An adhesive composition for flexible packaging materials and a method for preparing the same

Abstract

The application provides a kind of adhesive composition for soft package material, the composition includes the prepolymer of urethane modified by functional group, crosslinking curing agent;The prepolymer of urethane modified by functional group includes the prepolymer of urethane modified by hydroxyl and the prepolymer of urethane modified by isocyanate group, and the mass ratio of the two is (1-2) :1;By optimizing the raw material composition and preparation process of the composition, the adhesive composition of the application has the characteristics of low solid and high viscosity, excellent bonding strength, leveling property and high humidity resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of adhesive manufacturing, C08G18 / 00, and in particular to an adhesive composition for soft packaging materials and a preparation method thereof. BACKGROUND

[0002] Acrylic adhesives, silicone adhesives, urethane adhesives, etc. have been widely used in industry. Acrylic adhesives have poor durability, and their glass strength is significantly reduced in a high-temperature and high-humidity environment for a long time. The components of silicone adhesives are volatile and have adverse effects on the base of packaging materials. Therefore, urethane adhesives have a high market share in the field of packaging materials. However, the current urethane adhesives still have problems such as long curing time, high viscosity, poor coating effect, low bonding strength, poor softness, and inability to be used for soft packaging materials.

[0003] Chinese Patent CN114585706A discloses a polyurethane adhesive for structures, which includes a polyisocyanate component and a polyol component. The polyisocyanate includes a urethane prepolymer having an isocyanate group at the molecular end and a derivative of xylylene diisocyanate. The combination of the above components can obtain an adhesive with high bonding strength. Chinese Patent CN105143388B discloses an ultraviolet-curable adhesive composition and an adhesive. The composition contains urethane (meth) acrylate, (meth) acrylate monomer, and photopolymerization initiator. The composition has high adhesion and resistance to wet heat yellowing. However, the above technologies do not solve the problems of long curing time, high viscosity, and poor coating effect of the adhesive, and the bonding strength needs to be improved. SUMMARY

[0004] To solve the above technical problems, the present application first provides an adhesive composition for soft packaging materials, which includes a prepolymer of urethane modified by a functional group and a cross-linking curing agent.

[0005] Further, the functional group includes at least one of a hydroxyl group, a carboxyl group, a mercapto group, an isocyanate group, and a cyano group.

[0006] Further, the prepolymer of urethane modified by the functional group includes a prepolymer of urethane modified by a hydroxyl group.

[0007] In the traditional adhesive technology, only the prepolymer of urethane modified by isocyanate group is used as the main bonding material. The viscosity of the adhesive prepared by this method is not enough, and other substances are often introduced to increase the solid content of the adhesive to more than 75%. However, the high solid content adhesive is not easy to be coated on the substrate because of its poor flowability, and it is easy to produce pitting during the coating process, resulting in low adhesive strength. On this basis, the present application uses the prepolymer of urethane modified by hydroxyl group and the prepolymer of urethane modified by isocyanate group. Both of them have a certain content of active hydrogen and isocyanate group. The active hydrogen at the end of the prepolymer of urethane modified by hydroxyl group and the isocyanate group at the end of the prepolymer of urethane modified by isocyanate group crosslink or polymerize, increasing the intermolecular interaction in the network structure of the adhesive composition. Through these intermolecular forces, the viscosity of the composition is improved. The prepared composition has high initial adhesion at low solid content (70%), and also has excellent flowability, no pitting phenomenon during the coating process, and finally the adhesive strength is more excellent.

[0008] Further, the prepolymer of urethane modified by hydroxyl group is polymerized from a compound containing active hydrogen group, at least one isocyanate or polyisocyanate.

[0009] Further, the compound containing active hydrogen group is selected from at least one of polyester polyol, polycarbonate polyol, polyolefin polyol, acrylic polyol, and polyether polyol.

[0010] Further, the polyester polyol includes but is not limited to at least one of polyethylene adipate glycol, polypropylene adipate glycol, polybutylene adipate glycol, polyhexamethylene adipate glycol, polyethylene adipate glycol, polyhexamethylene adipate glycol, and poly-2-methylpropylene adipate glycol.

