Polyester film

Abstract

A polyester film belongs to the technical field of polyester film materials. The polyester film comprises A / B / A layers which are sequentially overlapped, the layer B is a layer which does not contain particles; the layer A comprises first spherical particles with the particle size of 0.8-1.5 mu m and second spherical particles with the particle size of 0.05-0.3 mu m, the adding amount of the first spherical particles is 100-1000 ppm, and the mass ratio of the first spherical particles to the second spherical particles is 1: 9-3: 7; the refractive index n1 of the first spherical particles meets the formula that n1-n0 is smaller than or equal to 0.15, and n0 is the refractive index of PET. The polyester film has both easy unwinding performance and low haze performance, the haze is 0.3%-0.8%, and the friction coefficient of the surface of the layer A is 0.30-0.35.

Description

Technical Field

[0001] This invention relates to the field of polyester film material technology, specifically to a polyester film that combines easy unwinding and low haze. Background Technology

[0002] Polyester film is a high-performance polymer film material made from polyethylene terephthalate (PET) through a biaxial stretching process. Due to its high strength, high transparency, low haze, and temperature resistance, it can be widely used in optical film substrates, base films for electronic component manufacturing and packaging, and protective base films.

[0003] For example, CN118698837B discloses a high-definition biaxially oriented polyester film and its coating process. The polyester film is composed of PET raw material and organic additives. The high-definition biaxially oriented polyester film is obtained by drying, melting, casting, longitudinal stretching, cooling, transverse stretching, heat setting, and cooling of the PET raw material. The crystallinity of the PET raw material is <2%. The organic additive is cross-linked polystyrene, and the amount used is 1~5% of the PET raw material. The coating process of the high-definition biaxially oriented polyester film includes: preparation of coating solution, supply of coating solution, film corona treatment, and gravure roller coating.

[0004] However, after the aforementioned biaxially oriented polyester films are wound into rolls, the small inter-film spacing makes it easy for adjacent film surfaces to stick together due to vacuum adsorption, leading to difficulties in unwinding. The industry typically improves unwinding performance by adding opening agent particles to create surface irregularities, increasing the inter-film spacing, reducing the contact area, and enhancing vacuum adsorption. However, the addition of opening agents can increase film haze due to the scattering or reflection of light by the particles. Therefore, balancing unwinding performance and low haze is a pressing problem that needs to be solved in the industry. Summary of the Invention

[0005] This application further improves the composition and structure of the polyester film in order to solve the above-mentioned technical problems. The object of this invention is to provide a polyester film.

[0006] The specific technical solution is explained below:

[0007] Polyester film, comprising sequentially stacked A / B / A layers;

[0008] Layer B is a layer without particles; Layer A contains first spherical particles with a particle size of 0.8~1.5μm and second spherical particles with a particle size of 0.05~0.3μm. The amount of the first spherical particles added is 100~1000ppm, and the mass ratio of the first spherical particles to the second spherical particles is 1:9~3:7. The refractive index n1 of the first spherical particles satisfies the formula: |n1-n0|≤0.15, where n0 is the refractive index of PET. Here, the refractive index n0 of PET is determined using the Abbe refractometer method specified in ASTM D542, and the measured refractive index n0 of PET is 1.57~1.58.

[0009] The above technical solution controls the amount, size, and shape of particles added to layer A, maintaining a mass ratio of large-diameter first spherical particles to small-diameter second spherical particles between 1:9 and 3:7, while adding no particles to layer B. This allows the film to possess both low haze and easy unwinding. The principle is as follows: the first spherical particles have a refractive index similar to PET resin; therefore, adding a small amount of large-diameter first spherical particles can improve unwinding performance with minimal impact on film haze. Simultaneously, adding a large amount of small-diameter second spherical particles further improves unwinding performance without reducing film haze. When the mass ratio of first to second spherical particles is less than 1:9, there are relatively too few large-diameter first spherical particles, resulting in poor surface venting and poor unwinding performance. When the mass ratio is greater than 3:7, there are relatively too many large-diameter first spherical particles, exceeding the adjustable range, and the film haze will significantly increase.

