Reflective leather polyurethane adhesive and preparation method thereof

Abstract

The application discloses a polyurethane adhesive for reflective leather, characterized in that the adhesive comprises component A and component B, wherein the component A comprises the following components in parts by weight: 35-45 parts of high-molecular-weight polyester; 5-10 parts of epoxy resin; 0.5-1 part of coupling agent; 0.01-0.05 part of catalyst; and 30-40 parts of organic solvent; the component B is any one or more of isocyanate adducts or isocyanate trimers; the high-molecular-weight polyester is obtained by catalytic polymerization of a polybasic acid component and a polyhydric alcohol component, has a number-average molecular weight of 10000-40000 and a glass transition temperature of less than 10 DEG C; and the weight ratio of the component A to the component B is 100:2-100:6. The polyurethane adhesive is prepared by using high-molecular-weight polyester as a base resin and compounding epoxy resin and a coupling agent, and has excellent yellowing resistance, high tensile strength and excellent elongation at break, and the reflective leather prepared from the adhesive has the characteristics of resisting 25 times of alkali water washing and rubbing.

Description

Technical Field

[0001] This invention relates to the field of polyurethane adhesives for reflective leather, and specifically to a polyurethane adhesive for reflective leather and its preparation method. Background Technology

[0002] Reflective materials are widely used as safety protection materials in transportation, personal protective equipment, footwear, and apparel. With the continuous development and progress of society and science and technology, the application of reflective materials in footwear and apparel is increasing, combining safety protection and decorative functions. Reflective leather is one of the most widely used types. The leather surface and reflective layer of PU leather require a high-performance adhesive layer to bond them together. If the adhesive performance is insufficient, problems such as delamination after washing, poor brightness after washing, and severe shedding during rubbing will occur.

[0003] Acrylic adhesives are widely used in high-brightness reflective fabrics due to their excellent performance and price advantage. Acrylic adhesives should be preferred as the bonding material for reflective leather (e.g., CN103881630A). Although the washing brightness meets the product performance requirements, it often has problems such as water washing delamination and poor abrasion resistance.

[0004] To address the aforementioned shortcomings, polyurethane adhesives, another widely used type of reflective material, should be an important research direction. Most commercially available polyurethane adhesive systems for reflective materials use diphenylmethane-4,4-diisocyanate (MDI) prepolymer polyols to synthesize adhesives (e.g., CN201510357292), but their bonding effect on glass microspheres and substrates is not good. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the purpose of this invention is to provide a polyurethane adhesive for reflective leather and its preparation method.

[0006] To achieve the objectives of this invention, the technical solution adopted is as follows:

[0007] A polyurethane adhesive for reflective leather, comprising component A and component B, wherein component A, by weight, comprises the following components:

[0008] 35-45 parts of high molecular weight polyester;

[0009] 5-10 parts epoxy resin;

[0010] 0.5-1 part coupling agent;

[0011] Catalyst 0.01-0.05 parts;

[0012] 30-40 parts organic solvent;

[0013] Component B is any one or more of isocyanate adducts or isocyanate trimers;

[0014] The high molecular weight polyester is formed by catalytic polymerization of polyacid components and polyol components, and the number average molecular weight of the high molecular weight polyester is 10,000-40,000, and the glass transition temperature is less than 10°C.

[0015] The weight ratio of component A to component B is 100:2-100:6.

[0016] The preferred molecular weight is 20,000-40,000 and the glass transition temperature is less than 0℃.

[0017] The catalytic polymerization specifically refers to:

[0018] In a reaction vessel, polyacid and polyol components are added and esterified at 140℃-240℃ under the catalysis of an organotitanium catalyst. Then, polycondensation is carried out at 240℃-250℃ until the acid value is less than 1, the number average molecular weight reaches 10,000-40,000, the acid value is <1, and the hydroxyl value is 2-4. The reaction is then stopped and the vessel is cooled down.

[0019] The amount of the organic titanium catalyst added is 0.01-0.05 parts. The organic titanium catalyst is tetrabutyl titanate.

[0020] The polybasic acid component is any one or more of terephthalic acid, isophthalic acid, phthalic anhydride, 1,4-cyclohexanediol (CHDA), hexahydrophthalic anhydride, adipic acid, succinic acid, sebacic acid, or dodecanoic acid.

[0021] Preferably, it is one or more of terephthalic acid, isophthalic acid, phthalic anhydride, adipic acid, sebacic acid or dodecanoic acid;

[0022] The preferred choice is any one or more of terephthalic acid, isophthalic acid, and sebacic acid;

[0023] The structural units of terephthalic acid or isophthalic acid account for 30-55% of the weight of the high molecular weight polyester.

