A low-haze, high-transparency release film polyester film and its preparation method

Abstract

This application discloses a polyester film for low-haze, high-transparency release membranes and its preparation method. The polyester film includes an upper surface layer, a lower surface layer, and a core layer. The upper and lower surface layers are composed of the following raw materials in the following mass percentages: 8%-10% anti-adhesion particles, 90%-92% polyester chips with a refractive index of 1.63-1.65, and the anti-adhesion particles are poly-4-methyl-1-pentene with a refractive index of 1.46. The core layer is composed of the following raw materials in the following mass percentages: 5%-7% antistatic particles, 92-95% polyester chips with a refractive index of 1.63-1.65, and the antistatic particles are zinc oxide with a refractive index of 2.0. This application uses high-refractive-index polyester chips as a base, low-refractive-index anti-sticking particles as the surface layer, and high-refractive-index antistatic particles as the core layer, forming a combination of a high-refractive-index core layer and a low-refractive-index surface layer. By using refractive index matching, the overall light transmittance is improved by changing the propagation characteristics of light waves. At the same time, the organic anti-sticking particles used in the surface layer can effectively avoid the influence of inorganic particles on haze, and can effectively reduce the haze of the film.

Description

Technical Field

[0001] This application relates to a polyester film in the field of polymers, and more particularly to a polyester film used as a release film in fields such as optics, and especially to a polyester film for low-haze and high-transparency release film and its preparation method. Background Technology

[0002] Polyester films, produced in the polymer field, exhibit excellent mechanical properties, dimensional stability, chemical resistance, and electrical insulation, and are widely used in packaging, electronics, and optics. In optics, various release films are frequently applied. For example, in CA optical adhesives used to bond transparent optical components, both sides are coated with a release film. Similarly, in polarizers used in LCD displays, the outer surface of the PSA pressure-sensitive adhesive layer is typically coated with a release film.

[0003] Release films used in the optical field sometimes need to possess certain optical properties, thus requiring high transparency and low haze to improve the utilization efficiency of transmitted light.

[0004] CN 111634088 A discloses a high-transparency antistatic BOPET release film and its preparation method. The prior art BOPET release film consists of an upper surface layer, a lower surface layer and a core layer. The upper surface layer and the lower surface layer are anti-sticking layers, and their raw materials contain 3.0-5.0% anti-sticking masterbatch by weight, with the balance being ultra-bright polyester chips. The core layer is a support layer, and its raw materials contain 2.0-4.0% antistatic masterbatch by weight, with the balance being ultra-bright polyester chips.

[0005] As can be seen from the embodiments and comparative examples described in this prior art, the organic spherical anti-adhesion particles used in this technology are helpful in reducing haze and improving transparency compared to silica particles. However, this technology does not disclose in detail the materials used to prepare the organic spherical anti-adhesion particles, only emphasizing that their refractive index is 1.52, close to the refractive index of polyester film (1.57).

[0006] Typically, PET polyester films used in general optical applications have a high refractive index, usually between 1.63 and 1.65. However, in general food packaging and other fields, where light transmittance requirements are lower, the refractive index of the polyester film used is typically 1.57. Therefore, based on the performance parameters provided by this prior art embodiment, the release film base film of this technology has relatively low haze, but its transparency parameter is unclear. Furthermore, both the core layer and the surface layer of this technology use low-refractive-index polyester materials, which makes it unsuitable for high-refractive-index applications in the optical field. Summary of the Invention

[0007] The technical problem to be solved by this application is to provide a polyester film for low-haze, high-transparency release film and a method for preparing the same, so as to reduce or avoid the problems mentioned above.

