Easy-to-clean thermoplastic polyurethane pressure sensitive adhesive and method of making

Abstract

The application discloses an easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive and a preparation method thereof. The easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive comprises the following raw materials in parts by mass: A. polyethylene glycol: 100 parts; B. polyisocyanate: 26-40 parts; C. chain extender: 20-36 parts; D. retarder: 1-2 parts; E. catalyst: 0.1-0.5 parts; F. antioxidant: 0.1-0.5 parts; G. hydrolysis stabilizer: 0.1-0.5 parts; and H. flame retardant: 1-5 parts. The application is prepared from polyethylene glycol, diisocyanate, chain extender and catalyst and the like, and the introduction of a suitable main chain structure and chain extender in the preparation process of the polyurethane pressure-sensitive adhesive can effectively improve the hydrophilicity of the polyurethane pressure-sensitive adhesive. The ether oxygen bond of the polyethylene glycol is easy to bend and fold, and water molecules are easy to form hydrogen bonds with the ether oxygen bond, thereby showing good hydrophilicity. The pressure-sensitive adhesive is particularly suitable for the processing technology of optical elements such as lenses and spectacle lenses.

Description

Technical Field

[0001] This invention relates to an easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive and its preparation method. Background Technology

[0002] Currently, synthetic rubber and acrylic resin are the main materials used in pressure-sensitive adhesives (PSAs). However, polyurethane PSAs are becoming increasingly important for applications requiring special performance. PSAs must possess excellent cohesive and adhesive strength, ensuring both no residue and no contamination upon peeling off the protected surface, and easy peeling. Polyurethane PSAs are multi-block copolymers, consisting of alternating hard and soft segments. The soft segments are typically polyethers, polyesters, or polyolefins, while the hard segments are generally composed of isocyanates and chain extenders. The polyurethane structure contains highly polar urethane groups (NHCOO-), which readily form hydrogen bonds, resulting in strong cohesive strength and adhesion to polar materials.

[0003] Currently, synthetic rubber pressure-sensitive adhesives are non-polar and inherently hydrophobic. Acrylic pressure-sensitive adhesives have strong adhesion but easily cause surface contamination and are difficult to clean. In some applications, such as paper labels, residue is unavoidable, affecting product use and appearance; moreover, the residue is insoluble in water and difficult to remove. Traditional rubber and acrylic pressure-sensitive adhesives, due to their poor hydrophilicity, still require organic solvents for residue removal. However, polyurethane pressure-sensitive adhesives, when prepared using hydrophobic polypropylene glycol as both soft and hard segments, showed no change in bond strength after 10 months of underwater bonding with carbon steel plates, demonstrating excellent water resistance. Ordinary polyurethane pressure-sensitive adhesives also leave residues on the bonded surfaces, usually requiring organic solvents for cleaning. These organic solvents pollute the environment and harm human health. Optical components such as eyeglass lenses and camera lenses require surface protection and sufficient adhesion to meet processing requirements during manufacturing, and the finished surface must be free of residue. This invention provides a water-washable thermoplastic polyurethane pressure-sensitive adhesive that offers surface protection for optical components such as eyeglass lenses and camera lenses during processing, with residual adhesive easily washable with water. Since polyisocyanate compounds lack hydrophilic groups, the hydrophilicity of the water-soluble polyurethane pressure-sensitive adhesive is determined by the hydrophilicity of the polyether polyol and chain extender. Polyethylene glycol is a water-soluble polyether polyol and can be used as a raw material for synthesizing hydrophilic polyurethane pressure-sensitive adhesives. This invention imparts hydrophilicity to the pressure-sensitive adhesive by introducing hydrophilic polyethylene glycol blocks into the polyurethane backbone, while utilizing the hydrophilic —CH2—CH2—O— structure of the chain extender polyethylene glycol 200 to give its polyurethane product exceptional water solubility.

[0004] There are no publicly available technical documents on easily cleanable thermoplastic polyurethane pressure-sensitive adhesives, such as CN1456630A, CN101418192A, CN102492287A, CN102703015A, CN103173006A, CN103435760A, CN103820070A, CN103820071A, CN106398629A, CN106753173A, CN108949088A, CN108977115A, CN109401712A, CN109593506A, CN110117351A, CN111269687A, and CN111978709A. Summary of the Invention

[0005] The purpose of this invention is to provide an environmentally friendly thermoplastic polyurethane pressure-sensitive adhesive that can be cleaned with water.

[0006] The present invention adopts the following technical solution:

[0007] An easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive, comprising the following raw materials in parts by weight:

[0008] A. Polyethylene glycol: 100 parts

[0009] B. Polyisocyanates: 26–40 parts

[0010] C. Chain extender: 20-36 parts

[0011] D. Retarder: 1-2 parts

[0012] E. Catalyst: 0.1–0.5 parts

[0013] F. Antioxidant: 0.1–0.5 parts

[0014] G. Hydrolysis stabilizer: 0.1–0.5 parts

[0015] H. Flame retardant: 1-5 parts.