[0011] Further, the polyolefin polyol includes but is not limited to at least one of polybutadiene alcohol, polyisoprene alcohol, hydroxyl-terminated epoxidized polybutadiene resin, hydroxyl-terminated polybutadiene-acrylonitrile, hydroxyl-terminated butadiene-styrene liquid rubber, and polystyrene polyol.

[0012] Further, the polyether polyol includes but is not limited to at least one of polyethylene glycol, polypropylene glycol, and polybutylene glycol.

[0013] Further, in the raw material for preparing the prepolymer of urethane modified by hydroxyl group, the molar ratio of active hydrogen group to isocyanate group is (1-2.5):1, preferably (1.3-2.2):1.

[0014] In a preferred embodiment, the molar ratio of active hydrogen groups to isocyanate groups in the raw materials for preparing the prepolymers of the hydroxyl-modified urethanes is (1.6-1.9): 1.

[0015] Further, the isocyanate-based substances include, but are not limited to, at least one of trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, propylene diisocyanate, triisocyanate octane, isophorone diisocyanate, cyclohexane diisocyanate, diphenyl diisocyanate, diphenylmethane diisocyanate, phenylene diisocyanate, toluene diisocyanate, triisocyanate benzene, triisocyanate toluene, triphenylmethane triisocyanate, diisocyanate dimethyl benzene, bis(isocyanate methyl) cyclohexane.

[0016] Further, the prepolymers of the hydroxyl-modified urethanes have a number average molecular weight of 1500-5000, preferably 2000-4000.

[0017] In a preferred embodiment, the prepolymers of the hydroxyl-modified urethanes have a number average molecular weight of 2300-2800.

[0018] Further, the prepolymers of the functional group-modified urethanes also include prepolymers of isocyanate group-modified urethanes.

[0019] Further, the prepolymers of the isocyanate group-modified urethanes have at least two isocyanate groups at the molecular chain ends.

[0020] Further, the prepolymers of the isocyanate group-modified urethanes are prepared by polymerization of a polyisocyanate and a polyol.

[0021] Further, the prepolymers of the isocyanate group-modified urethanes have a molar ratio of isocyanate groups to hydroxyl groups of (1.5-5.0): 1, preferably (1.7-3.0): 1, in the raw materials for preparing the prepolymers.

[0022] In a preferred embodiment, the prepolymers of the isocyanate group-modified urethanes have a molar ratio of isocyanate groups to hydroxyl groups of (1.8-2.5): 1, in the raw materials for preparing the prepolymers.

[0023] Further, the isocyanate groups are derived from at least one of xylylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, lysine diisocyanate, hexamethylene diisocyanate, methylcyclohexane diisocyanate, dicyclohexane methane diisocyanate, isophorone diisocyanate.

[0024] Further, the polyol includes, but is not limited to, at least one of ethylene glycol, propylene glycol, glycerol, dipropylene glycol, butylene glycol, pentylene glycol, isopentyl glycol, neopentyl glycol, hexylene glycol, heptylene glycol, hexamethyl glycol, sorbitol, hydrogenated bisphenol A, bisphenol A, dihydroxydiphenyl, and a polymer polyol of the above.

[0025] Further, a catalyst, a polymerization inhibitor, an anti-aging agent, and the like can be added during the preparation of the isocyanate-modified urethane prepolymer.

[0026] Further, the isocyanate-modified urethane prepolymer has an isocyanate group content of 25-40% and a viscosity of 400-5000 mpa·s at 25°C. The isocyanate-modified urethane prepolymer is prepared by the polymerization of a polyisocyanate and a polyol. The polyisocyanate provides crosslinking sites for the polymerization. An increase in the content of the polyisocyanate to a certain extent is beneficial to the adhesive strength of the adhesive composition. However, when the content of the polyisocyanate is too high, the content of the polyol is relatively low. In this case, the isocyanate-modified urethane prepolymer has a high content of hard segments and a low content of soft segments, and the flexibility of the prepolymer is reduced. After the prepolymer is reacted with the hydroxyl-modified urethane prepolymer, the crosslinking sites of the adhesive composition are further increased, and the intermolecular forces in the system are also increased. The cured composition has a high brittleness, and cracks are easily generated after the composition is coated on a soft substrate, cured, and bent.

[0027] Further, the isocyanate-modified urethane prepolymer has an isocyanate group content of 28-32% and a viscosity of 500-2500 mpa·s at 25°C.