[0008] To address the aforementioned technical problems, this application proposes a polyester film for low-haze, high-transparency release films, comprising an upper surface layer, a lower surface layer, and a core layer. The upper and lower surface layers are anti-adhesion layers containing anti-adhesion particles; the core layer is a support layer containing antistatic particles. The upper and lower surface layers are composed of the following raw materials by mass percentage: 8%-10% anti-adhesion particles and 90%-92% polyester chips with a refractive index of 1.63-1.65, wherein the anti-adhesion particles are poly-4-methyl-1-pentene with a refractive index of 1.46. The core layer is composed of the following raw materials by mass percentage: 5%-7% antistatic particles and 92-95% polyester chips with a refractive index of 1.63-1.65, wherein the antistatic particles are zinc oxide with a refractive index of 2.0.

[0009] Preferably, the outer side of the upper and / or lower surface layers is coated with a high refractive index coating, and the overall refractive index of the polyester film for low-haze, high-transparency release film having the high refractive index coating is 1.69-1.73.

[0010] Preferably, the high refractive index coating is composed of tri(2-hydroxyethyl)isocyanurate triacrylate, cyclohexanediethanol diacrylate, nano-silicon nitride, and n-octyltrimethoxysilane.

[0011] Preferably, the mass ratio of each component of the high refractive index coating is (25-35): (20-30): (5-10): (30-60).

[0012] This application also proposes a method for preparing the above-mentioned low-haze, high-transparency release film polyester film, comprising the following steps: mixing poly(4-methyl-1-pentene) with a refractive index of 1.46 and optical-grade PET polyester chips with a refractive index of 1.63-1.65 to form a surface layer mixture; mixing zinc oxide with a refractive index of 2.0 and optical-grade PET polyester chips with a refractive index of 1.63-1.65 to form a core layer mixture; using the surface layer mixture as raw material, the material melt-extruded by an extruder is used as the upper and lower surface layers, and using the core layer mixture as raw material, the material melt-extruded by an extruder is used as the core layer; and a three-layer structure thick sheet is prepared by multi-layer co-extrusion process; and then the thick sheet is biaxially stretched to prepare the low-haze, high-transparency release film polyester film.

[0013] This application further proposes another method for preparing the above-mentioned low-haze, high-transparency release film polyester film, comprising the following steps: mixing poly-4-methyl-1-pentene with a refractive index of 1.46 with optical-grade PET polyester chips with a refractive index of 1.63-1.65 to form a surface layer mixture; mixing zinc oxide with a refractive index of 2.0 with optical-grade PET polyester chips with a refractive index of 1.63-1.65 to form a core layer mixture; using the surface layer mixture as raw material, the material melt-extruded by an extruder is used as the upper and lower surface layers, and using the core layer mixture as raw material, the material melt-extruded by an extruder is used as the core layer; a three-layer structure thick sheet is formed by multi-layer co-extrusion process; the prepared high-refractive-index coating is coated onto the thick sheet; and then the thick sheet is biaxially stretched to prepare a low-haze, high-transparency release film polyester film with a high-refractive-index coating.

[0014] This application uses high-refractive-index polyester chips as a base, low-refractive-index anti-sticking particles as the surface layer, and high-refractive-index antistatic particles as the core layer, forming a combination of a high-refractive-index core layer and a low-refractive-index surface layer. By using refractive index matching, the overall light transmittance is improved by changing the propagation characteristics of light waves. At the same time, the organic anti-sticking particles used in the surface layer can effectively avoid the influence of inorganic particles on haze, and can effectively reduce the haze of the film. Attached Figure Description

[0015] The accompanying drawings are intended only to illustrate and explain this application and do not limit the scope of this application.

[0016] Figure 1 The diagram shown is a structural schematic of a polyester film for low-haze, high-transparency release film according to a specific embodiment of this application.

[0017] Figure 2 The diagram shown is a structural schematic of a polyester film for a low-haze, high-transparency release film according to another specific embodiment of this application. Detailed Implementation

[0018] To provide a clearer understanding of the technical features, objectives, and effects of this application, specific embodiments are now described with reference to the accompanying drawings. Identical components are denoted by the same reference numerals.

