Medium-matte polyester film and preparation method thereof

Abstract

The invention discloses a medium-matte polyester film which is composed of a base material layer A, a surface matte layer B and a matte coating C sprayed on the outer side of the surface matte layer B. The base material layer A is composed of polyethylene glycol terephthalate and silicon dioxide nanoparticles. The surface matte layer B is composed of polyethylene glycol terephthalate, polytetrafluoroethylene and polyethylene glycol nanoparticles; the matte coating C is prepared from polyurethane acrylate, organic silicon silicon dioxide particles, triethylene glycol tripropoxy acrylate, benzophenone, polyether siloxane and polydimethylsiloxane. According to the medium-matt-degree polyester film, by optimizing the proportion of components such as PET, SiO2, PTFE and PEG, the good mechanical strength, wear resistance and matt effect are balanced, and the medium-matt-degree polyester film has excellent light transmittance and ultraviolet resistance. The film not only has low glossiness and high haze, but also shows excellent chemical resistance, scratch resistance and long-term stability, and is suitable for high-end applications such as polaroid release films and optical devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of matte film, in particular to a medium matte polyester film and a preparation method thereof. BACKGROUND

[0002] Matte film has a great demand in the fields of packaging, labeling, decoration, printing, etc. Generally, the reflectivity of the film surface below 10% is considered to be matte; the reflectivity between 10% and 30% is considered to be semi-matte; and the reflectivity above 30% is considered to be glossy. The degree of matte is generally represented by glossiness, which is usually in the range of 0% to 100%. 0% represents complete matte (e.g. matte surface), and 100% represents maximum glossiness (e.g. mirror surface). Glossiness is usually measured by a gloss meter. High matte film generally refers to the surface glossiness below 10%, which has almost no gloss. Medium matte film generally refers to the surface glossiness between 10% and 30%, which has a certain gloss but still maintains a relatively low reflectivity. Low matte film has a surface glossiness between 30% and 50%, which is relatively smooth and has obvious gloss but does not belong to the category of high gloss.

[0003] CN 106739367 B discloses a single-side matte polyester film having a co-extrusion double-layer structure composed of a matte film layer and a base film layer. The matte film layer is composed of a polyester masterbatch containing an additive and a balance of a polyester base material. The additive in the polyester masterbatch is composed of silicon dioxide and an auxiliary filler selected from at least one of calcium carbonate, hollow glass microbeads, aluminum oxide, kaolin and titanium dioxide.

[0004] The matte film of the prior art described above forms scattering of light in the film layer by adding inorganic solid particles, reduces the direct reflection of the film layer to light of the same angle of incidence, and obtains a certain matte effect. The scattering of light by the solid particles also hinders the projection of light, thereby reducing the light transmission performance of the film. At the same time, although there is scattering of light by the solid particles in the film layer, the influence on the surface of the film is limited, and the roughness of the film surface is difficult to effectively reduce, and the smooth surface is difficult to reduce the light reflectivity. In addition, in order to obtain sufficient matte effect, the particle size of the added solid particles needs to reach a certain degree, and a sufficient amount is also required. The addition of too many large-diameter solid particles will form cavities in the interior of the matte layer during film stretching, reducing the density and strength of the matte layer, thereby resulting in insufficient tear resistance of the outer matte layer and easy breakage and fragmentation, and the surface texture will quickly decrease due to the pores of the stretched film layer which are easily penetrated by colorants to present patches. SUMMARY

[0005] The technical problem solved by the present application is to provide a medium matte polyester film and a preparation method thereof to reduce or avoid the problems mentioned above.

[0006] To solve the above technical problem, the present application provides a medium matte polyester film, which is composed of a base material layer A, a surface matte layer B and a matte coating layer C sprayed on the outside of the surface matte layer B, wherein the base material layer A is composed of 85-90% by mass of polyethylene terephthalate and 10-15% by mass of silica nanoparticles; the surface matte layer B is composed of 80-85% by mass of polyethylene terephthalate, 5-7% by mass of polytetrafluoroethylene and 10-13% by mass of polyethylene glycol nanoparticles; and the matte coating layer C is formed by ultraviolet curing of a coating material composed of 60-65% by mass of polyurethane acrylate, 15-20% by mass of silicone silica microparticles, 15-20% by mass of tripropoxy acrylate, 1.5-3% by mass of benzophenone, 0.5% by mass of polyether siloxane and 0.5% by mass of polydimethylsiloxane.