[0016] in:

[0017] The molecular weight of polyethylene glycol is 2000-4000.

[0018] The polyisocyanate is toluene diisocyanate (TDI).

[0019] The chain extender is polyethylene glycol 200.

[0020] The retarder is phosphoric acid.

[0021] The catalyst is dibutyltin dilaurate and triethylenediamine in a mass ratio of 3:1.

[0022] The antioxidant is antioxidant 1010.

[0023] The hydrolysis stabilizer is carbodiimide.

[0024] The flame retardant is dimethyl methyl phosphate.

[0025] A method for preparing an easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive includes the following steps:

[0026] Step 1: Polyethylene glycol adsorption for impurity removal

[0027] Add 500g of polyethylene glycol and 500g of deionized water to a 2L three-necked glass reaction flask, heat to 50℃ and stir to dissolve. After the polyethylene glycol has dissolved, add 30g of activated carbon to the reaction flask, stir for 2 hours, and then filter to remove impurities to obtain an intermediate solution.

[0028] Step 2: Polyethylene glycol extraction to remove impurities

[0029] Add the above intermediate solution to a 3L separatory funnel, add 500g of diethyl ether, stir for 5 minutes, then let stand, retaining the aqueous phase, to remove organic impurities such as ethylene oxide and obtain the intermediate solution.

[0030] Step 3: Vacuum concentration of polyethylene glycol solution

[0031] The above intermediate solution was concentrated under reduced pressure at a temperature of 40-45°C and a vacuum degree of less than -0.08 MPa. After concentration under reduced pressure, 800 g of dichloromethane was added and stirred to dissolve it in the dichloromethane. Then, diethyl ether was added dropwise. After the addition was complete, the mixture was stirred at room temperature for 2 hours to precipitate.

[0032] Step 4: Filtering

[0033] After filtering the polyethylene glycol precipitate with a water pump, it was placed in a vacuum drying oven. The oven temperature was controlled at 30℃ and the vacuum degree was less than -0.08MPa. The oven was then dried under reduced pressure for 6 hours.

[0034] Step 5: Polyethylene glycol is purified using a cation exchange resin.

[0035] Add 500g of polyethylene glycol to a three-necked flask, add 500g of deionized water, stir and heat to 60℃, pass the solution through a cation exchange resin adsorption column at a rate of 250g / h, after which heat the solution to 75℃, dehydrate under vacuum for 1 hour, then heat the temperature to 105℃, dehydrate under vacuum for 2 hours, and then filter.

[0036] Step 6: Vacuum dehydration

[0037] Polyethylene glycol, chain extender and retarder are added to the reactor, and dehydrated at 110-120℃ and vacuum degree -0.095MPa for 2-3 hours. The mixture is then cooled to 40-50℃ to make the water content ≤0.05%.

[0038] Step 7: Synthesis of thermoplastic polyurethane

[0039] Polyisocyanate was added to the reactor under nitrogen protection and stirred for 0.4 to 0.6 hours. The mixture was then placed in a vacuum oven and heated to 130 to 150°C. The reaction was continued for 2 to 3 hours to obtain viscous thermoplastic polyurethane.

[0040] Step 8: Preparation of easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive

[0041] Add catalyst, antioxidant, hydrolysis stabilizer and flame retardant to the viscous thermoplastic polyurethane obtained in step 7 and mix and stir evenly. Coat the mixed adhesive onto a PET film and place it in an oven at 90-110℃ for 15-17 hours of vulcanization. After completion, place the test piece at room temperature for 6-8 days to test its performance.

[0042] The present invention has the following beneficial effects:

[0043] The easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive is composed of polyethylene glycol, diisocyanate, chain extender, catalyst, and other additives. Introducing a suitable main chain structure and chain extender during the preparation of the polyurethane pressure-sensitive adhesive can effectively improve its hydrophilicity. Utilizing the hydrophilic properties of polyethylene glycol, this invention uses polyethylene glycol 200 as the chain extender to develop a water-cleanable, environmentally friendly thermoplastic polyurethane pressure-sensitive adhesive. The ether-oxygen bonds in polyethylene glycol are easily bent and folded, and water molecules readily form hydrogen bonds with these bonds, exhibiting excellent hydrophilicity. This pressure-sensitive adhesive is particularly suitable for the processing of optical components such as lenses and spectacle lenses. Detailed Implementation

[0044] Example 1:

[0045] This invention discloses an easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive, comprising the following raw materials in parts by weight: 100 parts of polyethylene glycol with a molecular weight of 2000, 26.1 parts of toluene diisocyanate (TDI), 20 parts of chain extender polyethylene glycol 200 (molecular weight of 200), 1.5 parts of retarder phosphoric acid, 0.15 parts of catalyst dibutyltin dilaurate and triethylenediamine (mass ratio of 3:1), 0.2 parts of antioxidant 1010, 0.2 parts of hydrolytic stabilizer carbodiimide, and 1 part of flame retardant dimethyl phosphate. Refined polyethylene glycol, chain extender, and retarder were added to the reactor and dehydrated at 110°C and a vacuum of -0.095 MPa for 2 hours. The mixture was then cooled to 40°C to ensure a water content of ≤0.05%. Toluene diisocyanate (TDI) was added to the reactor under nitrogen protection and stirred for 0.4 hours. The mixture was then placed in a vacuum oven and heated to 150°C for 3 hours to obtain a viscous thermoplastic polyurethane. A catalyst, antioxidant, hydrolysis stabilizer, and flame retardant were added to the viscous thermoplastic polyurethane and mixed thoroughly. The mixture was then coated onto a PET film and placed in an oven at 100°C for 15 hours of curing. After curing, the test pieces were left at room temperature for 6 days before performance testing.

[0046] Example 2:

[0047] This invention discloses an easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive, comprising the following raw materials in parts by weight: 100 parts of polyethylene glycol with a molecular weight of 2000, 30.5 parts of toluene diisocyanate (TDI), 25 parts of chain extender polyethylene glycol 200 (molecular weight of 200), 1.5 parts of retarder phosphoric acid, 0.15 parts of catalyst dibutyltin dilaurate and triethylenediamine (mass ratio of 3:1), 0.2 parts of antioxidant 1010, 0.2 parts of hydrolytic stabilizer carbodiimide, and 1 part of flame retardant dimethyl methyl phosphate. Refined polyethylene glycol, chain extender, and retarder were added to the reactor and dehydrated at 110°C and a vacuum of -0.095 MPa for 2 hours. The mixture was then cooled to 40°C to ensure a water content of ≤0.05%. Toluene diisocyanate (TDI) was added to the reactor under nitrogen protection and stirred for 0.4 hours. The mixture was then placed in a vacuum oven and heated to 150°C for 3 hours to obtain a viscous thermoplastic polyurethane. A catalyst, antioxidant, hydrolysis stabilizer, and flame retardant were added to the viscous thermoplastic polyurethane and mixed thoroughly. The mixture was then coated onto a PET film and placed in an oven at 100°C for 15 hours of curing. After curing, the test pieces were left at room temperature for 6 days before performance testing.

[0048] Example 3:

[0049] This invention discloses an easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive, comprising the following raw materials in parts by weight: 100 parts of polyethylene glycol with a molecular weight of 2000, 39.2 parts of toluene diisocyanate (TDI), 35 parts of chain extender polyethylene glycol 200 (molecular weight of 200), 1.5 parts of retarder phosphoric acid, 0.15 parts of catalyst dibutyltin dilaurate and triethylenediamine (mass ratio of 3:1), 0.2 parts of antioxidant 1010, 0.2 parts of hydrolytic stabilizer carbodiimide, and 1 part of flame retardant dimethyl phosphate. Refined polyethylene glycol, chain extender, and retarder were added to the reactor and dehydrated at 110°C and a vacuum of -0.095 MPa for 2 hours. The mixture was then cooled to 40°C to ensure a water content of ≤0.05%. Toluene diisocyanate (TDI) was added to the reactor under nitrogen protection and stirred for 0.4 hours. The mixture was then placed in a vacuum oven and heated to 150°C for 3 hours to obtain a viscous thermoplastic polyurethane. A catalyst, antioxidant, hydrolysis stabilizer, and flame retardant were added to the viscous thermoplastic polyurethane and mixed thoroughly. The mixture was then coated onto a PET film and placed in an oven at 100°C for 15 hours of curing. After curing, the test pieces were left at room temperature for 6 days before performance testing.

[0050] The above three embodiments yielded three test pieces, and the following are the test data for the three test pieces.

[0051] Polyethylene glycol 2000 Polyethylene glycol 200 TDI Bond strength N / 25mm molecular weight 2000.00 200 174.16 - Example 1: Number of moles 1.0 2.0 3.0 1.6 Example 2: Number of moles 1.0 2.5 3.5 1.9 Example 3: Number of moles 1.0 3.5 4.5 2.1

[0052] The data from the above samples show that the synthesized TPU has an R value (NCO / OH molar ratio) of 1.0. When the R value is 1, the polyurethane molecule is linear and has no cross-linking bonds. The hydrophilicity of polyethylene glycol-type thermoplastic polyurethane originates from the hydrogen bonding between the —CH2—CH2—O— groups in the polyethylene glycol molecular chain and water molecules. Therefore, hydrophobic 1,4-butanediol was not chosen as a chain extender. Typically, polyurethane adhesives contain isocyanate monomers, which are highly volatile, have a strong irritating odor, and are highly toxic. However, the thermoplastic polyurethane described in this invention does not contain free NCO groups, and the pressure-sensitive adhesive is water-soluble, making washing and wiping with water more environmentally friendly. This solves the problem of difficult removal of adhesive residue in optical component applications.