[0019] As described in the background section, the polyester film used for release films in CN 111634088 A uses ordinary packaging polyester chips, which cannot meet the requirements of high refractive index applications in the optical field. Therefore, based on this prior art, this application proposes an improved polyester film for low-haze, high-transparency release films and its preparation method.

[0020] Specifically, such as Figure 1As shown, the low-haze, high-transparency release liner polyester film of this application also includes an upper surface layer 1, a lower surface layer 2, and a core layer 3. The upper surface layer 1 and lower surface layer 2 are anti-adhesion layers containing anti-adhesion particles; the core layer is a support layer containing antistatic particles. Unlike existing technologies, to meet the diverse needs of the optical field, this application's polyester film does not use ultra-bright polyester chips with a refractive index of 1.57, but instead uses polyester chips with a refractive index of 1.63-1.65. The raw material composition mass percentages of the upper surface layer 1 and lower surface layer 2 are: 8%-10% anti-adhesion particles and 90%-92% polyester chips with a refractive index of 1.63-1.65. The anti-adhesion particles are poly-4-methyl-1-pentene with a refractive index of approximately 1.46. The raw material composition mass percentages of the core layer are: 5%-7% antistatic particles and 92-95% polyester chips with a refractive index of 1.63-1.65. The antistatic particles are zinc oxide with a refractive index of approximately 2.0.

[0021] The preparation method of the low-haze, high-transparency release liner polyester film of this application includes the following steps: mixing poly-4-methyl-1-pentene with a refractive index of 1.46 with optical-grade PET polyester chips with a refractive index of 1.63-1.65 to form a surface layer mixture; mixing zinc oxide with a refractive index of 2.0 with optical-grade PET polyester chips with a refractive index of 1.63-1.65 to form a core layer mixture; using the surface layer mixture as raw material, the material melt-extruded by an extruder is used as the upper surface layer 1 and the lower surface layer 2, respectively; and using the core layer mixture as raw material, the material melt-extruded by an extruder is used as the core layer 3. The three-layer structure thick sheet is made by multi-layer co-extrusion process, and then the thick sheet is biaxially stretched to prepare the low-haze, high-transparency release liner polyester film.

[0022] Example 1

[0023] The raw material mass percentage of the top layer 1 is: 8% poly4-methyl-1-pentene, and the remainder is PET polyester chips.

[0024] The percentage of raw materials in the lower layer 2 is as follows: 8% poly4-methyl-1-pentene, and the remainder is PET polyester chips.

[0025] Core layer 3 raw material mass percentage: 5% zinc oxide with a particle size of 5μm, the remainder is PET polyester chips.

[0026] The parameters of the prepared three-layer low-haze, high-transmittance release liner polyester film are as follows: tensile strength 310 MPa, light transmittance 93%, haze less than 0.5%. The thickness of the upper layer 1 is 8 μm, the thickness of the lower layer 2 is 8 μm, and the thickness of the core layer 3 is 40 μm.

[0027] Example 2

[0028] The raw material mass percentage of the top layer 1 is: 10% poly-4-methyl-1-pentene, and the remainder is PET polyester chips.

[0029] The percentage of raw materials in the lower layer 2 by mass is: 10% poly-4-methyl-1-pentene, and the remainder is PET polyester chips.

[0030] Core layer 3 raw material mass percentage: 7% zinc oxide with a particle size of 8μm, the remainder is PET polyester chips.

[0031] The parameters of the prepared three-layer low-haze, high-transmittance release liner polyester film are as follows: tensile strength 325 MPa, light transmittance 94%, haze less than 0.5%. The thickness of the upper layer 1 is 10 μm, the thickness of the lower layer 2 is 10 μm, and the thickness of the core layer 3 is 50 μm.

[0032] Example 3

[0033] The raw material mass percentage of the top layer 1 is: 8% poly4-methyl-1-pentene, and the remainder is PET polyester chips.

