阅读说明：本技术 一种光学聚酯薄膜及其制备方法 (Optical polyester film and preparation method thereof ) 是由 鲍时萍 程龙宝 高青 王钦 周通 宋瑞然 杜坤 于 2019-10-14 设计创作，主要内容包括：一种光学聚酯薄膜及其制备方法,包括芯层和至少一层表层,所述芯层和表层经共挤模头挤出和双向拉伸工艺制得：所述芯层由50wt％-99wt％重量份的共聚聚酯和1wt％-50wt％重量份的聚萘二甲酸乙二醇酯制成；所述表层由40wt％-84.9wt％重量份的共聚聚酯、15wt％-50wt％重量份的聚萘二甲酸乙二醇酯、0.1wt％-10wt％重量份的功能母料制成,所述功能母料中含有爽滑粒子；所述聚萘二甲酸乙二醇酯的特性粘度为0.65dL/g-0.85dL/g。本发明制备工艺简单,不需要采用涂布的方式对低聚物进行封堵,在180℃条件下经过30分钟热处理后,表面低聚物的析出量小于6.13E-03mg/cm<Sup>2</Sup>。(The optical polyester film comprises a core layer and at least one surface layer, wherein the core layer and the surface layer are prepared by a co-extrusion die head extrusion and biaxial stretching process: the core layer is made of 50 wt% -99 wt% of copolyester and 1 wt% -50 wt% of polyethylene naphthalate; the surface layer is prepared from 40 wt% -84.9 wt% of copolyester, 15 wt% -50 wt% of polyethylene naphthalate and 0.1 wt% -10 wt% of functional master batch, and the functional master batch contains smooth particles; the inherent viscosity of the polyethylene naphthalate is from 0.65dL/g to 0.85 dL/g. The preparation method is simple in preparation process, the oligomer does not need to be blocked in a coating mode, and after the oligomer is subjected to heat treatment for 30 minutes at 180 ℃, the precipitation amount of the surface oligomer is less than 6.13E-03mg/cm 2 。)

1. An optical polyester film comprises a core layer and at least one surface layer, and is characterized in that the core layer and the surface layer are obtained by a co-extrusion die head extrusion and biaxial stretching process:

(1) the core layer is made of 50 wt% -99 wt% of copolyester and 1 wt% -50 wt% of polyethylene naphthalate;

(2) the surface layer is made of 40 wt% -84.9 wt% of copolyester, 15 wt% -50 wt% of polyethylene naphthalate and 0.1 wt% -10 wt% of functional master batch; the functional master batch contains smooth particles;

(3) the inherent viscosity of the polyethylene naphthalate is from 0.65dL/g to 0.85 dL/g.

2. The optical polyester film according to claim 1, wherein the copolyester is formed by copolymerizing at least one of ethylene glycol, polyethylene glycol, propylene glycol and 1, 4-cyclohexanedimethanol with at least one of isophthalic acid, terephthalic acid, phthalic acid and 2, 6-naphthalenedicarboxylic acid.

3. The optical polyester film of claim 2, wherein the initial inherent viscosity of the copolyester synthesis is from 0.50dL/g to 0.60dL/g and the inherent viscosity of the copolyester after solid state polymerization is from 0.65dL/g to 0.80 dL/g.

4. The optical polyester film according to claim 1, wherein the amount of oligomer precipitated on the surface of the optical polyester film after the optical polyester film is heat-treated at 180 ℃ for 30 minutes is less than 6.13E-03mg/cm²。

5. A process for producing the optical polyester film according to any one of claims 1 to 4, which comprises the steps of:

(1) melt extrusion: uniformly mixing copolyester and polyethylene naphthalate, feeding the mixture into a single-screw extruder for melting, uniformly mixing the copolyester, the polyethylene naphthalate and the functional master batch containing smooth particles, feeding the mixture into a double-screw extruder for melting, and extruding a melt through a co-extrusion die head;

(2) cooling the cast sheet: forming an amorphous polyester cast slab from the melt on a rotating chill roll;

(3) and (3) bidirectional stretching: preheating the thick sheet, longitudinally stretching for 2.8-4.4 times, and transversely stretching for 2.5-4.5 times;

(4) shaping and rolling: and (3) performing heat setting on the biaxially oriented film, and then cooling and rolling to obtain the optical polyester film.

Technical Field

The invention relates to a film, in particular to a polyester film with good optical performance.

Background

An optical polyester film is a film made of polyethylene terephthalate (PET) through a biaxial stretching process, is known to have good mechanical properties, optical properties, heat and cold resistance, electrical properties, etc., and is widely used as a film for optical members of displays, mainly as an optical material for a backlight unit (BLU) of a Liquid Crystal Display (LCD), or as an optical material for protecting the surface of each display, such as an LCD, a plasma display panel, a touch screen, etc.

In the production of PET, oligomers are produced by side reactions, which are white crystalline powders with a melting point of 319 ℃, and are prone to contamination both during production and during subsequent processing, and therefore the production line needs to be shut down and cleaned from time to time. On the other hand, the oligomer volatilizes and gathers on the surface of the polyester film, which not only affects the cleanliness and optical performance of the film, but also has a very obvious fogging phenomenon after long-time sunlight exposure, and cannot meet the requirements of high-end optical films.