[0024] The polyol component is any one or more of ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, dipropylene glycol, 1,4-butanediol, methylpropylene glycol, neopentyl glycol, 1,6-hexanediol, 1,4-cyclohexanediol (CHDM), ethyl butyl propylene glycol, hydrogenated bisphenol A, trimethylpentanediol, trimethylolpropane, polypropylene glycol, polytetrahydrofuran diol, or polycarbonate polyol.

[0025] Preferred ingredients include polypropylene glycol with a molecular weight of 200-400, polytetrahydrofuran diol with a molecular weight of 500-1000, polycarbonate polyol with a molecular weight of 500-1000, ethylene glycol, 1,4-butanediol, 1,6-hexanediol, or neopentyl glycol.

[0026] The preferred materials are ethylene glycol, 1,4-butanediol, 1,6-hexanediol, or any one or more polycarbonate polyols with a molecular weight of 500-1000.

[0027] The epoxy resin is any one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, alicyclic epoxy resin, and phenolic epoxy resin.

[0028] Bisphenol A type epoxy resin with an epoxy equivalent of 220-600 is preferred.

[0029] The preferred options are semi-solid bisphenol A epoxy resin (olin DER337) and solid epoxy resin (olin D.E.R671).

[0030] The coupling agent is a silane coupling agent.

[0031] The silane coupling agent is an epoxy silane coupling agent, an amino silane coupling agent, or an isocyanate silane coupling agent. Epoxy silane coupling agents are preferred, and γ-glycidoxypropyltrimethoxysilane coupling agents are more preferred.

[0032] The catalyst is an organobismuth or an organozinc.

[0033] DY-20 (Deyin Chemical), BiCAT®8108, and BiCAT®Z are preferred.

[0034] Component B is preferably an aliphatic isocyanate trimer or an aromatic isocyanate adduct.

[0035] The aliphatic isocyanate trimers are Covestro Desmodur N3300, Desmodur N3390, and Wanhua Chemical HT-100.

[0036] The aliphatic isocyanate adducts are Wanhua Chemical HT-75 and Covestro Desmodur N75.

[0037] The alicyclic isocyanate trimer is Covestro Desmodur Z4470.

[0038] The aromatic isocyanate adduct is Covestro Desmodur L75.

[0039] A method for preparing a polyurethane adhesive for reflective leather includes the following steps:

[0040] Add each component of component A to the organic solvent and mix well;

[0041] Then add component B in the specified proportion and mix well.

[0042] The organic solvent is ethyl acetate.

[0043] The beneficial effects of this invention are as follows:

[0044] This invention is the first to use high molecular weight polyester as the base resin, and to prepare polyurethane adhesive by compounding epoxy resin and coupling agent. It has excellent yellowing resistance, high tensile strength and excellent elongation at break. The reflective leather made from it can withstand 25 alkaline water washes and is resistant to rubbing. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below through embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention. Furthermore, in the following descriptions, well-known structures and technologies are omitted to avoid unnecessarily obscuring the concept of the invention.

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below through embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention. Furthermore, in the following descriptions, well-known structures and technologies are omitted to avoid unnecessarily obscuring the concept of the invention.

[0047] Synthesis of high molecular weight polyester

[0048] 1. Add 100g of terephthalic acid, 200g of isophthalic acid, 80g of sebacic acid, 60g of ethylene glycol, 220g of 1,6-hexanediol, and 0.01g of tetrabutyl titanate to the reaction vessel;

[0049] Introduce nitrogen gas while stirring, and gradually increase the temperature;

[0050] Esterification and polycondensation are carried out at 140-240℃ until the acid value drops below 1 mg KOH / g and the hydroxyl value is 2-4 mg KOH / g. This is denoted as high molecular weight polyester P1.

[0051] 2. Add 100g of terephthalic acid, 200g of isophthalic acid, 150g of sebacic acid, 90g of ethylene glycol, 220g of 1,6-hexanediol, and 0.01g of tetrabutyl titanate to the reaction vessel;

[0052] Introduce nitrogen gas while stirring, and gradually increase the temperature;

[0053] At 140-240℃, esterification and polycondensation are carried out until the acid value drops below 1 mg KOH / g and the hydroxyl value is 2-4 mg KOH / g. This is denoted as high molecular weight polyester P2.

[0054] 3. Add 100g of terephthalic acid, 200g of isophthalic acid, 150g of sebacic acid, 80g of ethylene glycol, 180g of 1,4-butanediol, and 0.01g of tetrabutyl titanate to the reaction vessel;

[0055] Introduce nitrogen gas while stirring, and gradually increase the temperature;

[0056] Esterification and polycondensation are carried out at 140-240℃ until the acid value drops below 1 mg KOH / g and the hydroxyl value is 2-4 mg KOH / g. This is denoted as high molecular weight polyester P3.

