A protecting film for optical adhesive and a preparation method thereof

Abstract

The application discloses a kind of optical adhesive protective group film, comprising: core layer, it is arranged between first surface layer and second surface layer;Core layer includes first polyester;First surface layer and second surface layer include the mass ratio of (45~50) and functional master batch of (50~55) first polyester, and functional master batch includes polyethylene naphthalate, second polyester and modified barium sulfate.By mixing the dispersibility of functional master batch and first polyester is improved, and then the haze and light transmittance of base film are optimized;By polyethylene naphthalate preparation functional master batch, the heat resistance and stability of base film are optimized, and its transmittance is improved and haze is reduced.

Description

Technical Field

[0001] This invention relates to the field of optical film technology, and more specifically to a protective base film for optical adhesives and its preparation method. Background Technology

[0002] Optical transparent adhesive, also known as OCA optical adhesive protective base film, possesses extremely high light transmittance, excellent optical properties, and strong adhesion, and is widely used in capacitive and resistive touchscreen technologies. At least one surface of the optical transparent adhesive has a protective film, which needs to have high light transmittance to ensure it does not affect the optical performance of the final product. The commonly used substrate for the protective film is biaxially oriented polyester film (BOPET). To improve the film's slip properties, reduce the surface friction coefficient, and thus improve the winding effect of the polyester film, facilitating subsequent processing and preventing sticking, a certain amount of additives and auxiliary materials are often added. However, the addition of these materials can affect the transparency and haze of the polyester film.

[0003] Therefore, it is necessary to improve the protective base film for optical adhesives in the existing technology. Summary of the Invention

[0004] One of the objectives of this invention is to overcome the deficiencies in the prior art and provide a protective base film for optical adhesives. By mixing functional masterbatch with a first polyester, the dispersibility is improved, thereby optimizing the haze and transmittance of the base film. The functional masterbatch formulated with polyethylene naphthalate optimizes the heat resistance and stability of the base film, and improves its transmittance and reduces haze.

[0005] To achieve the above-mentioned process effects, the technical solution of the present invention is: a protective base film for optical adhesives, comprising:

[0006] The core layer is sandwiched between the first and second surface layers;

[0007] The core layer comprises a first polyester;

[0008] Both the first and second surface layers comprise a first polyester and a functional masterbatch in a mass ratio of (45-50):(50-55), wherein the functional masterbatch comprises polyethylene naphthalate, a second polyester, and modified barium sulfate.

[0009] The preferred technical solution is as follows: by mass parts, the functional masterbatch comprises 30-40 parts of polyethylene naphthalate, 60-70 parts of the second polyester, and 1-2 parts of modified barium sulfate.

[0010] The preferred technical solution is that the modifier of the modified barium sulfate is a silicate and / or an aluminum salt.

[0011] The preferred technical solution is as follows: the second polyester is obtained by esterification of a diacid and a diol with a catalyst, wherein the diacid includes terephthalic acid and 1,4-cyclohexanedicarboxylic acid, and the diol includes ethylene glycol and isomannitol.

[0012] The preferred technical solution is that the molar ratio of terephthalic acid, 1,4-cyclohexanedicarboxylic acid, isomannitol and ethylene glycol is (97-98):(2-3):(2-2.5):(97.5-98).

[0013] The preferred technical solution is that the catalyst is an antimony-based catalyst.

[0014] A preferred technical solution is that the thickness ratio of the first surface layer, the core layer, and the second surface layer is (4-4.5):(91-92):(4-4.5). The total thickness of the protective base film is 38-100 μm.

[0015] The second objective of this invention is to overcome the deficiencies in the prior art and provide a method for preparing a protective base film for optical adhesives, comprising the following steps:

[0016] S1: Formulate functional masterbatch;

[0017] S2: The raw materials for the first surface layer, core layer and second surface layer are melted separately and cast into sheets;

[0018] S3: First preheating of the molded casting, longitudinal stretching, and first cooling;

[0019] S4: The longitudinally stretched casting is sequentially preheated a second time, heated while being stretched laterally, heat-set and cooled a second time to obtain the protective base film;

[0020] The raw material for the core layer is melted using a single screw extruder. The temperatures of the melt extruder are sequentially set to 180±2℃, 270±2℃, 280±2℃, 285±2℃, 285±2℃, 285±2℃, 285±2℃, 285±2℃, 285±2℃, and 280±2℃, while the temperature of the metering extruder is set to 270~280℃.