[0010] In a further embodiment, the A layer comprises 10-20 wt% masterbatch and 80-90 wt% PET resin; the masterbatch is made of the first spherical particles, the second spherical particles and PET matrix resin to improve the distribution uniformity of the first spherical particles and the second spherical particles.

[0011] In a further embodiment, layer A includes a resin base layer adjacent to layer B and a coating layer adjacent to the resin base layer. The first spherical particle is located within the resin base layer, and the second spherical particle is located within the coating layer. The coating layer further includes an acrylic matrix resin to appropriately reduce the amount of the first and second spherical particles added, thereby improving haze without affecting unwinding properties.

[0012] In a further preferred embodiment, the amount of the first spherical particles added in layer A is 100~300ppm.

[0013] In a further preferred embodiment, the particle size of the second spherical particle is 0.05~0.2μm.

[0014] In a further preferred embodiment, the thickness of the coating layer is 50~150nm.

[0015] In a preferred embodiment, the thickness of the A layer is 4% to 5% of the total thickness of the polyester film. Here, the A layer refers to a single A layer. If the A layer is too thick, it will affect the haze of the base film; if it is too thin, the particles may fall off.

[0016] In a preferred embodiment, the first spherical particle is selected from one of barium sulfate particles, PMMA (polymethyl methacrylate) organic particles, and melamine particles, and the second spherical particle is selected from one or a combination of barium sulfate particles, silica particles, and calcium carbonate particles.

[0017] In the above technical solution, the refractive index of barium sulfate particles can be measured using the microscopic immersion method (Method B) specified in GB / T 39691-2020, and the measured refractive index is 1.63 to 1.65. After PMMA organic particles and melamine particles are pressed into smooth and transparent thin sheets, their refractive index can be determined using the Abbe refractometer method specified in ASTM D542. The refractive index of PMMA organic particles is 1.49 to 1.50, and the refractive index of melamine particles is 1.55. The refractive indices of the above materials are similar to those of PET.

[0018] In a preferred embodiment, the haze of the polyester film is 0.3% to 0.8%, and the coefficient of friction of the surface of layer A is 0.30 to 0.35.

[0019] The method for preparing the polyester film according to any one of the above technical solutions:

[0020] The three layers of raw materials, A, B, and A, are melted and extruded through a die to form a PET casting sheet with layers A, B, and A stacked in sequence; then, through longitudinal stretching, transverse stretching, and heat setting, a polyester film is obtained.

[0021] In summary, the technical solution described in this invention has the following main beneficial effects:

[0022] Compared with the prior art, the polyester film described in this invention can balance easy unwinding and low haze, that is, it achieves easy unwinding of the polyester film with minimal sacrifice of haze.

[0023] Further or more detailed beneficial effects will be described in conjunction with specific embodiments in the detailed implementation. Detailed Implementation

[0024] The present invention will be further explained in conjunction with the embodiments:

[0025] The core technical problem faced by the technical solutions of this application's embodiments stems from the inventor's accurate understanding of the prior art. Therefore, how to obtain a polyester film that can balance easy unwinding and low haze is a technical problem that the inventor urgently needs to solve.

[0026] It should be noted that the embodiments do not constitute a limitation on the scope of protection of the claims of this invention. All technical solutions that can be reasonably expected by those skilled in the art based on the technical concepts provided / proved by the embodiments should be covered within the scope of protection of the claims of this invention.

[0027] In the implementation method:

[0028] Haze test method: Use a transmission haze meter and test according to GB / T 2410-2008 standard.

[0029] Friction coefficient test method: The friction coefficient tester shall be used to conduct the test in accordance with the GB / T 10006-2021 standard.

[0030] The specific implementation examples are detailed below:

[0031] Example 1:

[0032] This embodiment provides a polyester film having a layer-A-B-A structure stacked sequentially, wherein the thickness of layer A is 1.0 μm, the thickness of layer B is 18.4 μm, and the thickness of layer B accounts for 4.9% of the film thickness;

[0033] Layer A contains 600 ppm of first spherical particles and 2000 ppm of second spherical particles. The first spherical particles are spherical barium sulfate particles with a particle size of 1.2~1.5 μm, and the second spherical particles are barium sulfate particles with a particle size of 0.15~0.3 μm. The remainder is PET resin without particles.

