A low modulus polyurethane pressure sensitive adhesive and a low peel force protective film prepared therefrom

Abstract

The present application relates to the technical field of protective film for OLED process, in particular to a low modulus polyurethane pressure sensitive adhesive and a low peeling force protective film prepared by the low modulus polyurethane pressure sensitive adhesive. The low modulus polyurethane pressure sensitive adhesive has an energy storage modulus of 200-400 kpa, and the rheological performance characterization experiment of the pressure sensitive adhesive film is carried out at 1 Hz frequency, 0.1% strain and 25 DEG C environmental temperature. The low modulus polyurethane pressure sensitive adhesive comprises low molecular weight low PDI polyurethane polymer, curing agent and antistatic agent, the weight average molecular weight of the low molecular weight low PDI polyurethane polymer is 20000-30000, and the molecular weight distribution PDI is 1.3-2.5. The protective film prepared by the low modulus polyurethane pressure sensitive adhesive has a 180 DEG room temperature peeling force of 1.0-2.0 gf / in on a glass plate, a 180 DEG peeling force of 1.2-2.5 gf / in after 65 DEG C 90% humidity for 240 H, and a change rate less than 25%.

Description

Technical Field

[0001] This invention relates to the field of protective film technology for OLED manufacturing processes, specifically to a low-modulus polyurethane pressure-sensitive adhesive and a low-peel-force protective film prepared therefrom. Background Technology

[0002] OLED display technology boasts advantages such as self-emissiveness, wide viewing angle, high contrast, fast response time, and flexibility, making it widely used in the display industry. OLED devices are sensitive to water and oxygen, requiring protective film encapsulation and protection. This protective film must possess good adhesion, weather resistance, antistatic properties, and ease of peeling.

[0003] Polyurethane pressure-sensitive adhesives (PSAs) have attracted attention due to their superior performance and have broader application prospects. Compared with traditional rubber-based and acrylic-based PSAs, polyurethane PSAs offer greater flexibility, abrasion resistance, and chemical resistance, making them suitable for a variety of industrial applications. However, traditional polyurethane PSAs have high molecular weight, high PDI, and high modulus, resulting in a hard adhesive layer and high peel strength. Furthermore, the high molecular weight and high PDI may affect processing flowability and coating quality.

[0004] To address the above problems, the present invention provides a low-modulus polyurethane pressure-sensitive adhesive and a low-peel-force protective film prepared therefrom. Summary of the Invention

[0005] This invention designs a low molecular weight, low PDI polyurethane polymer with a weight-average molecular weight of 20,000-30,000 and a molecular weight distribution PDI of 1.3-2.5. The polyurethane pressure-sensitive adhesive prepared from it has a modulus of 200-400 kPa, enabling the polyurethane protective film to achieve a low peel force of <2.0 gf / in at 180° while having excellent wetting and adhesion effects.

[0006] The first aspect of this invention provides a low-modulus polyurethane pressure-sensitive adhesive. Rheological properties of the pressure-sensitive adhesive film were characterized by a storage modulus of 200~400 kPa at a frequency of 1 Hz, a strain of 0.1%, and an ambient temperature of 25°C. Polyurethane pressure-sensitive adhesives with storage modulus in this range possess the unique elastomer properties of polyurethane and have stable low peel force.

[0007] The low-modulus polyurethane pressure-sensitive adhesive comprises a low molecular weight, low PDI polyurethane polymer, a curing agent, and an antistatic agent. The low molecular weight, low PDI polyurethane polymer is also referred to as the "main adhesive" in this invention, with a weight-average molecular weight of 20,000-30,000 and a molecular weight distribution PDI of 1.3-2.5. When the molecular weight of the main adhesive is within this range, the resulting polyurethane pressure-sensitive adhesive exhibits good coating performance, and the prepared protective film possesses good temperature and humidity resistance as well as stable low peel strength. If the molecular weight of the main adhesive is too high or too low, phenomena such as overflow, poor leveling, and bubbles will occur during the coating of the polyurethane pressure-sensitive adhesive, and the resulting protective film will also have a higher peel strength and poorer temperature and humidity resistance. If the molecular weight distribution of the main adhesive is too wide or too narrow, the peel strength of the resulting protective film will be very high, far exceeding 2.0 gf / in.