[0021] The raw materials for the first and second surface layers are melted using a twin-screw extruder, integrating melting and metering. The extrusion temperatures are set sequentially to 290±2℃, 290±2℃, 285±2℃, 280±2℃, 275±2℃, 270±2℃, and 270±2℃.

[0022] The preferred technical solution is that the temperature of raw material mixing and melting is 290-295℃ during the preparation of the functional masterbatch in S1.

[0023] The preferred technical solution is as follows: in S3, the temperature of the first preheating is 60-90℃, the longitudinal stretching temperature is 70-100℃, the longitudinal stretching ratio is 3-3.6 times, and the longitudinal stretching rate is 80-120m / min;

[0024] In step S4, the temperature of the second preheating is 60-90℃, the transverse stretching temperature is 180-200℃, the transverse stretching ratio is 3-3.8 times, and the transverse stretching rate is 80-120m / min.

[0025] The heat setting temperature is 220–240°C.

[0026] The advantages and beneficial effects of this invention are as follows:

[0027] The protective base film for this optical adhesive improves dispersibility by mixing functional masterbatch with the first polyester, thereby optimizing the haze and transmittance of the base film; the functional masterbatch formulated with polyethylene naphthalate optimizes the heat resistance and stability of the base film, and improves its transmittance and reduces haze. Detailed Implementation

[0028] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0029] First Polyester

[0030] It is a bright polyester chip, and further, it is Sinopec FG600.

[0031] Functional Masterbatch

[0032] By weight, it includes 30-40 parts of polyethylene naphthalate, 60-70 parts of the second polyester, and 1-2 parts of modified barium sulfate.

[0033] Polyethylene naphthalate (PEN) exhibits superior gas barrier properties compared to polyethylene terephthalate (PET), thus improving the gas barrier performance of the base film. PEN's glass transition temperature (Tg) is approximately 40°C higher than PET, meaning it maintains shape and dimensional stability at higher temperatures, thus improving the heat resistance of the base film. Due to the rigid naphthalene ring in its molecular structure, PEN typically exhibits lower birefringence and higher transparency, optimizing the base film's transparency and addressing the issue of excessive haze increase caused by the addition of inorganic particles. This approach balances the economic advantages of PET with the heat resistance and gas barrier properties of PEN. Excessive PEN addition leads to poor compatibility with PET and increased costs, while insufficient addition results in poor haze optimization on the base film surface.

[0034] To optimize the compatibility between raw materials, and the compatibility between the first and second surface layers and the core layer, the second polyester is prepared by esterification of diacids and diols via a catalyst. The diacids include terephthalic acid and 1,4-cyclohexanedicarboxylic acid, and the diols include ethylene glycol and isomannitol. Further, the molar ratio of terephthalic acid, 1,4-cyclohexanedicarboxylic acid, isomannitol, and ethylene glycol is (97–98):(2–3):(2–2.5):(97.5–98). Isomannitol is derived from plant-based components such as starch and cellulose; the utilization of biomass resources is a key component in building a green circular economy system. The addition of isomannitol can improve the transmittance of the base film and reduce haze, but excessive addition can lead to increased yellowing of the base film, resulting in decreased light transmittance. To address the yellowing issue of polyester during synthesis, 1,4-cyclohexanedicarboxylic acid is used to improve the situation. This reduces the haze of the base film by disrupting the regularity of the polyester chain segment structure, increasing the steric hindrance of chain segment thermal motion, and decreasing crystallinity. However, excessive addition can lead to a decrease in the heat resistance of the base film surface. Antimony-based catalysts are highly efficient and stable, and can effectively control the degree of polymerization. Further, antimony trioxide (Sb₂O₃) and / or antimony glycolide (EGS) are preferred. The optimal addition amount of antimony-based catalyst is 100 ppm to 200 ppm relative to the polyester mass. Titanium-based catalysts have high activity, effectively promoting esterification reactions and are environmentally friendly, but the resulting polyester product has relatively high haze.