[0007] Preferably, the thickness of the base material layer A is 30-35 μm; the thickness of the surface matte layer B is 8-10 μm; and the thickness of the matte coating layer C is 1-5 μm.

[0008] The present application also provides a preparation method of the medium matte polyester film, which comprises the following steps: weighing the raw materials for the base material layer A and the surface matte layer B, and respectively feeding them into respective mixers for melt blending, with the melt temperature controlled at 250-270°C; melt extruding the base material layer A by a main extruder at 250-260°C, with the cooling roll temperature controlled at 20°C; melt extruding the surface matte layer B by an auxiliary extruder at 260-270°C, with the cooling roll temperature controlled at 15°C; making the two extruded film layers enter a cooling system to be laminated to form a double-layer thick sheet, with the cooling temperature of the thick sheet controlled at 15-20°C; performing 2 times of longitudinal stretching of the double-layer thick sheet at 85-90°C, and then performing 3.5 times of transverse stretching at 110-120°C; uniformly spraying the coating material for the matte coating layer C on the surface of the surface matte layer B, with the coating thickness controlled at 5-10 μm; then performing ultraviolet light initiation treatment, with the ultraviolet light wavelength controlled at 365 nm, the irradiation intensity controlled at 300 mW / cm2, the time controlled at 3 minutes, and the cooling temperature controlled at room temperature, to form the matte coating layer C; and finally performing heat setting treatment on the film with the matte coating layer. 2

[0009] ​Preferably, the preparation method further comprises the step of preparing the matte coating: mixing polyurethane acrylate and tripropylene glycol triacrylate in a mass ratio, and stirring at room temperature until completely dissolved to form a uniform solution; adding silicone silica microparticles to the above solution, stirring for 10-15 minutes to ensure uniform dispersion; adding benzophenone, polyether siloxane, and polydimethylsiloxane in proportion, and slowly stirring for 5 minutes to completely dissolve each component; filtering the solution with a 100-mesh filter to remove undispersed particles or impurities.

[0010] Preferably, the matte coating layer is heat set at 200-210°C for 5-10 seconds.

[0011] The matte polyester film of the present application balances good mechanical strength, wear resistance, and matte effect by optimizing the ratio of PET, SiO2, PTFE, PEG, and other components, and has excellent light transmittance and ultraviolet resistance. The film not only has low gloss and high haze, but also exhibits excellent chemical resistance, scratch resistance, and long-term stability, and is suitable for polarizing sheet release film and optical devices and other high-end applications. BRIEF DESCRIPTION OF DRAWINGS

[0012] The following drawings are merely intended to illustrate and explain the present application, and do not limit the scope of the present application.

[0013] Figure 1 A structure diagram of a matte polyester film according to one embodiment of the present application is shown. DETAILED DESCRIPTION

[0014] In order to have a clearer understanding of the technical features, objectives, and effects of the present application, the specific embodiments of the present application will be described with reference to the drawings. Identical components are denoted by identical reference numerals.

[0015] As shown in Figure 1 The present application proposes a matte polyester film, which is composed of a substrate layer A, a surface matte layer B, and a matte coating layer C sprayed on the outer side of the surface matte layer B.

[0016] In one embodiment, the thickness of the substrate layer A is 30-35 μm; the thickness of the surface matte layer B is 8-10 μm; and the thickness of the matte coating layer C is 1-5 μm. When the thickness of the matte coating layer C is preferably 1-3 μm, the matte effect of the film does not significantly affect the transparency of the film, and is suitable for applications requiring high light transmittance. When the thickness of the matte coating layer C is preferably 3-5 μm, it is suitable for occasions with high requirements for low gloss, such as anti-glare applications.

[0017] The total thickness of the matte polyester film of the present application is preferably designed to be about 40 pm, so that the film maintains flexibility and light transmittance while meeting mechanical strength. The thickness of the matte coating C is 1-5 pm, which can ensure uniform distribution of the coating while maintaining low gloss and wear resistance, without causing excessive impact on the mechanical properties of the substrate.

[0018] In another specific embodiment, the substrate layer A is composed of 85-90% by mass of polyethylene terephthalate (PET) and 10-15% by mass of silica (SiO2) nanoparticles.