[0008] Furthermore, the viscosity of the low molecular weight, low PDI polyurethane polymer is 300~1500cp, and the viscosity change is <5% under 23℃×168H conditions; the polyurethane pressure-sensitive adhesive prepared from it has good leveling when coated, and the resulting protective film has no bubbles, streaks, or defects. The low viscosity change rate makes the polyurethane have good stability, with a long storage time and a wide process window.

[0009] Furthermore, the low molecular weight, low PDI polyurethane polymer comprises a polyol polymer, an aliphatic diisocyanate, a hydroxyl functional monomer, a catalyst, and a solvent.

[0010] Further, the polyol polymer is a polyether polyol and a polyester polyol, with the weight ratio of the polyether polyol to the polyester polyol being (25-45):(5-15); the molar ratio (R value) of NCO in the aliphatic diisocyanate to OH in the polyol polymer is in the range of 0.5 to 1.3. Setting the R value within this range yields the low molecular weight, low PDI, low viscosity, and viscosity-stable polyurethane polymer required by this invention.

[0011] More preferably, the mass ratio of the polyether polyol to the polyester polyol is (30-40):(10-15).

[0012] More preferably, the molar ratio of NCO in the aliphatic diisocyanate to OH in the polyol polymer is in the range of 0.65-1.25, for example, 0.65, 0.7, 0.8, 0.9, 1.0, 1.1, 1.25, etc.

[0013] Furthermore, the polyether polyol has a weight-average molecular weight of 2000-4000 and a functionality of 2-4; the polyester polyol has a weight-average molecular weight of 1000-3000 and a functionality of 2-4.

[0014] More preferably, the polyether polyol is one or more of EP551C, EP553, and DEP5631 from Sinochem Dongda (Zibo) Co., Ltd.

[0015] More preferably, the polyester polyol is one or more of HDPOL-5520M (Shanghai Huide Technology Co., Ltd.), POL138 (Qingdao Xinyutian Chemical Co., Ltd.), and CMA-66 (Huada Chemical (Yantai) Co., Ltd.).

[0016] Furthermore, the aliphatic diisocyanate is one or more of hexamethylene isocyanate, isoflurane diisocyanate, and dicyclohexylmethane diisocyanate.

[0017] Further, the hydroxyl functional monomer is one or more of 1,4-butanediol (BDO), ethylene glycol (EG), dipropylene glycol, pentaerythritol, and trimethylolpropane, and the mass ratio of the hydroxyl functional monomer to the total mass of the polyol polymer and aliphatic diisocyanate is (2.5-5.0):(95-97.5). The hydroxyl functional monomer helps to precisely control the molecular weight of the polyurethane polymer.

[0018] Further, the catalyst is one or more of the following: triethylenediamine (TEDA), bis(dimethylaminoethyl) ether, triethylamine, dibutyltin dilaurate, stannous octanoate, bismuth isooctanoate, etc. The amount of catalyst used is 100-200 ppm by mass of the polyol mixture.

[0019] Further, the solvent is one or more of ethyl acetate, toluene, xylene, N,N-dimethylformamide (DMF), methyl isobutyl ketone (MIBK), and methyl ethyl ketone (MEK); the amount of solvent added makes the solid content of the low molecular weight, low PDI polyurethane polymer 60%-80%.

[0020] Furthermore, the solvent is selected from one or more of the easily volatile ethyl acetate, toluene, and methyl ethyl ketone (MEK), and one or more of the highly soluble xylene, methyl isobutyl ketone (MIBK), and N,N-dimethylformamide (DMF). Easily volatile solvents facilitate the thermal drying and molding of the pressure-sensitive adhesive during the coating process, resulting in good mass production and high efficiency; highly soluble solvents facilitate the blending of polyurethane during synthesis, promote the reaction process, and facilitate the mixing of various raw materials during the preparation of the pressure-sensitive adhesive.

