Polyester film for laser embossing and method for producing the same

Abstract

The present invention discloses a polyester film for laser embossing and a manufacturing method thereof, wherein the polyester film for laser embossing comprises a base layer and at least one epidermis layer formed on the base layer. The epidermis layer is used as an easy-to-emboss layer, and the material is a polyester base copolymer, the polyester base copolymer comprises a residue derived from a diacid component and a residue derived from a diol component, wherein the diacid component comprises terephthalic acid accounting for 85 to 95 mole percent of the total molar amount of the diacid and 5 to 15 mole percent of isophthalic acid, and the diol component comprises ethylene glycol accounting for 35 to 74 mole percent of the total molar amount of the diol, neopentyl glycol accounting for 1 to 15 mole percent, and 1,4-butanediol accounting for 25 to 50 mole percent.

Description

Technical Field

[0001] The invention relates to a polyester film, in particular to a polyester film for laser embossing and a manufacturing method thereof. Background Art

[0002] As people's living standards gradually improve, electronic products such as mobile phones, tablet computers, laptops, home appliances, and automobile products have become popular, and people's pursuit of personalized quality of the appearance of these products has become increasingly diverse. In addition, the personalized decoration of interior decoration materials such as furniture, door walls, and door handles is becoming more and more abundant. The external surfaces of these products usually have personalized 2D, 3D patterns or special color effects, such as imitation wood grain, soft touch, metallization and other special effects of high-end car interiors and furniture.

[0003] Polyester films (such as polyethylene terephthalate, polyethylene 2,6-naphthalate, etc.) have good performance in formability, mechanical properties, thermal properties, electrical properties and chemical resistance, and can be used for various purposes. As a decorative film, polyester film can obtain a variety of patterns or designs through embossing or printing processes to attract consumers. The embossing process is a technology that uses a die (or template) with a concave and convex three-dimensional pattern or pattern to extrude the target object from the surface to accurately transfer the three-dimensional pattern or pattern to the surface of the target object; therefore, compared with a flat pattern, the embossed pattern can better present a three-dimensional effect.

[0004] The existing method for making decorative polyester film is to first apply a polyester surface coating on a polyester substrate, then dry and solidify it, and then extrude the desired pattern or design with a die. However, this method is not only complicated and the yield cannot be improved, but also difficult to extrude clear and obvious patterns or designs. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a polyester film for laser embossing and a method for manufacturing the same in view of the deficiencies in the prior art.

[0006] In order to solve the above technical problems, one of the technical solutions adopted by the present invention is to provide a polyester film for laser embossing, which includes a base layer and at least one skin layer. The at least one skin layer is formed on the base layer, wherein the material of the at least one skin layer is a polyester base copolymer, the polyester base copolymer includes a residue derived from a diacid component and a residue derived from a diol component, the diacid component includes terephthalic acid accounting for 85 to 95 mole percent of the total molar amount of the diacid and 5 to 15 mole percent of isophthalic acid, and the diol component includes ethylene glycol accounting for 35 to 74 mole percent of the total molar amount of the diol, neopentyl glycol accounting for 1 to 15 mole percent, and 1,4-butanediol accounting for 25 to 50 mole percent.

[0007] Preferably, the base layer is made of polyethylene terephthalate.

[0008] Preferably, at least one of the skin layers contains 0.0003 to 3 weight percent of a crystal nucleating agent based on the total weight of the skin layer.

[0009] Preferably, the base layer contains 0.0003 to 2 weight percent of a crystal nucleating agent based on the total weight of the base layer.

[0010] Preferably, the thickness of at least one skin layer accounts for 2% to 20% of the total thickness of the polyester film.

[0011] Preferably, the inorganic polyester modifier is inorganic filler particles, and the average particle size thereof is 5 microns to 10 microns.

[0012] Preferably, the thickness of at least one skin layer accounts for 3% to 15% of the total thickness of the polyester film.

[0013] Preferably, the polyester base copolymer has a melting point of 190°C to 240°C.

[0014] Preferably, the polyester base copolymer has a melting point of 195°C to 230°C.