[0034] Layer B is a PET resin layer without particles.

[0035] Example 2:

[0036] The difference from Example 1 is as follows:

[0037] The content of the second spherical particles in layer A is 5400 ppm.

[0038] Example 3:

[0039] The difference from Example 1 is as follows:

[0040] The content of the second spherical particles in layer A is 1500 ppm.

[0041] Example 4:

[0042] The difference from Example 1 is as follows:

[0043] The second spherical particle has a particle size of 0.05~0.2μm.

[0044] Comparative Example 1:

[0045] The difference from Example 1 is as follows:

[0046] The content of the second spherical particles in layer A is 5600 ppm.

[0047] Comparative Example 2:

[0048] The difference from Example 1 is as follows:

[0049] The content of the second spherical particles in layer A is 1400 ppm.

[0050] The methods and properties of polyester films prepared in Examples 1-4 and Comparative Examples 1-2 are as follows:

[0051] The two portions of A-layer raw material and one portion of B-layer raw material are added to three extruders, melted and extruded through three-layer dies to form a three-layer casting sheet with A-layer, B-layer, and A-layer stacked in sequence. After passing through cooling rollers, the casting sheet is subjected to longitudinal stretching, transverse stretching and heat setting in sequence to form a polyester base film.

[0052] The preheating temperature for longitudinal stretching is 70℃, the stretching temperature is 80℃, the stretching ratio is 3.5 times, and the stretching gap is 290mm; the preheating temperature for transverse stretching is 70℃, the stretching temperature is 110℃, the stretching ratio is 3.7; and the heat setting temperature is 210℃.

[0053] The properties of the polyester films prepared in Examples 1-3 and Comparative Examples 1-2 are shown in Table 1 below:

[0054] Table 1. Performance of polyester films prepared in Examples 1-3 and Comparative Examples 1-2 Performance / Number Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Haze / % 0.65 0.78 0.52 0.49 1.5 0.51 Static friction coefficient (μs) 0.322 0.334 0.315 0.314 0.349 0.298 Coefficient of kinetic friction (μd) 0.312 0.317 0.305 0.301 0.329 0.276

[0055] As can be seen from Table 1:

[0056] The films prepared in Examples 1-4 all maintain good unwinding properties and low haze. Among them, Example 4 uses second spherical particles with a smaller particle size range compared to Example 1, which has better haze.

[0057] The haze of the film prepared in Comparative Example 1 was significantly higher than that in Examples 1 and 2, indicating that when the mass ratio of the first spherical particle to the second spherical particle is less than 1:9, there are too many small-diameter second spherical particles, which improves the unwinding performance, but increases the haze and affects the low haze properties of the film.

[0058] The friction coefficient of the film prepared in Comparative Example 2 is significantly lower than that in Examples 1 and 3, indicating that when the mass ratio of the first spherical particle to the second spherical particle is greater than 3:7, there are too few small-diameter second spherical particles, resulting in a decrease in the friction coefficient and a deterioration in the unwinding performance.

[0059] Example 5:

[0060] This embodiment provides a polyester film having a sequentially stacked A-B-A layer structure, wherein the thickness of layer A is 0.9 μm, the thickness of layer B is 20 μm, and the thickness of layer B accounts for 4.1% of the film thickness.

[0061] Layer A contains 300 ppm of first spherical particles and 2700 ppm of second spherical particles. The first spherical particles are spherical barium sulfate particles with a particle size of 0.8~1.2 μm, and the second spherical particles are silica particles with a particle size of 0.1~0.25 μm. The remainder is PET resin without particles.

[0062] Layer B is a PET resin layer without particles.

[0063] The polyester film was prepared using the same method as in Examples 1-3. The resulting polyester film had a haze of 0.42%, a static friction coefficient (μs) of 0.312, and a dynamic friction coefficient (μd) of 0.309 for layer A.

[0064] Example 6:

[0065] This embodiment provides a polyester film having a layer-A-B-A structure stacked sequentially, wherein the thickness of layer A is 1.1 μm, the thickness of layer B is 21 μm, and the thickness of layer B accounts for 4.7% of the film thickness.