[0021] Further, the curing agent is one or more selected from hexamethylene diisocyanate trimer, toluene diisocyanate trimer, and vinyltriamine; the antistatic agent is one or more selected from quaternary ammonium salts, alkyl sulfonates, and inorganic salts, specifically, antistatic agents such as lithium bis(trifluoromethanesulfonyl)imide, cocoyl ethyl dimethyl ammonium ethyl sulfate, polyalkylene glycol, sodium allyl sulfonate derivatives, etc. The low molecular weight, low PDI polyurethane polymer is used in quantities of 100 parts by weight, the curing agent is used in quantities of 4-12 parts by weight, and the antistatic agent is used in quantities of 0.2-0.6 parts by weight.

[0022] It is understood that, in addition to the components mentioned above, the low-modulus polyurethane pressure-sensitive adhesive may also contain any necessary and unnecessary components required by conventional pressure-sensitive adhesives without compromising the performance of the present invention. For example, antioxidants, plasticizers, fillers, crosslinking agents, etc., may be required.

[0023] A second aspect of the present invention provides a low-peel-strength polyurethane protective film, comprising an adhesive layer formed of the aforementioned polyurethane pressure-sensitive adhesive. When the polyurethane protective film is placed at 23°C / 50% humidity for 24 hours, its water absorption rate is <1.0%. After the polyurethane protective film is adhered to a glass plate at 23°C, when peeled at a peeling speed of 300 mm / min at 180°, the peeling force is 1.0~2.0 gf / in. After the polyurethane protective film is subjected to 65°C / 90% humidity for 240 hours, the 180° peeling force is 1.2~2.5 gf / in, with a change rate of less than 25%.

[0024] A third aspect of the present invention provides a method for preparing a polyurethane protective film, comprising the following steps:

[0025] S1: A low molecular weight, low PDI polyurethane polymer is prepared by reacting polyol polymer, aliphatic diisocyanate, and hydroxyl functional monomer under the action of a catalyst, adding solvent, and stirring evenly.

[0026] S2: Add curing agent and antistatic agent to low molecular weight, low PDI polyurethane polymer, stir evenly, and obtain low modulus polyurethane pressure-sensitive adhesive.

[0027] S3: A polyurethane protective film is prepared by coating a low-modulus polyurethane pressure-sensitive adhesive onto a substrate and curing it at 120~140℃ and aging it at 42~48℃.

[0028] Furthermore, the curing time is 2-5 minutes, and the ripening time is 48-72 hours.

[0029] Beneficial effects:

[0030] 1. This invention designs the polyurethane polymer to have a low weight-average molecular weight (20,000~30,000) and low PDI (1.5~2.5), enabling the protective film containing the polyurethane polymer to achieve low peel strength, specifically a 180° peel strength of <2.0 gf / in, ensuring low adhesion and excellent peel performance of the protective film; the low molecular weight results in low viscosity, good flowability, and fast spreading, while the low PDI leads to more stable rheological behavior. The low molecular weight and low PDI also enable the pressure-sensitive adhesive prepared to have good wetting and adhesion to the substrate.

[0031] 2. In this invention, the molar ratio of NCO in the aliphatic diisocyanate to OH in the polyol polymer is within the range of 0.65~1.25, ensuring stable polyurethane synthesis and preventing phenomena such as explosive polymerization and gelation. The design of the polyurethane polymer with a low molecular weight and narrow PDI allows for the production of a low-viscosity main adhesive with a viscosity change of <5% (23℃×168H), avoiding the need for viscosity reducers and thus avoiding the shortcomings caused by their use. Simultaneously, the polyurethane polymer viscosity is between 300-1500cp, effectively improving the flowability and coating uniformity of the polyurethane pressure-sensitive adhesive prepared from it. The resulting protective film has a good appearance, free from defects such as bubbles, horizontal lines, and pinholes; the viscosity change rate is <5% (23℃×168H), ensuring the stability of the product in subsequent processing and its long-term reliability.

[0032] 3. By optimizing polymerization conditions and molecular structure design, the polyurethane pressure-sensitive adhesive prepared by this invention has a modulus of 200~400kPa, which ensures that the pressure-sensitive adhesive has a good wetting effect with the substrate during the coating process, and still has a good adhesion effect while ensuring low peel force. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0034] Figure 1 The image shows the GPC molecular weight and molecular weight distribution of the low molecular weight, low PDI polyurethane polymer prepared in Example 4.