[0015] In order to solve the above technical problems, another technical solution adopted by the present invention is to provide a method for manufacturing a polyester film for laser embossing, which comprises: forming a base layer and at least one skin layer located on the base layer by multi-layer co-extrusion; and performing longitudinal (MD) stretching and transverse (TD) stretching on the base layer and at least one skin layer. The material of at least one skin layer is a polyester base copolymer, and the polyester base copolymer includes a residue derived from a diacid component and a residue derived from a diol component, and the diacid component includes terephthalic acid accounting for 85 to 95 mole percent of the total molar amount of the diacid and 5 to 15 mole percent of isophthalic acid, and the diol component includes ethylene glycol accounting for 35 to 74 mole percent of the total molar amount of the diol, neopentyl glycol accounting for 1 to 15 mole percent, and 1,4-butanediol accounting for 25 to 50 mole percent.

[0016] Preferably, the polyester composition forming at least one of the skin layers further comprises 2 to 10 weight percent of silicon dioxide particles based on the total weight of the polyester composition, and the particle size of the silicon dioxide particles is between 5 microns and 10 microns.

[0017] Preferably, at least one of the skin layers contains 0.0003 to 2 weight percent of a crystal nucleating agent based on the total weight of the skin layer.

[0018] Preferably, the base layer contains 0.0003 to 2 weight percent of a crystal nucleating agent based on the total weight of the base layer.

[0019] Preferably, the thickness of at least one of the skin layers is 1% to 30% of the total thickness of the polyester film, and the thickness of the base layer is 11 micrometers to 100 micrometers.

[0020] Preferably, the thickness of at least one skin layer accounts for 2% to 20% of the total thickness of the polyester film.

[0021] Preferably, the thickness of at least one skin layer accounts for 3% to 15% of the total thickness of the polyester film.

[0022] Preferably, the polyester base copolymer has a melting point of 190°C to 240°C.

[0023] Preferably, the polyester base copolymer has a melting point of 195°C to 230°C.

[0024] One of the beneficial effects of the present invention is that the polyester film for laser embossing provided by the present invention can clearly present embossed patterns of different depths on the surface through the technical scheme of "at least one of the epidermal layers is formed on the base layer, wherein the material of at least one of the epidermal layers is a polyester base copolymer, and the polyester base copolymer includes residues derived from diacid components and residues derived from diol components, and the diacid components include terephthalic acid accounting for 85 to 95 mole percent of the total molar amount of the diacids and isophthalic acid accounting for 5 to 15 mole percent, and the diol components include ethylene glycol accounting for 35 to 74 mole percent of the total molar amount of the diols, neopentyl glycol accounting for 1 to 15 mole percent, and 1,4-butanediol accounting for 25 to 50 mole percent."

[0025] In addition, the method for manufacturing the polyester film for laser embossing provided by the present invention adopts a multi-layer co-extrusion method to form two, three or more stacked functional polyester layers, which can effectively reduce the process difficulty and improve the yield of the finished product.

[0026] To further understand the features and technical contents of the present invention, please refer to the following detailed description and drawings of the present invention. However, the drawings provided are only for reference and description and are not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 FIG. 4 is a schematic structural diagram of a polyester film for laser embossing according to one embodiment of the present invention.

[0028] Figure 2 FIG. 4 is a schematic diagram of a polyester film for laser embossing according to an embodiment of the present invention in use.

[0029] Figure 3FIG. 4 is a schematic structural diagram of a polyester film for laser embossing according to another embodiment of the present invention.

[0030] Figure 4 This is a schematic structural diagram of a polyester film for laser embossing according to yet another embodiment of the present invention.

[0031] Figure 5 The figure is a flow chart of a method for manufacturing a polyester film for laser embossing according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] Polyester film has a wide range of uses, including at least processing paper products, flat printed products, packaging and labels for articles or foods, decorative stickers, etc. In addition, embossed patterns can enhance the aesthetics and uniqueness of polyester film products, while increasing the added value of polyester film products. In particular, there are many styles of laser embossed patterns, and the effects presented are beyond the reach of general printed patterns. Therefore, the present invention provides a technical solution for easily forming a concave-convex three-dimensional embossed pattern on the surface of a polyester film.