[0066] Layer A contains 1000 ppm of first spherical particles and 4000 ppm of second spherical particles. The first spherical particles are spherical barium sulfate particles with a particle size of 0.8~1.2 μm, and the second spherical particles are calcium carbonate particles with a particle size of 0.12~0.18 μm. The remainder is PET resin without particles.

[0067] Layer B is a PET resin layer without particles.

[0068] The polyester film was prepared using the same method as in Examples 1-3. The resulting polyester film had a haze of 0.67%, a static friction coefficient (μs) of 0.346, and a dynamic friction coefficient (μd) of 0.327 for layer A.

[0069] Example 7:

[0070] This embodiment provides a polyester film, which differs from Embodiment 1 in that:

[0071] In layer A, barium sulfate particles of 1.0~1.5μm and 0.1~0.3μm are first melt-granulated with PET matrix resin without particles to form a masterbatch, and then the masterbatch and PET resin without particles are used as raw materials for layer A.

[0072] In this embodiment, the masterbatch accounts for 10% of the mass of the raw material in layer A, and the remaining particle-free PET resin accounts for 90% of the mass of the raw material in layer A.

[0073] The polyester film was prepared using the same method as in Example 1.

[0074] Example 8:

[0075] This embodiment provides a polyester film, which differs from Embodiment 7 in that:

[0076] The masterbatch accounts for 20% of the raw material in layer A, and the remaining PET resin without particles accounts for 80% of the raw material in layer A.

[0077] The polyester film was prepared using the same method as in Example 1.

[0078] The properties of the polyester films prepared in Examples 1 and 7-8 are shown in Table 2 below:

[0079] Table 2 Performance of polyester films prepared in Examples 1 and 7-8 Performance / Number Example 1 Example 7 Example 8 Haze / % 0.65 0.53 0.58 Static friction coefficient (μs) 0.322 0.335 0.342 Coefficient of kinetic friction (μd) 0.312 0.324 0.331

[0080] As can be seen from Table 2, the films prepared in Examples 7 and 8 show improvements in both haze and unwinding performance compared to Example 1. This may be due to the addition of the first and second spherical particles in the form of masterbatch, which makes the particle dispersion more uniform, reduces the haze of the film, and improves the unwinding properties of the film.

[0081] Example 9:

[0082] This embodiment provides a polyester film, which differs from Embodiment 1 in that:

[0083] Layer A includes a resin base layer and a coating layer applied to the resin base layer. The coating layer is an exposed layer with a thickness of approximately 100 nm. The resin base layer is composed of barium sulfate particles and particle-free PET resin, while the coating layer is composed of silica particles and acrylic matrix resin.

[0084] The preparation method is as follows: two parts of resin base material and one part of B layer material are added to three extruders respectively. After melting, they are extruded through three-layer dies to form a three-layer film consisting of resin base, B layer and resin base layer stacked in sequence. After passing the film through cooling rollers, it is stretched longitudinally, stretched laterally and heat-set in sequence to form a pre-formed polyester base film. An acrylic water-based coating liquid is coated on the resin base material and dried to form a polyester base film.

[0085] The water-based coating solution comprises: 10 parts acrylic resin (brand name KB-001), 1 part curing agent (brand name ASSONR KB), silica particles, and the balance water;

[0086] In this embodiment, the amount of barium sulfate particles added to layer A is 150 ppm, with a particle size of 1.2~1.5 μm, and the amount of silica particles added to layer A is 600 ppm, with a particle size of 0.1~0.2 μm.

[0087] Example 10:

[0088] This embodiment provides a polyester film, which differs from Embodiment 9 in that:

[0089] Layer A includes a resin base layer and a coating layer coated on the resin base layer. The coating layer is an exposed layer with a thickness of approximately 150 nm. The resin base layer is composed of barium sulfate particles and particle-free PET resin, while the coating layer is composed of barium sulfate particles and an acrylic matrix resin. The preparation method of layer A is the same as in Example 9.

[0090] In this embodiment, the amount of barium sulfate particles added to layer A is 100 ppm, and the amount of barium sulfate particles added to layer A is 250 ppm.