[0035] Figure 2 The image shows the storage modulus characterization of the polyurethane pressure-sensitive adhesive prepared in Example 4.

[0036] Figure 3 The image shows the wetting and spreading pattern of the polyurethane pressure-sensitive adhesive prepared in Example 1 on a PET substrate.

[0037] Figure 4 The image shows the wetting and spreading of the polyurethane pressure-sensitive adhesive prepared in Comparative Example 1 on a PET substrate. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The terms "optional" and "discretionary" mean that they may or may not be included (or may or may not be present).

[0040] The raw materials used in the following comparative examples are shown in Table 1:

[0041] Table 1

[0042]

[0043] Example 1

[0044] 1. Mix 35 parts by weight of polyether polyol PU-1 (EP-551C) (weight average molecular weight 3000) and 12 parts by weight of polyester polyol PU-2 (HDPOL-5520M) (weight average molecular weight 2000), and stir under vacuum at 95°C for 2 hours to ensure thorough mixing.

[0045] 2. Add 150 ppm of dibutyltin dilaurate catalyst to the PU-1 / PU-2 polyol mixture and stir; purge with nitrogen, adjust the temperature to 50°C, add 3 parts by weight of hexamethylene diisocyanate and 2 parts by weight of 1,4-butanediol, and polymerize at 50°C for 2 hours.

[0046] 3. Add 25 parts by weight of toluene solvent, stir and mix for 1 hour, and the reaction is complete to prepare a low molecular weight, low PDI polyurethane polymer.

[0047] 4. Add 6 parts by weight of hexamethylene diisocyanate trimer curing agent and 0.3 parts by weight of antistatic agent lithium bis(trifluoromethanesulfonyl)imide, and stir evenly to prepare low modulus polyurethane pressure-sensitive adhesive.

[0048] 5. Apply polyurethane pressure-sensitive adhesive to the surface of a 50μm PET substrate layer, cure at 140℃ for 3 minutes, then laminate with a 50μm release film, roll up, and then cure at 48℃ for 72 hours to obtain a protective film with an adhesive layer thickness of 75μm.

[0049] Example 2

[0050] The preparation method is similar to that in Example 1, except that dioctyltin dilaurate is used as a catalyst in step 2.

[0051] Example 3

[0052] The preparation method is similar to that of Example 1, except that in step 1, 40 parts by weight of polyether polyol PU-1 (weight average molecular weight 3000) and 8 parts by weight of polyester polyol PU-2 (weight average molecular weight 2000) are added.

[0053] Example 4

[0054] The preparation method is similar to that in Example 2, except that 25 parts by mass of toluene solvent in step 3 is replaced with 12.5 parts by mass of methyl isobutyl ketone and 12.5 parts by mass of ethyl acetate.

[0055] Comparative Example 1

[0056] The preparation method is similar to that of Example 1, except that 5 parts by weight of hexamethylene diisocyanate are added in step 2.

[0057] Comparative Example 2

[0058] The preparation method is similar to that in Example 1, except that the 150 ppm dibutyltin dilaurate catalyst in step 2 is replaced with 50 ppm dibutyltin dilaurate.

[0059] Comparative Example 3

[0060] The preparation method is similar to that of Example 1, except that the polymerization process in step 2 is performed at 50°C for 4 hours.

[0061] Comparative Example 4

[0062] The preparation method is similar to that in Example 2, except that 25 parts by mass of toluene solvent in step 3 is replaced with 12.5 parts by mass of methyl isobutyl ketone and 12.5 parts by mass of butyl acetate.

[0063] Test method:

[0064] (1) Peel strength: The peel strength was determined by an electronic universal testing machine in accordance with GB / T2792-1998 "Test method for 180° peel strength of pressure sensitive adhesive tape" (the adhered materials are glass plates and the peel rate is 300 mm / min).