[0028] Further, the mass ratio of the pre-polymer of hydroxyl-modified urethane and the pre-polymer of isocyanate-modified urethane in the adhesive composition is (0.3-6):1. The addition of the pre-polymer of hydroxyl-modified urethane in the present application not only increases the viscosity of the adhesive, but also accelerates the curing process of the adhesive composition, shortens the curing time, and makes the product available for use faster. However, the relative mass of the pre-polymer of hydroxyl-modified urethane and the pre-polymer of isocyanate-modified urethane needs to be strictly controlled in the present application, so that a specific reaction rate can be generated between the two with a specific content of active cyan and isocyanate, and between the two and a specific cross-linking curing agent, so that the copolymer formed after the reaction of the two has a uniform cross-linking network state, effectively alleviates the damage of external force to the structure, and makes the adhesive composition have excellent flexibility and bonding strength. When the amount of the pre-polymer of hydroxyl-modified urethane used is less than the specified range, the viscosity and bonding strength of the composition are not enough, and when it exceeds the specified value, the reaction rate of the two is too fast, the viscosity of the adhesive composition is too high, the leveling property is not good, and the brittleness after curing is large, which is not suitable for soft packaging materials. Controlling the content of the two within a specific range can also effectively avoid the hygroscopicity of the adhesive composition, and the prepared composition will not have a curing reaction after being placed in a high-humidity environment at 26-28°C for 12h.

[0029] Further, the mass ratio of the pre-polymer of hydroxyl-modified urethane and the pre-polymer of isocyanate-modified urethane in the adhesive composition is (0.5-3):1.

[0030] In a preferred embodiment, the mass ratio of the pre-polymer of hydroxyl-modified urethane and the pre-polymer of isocyanate-modified urethane is (1-2):1.

[0031] Further, the cross-linking curing agent is an isocyanate cross-linking curing agent, including but not limited to at least one of toluene diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate.

[0032] Preferably, the cross-linking curing agent is diphenylmethane diisocyanate.

[0033] Further, the addition amount of the cross-linking curing agent accounts for 2-8% of the total mass of the pre-polymer of urethane modified by a functional group, preferably 3-6%, and more preferably 4.9%.

[0034] Further, the adhesive composition further includes a solvent, including but not limited to at least one of ethyl acetate, dimethyl adipate, dioctyl adipate, polyethylene wax, butanone, toluene, dioctyl phthalate, diisodecyl phthalate, and tributyl phosphate.

[0035] Further, any one or a combination of anti-aging agents, flame retardants, antistatic agents, defoaming agents, leveling agents, antioxidants and other auxiliary agents can be added to the adhesive composition; the present application does not make strict limitations thereon, and the use thereof can be selected according to the needs.

[0036] Further, the solvent includes ethyl acetate.

[0037] Further, the viscosity of the adhesive composition is controlled by using the solvent; the use amount of the solvent is not strictly regulated by the present application, and can be adjusted according to the actual needs.

[0038] Preferably, the use amount of the solvent is to ensure that the viscosity of the adhesive composition is 4# cup, 8-30s; more preferably, 4# cup, 10-20s.

[0039] In a preferred embodiment, the viscosity of the adhesive composition is 4# cup, 11-14s.

[0040] Further, the solid content of the adhesive composition is 63-75%, preferably 68-72%.

[0041] Further, the preparation method of the adhesive composition is to first stir and mix the urethane prepolymer modified by the functional group and the solvent, and then stir and mix the cross-linking curing agent.

[0042] Further, the adhesive composition is used for bonding soft packaging materials.

[0043] Further, the curing temperature of the adhesive composition after bonding the product is 40-50℃, and the curing time is 18-25h.

[0044] Advantages

[0045] 1. The present application optimizes the isocyanate group content and viscosity of the urethane prepolymer modified by the isocyanate group, improves the flexibility of the adhesive composition, and makes it more suitable for bonding soft packaging materials;

[0046] 2. The present application uses the urethane prepolymer modified by the hydroxyl group and the urethane prepolymer modified by the isocyanate group in combination, so that the adhesive composition has the characteristics of high viscosity and low solid content, further improves the leveling property and bonding strength of the composition, and effectively avoids the generation of pitting during coating;