[0035] The refractive index of barium sulfate is similar to that of the first polyester, and the uniform dispersion of barium sulfate has a positive impact on the haze and transparency of the base film. The particle size of barium sulfate is 100–120 nm. To improve the dispersibility of barium sulfate, the surface of barium sulfate is modified. The modifiers for barium sulfate are silicates and / or aluminum salts. Water-soluble NaSiO3 is added to the BaSO4 slurry and neutralized with acid to a pH of 8–9, causing silicon to precipitate on the surface of BaSO4 particles in the form of Si(OH)4, forming a dense, amorphous, hydrated silica skin film. Soluble NaAlO2 is added to the BaSO4 slurry and neutralized with acid to a pH of 9–10, causing aluminum to precipitate on the surface of BaSO4 particles in the form of Al(OH)3, forming a dense inorganic film. The particle size of the modified barium sulfate is 200–220 nm.

[0036] In the preparation of functional masterbatch, the temperature of the internal mixer in which the raw materials are melted and mixed is controlled at 290-295℃ to improve the esterification reaction between PEN and PET, thereby improving compatibility. Furthermore, the mixing time is 18-20 min.

[0037] Example 1

[0038] The protective base film for optical adhesives includes a core layer, a first surface layer, and a second surface layer, with the core layer sandwiched between the first and second surface layers. The core layer is composed of high-brightness polyester chips FG600. Both the first and second surface layers include high-brightness polyester chips FG600 and functional masterbatch in a mass ratio of 47.5:52.5. By mass parts, the functional masterbatch includes 35 parts of polyethylene naphthalate, 65 parts of the second polyester, and 1.5 parts of modified barium sulfate.

[0039] The second polyester is prepared by esterification of terephthalic acid, 1,4-cyclohexanedicarboxylic acid, isomannitol, and ethylene glycol in a molar ratio of 97.5:2.5:2.2:97.8 using a catalyst. The modifier for the modified barium sulfate is a silicate.

[0040] The preparation method of the above-mentioned protective base film for optical adhesives includes the following steps:

[0041] S1: To prepare the functional masterbatch, put the raw materials into an internal mixer for melting and mixing, control the temperature at 292℃, and mix for 18 minutes.

[0042] S2: The raw materials for the first surface layer, core layer, and second surface layer are melted separately and cast into sheets. The core layer raw material is melted using a single-screw extruder, with the extrusion temperatures sequentially set to 180℃, 270℃, 282℃, 285℃, 285℃, 285℃, 285℃, 285℃, 285℃, and 280℃. The metering extruder has nine zones with temperatures sequentially set to 270℃, 270℃, 270℃, 270℃, 270℃, 270℃, 270℃, and 282℃. The first and second surface layers are melted using a twin-screw extruder, integrating melting and metering. The extrusion temperatures are sequentially set to 290℃, 290℃, 285℃, 280℃, 275℃, 270℃, and 270℃. This ensures uniform mixing of the first polyester and the functional masterbatch, promotes esterification of the raw materials, and further improves their compatibility.

[0043] S3: The first preheating temperature of the molded casting is 80℃, the longitudinal stretching temperature is 88℃, the stretching ratio is 3.4 times, the stretching rate is 100m / min, and the first cooling is performed.

[0044] S4: The longitudinally stretched casting is preheated a second time at 80°C, then stretched laterally at 185°C, with a stretching ratio of 3.6 times and a stretching rate of 110 m / min. The heat-setting temperature is 230°C, followed by a second cooling, to obtain the protective base film.

[0045] The first surface layer has a thickness of 2 μm, the core layer has a thickness of 46 μm, and the second surface layer has a thickness of 2 μm.

[0046] Example 2

[0047] Example 2 is based on Example 1, except that both the first and second surface layers include bright polyester chips FG600 and functional masterbatch in a mass ratio of 50:50. All other components and processes remain unchanged.

[0048] Example 3

[0049] Example 3 is based on Example 1, except that both the first and second surface layers include bright polyester chips FG600 and functional masterbatch in a mass ratio of 45:55. Other components and processes remain unchanged.

[0050] Example 4

[0051] Example 4 is based on Example 1, except that the functional masterbatch includes 30 parts of polyethylene naphthalate, 70 parts of the second polyester, and 1.5 parts of modified barium sulfate. Other components and processes remain unchanged.

[0052] Example 5

[0053] Example 5 is based on Example 1, except that the second polyester is prepared by esterification of terephthalic acid, 1,4-cyclohexanedicarboxylic acid, isomannitol and ethylene glycol in a molar ratio of 95:5:2.2:97.8 via a catalyst. Other components and processes remain unchanged.