[0065] (2) High temperature and high humidity test: Cut the protective film into 150×25mm size, attach it to the surface of the glass plate, put it into a programmable constant temperature and humidity test chamber, and after 240h at 65℃ and 90% humidity, observe whether the protective film surface is detached or has bubbles. If not, it is judged as qualified and the peel strength is tested; if it is, it is judged as unqualified.

[0066] (3) Molecular weight and distribution test: According to GB / T 36214.4-2018 "Plastics: Determination of molecular weight distribution by gel permeation chromatography", the weight-average molecular weight (Mw) of a specific polyurethane molecule was determined under the following conditions. Measuring device: high-speed GPC [model: HLC-8220GPC, manufactured by Tosoh Corporation], detector: differential refractive index meter (RI) [assembled in HLC-8220, manufactured by Tosoh Corporation], column: 4 TSK-GEL GMHXL [manufactured by Tosoh Corporation] connected in series, column temperature: 40℃, eluent: tetrahydrofuran, sample concentration: 0.2% by mass, injection volume: 100 μL, flow rate: 0.6 mL / min.

[0067] (4) Storage modulus test: The modulus and dissipation factor of the film as a function of frequency were characterized using a rotational rheometer (MARS 60, HAAKE GmbH, Germany). The samples were cut into circles with a diameter of 20 mm, the scanning frequency was 0.1~100 rad / s, and the strain was controlled at 0.5%.

[0068] (5) Adhesive viscosity test: Refer to GB / T 2794-2022 "Determination of viscosity of adhesives" to determine the apparent viscosity of the adhesive; use a rotational viscometer NDJ-5S and test at 23±2℃.

[0069] (6) Water absorption rate test: Cut three protective film samples with an area of ​​5cm*5cm, weigh the three samples respectively, and record them as M01, M02 and M03. Place them at 23℃ and 50% humidity for 72h, and weigh the three samples again, and record them as M11, M12 and M13; then the water absorption X* = (M1*-M0*) / M1*×100%, calculate the average value, and * is the sample number.

[0070] (7) Determination of adhesive wetting properties: Apply the prepared adhesive to the PET surface and observe its wetting effect on the substrate. If the surface is smooth, evenly spread, and without pinholes, the wetting properties are considered good. Figure 3As shown; if the surface is uneven and has large areas of pinholes, then the wettability is considered poor, such as... Figure 4 As shown.

[0071] The test data for the examples and comparative examples are shown in Table 2.

[0072] Table 2

[0073]

[0074] Conclusion Analysis:

[0075] The test data shows that the weight-average molecular weight of the main adhesive in Examples 1-4 of this invention is between 20,000 and 30,000, and the PDI is between 1.3 and 2.5. The storage modulus of the prepared pressure-sensitive adhesive is between 200 and 400 kPa. The final protective film has a peel force of less than 2.0 gf / in at 180°C on glass materials, a peel force increase of less than 25% after 240 hours at 65°C / 90% humidity, and a water absorption rate of less than 1% after 168 hours at 23°C / 50% humidity. It has good wetting and adhesion to the substrate and no defects such as bubbles, horizontal lines, or pinholes. It can meet the current market requirements for bonding OLED displays, screens, and back panels, as well as the requirements for high-temperature and high-humidity bonding.

[0076] In Comparative Example 1, adding an excessive amount of hexamethylene isocyanate to synthesize monomers resulted in a polyurethane base adhesive with a significantly higher molecular weight and viscosity. Consequently, the resulting protective film exhibited excessive peel strength, poor wetting adhesion, and a suboptimal appearance.

[0077] Compared with Comparative Example 2, which added less catalyst, the polyurethane main adhesive prepared by the reaction had a wider molecular weight distribution, and the resulting protective film had significantly higher peel strength, higher viscosity, and poorer wetting adhesion and appearance.

[0078] Comparative Example 3, by changing the polymerization conditions, prepared a polyurethane pressure-sensitive adhesive film with a higher energy storage modulus. The resulting protective film had a higher peel strength but did not meet the requirements, and had poor wetting and adhesion to the substrate, resulting in a poor appearance.