[0033] The following is an explanation of the implementation methods of the "polyester film for laser embossing and its manufacturing method" disclosed in the present invention through specific embodiments. Those skilled in the art can understand the advantages and effects of the present invention from the contents disclosed in this specification. The present invention can be implemented or applied through other different specific embodiments, and the details in this specification can also be modified and changed in various ways based on different viewpoints and applications without departing from the concept of the present invention. In addition, the drawings of the present invention are only simple schematic illustrations and are not depicted according to actual dimensions. It is stated in advance. The following embodiments will further explain the relevant technical contents of the present invention in detail, but the disclosed contents are not intended to limit the scope of protection of the present invention.

[0034] It should be understood that, although the terms "first", "second", "third", etc. may be used herein to describe various components or signals, these components or signals should not be limited by these terms. These terms are mainly used to distinguish one component from another component, or one signal from another signal. In addition, the term "or" used herein may include any one or more combinations of the associated listed items depending on the actual situation.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art. When a term appears in the singular, the plural form of the term is included. When a series of upper and lower limits are provided, all combinations of the ranges mentioned are included, as if each combination was explicitly listed.

[0036] First embodiment

[0037] See also Figure 1As shown, the first embodiment of the present invention provides a polyester film 1 for laser embossing, which is a double-layer structure, including a base layer 11 and a first skin layer 12. The base layer 11 has a first surface 111 and a second surface 112 opposite to each other, the first surface 111 is, for example, the upper surface of the base layer 11, and the second surface 112 is, for example, the lower surface of the base layer 11; the first skin layer 12 is formed on the first surface 111 of the base layer 11, and the first skin layer 12 is an easy-embossing layer.

[0038] When in use, a three-dimensional embossed pattern M1 can be formed on a metal template M by laser engraving technology, and then the metal template M is used to extrude the first skin layer 12 of the laser embossed polyester film 1, and the metal template M can be heated to a predetermined temperature (such as 200° C.) as needed, so that the first skin layer 12 has another three-dimensional embossed pattern P2 with a concave and convex shape opposite to the three-dimensional embossed pattern P1. However, these details are only feasible implementations provided by this embodiment, and are not intended to limit the present invention.

[0039] In this embodiment, the material of the first skin layer 12 is a polyester based copolymer, which includes residues derived from diacid components and residues derived from diol components, wherein the diacid components include 90 mole percent of terephthalic acid and 10 mole percent of isophthalic acid, and the diol components include 49 mole percent of ethylene glycol, 1 mole percent of neopentyl glycol, and 50 mole percent of 1,4-butanediol. The total thickness of the prepared film is 12 microns, wherein the thickness of the first skin layer 12 is 1 micron; the glass transition point (Tg) of the polyester based copolymer is 45°C, and the melting point (Tm) is 223°C. The post-processing performance (such as calendering processing performance) of the film is very excellent, and the embossing process can be easily performed.

[0040] It is worth mentioning that the aforementioned component composition can improve the crystallinity of the polyester base copolymer, thereby improving the heat resistance of the first skin layer 12; in addition, the aforementioned component group can also reduce the melting point of the polyester base copolymer, so that the embossing performance of the first skin layer 12 is improved.

[0041] The term "residue" as used herein refers to a group or unit derived from a specific compound in a chemical reaction result. That is, a "residue of a diacid component" is a group derived from a diacid component in a polyester or copolyester synthesized by esterification or polycondensation reaction; a "residue of a diol component" is a group derived from a diol component in a polyester or copolyester synthesized by esterification or polycondensation reaction.

[0042] Furthermore, the melting point of the polyester-based copolymer of the first epidermis layer 12 is 190°C to 240°C, preferably 195°C to 230°C. If the melting point of the polyester-based copolymer is higher than 240°C, the embossing processability will be impaired; if the melting point of the polyester-based copolymer is lower than 190°C, the film-making processability will be impaired. Some components cannot measure the melting point under general DSC thermal analysis conditions, and need to be analyzed by special instruments or pre-treatment methods. In addition, the thickness of the first epidermis layer 12 accounts for 1% to 30% of the thickness of the polyester film, preferably 2% to 20%, and more preferably 3% to 15%. If the thickness of the first epidermis layer 12 is higher than 30% of the total thickness, the film-making processability will be impaired; if the thickness of the first epidermis layer 12 is lower than 1% of the total thickness, the embossing pattern effect may not be ideal. It is worth mentioning that the post-processing performance (such as calendering processing performance) of the first epidermis layer 12 is very excellent, and an embossing process can be easily performed.