[0019] Further, the polyethylene terephthalate preferably uses optical grade PET particles or chips, preferably raw material products with a melting point of about 255°C, such as high-purity optical grade PET provided by Toray, DuPont, etc., with a light transmittance of more than 90%. The silica nanoparticles preferably use products with a particle size of 50-100 nm, such as Aerosil series from Evonik, such as Aerosil 200, or Cab-O-Sil series from Cabot.

[0020] In yet another specific embodiment, the surface matte layer B is composed of 80-85% by mass of polyethylene terephthalate (PET), 5-7% by mass of polytetrafluoroethylene (PTFE), and 10-13% by mass of polyethylene glycol (PEG) nanoparticles.

[0021] Further, the polyethylene terephthalate preferably uses optical grade PET particles or chips, preferably raw material products with a melting point of about 255°C, such as high-purity optical grade PET provided by Toray, DuPont, etc., with a light transmittance of more than 90%. The silica nanoparticles preferably use products with a particle size of 50-100 nm, such as Aerosil series from Evonik, such as Aerosil 200, or Cab-O-Sil series from Cabot. TM PTFE or Solvay's PTFE series. The polyethylene glycol preferably uses products with a molecular weight range of 2000-6000, such as PEG produced by Merck or Sigma-Aldrich, etc.

[0022] In yet another specific embodiment, the matte coating C is composed of the following mass fractions of raw materials: 60-65% of polyurethane acrylate (PUA), 15-20% of silicone silica microparticles, 15-20% of tripropoxy acrylate (TMPTA), 1.5-3% of benzophenone (BP), 0.5% of polyether siloxane, and 0.5% of polydimethylsiloxane.

[0023] Further specifically, the polyurethane acrylate (PUA) preferably adopts a product with a viscosity range of 3000-5000 cps, such as the polyurethane acrylate resin provided by BASF, Mitsubishi Chemical and the like; further preferably, the PUA suitable for UV curing coating, such as the Laromer series of Merck KGaA (Germany Merck). The silicone silica microparticle preferably adopts a product with a particle size of 3-5 μm, such as the Sipernat series of Degussa, or the Syloid series of Grace. The tripropoxy acrylate of triethylene glycol preferably adopts a product with a purity of greater than or equal to 98%, such as the high-purity TMPTA supplied by Sigma-Aldrich or Allnex. The benzophenone preferably has a spectral range of about 365 nm, with a purity of ≥ 99%. For example, the UV curing series product of IGM Resins or BASF. Both the polyether siloxane and the polydimethylsiloxane can adopt the products of BYK Chemical Company, such as the polyether siloxane can adopt BYK-333, and the polydimethylsiloxane can adopt BYK-016.

[0024] Further specifically, the coating material constituting the matte coating layer C can be prepared by the following process. For example, the polyurethane acrylate and TMPTA are mixed in a mass ratio, and stirred at room temperature until completely dissolved, forming a uniform solution. The silicone silica microparticle is added to the above solution, and stirred for 10-15 minutes to ensure uniform dispersion. The use of high-speed stirring equipment (about 1000 rpm) is better. The benzophenone, polyether siloxane, and polydimethylsiloxane are added in proportion, and slowly stirred for 5 minutes to completely dissolve each component. The solution is filtered with a 100-mesh screen to remove undispersed particles or impurities, ensuring the uniformity and transparency of the coating.

[0025] The matte coating material of the present application significantly reduces the gloss of the coating layer by adding silicone silica microparticles and forming a surface rough structure, achieving a medium matte effect. The cross-linked structure of the PUA matrix resin and TMPTA improves the hardness and wear resistance of the coating layer. The composite structure of the silicone silica microparticle and PUA not only reduces the gloss, but also has the function of resisting ultraviolet rays, prolonging the service life of the film. The design and process of the coating material help to form a uniform and stable matte layer on the surface, ensuring a low gloss effect, while enhancing the durability of the film.

[0026] Further, the medium matte polyester film of the present application can be prepared by the following process.

[0027] The raw materials constituting the substrate layer A and the surface matte layer B are weighed and respectively put into the respective mixing machines for melt blending, with the melt temperature controlled at 250-270°C.

[0028] The base layer A was melt-extruded by the main extruder at 250-260°C, and the cooling roll temperature was 20°C. The surface matte layer B was melt-extruded by the auxiliary extruder at a temperature of 260-270°C, and the cooling roll temperature was 15°C. The two extruded film layers were simultaneously fed into the cooling system to form a double-layered thick sheet, and the cooling temperature of the thick sheet was set at 15-20°C.