[0057] 4. Add 100g of terephthalic acid, 200g of isophthalic acid, 150g of sebacic acid, 80g of ethylene glycol, 200g of neopentyl glycol, and 0.01g of tetrabutyl titanate to a reactor. Purge with nitrogen and stir, then gradually increase the temperature. Esterification and polycondensation occur at 140-240℃. The acid value decreases to below 1mgKOH / g, and the hydroxyl value is 2-4mgKOH / g. This is designated as high molecular weight polyester P4.

[0058] Example

[0059] An embodiment of the preparation method of a polyurethane adhesive for reflective leather is as follows:

[0060] High molecular weight polyester, epoxy resin, coupling agent, catalyst, and ethyl acetate solvent are added to a reaction vessel, mixed and dissolved, and labeled as component A. Isocyanate curing agent is designated as component B. The components are mixed evenly in a specific ratio and then coated onto a sample. Specific examples and comparative test formulations are as follows:

[0061]

[0062] Among them, polyesters P1-P4 are synthetic high molecular weight polyesters;

[0063] DER337 and DER671 are epoxy resins from Olin Corporation (formerly DOW Corporation).

[0064] 6040 is Dow Corning's γ-glycidyl etheroxypropyltrimethoxysilane.

[0065] BiCAT® 8108 is a leading chemical organic bismuth catalyst.

[0066] L75 is a Covestro isocyanate curing agent.

[0067] Sample testing methods

[0068] The mixed adhesive sample (diluted to 40% solid content) was evenly coated on the bead surface of the beaded film. After the adhesive dried, the adhesive surface was hot-pressed with PU leather under certain pressure and temperature, and then placed in a 60℃ oven for 72 hours of curing.

[0069] Cut the cured reflective leather sample into strips 5cm wide and 30cm long. After removing the beads, sew the strips onto a 40cm*40cm cotton fabric.

[0070] According to the EN20471 test method, the backlight reflection coefficient was tested after 25 washes. The reflective leather sample was folded with the reflective side facing up and rubbed vigorously 50 times. The glass microbeads on the reflective side were observed to fall off, and it was best if no large area was observed to fall off.

[0071]

[0072] The experimental data above shows that:

[0073] The addition of a large amount of solid epoxy resin and the use of branched polyols (highly sterically hindered polyols) increased the glass transition temperature (Tg) of the adhesive. It can be seen that the higher the Tg of the polyurethane adhesive composition, the lower the resistance to rubbing and washing.

[0074] An appropriate amount of epoxy resin can improve the resistance to rubbing and washing, thereby enhancing the adhesion between glass microspheres and the substrate.

[0075] The foregoing has shown and described the basic principles and main features of the invention and the advantages of the invention.

[0076] Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope. All such changes and modifications fall within the scope of the present invention as claimed, which is defined by the appended claims and their equivalents.

Claims

1. A polyurethane adhesive for reflective leather, characterized in that, It includes component A and component B. Component A, by weight, includes the following components: 35-45 parts of unbranched high molecular weight polyester; 5-10 parts epoxy resin; 0.5-1 part coupling agent; Catalyst 0.01-0.05 parts; 30-40 parts organic solvent; Component B is any one or more of isocyanate adducts or isocyanate trimers; The unbranched high molecular weight polyester is formed by catalytic polymerization of polyacid and polyol components. The number average molecular weight of the unbranched high molecular weight polyester is 10,000-40,000 and the glass transition temperature is less than 10°C. The catalytic polymerization specifically refers to: In a reaction vessel, polyacid and polyol components are added and esterified at 140℃-240℃ under the catalysis of an organotitanium catalyst. Then, polycondensation is carried out at 240℃-250℃ until the acid value is less than 1, the number average molecular weight reaches 10000-40000, the acid value is <1, and the hydroxyl value is 2-4. The reaction is then stopped and the vessel is cooled down. The polybasic acid component is a mixture of terephthalic acid, isophthalic acid, and sebacic acid. The mixing ratio is 100:200:80 or 100:200:150; The polyol component is a mixture of ethylene glycol and 1,4-butanediol, with a mixing ratio of 80:

180. Or a mixture of ethylene glycol and 1,6-hexanediol, in a mixing ratio of 60:220 or 90:220; The weight ratio of component A to component B is 100:2-100:6; The epoxy resin is any one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, alicyclic epoxy resin, and phenolic epoxy resin.

2. The polyurethane adhesive for reflective leather as described in claim 1, characterized in that, The coupling agent is a silane coupling agent.

3. The polyurethane adhesive for reflective leather as described in claim 1, characterized in that, The catalyst is an organobismuth or an organozinc.

4. A polyurethane adhesive for reflective leather as described in any one of claims 1-3, characterized in that, Includes the following steps: Add each component of component A to the organic solvent and mix well; Then add component B in the specified proportion and mix well.

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