[0047] 3、The mass ratio of the pre-polymer of hydroxyl-modified urethane and the pre-polymer of isocyanate-modified urethane is preferably (0.5-3):1, which produces a specific reaction speed in the system, makes the adhesive composition have a uniform crosslinking network state, further improves its softness, effectively shortens the curing time of the adhesive composition, and improves the production efficiency of related products;

[0048] 4、The adhesive composition of the present application has ultra-low sensitivity to moisture in the air, and the prepared composition does not have a curing reaction even after being placed in a high-humidity environment at 26-28℃ for 12h, effectively improving the industrial production use time and operation convenience of the adhesive composition;

[0049] 5、The adhesive composition of the present application has high bonding strength, is not prone to delamination and peeling, and has high softness, and can be used for bonding the matrix of soft package materials. DETAILED DESCRIPTION

[0050] EMBODIMENT

[0051] EMBODIMENT 1

[0052] The present embodiment provides an adhesive composition for soft package materials, and the preparation raw materials of the composition include: a pre-polymer of hydroxyl-modified urethane (TAKELAC PP-9530), a pre-polymer of isocyanate-modified urethane (TAKENATE I-9300), diphenylmethane diisocyanate, and ethyl acetate.

[0053] The mass ratio of the pre-polymer of hydroxyl-modified urethane and the pre-polymer of isocyanate-modified urethane is 1:1

[0054] The addition amount of the diphenylmethane diisocyanate accounts for 4.9% of the total mass of the pre-polymer of hydroxyl-modified urethane and the pre-polymer of isocyanate-modified urethane;

[0055] The addition amount of the ethyl acetate is: the viscosity of the composition is 4# cup, 12s;

[0056] The preparation method of the adhesive composition is: first, stir and mix the pre-polymer of isocyanate-modified urethane and ethyl acetate, then add the pre-polymer of hydroxyl-modified urethane after stirring to no bubbles, and finally add the crosslinking curing agent and stir to mix.

[0057] EMBODIMENT 2

[0058] The present embodiment provides an adhesive composition for soft package materials, and the raw materials for preparing the composition include a hydroxyl-modified urethane prepolymer (TAKELAC PP-9530), an isocyanate group-modified urethane prepolymer (TAKENATE I-9300), diphenylmethane diisocyanate, and ethyl acetate;

[0059] The mass ratio of the hydroxyl-modified urethane prepolymer and the isocyanate group-modified urethane prepolymer is 0.5:1;

[0060] The added amount of the diphenylmethane diisocyanate accounts for 6% of the total mass of the hydroxyl-modified urethane prepolymer and the isocyanate group-modified urethane prepolymer;

[0061] The added amount of the ethyl acetate is consistent with the added mass in Example 1;

[0062] The preparation method of the adhesive composition is the same as that in Example 1.

[0063] Example 3

[0064] The present embodiment provides an adhesive composition for soft package materials, and the raw materials for preparing the composition include a hydroxyl-modified urethane prepolymer (TAKELAC PP-9530), an isocyanate group-modified urethane prepolymer (TAKENATE I-9300), diphenylmethane diisocyanate, and ethyl acetate;

[0065] The mass ratio of the hydroxyl-modified urethane prepolymer and the isocyanate group-modified urethane prepolymer is 3:1;

[0066] The added amount of the diphenylmethane diisocyanate accounts for 3% of the total mass of the hydroxyl-modified urethane prepolymer and the isocyanate group-modified urethane prepolymer;

[0067] The added amount of the ethyl acetate is consistent with the added mass in Example 1;

[0068] The preparation method of the adhesive composition is the same as that in Example 1.

[0069] Comparative Example 1

[0070] The present comparative example provides an adhesive composition for soft package materials, and the raw materials for preparing the composition include a hydroxyl-modified urethane prepolymer (Mitsui Chemical 7530), diphenylmethane diisocyanate, and ethyl acetate;

[0071] The added amount of the diphenylmethane diisocyanate accounts for 4.9% of the mass of the hydroxyl-modified urethane prepolymer.

[0072] The amount of ethyl acetate added is the same as that in Example 1.

[0073] The adhesive composition is prepared in the same manner as in Example 1.

[0074] Comparative Example 2

[0075] This comparative example provides an adhesive composition for a flexible packaging material, the raw materials for preparing the composition including: isocyanate group-modified urethane prepolymer (Mitsui Chemical 7300), diphenylmethane diisocyanate, and ethyl acetate.