[0029] The double-layered thick sheet was subjected to 3 times of longitudinal stretching at 85-90°C, and then 3.5 times of transverse stretching at 110-120°C.

[0030] The coating material constituting the matte coating layer C was uniformly sprayed on the surface of the surface matte layer B, and the coating thickness was controlled at 5-10 μm. Then, the coating was treated by UV initiation, the wavelength of the UV light was 365 nm, the irradiation intensity was 300 mW / cm 2 , the time was controlled at 3 minutes, and the coating was cooled to room temperature to form the matte coating layer C.

[0031] Finally, the film with the matte coating layer was heat-set at 200-210°C for 5-10 seconds to ensure the stability of the layered structure and to enhance the dimensional stability and durability of the film.

[0032] The polyester film prepared was subjected to performance tests. The gloss, haze, and light transmittance of the film were tested by using a BYK or HunterLab gloss meter and haze meter. The tensile strength and elongation at break were tested by using an Instron tensile testing machine according to the ASTM standard specification. The UV aging performance was tested by setting the Q-SUN of Q-Lab or the UV testing box of Atlas for 500 hours weatherability.

[0033] The measurement standards of the relevant performance parameters are shown below.

[0034] Gloss test standard: ASTM D523, measured with 60° gloss meter. Haze test standard: ASTM D1003, measured with haze meter, tested the scattering effect, anti-glare performance of the film. Transmittance test standard: ASTM D1003, measured with light transmittance tester, tested the light transmittance of the film under the matte effect. Tensile strength test standard: ASTM D882, tested on machine direction (MD) and transverse direction (TD) with tensile tester, tested the durability of the film. Elongation at break test standard: ASTM D882, characterized the flexibility and durability of the film. Coefficient of friction (COF) test standard: ASTM D1894, measured with coefficient of friction tester, tested the surface smoothness of the film. Surface hardness test standard: ASTM D3363, pencil hardness test, evaluated the scratch resistance of the coating, tested the wear resistance of the film during use. Anti-UV performance: maintained at least 90% above transmittance and gloss after 500 hours of exposure to ultraviolet light, tested whether the change rate exceeded 10%. Test standard: ASTM G154, ultraviolet aging test, simulated the stability under long-term exposure. Chemical resistance: resistant to wiping with common chemical solvents such as ethanol, isopropanol, etc., whether there was obvious damage to the surface. Test standard: ASTM D5402, coating chemical resistance test, tested the stability of the surface matte layer. Matt coating adhesion test standard: ASTM D3359, used crosshatch method to test the adhesion of the coating to the substrate, tested the stability of the matt coating during use.

[0035] Example 1

[0036] The matte polyester film of this example is composed of a 33 μm thick substrate layer A, a 9 μm thick surface matte layer B, and a 3 μm thick matt coating layer C.

[0037] The substrate layer A contains 87% polyethylene terephthalate (PET), 13% silicon dioxide (SiO2); the surface matte layer B contains 83% PET, 6% polytetrafluoroethylene (PTFE), and 11% polyethylene glycol (PEG) nanoparticles; the matt coating layer C is composed of 63% polyurethane acrylate (PUA), 17% silicone silica microparticles, 16.5% tripropoxy acrylate (TMPTA), 2.5% benzophenone (BP), 0.5% polyether siloxane, and 0.5% polydimethylsiloxane.

[0038] The film of Example 1 has a gloss of 16%, a haze of 18%, a transmittance of 89%, a tensile strength of 131 MPa, an elongation at break of 115%, a coefficient of friction of 0.4, a surface hardness of 2H, a change in transmittance and gloss of 8% after 500 hours of ultraviolet light aging, excellent resistance to common chemical solvents, and a matt coating adhesion of 5B.

[0039] Example 2

[0040] The matte polyester film of this example is composed of a 30 μm thick base layer A, an 8 μm thick surface matte layer B, and a 1 μm thick matte coating layer C.

[0041] The base layer A contains 85% PET and 15% SiO2; the surface matte layer B contains 80% PET, 7% PTFE, and 13% PEG; and the matte coating layer C contains 60% PUA, 16% silicone silica particles, 20% TMPTA, 3% BP, 0.5% polyether siloxane, and 0.5% dimethicone.