[0043] In order to further improve the heat resistance and processability of the first skin layer 12, the first skin layer 12 may contain a crystal nucleating agent accounting for 0.0003 to 2 weight percent of the total weight of the first skin layer 12; the crystal nucleating agent may be a mineral material, a metal oxide, a silicon compound, a metal salt of an organic acid or an inorganic acid, an aromatic phosphate metal salt, a polyol derivative, a sulfonimide compound, a glass powder, a metal powder or any combination thereof. The crystal nucleating agent can increase the total crystallinity and improve the heat resistance of the first skin layer 12; in addition, the crystal nucleating agent can promote crystal growth, refine the crystal size, reduce the generation of large spherulites, and avoid embrittlement of the film surface.

[0044] Specific examples of mineral materials include graphite, talc and kaolin; specific examples of metal oxides include zinc oxide, aluminum oxide and magnesium oxide; specific examples of silicon compounds include silicon oxide, calcium silicate and magnesium silicate; specific examples of metal salts of organic acids or inorganic acids include metal carbonates such as magnesium carbonate, calcium carbonate, sodium carbonate, potassium carbonate, barium sulfate, calcium sulfate, sodium benzoate and aluminum p-tert-butylbenzoate; phosphate metal salts include aromatic phosphate metal salts; polyol derivatives include dibenzylidene sorbitol; considering heat resistance, the preferred nucleating agent is an inorganic material.

[0045] The base layer 11 is flexible and can provide good support for the first skin layer 12 to obtain the expected embossing effect; considering mechanical and thermal properties, the base layer 11 is made of polyester. Polyester can be formed by the reaction of a diacid component and a diol component; the diacid component can be an aromatic dibasic acid or an alicyclic dibasic acid, and the diol component can be an aromatic diol, an aliphatic diol, or an alicyclic diol.

[0046] Specific examples of aromatic dibasic acids include terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl ketone dicarboxylic acid, phenyl indan dicarboxylic acid, sodium sulfoisophthalic acid and dibromo terephthalic acid; specific examples of alicyclic dibasic acids include oxalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid and dimer acid. The diol may be an aromatic diol, an aliphatic diol, an alicyclic diol or any combination thereof.

[0047] Specific examples of aromatic diols include naphthalene diol, 2,2-bis(4-hydroxydiphenyl)propane, 2,2-bis(4-hydroxyethoxyphenyl)propane, bis(4-hydroxyphenyl)sulfone and hydroquinone; specific examples of aliphatic diols include ethylene glycol, propylene glycol, 1,4-butanediol, hexanediol, neopentyl glycol and diethylene glycol; specific examples of alicyclic diols include cyclohexanedimethanol and cyclohexanediol.

[0048] In some embodiments, the polyester forming the base layer 11 can be selected from polyethylene terephthalate (PET), polytrimethylene terephthalate (PPT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), polycyclohexanedimethylene terephthalate (PCT), polycarbonate (PC) or polyarylate, and the base layer 11 is preferably formed of polyethylene terephthalate (PET).

[0049] In order to further improve the heat resistance and processability of the base layer 11, the base layer 11 may also contain a crystal nucleating agent accounting for 0.0003 to 2 weight percent of the total weight of the base layer 11; the specific example of the crystal nucleating agent is as described above and will not be repeated here. In addition, the thickness of the base layer may be 5 micrometers to 300 micrometers, preferably 8 micrometers to 200 micrometers, and more preferably 11 micrometers to 100 micrometers.