[0053] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any substitution of features that achieves substantially the same function and effect as the technical features described in the present invention by substantially the same means, and that can be conceived by a person skilled in the art without creative effort at the time of the alleged infringement, is covered within the scope of protection of the present invention.

Claims

1. An easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive, characterized in that, Includes the following raw materials by weight: A. Polyethylene glycol: 100 parts, with a molecular weight of 2000-4000. B. Polyisocyanates: 26–40 parts C. Chain extender: 20-36 parts, the chain extender is polyethylene glycol 200 D. Retarder: 1-2 parts E. Catalyst: 0.1–0.5 parts F. Antioxidant: 0.1–0.5 parts G. Hydrolysis stabilizer: 0.1–0.5 parts H. Flame retardant: 1-5 parts; The preparation method of easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive includes the following steps: Step 1: Polyethylene glycol adsorption for impurity removal Add 500g of polyethylene glycol and 500g of deionized water to a 2L three-necked glass reaction flask, heat to 50℃ and stir to dissolve. After the polyethylene glycol has dissolved, add 30g of activated carbon to the reaction flask, stir for 2 hours, and then filter to remove impurities to obtain an intermediate solution. Step 2: Polyethylene glycol extraction to remove impurities Add the above intermediate solution to a 3L separatory funnel, add 500g of diethyl ether, stir for 5 minutes, then let stand, retaining the aqueous phase, to remove organic impurities of ethylene oxide and obtain the intermediate solution. Step 3: Vacuum concentration of polyethylene glycol solution The above intermediate solution was concentrated under reduced pressure at a temperature of 40-45°C and a vacuum degree of less than -0.08 MPa. After concentration under reduced pressure, 800 g of dichloromethane was added and stirred to dissolve it in the dichloromethane. Then, diethyl ether was added dropwise. After the addition was complete, the mixture was stirred at room temperature for 2 hours to precipitate. Step 4: Filtering After filtering the polyethylene glycol precipitate with a water pump, it was placed in a vacuum drying oven. The oven temperature was controlled at 30℃ and the vacuum degree was less than -0.08MPa. The oven was then dried under reduced pressure for 6 hours. Step 5: Polyethylene glycol is purified using a cation exchange resin. Add 500g of polyethylene glycol to a three-necked flask, add 500g of deionized water, stir and heat to 60℃, pass the solution through a cation exchange resin adsorption column at a rate of 250g / h, after which heat the solution to 75℃, dehydrate under vacuum for 1 hour, then heat the temperature to 105℃, dehydrate under vacuum for 2 hours, and then filter. Step 6: Vacuum dehydration Polyethylene glycol, chain extender and retarder are added to the reactor, and dehydrated at 110-120℃ and vacuum degree -0.095MPa for 2-3 hours. The mixture is then cooled to 40-50℃ to make the water content ≤0.05%. Step 7: Synthesis of thermoplastic polyurethane Polyisocyanate was added to the reactor under nitrogen protection and stirred for 0.4 to 0.6 hours. The mixture was then placed in a vacuum oven and heated to 130 to 150°C. The reaction was continued for 2 to 3 hours to obtain viscous thermoplastic polyurethane. Step 8: Preparation of easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive Add catalyst, antioxidant, hydrolysis stabilizer and flame retardant to the viscous thermoplastic polyurethane obtained in step 7 and mix and stir evenly. Coat the mixed adhesive onto a PET film and place it in an oven at 90-110℃ for 15-17 hours of vulcanization. After completion, place the test piece at room temperature for 6-8 days to test its performance.

2. The easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive according to claim 1, characterized in that: The polyisocyanate is toluene diisocyanate (TDI).

3. The easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive according to claim 1, characterized in that: The retarder is phosphoric acid.

4. The easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive according to claim 1, characterized in that: The catalyst is dibutyltin dilaurate and triethylenediamine in a mass ratio of 3:

1.

5. The easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive according to claim 1, characterized in that: The antioxidant is antioxidant 1010.

6. The easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive according to claim 1, characterized in that: The hydrolysis stabilizer is carbodiimide.

7. The easy-to-clean thermoplastic polyurethane pressure-sensitive adhesive according to claim 1, characterized in that: The flame retardant is dimethyl methyl phosphate.