[0042] The film of Example 2 has a glossiness of 18%, a haze of 21%, and a light transmittance of 87%; a tensile strength of 135 MPa, an elongation at break of 121%; a friction coefficient of 0.4, a surface hardness of 2H; a change in light transmittance and glossiness of 7% after 500 hours of ultraviolet light aging; excellent resistance to common chemical solvents; and a matte coating adhesion of 5B.

[0043] Example 3

[0044] The matte polyester film of this example is composed of a 35 μm thick base layer A, an 10 μm thick surface matte layer B, and a 5 μm thick matte coating layer C.

[0045] The base layer A contains 90% PET and 10% SiO2; the surface matte layer B contains 85% PET, 5% PTFE, and 10% PEG; and the matte coating layer C contains 65% PUA, 15% silicone silica particles, 17.5% TMPTA, 1.5% BP, 0.5% polyether siloxane, and 0.5% dimethicone.

[0046] The film of Example 3 has a glossiness of 19%, a haze of 20%, and a light transmittance of 88%; a tensile strength of 133 MPa, an elongation at break of 122%; a friction coefficient of 0.4, a surface hardness of 2H; a change in light transmittance and glossiness of 6% after 500 hours of ultraviolet light aging; excellent resistance to common chemical solvents; and a matte coating adhesion of 5B.

[0047] Comparative Example 1

[0048] On the basis of Example 1, the polytetrafluoroethylene (PTFE) in the surface matte layer B was removed.

[0049] That is, the surface matte layer B contains 85% PET and 15% PEG.

[0050] The performance parameters changed as follows: the friction coefficient rose to 0.6, the wear resistance decreased, and the matte coating adhesion decreased to 4B, indicating the importance of PTFE in reducing the friction coefficient and improving the wear resistance.

[0051] Comparative Example 2

[0052] On the basis of Example 1, the benzophenone (BP) is absent in matte coating C.

[0053] That is, matte coating C: 63% PUA, 17% silicone silica microparticles, 18% TMPTA, 0.5% polyether siloxane, 0.5% polydimethylsiloxane.

[0054] Performance parameter change: light transmittance change of 12% and gloss change of 15% after UV aging for 500 hours, indicating the key role of BP in anti-UV performance.

[0055] Comparative Example 3

[0056] On the basis of Example 1, the SiO2 content in substrate layer A is reduced to 8%.

[0057] That is, substrate layer A: 92% PET, 8% SiO2.

[0058] Performance parameter change: gloss rises to 22% and haze drops to 15%, indicating that SiO2 microparticles contribute to matte effect and light scattering performance.

[0059] Comparative Example 4

[0060] On the basis of Example 2, PEG in surface matte layer B is replaced with PMMA.

[0061] That is, surface matte layer B: 80% PET, 7% PTFE, 13% PMMA.

[0062] Performance parameter change: light transmittance drops to 82%, surface hardness rises to 3H, but gloss rises to 22%, indicating the advantage of PEG in improving matte effect.

[0063] Comparative Example 5

[0064] On the basis of Example 2, the content of silicone silica microparticles in matte coating C is reduced to 10%.

[0065] That is, matte coating C: 60% PUA, 10% silicone silica microparticles, 24% TMPTA, 3% BP, 0.5% polyether siloxane, 0.5% polydimethylsiloxane.

[0066] Performance parameter change: gloss rises to 20% and haze drops to 17%, indicating the reinforcing effect of silica microparticles.

[0067] Comparative Example 6

[0068] On the basis of Example 2, the SiO2 microparticles in substrate layer A are replaced with aluminum oxide (Al2O3).

[0069] i.e. substrate layer A: 85% PET, 15% AI2O3.

[0070] Performance parameter changes: light transmittance dropped to 84%, haze rose to 25%, but glossiness dropped to 16%, indicating the advantage of SiO2 in comprehensive optical performance and matte effect.

[0071] Comparative Example 7

[0072] On the basis of Example 3, the PTFE content in the surface matte layer B was reduced to 3%.

[0073] i.e. surface matte layer B: 87% PET, 3% PTFE, 10% PEG.

[0074] Performance parameter changes: friction coefficient rose to 0.5, wear resistance decreased, indicating the contribution of PTFE content to surface slipperiness and wear resistance.

[0075] Comparative Example 8

[0076] On the basis of Example 3, PUA in the matte coating C was replaced with epoxy acrylate (EA).

