, and stannous octoate was added and reacted for 5 hours. Then the temperature was lowered to 50°C and 40 parts of ethyl acetate were added.

[0034] Example 2 This embodiment provides a solvent-based, media-resistant functional polyurethane curing agent, the preparation method of which is as follows (the amounts of each raw material are parts by weight): The polyester polyol required for preparing the prepolymer is the same as in Example 1.

[0035] Preparation of polyurethane prepolymer: 1 part of the polyester polyol prepared above was added to a four-necked flask, and then 12 parts of diphenylmethane diisocyanate were added to a flask. The mixture was heated to 80°C and stirred for 3 hours, and then cooled to below 50°C to obtain the polyurethane prepolymer.

[0036] Preparation of curing agent: 5 parts of hexafluorodianhydride and 55 parts of the above prepolymer were added to the reactor, heated to 150°C, and stannous octoate was added and reacted for 5 hours. Then the temperature was lowered to 50°C and 40 parts of ethyl acetate were added.

[0037] Example 3 This embodiment provides a solvent-based, media-resistant functional polyurethane curing agent, the preparation method of which is as follows (the amounts of each raw material are parts by weight): The polyester polyol required for preparing the prepolymer is the same as in Example 1.

[0038] Preparation of polyurethane prepolymer: Same as in Example 2.

[0039] Preparation of curing agent: 5 parts of bisphenol A type diether dianhydride and 55 parts of the above polyurethane prepolymer were added to a reaction vessel, heated to 150°C, and then dibutyltin dilaurate was added and reacted for 5 hours. Then the temperature was lowered to 50°C and 40 parts of ethyl acetate were added.

[0040] Comparative Example 1 This comparative example provides a polyurethane curing agent, the preparation method of which is as follows (the amounts of each raw material are parts by weight): Preparation of prepolymer: Add 1 part of polyether polyol with a molecular weight of 500-2000 to a four-necked flask, then add 10 parts of toluene diisocyanate to a flask, heat to 80℃ and stir for 3 hours, then cool to below 50℃ to obtain the prepolymer.

[0041] Preparation of curing agent: 5 parts of hexafluorodianhydride and 55 parts of the above prepolymer were added to the reactor, heated to 150°C, and stannous octoate was added and reacted for 5 hours. Then the temperature was lowered to 50°C and 40 parts of ethyl acetate were added.

[0042] Comparative Example 2 This comparative example provides a polyurethane curing agent, the preparation method of which is as follows (the amounts of each raw material are parts by weight): The polyester polyol required for preparing the prepolymer is the same as in Example 1.

[0043] Preparation of prepolymer: Same as in Example 1.

[0044] Preparation of curing agent: 5 parts of hexafluorodianhydride and 55 parts of the above prepolymer were added to the reactor, heated to 80°C, and then stannous octoate was added and reacted for 5 hours. Then the temperature was lowered to 50°C and 40 parts of ethyl acetate were added.

[0045] It is understood that the above comparative examples 1 and 2 are designed to compare and demonstrate the influence of certain raw materials of the curing agent in the embodiments of the present invention on the performance, and they do not belong to the prior art.

[0046] Comparative Example 3 The commonly used TDI-TMP type curing agent L75 has a solid content of 75%.

[0047] The curing agents from Examples 1-3 and Comparative Examples 1-3 were mixed with commercially available aluminum foil boiling-type adhesives at the same R value (i.e., the ratio of the amount of isocyanate group in the curing agent to the amount of hydroxyl group in the adhesive) to form a common PET / Al / PE structure in the art, with an adhesive application amount of 3-3.5 g / m³. 2 After curing at 45℃ for 48 hours, the composite film was made into bags, filled with different caustic contents, and the prepared samples were placed in a 50℃ oven for aging. The peel strength of the inner Al / PE structure was tested before aging, after 3 days of aging, and after 7 days of aging, according to the BB / T0039-2013 standard for retail packaging bags.

[0048] Table 1 shows the performance of Examples 1-3 and Comparative Examples 1-3 (tested with acetic acid of a certain concentration):

[0049] Table 2 shows the performance of Examples 1-3 and Comparative Examples 1-3 (with pesticide filling) in the test:

[0050] Table 3 shows the performance of Examples 1-3 and Comparative Examples 1-3 (tested with composite solvent):

[0051] Appearance after aging: This indicates the appearance of the bag after aging. ○ indicates a good appearance, △ indicates a slightly better appearance with a few pinholes, and × indicates a poor appearance.

[0052] Table 1-3 shows that in Examples 1-3, the solvent-based media-resistant functional polyurethane curing agent of the present invention was combined with commonly used main agents on the market to form a commonly used PET / Al / PE composite. After curing, different caustic contents (a certain concentration of acetic acid, pesticides, and composite solvents) were added for aging tests. After 7 days of aging, there was no significant change in appearance.