[0054] Example 6

[0055] Example 6 is based on Example 1, except that the second polyester is prepared by esterification of terephthalic acid, 1,4-cyclohexanedicarboxylic acid, isomannitol and ethylene glycol in a molar ratio of 97.5:2.5:6:94 via a catalyst. Other components and processes remain unchanged.

[0056] Example 7

[0057] Example 7 is based on Example 1, except that the thickness of the first surface layer is 1 μm, the thickness of the core layer is 48 μm, and the thickness of the second surface layer is 1 μm. All other components and processes remain unchanged.

[0058] Example 8

[0059] Example 8 is based on Example 1, except that the temperature at which the raw materials are mixed and melted is 280°C during the preparation of the functional masterbatch in S1. The composition remains the same, and other process steps and conditions are also unchanged.

[0060] Comparative Example 1

[0061] Comparative Example 1 is based on Example 1, except that the functional masterbatch includes 100 parts of the second polyester and 1.5 parts of modified barium sulfate. Other components and processes remain unchanged.

[0062] Comparative Example 2

[0063] Comparative Example 2 is based on Example 1, except that both the first and second surface layers include a first polyester, polyethylene naphthalate, a second polyester, and modified barium sulfate. That is, the polyethylene naphthalate, the second polyester, and the modified barium sulfate are not prepared as masterbatch for application, but are directly added and mixed with the first polyester.

[0064] Comparative Example 3

[0065] Comparative Example 3 is based on Example 1, except that the functional masterbatch includes 35 parts of polyethylene naphthalate, 65 parts of the first polyester, and 1.5 parts of modified barium sulfate. Other components and processes remain unchanged.

[0066] Performance testing of the base film:

[0067] 1. Haze, transmittance and stability tests

[0068] Instrument: BYK AT-4725 transmission fog imager (Germany); Test standard: according to ASTM D1003.

[0069] Five samples were taken from the obtained polyester film. The sample size was 10*10cm. The cutting direction of the samples was consistent with the transverse and longitudinal directions of the polyester film. The haze value and transmittance of the five samples were measured using a transmission haze meter to obtain the average haze value H1 and the average transmittance value T1.

[0070] 2. Heat resistance test

[0071] Five samples were taken from the obtained polyester film, each sample measuring 1000mm × 1000mm. The samples were laid flat on a smooth black marble slab. A feeler gauge was used to measure the gap between the angle and side length of the sample and the marble slab. The samples were then graded as follows: after heat treatment at 150℃ for 30 minutes, the number of protrusions with a height ≥ 1mm and a depth L ≥ 100mm, and the number of protrusions with a height ≥ 0.5mm and a depth L ≥ 10mm were determined.

[0072] △: The number of protrusions with a height ≥ 1mm and a depth L ≥ 100mm is ≤ 2, and the number of protrusions with a height ≥ 0.5mm and a depth L ≥ 10mm is ≤ 5;

[0073] ▲: The number of protrusions with a height ≥ 1mm and a depth L ≥ 100mm is ≤ 2, and the number of protrusions with a height ≥ 0.5mm and a depth L ≥ 10mm is ≤ 6;

[0074] ■: The number of protrusions with a height ≥ 1 mm and a depth L ≥ 100 mm > 2 or the number of protrusions with a height ≥ 0.5 mm and a depth L ≥ 10 mm > 6;

[0075] △ and ▲ are acceptable, while ■ is unacceptable.

[0076] 3. Measurement of friction coefficient

[0077] Instrument: Jinan Labthink PARAM MXD-02 friction coefficient tester; Test standard: According to ASTM D1894, a dynamic friction coefficient of 0.35 or higher and a static friction coefficient of 0.36 or higher indicate good anti-adhesion effect.

[0078] The measurement results of the examples and comparative examples are shown in the table below:

[0079]

[0080]

[0081] Compared to Example 1, in Examples 2 and 3, the reduction in the amount of functional masterbatch added negatively affected the heat resistance of the base film, while the increase in the amount of functional masterbatch added negatively affected the haze of the base film.

[0082] Compared to Example 1, Example 4 shows a reduction in the PEN content in the functional masterbatch, which negatively impacts both the haze and heat resistance of the base film.

[0083] Compared to Example 1, Example 6 shows an increased proportion of isomannitol, which reduces haze. However, due to the high content, the resulting film turns yellow, leading to reduced light transmittance and poor appearance.