[0077] i.e. matte coating C: 65% EA, 15% silicone silica particles, 17.5% TMPTA, 1.5% BP, 0.5% polyether siloxane, 0.5% polydimethylsiloxane.

[0078] Performance parameter changes: surface hardness rose to 3H, but flexibility decreased, and UV aging performance changed significantly, indicating the advantage of PUA in balancing hardness and flexibility.

[0079] Comparative Example 9

[0080] On the basis of Example 3, the PET content in the substrate layer A was reduced to 80%.

[0081] i.e. substrate layer A: 80% PET, 20% SiO2.

[0082] Performance parameter changes: film mechanical properties decreased, tensile strength decreased to 120 MPa, and elongation at break decreased to 110%, indicating the importance of PET to the mechanical properties of the substrate layer.

[0083] The performance comparison results are shown in the following table.

[0084]

[0085] From the comparative results of Examples 1-3 and Comparative Examples 1-9, it is shown that, in the base layer A, polyethylene terephthalate as the base material provides the mechanical strength, flexibility and stability of the film. The higher content of PET (85-90%) in the examples helps to maintain the optical clarity and durability of the film. In the comparative examples, the reduction of PET content (e.g. 80% in Comparative Example 9) significantly reduces the mechanical properties and durability of the film, resulting in a decrease in tensile strength. The silica nanoparticles help to increase the surface roughness of the base material, provide microstructure, enhance the mechanical adhesion of the coating, and improve the matte effect. The 13% SiO2 in Example 1 helps to optimize the surface optical effect and wear resistance. In Comparative Example 3, the reduction of SiO2 to 8% results in an increase in the surface gloss of the film and a decrease in the haze, indicating that the reduction of SiO2 has a negative impact on the matte effect.

[0086] In the surface matte layer B, similar to PET in the base layer, a high content of PET provides the stability and mechanical properties of the film. As the main component of the matte layer, it can effectively support the adhesion of the coating. The addition of PTFE significantly improves the friction properties of the film, reduces the friction coefficient, and helps to improve the wear resistance and smoothness. In Examples 2 and 3, the PTFE content is 5-7%, and in Comparative Example 1 (which lacks PTFE), the friction coefficient rises to 0.6, indicating that PTFE plays an important role in reducing the friction coefficient and enhancing the wear resistance. PEG can enhance the lubricity and wear resistance of the coating and help to improve the antistatic properties of the film. In the examples, the PEG content is 10-13%, which not only improves the friction coefficient, but also enhances the chemical stability and environmental adaptability of the film to some extent. In Comparative Example 4, PEG is replaced by PMMA, resulting in a decrease in the light transmittance of the film and an increase in the gloss, indicating that PEG plays an important role in optical properties and matte effect.

[0087] In the matte coating C, PUA is the main component of this coating, which has excellent adhesion, elasticity and durability. It helps the coating to solidify into a dense protective layer, enhancing the film's wear resistance, UV resistance and chemical resistance. In the comparative example 8, PUA is replaced by epoxy acrylate (EA), resulting in an increase in coating surface hardness but a decrease in flexibility, indicating that PUA plays a key role in balancing hardness and flexibility. Silicone silica particles contribute significantly to the coating's wear resistance, scratch resistance and matte effect. It forms a uniform microstructure in the coating, enhancing the coating's surface texture and light scattering ability. The examples contain 15%-20% of silicone silica particles, providing excellent wear resistance and good matte effect. Reducing this component (such as 10% in comparative example 5) will significantly affect the coating's wear resistance and matte effect, resulting in an increase in gloss and a decrease in haze. TMPTA as a crosslinking agent enhances the hardness and stability of the coating. Its content in the coating is 15%-20%, which has a positive effect on the stability and chemical resistance of the coating. BP is a UV absorber that can improve the UV resistance of the coating and delay the aging of the coating. In the examples, the content of BP is 2%-3%, and its absence or reduction (such as absence in comparative example 2) will significantly affect the UV aging performance, causing the change of light transmittance and gloss to be intensified.