[0034] The percentage of raw materials in the lower layer 2 by mass is: 10% poly-4-methyl-1-pentene, and the remainder is PET polyester chips.

[0035] Core layer 3 raw material mass percentage: 6% zinc oxide with a particle size of 6μm, the remainder being PET polyester chips.

[0036] The parameters of the prepared three-layer low-haze, high-transmittance release membrane polyester film are as follows: tensile strength 321 MPa, light transmittance 92%, haze less than 0.5%. The thickness of the upper layer 1 is 8 μm, the thickness of the lower layer 2 is 10 μm, and the thickness of the core layer 3 is 40 μm.

[0037] Comparative Example 1

[0038] The raw material mass percentage of the top layer 1 is: 8% silica with a particle size of 5μm, and the remainder is PET polyester chips.

[0039] Bottom layer 2 raw material mass percentage: 10% silica with a particle size of 5μm, the remainder is PET polyester chips.

[0040] Core layer 3 raw material weight percentage: 5% sodium dodecyl sulfate, the remainder is PET polyester chips.

[0041] The parameters of the prepared three-layer polyester film are as follows: tensile strength 250 MPa, light transmittance 85%, haze 2.5%. The thickness of the upper layer 1 is 8 μm, the thickness of the lower layer 2 is 10 μm, and the thickness of the core layer 3 is 40 μm.

[0042] This application uses high-refractive-index polyester chips as a base, low-refractive-index anti-sticking particles as the surface layer, and high-refractive-index antistatic particles as the core layer, forming a combination of a high-refractive-index core layer and a low-refractive-index surface layer. By using refractive index matching, the overall light transmittance is improved by changing the propagation characteristics of light waves. At the same time, the organic anti-sticking particles used in the surface layer can effectively avoid the influence of inorganic particles on haze, and can effectively reduce the haze of the film.

[0043] Furthermore, Figure 2 A schematic diagram of the structure of a low-haze, high-transparency release film polyester film according to another specific embodiment of this application is shown. The film layer shown by the dashed line in the figure is the release agent layer 4. Because the release agent layer 4 is not part of the low-haze, high-transparency release film polyester film of this application, therefore... Figure 2 The image is shown in detail below. In the aforementioned embodiments, the basic idea of ​​this application is to improve the light transmittance of the film by using a combination of film layers with different refractive indices. However, the release film is composed of a polyester film and a release agent layer, and the refractive index of silicone oil-based release agents is generally relatively low, usually around 1.4. Therefore, after the release agent layer is formed on the surface, the entire release film will produce rainbow patterns due to the refractive index mismatch.

[0044] Experiments have shown that rainbow patterns can be avoided by coating the outer surface of the surface with a high-refractive-index coating 5. Specifically, a high-refractive-index coating 5 can be applied to the outer surface of the upper surface layer 1 and / or the lower surface layer 2, adjusting the overall refractive index of the polyester film with the high-refractive-index coating 5 to 1.69-1.73. Figure 2 As shown in the illustration. In the specific embodiment, it is preferable to coat the high refractive index coating 5 only on the outer side of the upper surface layer 1 adjacent to the release agent layer 4 to save costs. Of course, in order to allow for use on both sides, the high refractive index coating 5 can also be coated on the outer sides of both the upper surface layer 1 and the lower surface layer 2.

[0045] In one specific embodiment, the high refractive index coating 5 is composed of tris(2-hydroxyethyl)isocyanurate triacrylate, cyclohexanedimethyl diacrylate, nano-silicon nitride, and n-octyltrimethoxysilane. Figure 2 In the specific embodiment shown, the high refractive index coating 5 is preferably formed on the outer side of the upper surface layer 1 by online coating. That is, after the three-layer thick sheet is made by multi-layer co-extrusion process, the prepared high refractive index coating can be applied to the thick sheet. Then, as the thick sheet is stretched into a film of the required thickness, the coating on its surface becomes thinner as it is stretched. During the stretching process, it undergoes mechanical deformation and high-temperature chemical changes and then solidifies to form the high refractive index coating 5.