[0076] The amount of diphenylmethane diisocyanate added is 4.9% of the mass of the isocyanate group-modified urethane prepolymer.

[0077] The amount of ethyl acetate added is the same as that in Example 1.

[0078] The adhesive composition is prepared in the same manner as in Example 1.

[0079] Comparative Example 3

[0080] The mass ratio of the hydroxyl group-modified urethane prepolymer and the isocyanate group-modified urethane prepolymer is 6:1, which is basically the same as in Example 1.

[0081] Comparative Example 4

[0082] The mass ratio of the hydroxyl group-modified urethane prepolymer and the isocyanate group-modified urethane prepolymer is 0.2:1, which is basically the same as in Example 1. The amount of ethyl acetate added is the same as that in Example 1.

[0083] Comparative Example 5

[0084] The diphenylmethane diisocyanate is replaced by hexamethylene diisocyanate, which is basically the same as in Example 1. The amount of ethyl acetate added is the same as that in Example 1.

[0085] Comparative Example 6

[0086] The adhesive composition is prepared by simultaneously adding the isocyanate group-modified urethane prepolymer and the hydroxyl group-modified urethane prepolymer into ethyl acetate and stirring to mix, and then adding a cross-linking curing agent and stirring to mix after the bubbles are removed, which is basically the same as in Example 1.

[0087] Note: The amount of ethyl acetate added in Comparative Examples 1-6 is the same as that in Example 1.

[0088] Peeling strength test: The compositions of the examples and the comparative examples were uniformly coated on the surface of an aluminum foil, the thickness of the dry adhesive was controlled to be 4 μm, the aluminum foil coated with the adhesive was compounded with a CPP by hot pressing at a temperature of 65°C, and the product was placed in an oven at 45°C for curing for 20 h. Then, the prepared product was cut into a sample with a width of 15 mm, and the sample was subjected to a peeling strength test according to the standard ASTM 254.

[0089] Performance test results:

[0090] The test results are shown in Table 1.

[0091] Table 1

[0092]

[0093]

[0094] Analysis of the above results:

[0095] The adhesive compositions prepared in Examples 1-3 have excellent bonding properties. In Comparative Examples 1-2, a urethane prepolymer modified with a functional group is used, and the adhesive compositions prepared have reduced initial adhesion and peeling strength, and also have a small viscosity. However, when the contents of both are too high in Comparative Examples 3-4, the adhesive properties of the compositions are also reduced. This is probably because only when the specific reaction rates between the two active cyan and isocyanate groups and the specific crosslinking curing agent are present, the formed composition has a uniform crosslinking network state, and effectively buffers external forces. In Comparative Example 5, an isocyanate with a short-chain alkane group is used, and the intermolecular crosslinking strength and relative activity of the composition are increased. Although the viscosity of the composition is reduced, the internal peeling strength is weakened. In the preparation method of Comparative Example 6, the urethane prepolymer modified with a hydroxyl group and the urethane prepolymer modified with an isocyanate group are mixed at the same time. When the mixture is not uniform, the two react at a local position at a higher temperature in the stirrer, which affects the uniform reaction rate in the composition, resulting in a slight decrease in the peeling strength.

Claims

1. An adhesive composition for flexible packaging materials, characterized by, The raw materials for preparing the adhesive composition include: a hydroxyl-modified urethane prepolymer, an isocyanate-modified urethane prepolymer, diphenylmethane diisocyanate and ethyl acetate; The hydroxyl-modified urethane prepolymer is TAKELAC PP-9530; The isocyanate-modified urethane prepolymer is TAKENATE I-9300; The mass ratio of the hydroxyl-modified urethane prepolymer and the isocyanate-modified urethane prepolymer is 1:1; The addition amount of the diphenylmethane diisocyanate accounts for 4.9% of the total mass of the hydroxyl-modified urethane prepolymer and the isocyanate-modified urethane prepolymer; The addition amount of the ethyl acetate is such that the viscosity of the adhesive composition is 4# cup, 12s; The preparation method of the adhesive composition is as follows: firstly, the isocyanate-modified urethane prepolymer and the ethyl acetate are stirred and mixed, then the hydroxyl-modified urethane prepolymer is added and stirred after the bubbles are removed, and finally the cross-linking curing agent is added and stirred.

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