[0088] The matte polyester film of the present application has the following advantages: (1) excellent mechanical properties and stability: by optimizing the PET and SiO2 content of the substrate layer A, the film has excellent tensile strength, elongation at break and surface hardness, ensuring its stability and long service life in various application environments. (2) good matte effect and optical performance: PTFE and PEG in the surface matte layer B help to improve the film's friction coefficient, wear resistance and lubricity, while the introduction of SiO2 further enhances the matte effect. Adjusting the ratio of these components can accurately control the gloss, haze and light transmittance, ensuring the balance between low gloss and high light transmittance of the film. (3) UV and chemical resistance: the optimized combination of silicone silica particles, PUA, BP and other components in the matte coating C effectively improves the film's UV resistance and chemical solvent resistance. Even under long-term UV irradiation, the film's light transmittance and gloss change is controlled at a low level. (4) enhanced wear resistance and scratch resistance: by selecting appropriate silicone particles and other fillers, the coating enhances the film's scratch resistance, wear resistance and anti-fouling ability, ensuring that the film maintains excellent appearance and function for a long time in high-end applications. (5) environmental protection and sustainability: this matte polyester film uses environmentally friendly materials by optimizing the components, which can meet the high performance requirements and has low environmental impact, meeting the requirements of modern industry for material sustainability.

[0089] Those skilled in the art should understand that, although the present application is described in the manner of multiple embodiments, not every embodiment contains only one independent technical solution. The description is only for the sake of clarity, and those skilled in the art should understand the specification as a whole and understand the technical solutions involved in each embodiment as being combined into different embodiments to understand the protection scope of the present application.

[0090] The above merely illustrates the specific embodiments of the present application, and is not intended to limit the scope of the present application. Any equivalent changes, modifications and combinations made by those skilled in the art without departing from the concept and principle of the present application shall fall within the scope of the present application.

Claims

1. A medium-matte polyester film, comprising a substrate layer A, a matte surface layer B, and a matte coating C sprayed onto the outer side of the matte surface layer B, characterized in that, The substrate layer A is composed of 85-90% polyethylene terephthalate and 10-15% silica nanoparticles by mass; the matte surface layer B is composed of 80-85% polyethylene terephthalate, 5-7% polytetrafluoroethylene, and 10-13% polyethylene glycol nanoparticles by mass; the matte coating C is formed by UV curing of a coating composed of the following raw materials in mass fractions: 60-65% polyurethane acrylate, 15-20% organosilicon silica microparticles, 15-20% tripropylene glycol triacrylate, 1.5-3% benzophenone, 0.5% polyether siloxane, and 0.5% polydimethylsiloxane.

2. The polyester film as described in claim 1, characterized in that, The thickness of the substrate layer A is 30-35 μm; the thickness of the surface matte layer B is 8-10 μm; and the thickness of the matte coating C is 1-5 μm.

3. A method for preparing a medium-dull polyester film as described in any one of claims 1-2, characterized in that, The preparation method includes the following steps: weighing the raw materials constituting the substrate layer A and the matte surface layer B, and separately feeding them into their respective mixers for melt blending, with the melt temperature controlled at 250-270℃; the substrate layer A is melt-extruded through the main extruder at 250-260℃, with the cooling roller temperature at 20℃; the matte surface layer B is melt-extruded through the auxiliary extruder at 260-270℃, with the cooling roller temperature at 15℃; the two extruded film layers are simultaneously fed into the cooling system to form a double-layer thick sheet, with the cooling temperature of the thick sheet set at 15-20℃; the double-layer thick sheet is subjected to a 2x longitudinal stretch at 85-90℃, and then a 3.5x transverse stretch at 110-120℃; The coating constituting the matte coating C was uniformly sprayed onto the surface of the matte layer B, with the coating thickness controlled at 5-10 μm; then, it was subjected to ultraviolet light initiation treatment with an ultraviolet light wavelength of 365 nm and an irradiation intensity of 300 mW / cm². 2 The time is controlled at 3 minutes, and the film is cooled to room temperature to form a matte coating C; finally, the film with the matte coating is heat-set.

4. The preparation method according to claim 3, characterized in that, The preparation method further includes the step of preparing a matte coating: mixing polyurethane acrylate and tripropylene glycol tripropoxyacrylate in a mass ratio and stirring at room temperature until completely dissolved to form a homogeneous solution; adding organosilicon silica microparticles to the above solution and stirring for 10-15 minutes to ensure uniform dispersion; adding benzophenone, polyether siloxane, and polydimethylsiloxane in proportion and stirring slowly for 5 minutes to ensure complete dissolution of each component; filtering the solution with a 100-mesh filter to remove undispersed particles or impurities.

5. The preparation method according to claim 4, characterized in that, The film forming the matte coating is heat-set at 200-210°C for 5-10 seconds.

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