[0079] Compared with Example 2, Comparative Example 4 used butyl acetate, which has poor volatility, as a solvent. The time required for the protective film to be heat-dried and formed was significantly doubled, failing to meet production expectations.

[0080] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A low modulus polyurethane pressure sensitive adhesive, characterized in that, The product includes a low molecular weight, low PDI polyurethane polymer, a curing agent, and an antistatic agent. The low molecular weight, low PDI polyurethane polymer has a weight-average molecular weight of 20,000 to 30,000 and a molecular weight distribution PDI of 1.3 to 2.

5. Rheological properties of the pressure-sensitive adhesive film were characterized at a frequency of 1 Hz, a strain of 0.1%, and an ambient temperature of 25°C. The storage modulus was 200 to 400 kPa. The raw materials for preparing the low molecular weight, low PDI polyurethane polymer include polyol polymers, aliphatic diisocyanates, hydroxyl functional monomers, catalysts, and solvents. The polyol polymer is a polyether polyol and a polyester polyol, the mass ratio of the polyether polyol to the polyester polyol is (25-45):(5-15), and the molar ratio of NCO in the aliphatic diisocyanate to OH in the polyol polymer is 0.5~1.

3. The hydroxyl functional monomer is one or more of 1,4-butanediol, ethylene glycol, dipropylene glycol, pentaerythritol, and trimethylolpropane, and the mass ratio of the hydroxyl functional monomer to the total mass of the polyol polymer and aliphatic diisocyanate is (2.5-5.0):(95-97.5).

2. The low modulus polyurethane pressure sensitive adhesive of claim 1, wherein, The viscosity of the low molecular weight, low PDI polyurethane polymer is 300~1500cp, and the viscosity change is <5% under the condition of 23℃×168H.

3. The low-modulus polyurethane pressure-sensitive adhesive according to claim 1, characterized in that, The polyether polyol has a weight-average molecular weight of 2000-4000 and a functionality of 2-4. The polyester polyol has a weight-average molecular weight of 1000-3000 and a functionality of 2-4.

4. The low modulus polyurethane pressure sensitive adhesive of claim 1, wherein, The catalyst is one or more of triethylenediamine, bis(dimethylaminoethyl) ether, triethylamine, dibutyltin dilaurate, stannous octanoate, and bismuth isooctanoate; the solvent is one or more of ethyl acetate, toluene, xylene, N,N-dimethylformamide, methyl isobutyl ketone, and methyl ethyl ketone.

5. The low modulus polyurethane pressure sensitive adhesive of claim 1, wherein, The curing agent is one or more of hexamethylene diisocyanate trimer, toluene diisocyanate trimer, vinyltriamine, and m-phenylenediamine, and the antistatic agent is one or more of quaternary ammonium salt, alkyl sulfonate, and inorganic salt.

6. A low peel polyurethane protective film characterized by, Includes an adhesive layer, said adhesive layer being formed of the polyurethane pressure-sensitive adhesive according to any one of claims 1-5, for bonding the polyurethane protective film 23. o Under 50% humidity conditions, the water absorption rate is <1.0% after 24 hours. When the polyurethane protective film is adhered to a glass plate at 23°C and peeled at a peeling speed of 300mm / min at 180°, the peeling force is 1.0~2.0gf / in. After the polyurethane protective film is exposed to 65°C and 90% humidity for 240 hours, the peeling force at 180° is 1.2~2.5gf / in, with a change rate of less than 25%.

7. A method for producing a polyurethane protective film, characterized by, The low-modulus polyurethane pressure-sensitive adhesive described in any one of claims 1-5 is prepared by the following steps: S1: A low molecular weight, low PDI polyurethane polymer is prepared by reacting polyol polymer, aliphatic diisocyanate, and hydroxyl functional monomer under the action of a catalyst, adding solvent, and stirring evenly. S2: Add curing agent and antistatic agent to low molecular weight, low PDI polyurethane polymer, stir evenly, and obtain low modulus polyurethane pressure-sensitive adhesive. S3: A polyurethane protective film is prepared by coating a low-modulus polyurethane pressure-sensitive adhesive onto a substrate and curing it at 120~140℃ and aging it at 42~48℃.

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