[0050] Second embodiment

[0051] In this embodiment, the material of the first skin layer 12 is a polyester based copolymer, which includes residues derived from diacid components and residues derived from diol components, wherein the diacid components include terephthalic acid accounting for 95 mole percent of the total molar amount of the diacid and isophthalic acid accounting for 5 mole percent, and the diol components include ethylene glycol accounting for 67 mole percent of the total molar amount of the diols, neopentyl glycol accounting for 8 mole percent, and 1,4-butanediol accounting for 25 mole percent. The total thickness of the prepared film is 15 microns, wherein the thickness of the first skin layer 12 is 1 micron; the glass transition point (Tg) of the polyester based copolymer is 55°C, and the melting point (Tm) is 225°C. The post-processing performance (such as calendering processing performance) of the film is very excellent, and the embossing process can be easily performed.

[0052] Third embodiment

[0053] In this embodiment, the material of the first skin layer 12 is a polyester based copolymer, which includes residues derived from diacid components and residues derived from diol components, wherein the diacid component includes 90 mole percent of terephthalic acid and 10 mole percent of isophthalic acid, accounting for the total molar amount of the diacid, and the diol component includes 50 mole percent of ethylene glycol, 14 mole percent of neopentyl glycol, and 36 mole percent of 1,4-butanediol, accounting for the total molar amount of the diol. The total thickness of the prepared film is 50 microns, wherein the thickness of the first skin layer 12 is 1.5 microns; the glass transition point (Tg) of the polyester based copolymer is 47°C. The post-processing performance (such as calendering processing performance) of the film is very excellent, and the embossing process can be easily performed.

[0054] Fourth embodiment

[0055] In this embodiment, the material of the first skin layer 12 is a polyester based copolymer, which includes residues derived from diacid components and residues derived from diol components, wherein the diacid components include 88 mole percent of terephthalic acid and 12 mole percent of isophthalic acid, and the diol components include 55 mole percent of ethylene glycol, 5 mole percent of neopentyl glycol, and 40 mole percent of 1,4-butanediol, respectively. In addition, the base layer 11 and the first skin layer 12 both contain 0.005 weight percent of a crystal nucleating agent. The total thickness of the obtained film is 50 microns, wherein the thickness of the first skin layer 12 is 2 microns. The glass transition point (Tg) of the polyester based copolymer is 50°C, and the melting point (Tm) is 195°C. The post-processing performance (such as calendering processing performance) of the film is very excellent, and the embossing process can be easily performed.

[0056] Fifth embodiment

[0057] See also Figure 3 As shown, the fifth embodiment of the present invention provides a polyester film 1 for laser embossing, which has a three-layer structure, including a base layer 11, a first skin layer 12 and a second skin layer 13. The base layer 11 has a first surface 111 and a second surface 112 opposite to each other, the first surface 111 is, for example, the upper surface of the base layer 11, and the second surface 112 is, for example, the lower surface of the base layer 11; the first skin layer 12 is formed on the first surface 111 of the base layer 11, and the second skin layer 13 is formed on the second surface 112 of the base layer 11. The first skin layer 12 and the second skin layer 13 are each an easy-to-emboss layer; when used, a three-dimensional embossed pattern (not shown in the figure) can be formed on the first skin layer 12 and the second skin layer 13 respectively, and the three-dimensional embossed pattern on the first skin layer 12 can be the same as or different from the three-dimensional embossed pattern on the second skin layer 13.

[0058] In this embodiment, the material of the first skin layer 12 and the second skin layer 13 is a polyester based copolymer, which includes residues derived from diacid components and residues derived from diol components, wherein the diacid component includes 85 mole percent of terephthalic acid and 15 mole percent of isophthalic acid accounting for the total molar amount of the diacid, and the diol component includes 35 mole percent of ethylene glycol, 15 mole percent of neopentyl glycol and 50 mole percent of 1,4-butanediol accounting for the total molar amount of the diol; in addition, the base layer 11 and the first and second skin layers 12, 13 all contain 0.01 weight percent of a crystal nucleating agent. The total thickness of the obtained film is 50 microns, wherein the thickness of the first and second skin layers 12, 13 respectively accounts for 1% to 30% of the thickness of the polyester film, preferably 2% to 20%, and more preferably 3% to 15%; the glass transition point (Tg) of the polyester based copolymer is 52°C. The post-processing performance (such as calendering processing performance) of the film is very excellent, and the embossing process can be easily performed. If the thickness of the first skin layer 12 / the second skin layer 13 is higher than 30% of the total thickness, the film processing performance will be impaired; if the thickness of the first skin layer 12 / the second skin layer 13 is lower than 1% of the total thickness, the embossing pattern effect may not be ideal. It is worth mentioning that the post-processing performance (such as calendering performance) of the first skin layer 12 / the second skin layer 13 is very good, and an embossing process can be easily performed.