[0084] Compared to Example 1, Example 7 has a thinner first and second surface layer, resulting in a relatively increased density of scattering points between barium sulfate particles and the substrate interface. This leads to more light scattering, which in turn increases haze, reduces heat resistance, increases roughness, and results in a poor appearance.

[0085] Compared to Example 1, Example 8 showed that the masterbatch melt mixing temperature was too low, resulting in poor esterification reaction of polyethylene naphthalate and the second polyester. This led to decreased compatibility between the two, negatively impacting haze, transmittance, and heat resistance.

[0086] Compared to Example 1, both Comparative Examples 1 and 3 require polyethylene naphthalate and the second polyester to modify the optical properties of the base film.

[0087] Compared to Example 1, in Comparative Example 2, polyethylene naphthalate, the second polyester, and modified barium sulfate were directly mixed with the first polyester. Due to the short melting and mixing time of polyethylene naphthalate with the first and second polyesters, the esterification reaction was insufficient, resulting in poor compatibility. Furthermore, the dispersibility of modified barium sulfate was also poor, with severe local adhesion, which negatively affected the haze, transmittance, and heat resistance of the base film.

[0088] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A protective base film for optical adhesives, comprising: The core layer is sandwiched between the first and second surface layers; The core layer is characterized in that it comprises a first polyester; Both the first and second surface layers comprise a first polyester and a functional masterbatch in a mass ratio of (45~50):(50~55), wherein the functional masterbatch comprises polyethylene naphthalate, a second polyester, and modified barium sulfate. The functional masterbatch comprises, by weight, 30-40 parts of polyethylene naphthalate, 60-70 parts of second polyester, and 1-2 parts of modified barium sulfate; The modifier for the modified barium sulfate is a silicate and / or an aluminum salt; The second polyester is prepared by esterification of a diacid and a diol using a catalyst, wherein the diacid includes terephthalic acid and 1,4-cyclohexanedicarboxylic acid, and the diol includes ethylene glycol and isomannitol.

2. The protective base film for optical adhesives according to claim 1, characterized in that, The molar ratio of terephthalic acid, 1,4-cyclohexanedicarboxylic acid, isomannitol and ethylene glycol is (97~98):(2~3):(2~2.5):(97.5~98).

3. The protective base film for optical adhesives according to claim 1, characterized in that, The catalyst is an antimony-based catalyst.

4. The protective base film for optical adhesives according to claim 1, characterized in that, The thickness ratio of the first surface layer, the core layer, and the second surface layer is (4~4.5):(91~92):(4~4.5).

5. A method for preparing a protective base film for optical adhesives, characterized in that, Includes the following steps: S1: Formulate functional masterbatch; S2: The raw materials for the first surface layer, core layer and second surface layer are melted separately and cast into sheets; S3: First preheating of the molded casting, longitudinal stretching, and first cooling; S4: The longitudinally stretched casting is sequentially preheated, heated while being transversely stretched, heat-set and cooled a second time to obtain the protective base film for optical adhesive as described in any one of claims 1 to 4; The raw material for the core layer is melted using a single screw extruder. The temperatures of the melt extruder are sequentially set to 180±2℃, 270±2℃, 280±2℃, 285±2℃, 285±2℃, 285±2℃, 285±2℃, 285±2℃, 285±2℃, and 280±2℃, while the temperature of the metering extruder is set to 270~280℃. The raw materials for the first and second surface layers are melted using a twin-screw extruder, integrating melting and metering. The extrusion temperatures are set sequentially to 290±2℃, 290±2℃, 285±2℃, 280±2℃, 275±2℃, 270±2℃, and 270±2℃.

6. The method for preparing a protective base film for optical adhesives according to claim 5, characterized in that, During the preparation of the functional masterbatch in S1, the temperature of raw material mixing and melting is 290~295℃.

7. The method for preparing the protective base film for optical adhesive according to claim 5, characterized in that, In step S3, the temperature of the first preheating is 60~90℃, the longitudinal stretching temperature is 70~100℃, the longitudinal stretching ratio is 3~3.6 times, and the longitudinal stretching rate is 80~120m / min. In step S4, the temperature of the second preheating is 60~90℃, the transverse stretching temperature is 180~200℃, the transverse stretching ratio is 3~3.8 times, and the transverse stretching rate is 80~120m / min; The heat setting temperature is 220~240℃.

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