[0046] Furthermore, in one specific embodiment, the mass ratio of each component of the high refractive index coating 5 is (25-35): (20-30): (5-10): (30-60).

[0047] In another specific embodiment, the coating constituting the high refractive index coating 5 can be prepared by the following steps: adding n-octyltrimethoxysilane and nano-silicon nitride to a heated stirring vessel, heating to 55-60°C and stirring once for 3-5 hours, cooling to room temperature to prepare a mixture for later use; adding tri(2-hydroxyethyl)isocyanurate triacrylate and cyclohexanediethanol diacrylate to a mixing vessel, stirring twice at room temperature for 30-60 minutes; adding the mixture to the mixing vessel, stirring at room temperature for 2-3 hours, thereby preparing the high refractive index coating.

[0048] To improve the dispersibility of silicon nitride and enhance the uniformity of the coating, this application also proposes a method for surface modification of silicon nitride, comprising the following steps: dispersing 100 parts by weight of 5-10 nm silicon nitride in a reactor containing 200-300 parts by weight of deionized water to form a dispersion; adding 30-40 parts by weight of ethylene glycol while stirring the dispersion in the reactor; adding 10-15 parts by weight of polydimethylsiloxane while continuing to stir, and stirring at 80°C for 12-18 hours; and finally, removing the silicon nitride from the reactor. The compound is transferred to a vacuum distillation apparatus for vacuum distillation to remove water. Then, 10-15 parts by weight of 30% ammonium hydroxide and 15-25 parts by weight of ethylene glycol are added to a vacuum rectifier, and vacuum distillation is carried out while stirring to concentrate the solid content in the vacuum rectifier to 55-65 wt%. The concentrate in the vacuum rectifier is transferred to a filter to filter out the solid. Finally, the filtered solid is sent to a dryer and dried at 180-200 degrees Celsius for 1-1.5 hours to obtain the surface-modified nano-silicon nitride.

[0049] Examples 4-6 and Comparative Examples 2-4

[0050] The high refractive index coating of this application was prepared using the following parameters, wherein each group of the high refractive index coating is represented by A, B, C, and D, respectively, as tris(2-hydroxyethyl)isocyanurate triacrylate, cyclohexanediethanol diacrylate, nano-silicon nitride, and n-octyltrimethoxysilane. Stirring in a heated stirred tank constitutes one stirring session, lasting for hours (h), while stirring in a mixing tank constitutes a second stirring session, lasting for minutes (m).

[0051]

[0052] The high-refractive-index coatings prepared in Examples 4-6 and Comparative Examples 2-4 were applied onto the thick sheet extruded in Example 1 using an online coating process. The thick sheet was then stretched to form a high-refractive-index coating 5 on the outer side of the upper surface layer 1. The performance parameters are shown in the table below. The transmittance and refractive index were tested using the polyester film and the high-refractive-index coating 5 as a whole.

[0053] Example 4 Example 5 Example 6 Comparative Example 2 Comparative Example 3 Comparative Example 4 transmittance % 95.1 94.3 96.5 73.4 65.6 70.7 Refractive index 1.69 1.73 1.71 1.60 1.55 1.61

[0054] As can be seen from the performance parameter comparison of the above embodiments and comparative examples, forming a high refractive index optical coating on the surface of a polyester film by online coating can achieve excellent light transmittance and refractive index.