[0053] Compared to Example 2, the adhesive in Example 3 is darker in color because the dianhydride used does not contain fluorine or ester ring structures, resulting in a darker polyimide and thus a darker adhesive. Comparative Example 1 used a polyether polyol, which has poorer crosslinking than polyester polyols, resulting in lower peel strength when used as a curing agent. Comparative Example 2 used a lower temperature during curing agent synthesis than Example 1, failing to form urea-formaldehyde bonds, thus exhibiting poor performance after aging and failing to effectively prevent the penetration of caustic substances. Comparative Example 3 used a commercially available TDI-TMP type curing agent, which delaminated after only one day of aging in this experiment, demonstrating extremely poor resistance to the medium.

[0054] Examples 1-3 and Comparative Examples 1-3 demonstrate that, in response to the problem of poor resistance to harsh media in commercially available packaging films, the solvent-based media-resistant functional polyurethane curing agent provided by this invention, when used in combination with commonly used packaging adhesive main agents, can significantly improve the media resistance of polyurethane adhesives and expand the application range of polyurethane packaging adhesives.

[0055] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

Claims

1. A solvent-based, media-resistant functional polyurethane curing agent, characterized in that, This polyurethane curing agent is obtained by modifying polyurethane prepolymer with dianhydride at high temperature.

2. The solvent-based, media-resistant functional polyurethane curing agent according to claim 1, characterized in that, The polyurethane curing agent is prepared by reacting 5 parts by weight of dianhydride and 55 parts by weight of polyurethane prepolymer in a reactor at 150°C with a catalyst for 5 hours, followed by cooling to 50°C and adding 40 parts by weight of solvent, resulting in a polyurethane curing agent with a solid content of 60% and an NCO value of 5-10.

3. The solvent-based media-resistant functional polyurethane curing agent according to claim 1 or 2, characterized in that, The dianhydride is one or more of bisphenol A type diether dianhydride, hexafluoro dianhydride, 1,4,5,8-naphthalenetetracarboxylic anhydride, 3,3′,4,4′-benzophenonetetracarboxylic anhydride, and 2,3,3',4'-biphenyltetracarboxylic anhydride.

4. The solvent-based media-resistant functional polyurethane curing agent according to claim 1 or 2, characterized in that, The polyurethane prepolymer is an isocyanate-terminated polyurethane prepolymer obtained by reacting a polyhydroxy resin with a diisocyanate in a molar ratio of 8 to 12:1, where the total NCO groups in the diisocyanate and the total hydroxyl groups in the polyhydroxy resin are present.

5. The solvent-based, media-resistant functional polyurethane curing agent according to claim 4, characterized in that, The polyhydroxy resin used in the polyurethane prepolymer is: One or more of polyester polyols, polycaprolactone, acrylates, and polycarbonates.

6. The solvent-based, media-resistant functional polyurethane curing agent according to claim 5, characterized in that, The average molecular weight of the polyhydroxy resin is 500-2000, and the average functionality is 2-3.

7. The solvent-based, media-resistant functional polyurethane curing agent according to claim 4, characterized in that, The diisocyanate used in the polyurethane prepolymer is: One or more of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

8. The solvent-based, media-resistant functional polyurethane curing agent according to claim 2, characterized in that, The catalyst is an organotin catalyst or an amine catalyst; The solvent is one or more of ethyl acetate, butyl acetate, methyl acetate, and toluene.

9. A method for preparing the solvent-based media-resistant functional polyurethane curing agent according to any one of claims 1-8, characterized in that, include: Dihydride and polyurethane prepolymer are added to a reactor, heated to 150°C, and then a catalyst is added and reacted for 5 hours. The temperature is then lowered to 50°C and ethyl acetate is added to obtain the polyurethane curing agent.

10. The method for preparing the solvent-based media-resistant functional polyurethane curing agent according to claim 9, characterized in that, The polyurethane prepolymer is prepared in the following manner, including: Preparation of polyester polyol: 2 parts by weight of adipic acid, 2 parts by weight of isophthalic acid, 3 parts by weight of neopentyl glycol, 2 parts by weight of glycerol, 500 ppm of antioxidant triphenyl phosphite and 50 ppm of catalyst tetrabutyl titanate are added to a polyester reactor. After condensation polymerization, a polyester polyol with a hydroxyl value of 56-224 mgKOH / g and a molecular weight of 500-2000 is obtained. Preparation of polyurethane prepolymer: 1 part by weight of the polyester polyol prepared above was added to a four-necked flask, followed by 10 parts by weight of toluene diisocyanate in a flask. The mixture was heated to 80°C and stirred for 3 hours, then cooled to below 50°C to obtain the polyurethane prepolymer.

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