[0059] Sixth embodiment

[0060] See also Figure 4As shown, the sixth embodiment of the present invention provides a polyester film 1 for laser embossing, which includes a base layer 11, a first skin layer 12 and a second skin layer 13. The base layer 11 is a structure of more than two layers, and has a first surface 111 and a second surface 112 opposite to each other, the first surface 111 is, for example, the upper surface of the base layer 11, and the second surface 112 is, for example, the lower surface of the base layer 11; the first skin layer 12 is formed on the first surface 111 of the base layer 11, and the second skin layer 13 is formed on the second surface 112 of the base layer 11. The first skin layer 12 and the second skin layer 13 are each an easy-to-emboss layer; when used, a three-dimensional embossed pattern (not shown in the figure) can be formed on the first skin layer 12 and the second skin layer 13 respectively, and the three-dimensional embossed pattern on the first skin layer 12 can be the same as or different from the three-dimensional embossed pattern on the second skin layer 13.

[0061] Furthermore, the base layer 11 may include a first base layer 11a and a second base layer 11b stacked together, such as Figure 4 As shown, but not limited thereto. The composition of the first substrate layer 11a may be the same as or different from that of the second substrate layer 11b; for example, the first substrate layer 11a and the second substrate layer 11b may be formed of different polyesters, or the functional additives contained in the first substrate layer 11a are different from the functional additives contained in the second substrate layer 11b. For other implementation details of the polyester film 1 for laser embossing of this embodiment, reference may be made to the first and second embodiments, and no further description will be given here.

[0062] See also Figure 5 , and cooperate with Figure 1 , Figure 3 and Figure 4 As shown, the present invention also provides a manufacturing method for manufacturing the polyester film 1 for laser embossing of the above-mentioned embodiment. The manufacturing method of the present invention mainly includes: step S1, which is a metering and mixing step, in which the required components are metered and mixed to obtain at least one polyester composition; step S2, which is a crystallization and drying step, in which the polyester raw material is subjected to crystallization and drying treatment at a temperature of 120°C to 180°C; step S3, which is a melt extrusion and cooling molding step, in which the polyester raw material is melt extruded, cast and cooled to form, and an unstretched polyester thick sheet is obtained; and step S4, which is a stretching processing step, in which the unstretched polyester thick sheet is preheated and stretched, and then subjected to transverse and / or longitudinal heat shrinkage.

[0063] In step S1, the general polyester pellets required for the base layer and the skin layer and at least one functional modifier (such as a crystal nucleating agent) polyester pellets are measured and uniformly mixed to prepare the mixed polyester pellet raw materials for the base layer and the skin layer. The functional raw materials of the functional modifier polyester pellets can be added in the polymerization process and / or in the mixing process.

[0064] Step S2 is a crystallization and drying step, in which the polyester raw material (polyester pellets) is crystallized and dried at a temperature of 120° C. to 180° C. to reduce the moisture content of the polyester raw material to less than 30 ppm. The crystallization and drying process may be performed for 3 to 8 hours, but is not limited thereto.

[0065] Step S3 is a melt extrusion and cooling molding step, which is to melt and extrude the polyester raw material, cast and cool to shape, and obtain an unstretched polyester thick sheet. Further, the polyester raw material can be formed into a melt with fluidity by a single-layer extrusion or a multi-layer co-extrusion method. This step can be achieved by a twin-screw extruder, and the melt is then cast between casting rollers into a film and cooled and solidified. However, these details are only feasible implementation methods provided by this embodiment, and are not intended to limit the present invention.

[0066] Step S4 is a stretching process step, which is to preheat and stretch the unstretched polyester thick sheet, and then perform transverse and / or longitudinal heat shrinkage; the stretching process can be a sequential biaxial stretching process or a synchronous biaxial stretching process. It is worth mentioning that under specific stretching process conditions, the crystal orientation of the polyester film can be completed, and the polyester film can have very low longitudinal and transverse heat shrinkage rates under high temperature environment.