[0055] Example 7

[0056] The high-refractive-index coatings prepared in Examples 4-6 and Comparative Examples 2-4 were applied to the thick sheet extruded in Example 1 using an online coating process. The sheet was then stretched to form a high-refractive-index coating 5 on the outer side of the upper surface layer 1. A release agent layer 4 was then further applied offline to the outer side of the high-refractive-index coating 2, thus preparing a release film. The performance parameters of the release film are shown in the table below. The transmittance and refractive index were tested using the polyester film and the high-refractive-index coating 5 as a whole. The release agent layer 4 used a commercially available silicone oil-based release agent with a refractive index of approximately 1.4, primarily composed of polyacrylate resin and polydimethylsiloxane. The transmittance of the liquid release agent was greater than or equal to 90%, and the coating thickness of the release agent layer 4 was 5 μm.

[0057] Example 4 Example 5 Example 6 Comparative Example 2 Comparative Example 3 Comparative Example 4 transmittance % 89.9 90.1 90.3 68.5 67.4 68.3 Does it have rainbow patterns? none none none have have have

[0058] As can be seen from the parameter comparison of the above embodiments, the polyester film prepared by matching the refractive indices of each film layer in this application has excellent high light transmittance and low haze characteristics. Moreover, by coating with a high refractive index coating, the anti-rainbow pattern performance of the release film can be further improved.

[0059] Those skilled in the art should understand that although this application is described by way of multiple embodiments, not every embodiment contains only one independent technical solution. This description is merely for clarity, and those skilled in the art should understand the specification as a whole and consider the technical solutions involved in each embodiment as being able to be combined with each other to form different embodiments to understand the scope of protection of this application.

[0060] The above description is merely an illustrative embodiment of this application and is not intended to limit the scope of this application. Any equivalent changes, modifications, and combinations made by those skilled in the art without departing from the concept and principles of this application shall fall within the scope of protection of this application.

Claims

1. A polyester film for a low-haze high-transmission polarizing film, comprising an upper surface layer, a lower surface layer, and a core layer, wherein, The upper and lower surface layers are anti-sticking layers with anti-sticking particles added; the core layer is a supporting layer with anti-static particles added; characterized in that the upper and lower surface layers are composed of the following raw materials in mass percentage: 8%-10% of anti-sticking particles, 90%-92% of polyester chips with a refractive index of 1.63-1.65, wherein the anti-sticking particles are poly-4-methyl-1-pentene with a refractive index of 1.46; the core layer is composed of the following raw materials in mass percentage: 5%-7% of anti-static particles, 92-95% of polyester chips with a refractive index of 1.63-1.65, wherein the anti-static particles are zinc oxide with a refractive index of 2.0; the outer side of the upper surface layer and / or the lower surface layer is coated with a high-refractive coating layer, the overall refractive index of the low-haze high-transmittance polarizing film with the high-refractive coating layer is 1.69-1.73; the high-refractive coating layer is composed of tri(2-hydroxyethyl) isocyanurate triacrylate, cyclohexane dimethanol diacrylate, nano-silicon nitride, and n-octyl trimethoxysilane; the mass ratio of each component of the high-refractive coating layer is as follows: tri(2-hydroxyethyl) isocyanurate triacrylate: cyclohexane dimethanol diacrylate: nano-silicon nitride: n-octyl trimethoxysilane is (25-35):(20-30):(5-10):(30-60).

2. A preparation method of the low-haze high-transmittance polarizing film polyester film according to claim 1, comprising the following steps: mixing poly-4-methyl-1-pentene with a refractive index of 1.46 and optical-grade PET polyester chips with a refractive index of 1.63-1.65 into a surface layer mixture, mixing zinc oxide with a refractive index of 2.0 and optical-grade PET polyester chips with a refractive index of 1.63-1.65 into a core layer mixture; taking the surface layer mixture as raw material, the material melted and extruded by an extruder as the upper and lower surface layers, taking the core layer mixture as raw material, the material melted and extruded by an extruder as the core layer, and preparing a three-layer structure thick sheet through a multi-layer co-extrusion process; coating the prepared high-refractive coating on the thick sheet, and then preparing a low-haze high-transmittance polarizing film polyester film with a high-refractive coating layer by stretching the thick sheet in two directions.

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