[0091] Example 11:

[0092] This embodiment provides a polyester film, which differs from Embodiment 9 in that:

[0093] In layer A, there is a coating layer on the resin base layer, wherein the coating layer is an exposed layer and has a thickness of about 50 nm. The resin base layer is composed of PET resin without barium sulfate particles, while the coating layer is composed of barium sulfate particles and acrylic matrix resin. The preparation method of layer A is the same as in Example 9.

[0094] In this embodiment, the amount of barium sulfate particles added to layer A is 300 ppm, and the amount of barium sulfate particles added to layer A is 700 ppm.

[0095] The properties of the polyester films prepared in Examples 1, 9-11 are shown in Table 3 below:

[0096] Table 3 Performance of polyester films prepared in Examples 1, 9-11 Performance / Number Example 1 Example 9 Example 10 Example 11 Haze / % 0.65 0.35 0.32 0.39 Static friction coefficient (μs) 0.322 0.322 0.318 0.339 Coefficient of kinetic friction (μd) 0.312 0.318 0.311 0.324

[0097] As can be seen from Table 3, the films prepared in Examples 9-11 show improved haze and unwinding performance compared to Example 1. This may be because the addition of easily unwindable particles through a coating layer can reduce the amount of particles added to the film without affecting its easy unwinding properties, thus achieving optimal haze.

[0098] Example 12:

[0099] The difference from Example 1 is as follows:

[0100] The first spherical particle is a spherical PMMA particle with a particle size of 1.2~1.5μm.

[0101] Example 13:

[0102] The difference from Example 1 is as follows:

[0103] The first spherical particle is a spherical melamine particle with a particle size of 1.2~1.5μm.

[0104] The properties of the polyester films prepared in Examples 1, 12, and 13 are shown in Table 4 below:

[0105] Table 4 Performance of polyester films prepared in Examples 1, 12-13 Performance / Number Example 1 Example 12 Example 13 Haze / % 0.65 0.65 0.65 Static friction coefficient (μs) 0.322 0.325 0.319 Coefficient of kinetic friction (μd) 0.312 0.323 0.316

[0106] As can be seen from Table 4, the haze and friction coefficient of the films prepared in Examples 12 and 13 are comparable to those in Example 1.

[0107] In the description of this specification, the references to terms such as "embodiment," "basic embodiment," "preferred embodiment," "other embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0108] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0109] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A polyester film comprising sequentially stacked A / B / A layers; Its features are: The B layer is a layer without particles; the A layer contains first spherical particles with a particle size of 0.8~1.5μm and second spherical particles with a particle size of 0.05~0.3μm, the amount of the first spherical particles added is 100~1000ppm, and the mass ratio of the first spherical particles to the second spherical particles is 1:9~3:7; the refractive index n1 of the first spherical particles satisfies the formula: |n1-n0|≤0.15, where n0 is the refractive index of PET.

2. The polyester film according to claim 1, characterized in that: The A layer comprises 10-20 wt% masterbatch and 80-90 wt% PET resin; The masterbatch is made of the first spherical particles, the second spherical particles, and PET matrix resin.

3. The polyester film according to claim 1, characterized in that: Layer A includes a resin base layer adjacent to Layer B and a coating layer adjacent to the resin base layer. The first spherical particle is located within the resin base layer, and the second spherical particle is located within the coating layer. The coating layer also includes an acrylic matrix resin.

4. The polyester film according to claim 3, characterized in that: In layer A, the amount of the first spherical particles added is 100~300ppm.

5. The polyester film according to claim 1, characterized in that: The particle size of the second spherical particle is 0.05~0.2μm.

6. The polyester film according to claim 3, characterized in that: The thickness of the coating layer is 50~150nm.

7. The polyester film according to claim 1, characterized in that: The thickness of layer A is 4% to 5% of the total thickness of the polyester film.

8. The polyester film according to claim 1, characterized in that: The first spherical particle is selected from one of barium sulfate particles, PMMA organic particles, and melamine particles.

9. The polyester film according to claim 1, characterized in that: The second spherical particle is selected from one or a combination of barium sulfate particles, silicon dioxide particles, and calcium carbonate particles.

10. The polyester film according to any one of claims 1 to 9, characterized in that: The polyester film has a haze of 0.3% to 0.8%, and the surface friction coefficient of layer A is 0.30 to 0.35.