[0067] Further, the unstretched polyester thick sheet can be first stretched in the longitudinal direction (or "length direction", MD) at a temperature of 70°C to 145°C using a stretching ratio of 2 to 6 times to form a uniaxially stretched polyester film, and then stretched in the transverse direction (or "width direction", TD) at a temperature of 90°C to 160°C using a stretching ratio of 2 to 6 times to form a biaxially stretched polyester film; according to actual needs, the order of the longitudinal stretching process and the transverse stretching process can be reversed. The stretching process of the polyester film can be achieved by a conventional tenter stretching machine, but is not limited thereto.

[0068] In addition, the unstretched polyester thick sheet can also be subjected to a synchronous biaxial stretching process. Further, the unstretched polyester thick sheet can be subjected to a longitudinal stretching process and a transverse stretching process at a temperature of 70° C. to 145° C. using a stretching ratio of 2 to 6 times to directly form a biaxially stretched polyester film.

[0069] It is worth mentioning that in step S4, the biaxially stretched polyester film is further subjected to transverse and / or longitudinal pre-shrinkage, which can improve the crystallinity of the polyester film and improve the shrinkage stress of the polyester film. Furthermore, the pre-shrinkage treatment can be performed by clamping the two ends of the polyester film in the width direction or the length direction with a clamp, and repeatedly stretching and relaxing the polyester film, and the stretching amplitude can be 500%, and the relaxation amplitude can be 10%. In this way, the thermal shrinkage of the polyester film at high temperature can be effectively suppressed, that is, the thermal dimensional stability of the polyester film can be improved, without the need for additional heat treatment after the stretching process.

[0070] Characteristics evaluation

[0071] The polyester films of Examples 1 to 4 and Comparative Examples 1 and 2 have the following characteristics: Figure 1 The A / B double-layer structure shown in Example 5 has a Figure 3 The A / B / A three-layer structure shown in the figure; A represents the epidermis layer; B represents the base layer; the composition of each layer is shown in Table 1. The key physical properties of these polyester films were tested, and the relevant test methods are described as follows, and the results are also shown in Table 1.

[0072] Light transmittance and haze test: A haze meter (model TC-HIIIDPK) manufactured by Tokyo Denshoku was used to test the light transmittance and haze values ​​of the polyester films of Examples 1 to 5 and Comparative Examples 1 and 2 before and after heating in accordance with JIS K7705 test standard, and the haze change (Haze) of these polyester films was calculated. This test was performed using an oven for heating at a temperature of 210° C. for 3 hours.

[0073] Embossing test: A nickel plate for embossing is placed on the lower die of a laminating machine. The processing conditions include a temperature of 200°C, a pressure of 50 kgf and a time of 1 second. The polyester film samples of Examples 1 to 5 and Comparative Examples 1 and 2 are placed between two steel plates for hot pressing. After processing, the polyester film is separated and taken out from between the two steel plates, and the embossed pattern is observed. The results are recorded in Table 1.

[0074] Heat resistance test: The embossed polyester film samples of Examples 1 to 5 and Comparative Examples 1 and 2 were cut into pieces of 15 cm × 15 cm in length and width, placed in an oven and heated at 180°C for 3 minutes, and then the samples were taken out to observe the integrity of the embossed lines; if the embossed lines of the sample were complete and the film surface was smooth, it was judged to have good heat resistance.

[0075]

[0076]

[0077] As can be seen from the above, in the polyester films of Examples 1 to 5, the material of the surface layer (i.e., the easy-embossing layer) is a polyester-based copolymer, which contains a specific molar percentage of ethylene glycol, neopentyl glycol, 1,4-butanediol, terephthalic acid and isophthalic acid residues, which can achieve the best comprehensive effect of lowering the melting point and improving embossing processability and heat resistance.

[0078] In the polyester films of Examples 4 and 5, both the base layer and the skin layer contain a crystal nucleating agent. Since the crystal nucleating agent can improve heat resistance and prevent the formation of large crystal particles, the skin layer of the polyester film has good heat resistance and excellent formability after embossing at 200°C. The base layer contains a crystal nucleating agent, which makes the base film have good heat resistance and excellent dimensional stability, and avoids shrinkage, deformation, and warping of the film after heating due to the difference in composition between the base layer and the skin layer.

[0079] In the polyester film of Comparative Example 1, the material of the skin layer is polyethylene terephthalate, and the embossing property of the related product is obviously poor.

[0080] Although the polyester film of Comparative Example 2 has good embossing performance, after a heat resistance test at 180° C. for 3 minutes, the embossed pattern on the surface layer is not obvious, and the film shrinks, deforms, and warps, which does not meet the requirements of laser embossed products.

[0081] Advantageous Effects of Embodiments

[0082] One of the beneficial effects of the present invention is that the polyester film for laser embossing provided by the present invention can clearly present embossed patterns of different depths on the surface through the technical scheme of "at least one of the epidermal layers is formed on the base layer, wherein the material of at least one of the epidermal layers is a polyester base copolymer, and the polyester base copolymer includes residues derived from diacid components and residues derived from diol components, and the diacid components include terephthalic acid accounting for 85 to 95 mole percent of the total molar amount of the diacids and isophthalic acid accounting for 5 to 15 mole percent, and the diol components include ethylene glycol accounting for 35 to 74 mole percent of the total molar amount of the diols, neopentyl glycol accounting for 1 to 15 mole percent, and 1,4-butanediol accounting for 25 to 50 mole percent."

[0083] In addition, the method for manufacturing a polyester film for laser embossing provided by the present invention adopts a multi-layer co-extrusion method to form two, three or more functional polyester layers, which can effectively reduce the process difficulty and improve the yield of the finished product. The above disclosed contents are only preferred feasible embodiments of the present invention, and do not limit the protection scope of the claims of the present invention. Therefore, all equivalent technical changes made by using the contents of the present invention description and drawings are included in the protection scope of the claims of the present invention.

Claims

1. A method for producing a polyester film for laser embossing, characterized in that: The method for producing the polyester film for laser embossing comprises: A polyester raw material is subjected to a crystallization drying treatment at a temperature of 120° C. to 180° C.; The polyester raw material is formed into a polyester thick sheet by a multi-layer co-extrusion method, wherein the polyester thick sheet includes a base layer and at least one skin layer located on the base layer; Performing longitudinal stretching and transverse stretching on the polyester thick sheet to form a biaxially stretched polyester film; and Repeatedly stretching and relaxing the biaxially stretched polyester film in the transverse direction and / or the longitudinal direction; Wherein, the material of at least one of the skin layers is a polyester-based copolymer, the polyester-based copolymer includes residues derived from diacid components and residues derived from diol components, the diacid components include terephthalic acid accounting for 85 to 95 mole percent of the total molar amount of the diacids and isophthalic acid accounting for 1 to 15 mole percent, the diol components include ethylene glycol accounting for 35 to 74 mole percent of the total molar amount of the diols, neopentyl glycol accounting for 1 to 15 mole percent, and 1,4-butanediol accounting for 25 to 50 mole percent; the base layer is formed of polyethylene terephthalate; Wherein, at least one of the skin layers contains 0.0003 to 2 weight percent of a crystal nucleating agent based on the total weight of the skin layer, and the base layer contains 0.0003 to 2 weight percent of a crystal nucleating agent based on the total weight of the base layer.

2. The method for producing a polyester film for laser embossing according to claim 1, characterized in that: The thickness of at least one of the skin layers is 1% to 30% of the total thickness of the polyester film, and the thickness of the base layer is 11 micrometers to 100 micrometers.

3. The method for producing a polyester film for laser embossing according to claim 2, characterized in that: The thickness of at least one of the skin layers accounts for 2% to 20% of the total thickness of the polyester film.

4. The method for producing a polyester film for laser embossing according to claim 3, characterized in that: The thickness of at least one skin layer accounts for 3% to 15% of the total thickness of the polyester film.

5. The method for producing a polyester film for laser embossing according to claim 1, characterized in that: The polyester-based copolymer has a melting point of 190°C to 240°C.

6. The method for producing a polyester film for laser embossing according to claim 5, characterized in that: The polyester base copolymer has a melting point of 195°C to 230°C.

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