Generally, methods for preventing the generation of oligomers mostly adopt coating on the surface of a polyester film, as shown in chinese patent 201120124338.X, an upper surface layer of polyester modified acrylate and a lower surface layer of polyester modified acrylate are respectively coated on the upper surface and the lower surface of a multilayer co-extrusion composite layer, the coating has very high stability, and the volatilization of oligomers is avoided. However, this coating method has the following disadvantages: (1) the process is more complex, and the production cost is increased; (2) in the coating process, the film appearance has the defects of uneven coating, generation of stripes, blooming and the like; (3) the method adopts a similar compatibility principle, utilizes the incompatibility between coating resin and PET to plug the oligomer, and cannot become a fundamental countermeasure; (4) there is no solution to oligomer contamination generated before the coating process.

In order to reduce the generation of oligomers in polyester films, it is proposed in the document "generation and prevention of oligomers in BOPET film processing" (plastic packaging, 24 th vol 2014, 2 nd p 7-10) that the generation of oligomers can be reduced by selecting equipment, selecting process conditions, and the like, and these methods can alleviate oligomers generated in the production process, but cannot be a palliative method.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides the optical polyester film, which has less surface oligomer amount, can solve the quality defect of the film appearance caused by a coating process and reduce the production cost.

The invention also aims to provide a preparation method of the film.

The technical scheme for solving the problems is as follows:

an optical polyester film comprises a core layer and at least one surface layer, wherein the core layer and the surface layer are obtained by a co-extrusion die head extrusion and biaxial stretching process:

(1) the core layer is made of 50 wt% -99 wt% of copolyester and 1 wt% -50 wt% of polyethylene naphthalate;

(2) the surface layer is made of 40 wt% -84.9 wt% of copolyester, 15 wt% -50 wt% of polyethylene naphthalate and 0.1 wt% -10 wt% of functional master batch; (ii) a The functional master batch contains smooth particles;

(3) the inherent viscosity of the polyethylene naphthalate is from 0.65dL/g to 0.85 dL/g.

The optical polyester film is characterized in that the copolyester is formed by copolymerizing at least one of ethylene glycol, polyethylene glycol, propylene glycol and 1, 4-cyclohexanedimethanol with at least one of isophthalic acid, terephthalic acid, phthalic acid and 2, 6-naphthalenedicarboxylic acid.

In the optical polyester film, the initial intrinsic viscosity of the synthesis of the copolyester is 0.50dL/g to 0.60dL/g, and the intrinsic viscosity of the copolyester after solid state polymerization is 0.65dL/g to 0.80 dL/g.

The optical polyester film is heat-treated at 180 ℃ for 30 minutes, and then the precipitation amount of the oligomer on the surface of the optical polyester film is less than 6.13E-03mg/cm²。

The smooth particles are silicon dioxide, organic silicon, calcium carbonate, barium sulfate, PMMA or PS, the particle size of the smooth particles is 0.5-3.0 mu m, and the adding amount is 1 wt% of the weight of the master batch.

The method for preparing the optical polyester film comprises the following steps:

(1) melt extrusion: uniformly mixing copolyester and polyethylene naphthalate, feeding the mixture into a single-screw extruder for melting, uniformly mixing the copolyester, the polyethylene naphthalate and the functional master batch containing smooth particles, feeding the mixture into a double-screw extruder for melting, and extruding a melt through a co-extrusion die head;

(2) cooling the cast sheet: forming an amorphous polyester cast slab from the melt on a rotating chill roll;

(3) and (3) bidirectional stretching: preheating the thick sheet, longitudinally stretching for 2.8-4.4 times, and transversely stretching for 2.5-4.5 times;

(4) shaping and rolling: and (3) performing heat setting on the biaxially oriented film, and then cooling and rolling to obtain the optical polyester film.

Compared with the prior art, the invention has the following advantages:

the invention adopts the co-extrusion die head extrusion and two-way stretching technology of the core layer and the surface layer, and controls the content of each component in the core layer and the surface layer, so that the precipitation amount of the low polymer on the surface of the film is less than 6.13E-03mg/cm²Meanwhile, the method solves the quality defect of the film appearance caused by the coating process, improves the product quality and reduces the production cost.

Detailed Description

The copolyester used in the invention is a copolyester formed by copolymerizing one or more alcohols selected from ethylene glycol, polyethylene glycol, propylene glycol and 1, 4-cyclohexanedimethanol with one or more acids selected from isophthalic acid, terephthalic acid, phthalic acid and 2, 6-naphthalenedicarboxylic acid.

The dibasic acid adopted by the invention comprises isophthalic acid, terephthalic acid, 2, 6-naphthalene dicarboxylic acid, isophthalic acid, phthalic acid and the like, preferably terephthalic acid, and a small amount of isophthalic acid modified copolyester can also be added; the diol is aliphatic diol with 2-4 carbon atoms, including ethylene glycol, propylene glycol, butanediol, 1, 3-propanediol, etc., preferably ethylene glycol.

The functional master batch adopted by the invention contains smooth particles, such as silicon dioxide, organic silicon, calcium carbonate, barium sulfate, PMMA, PS and the like, the particle size of the smooth particles is 0.5-3.0 mu m, and the addition amount is 1 wt% of the weight of the master batch.

The polyethylene naphthalate is novel PET homologous polyester, and has more excellent performances such as mechanical property, heat resistance, barrier property and the like compared with PET. On one hand, because PET and polyethylene naphthalate belong to thermoplastic polyester, the chemical structures have certain similarity, but the naphthalene ring structure replaces the benzene ring structure, so that the structure difference is larger, therefore, the PET and polyethylene naphthalate in a certain proportion are melted and blended to form a partially incompatible system, and the barrier property of the PET can be improved to a certain extent; on the other hand, the naphthalene rings in the polyethylene naphthalate have larger space volume, the molecular chains have larger rigidity, and the free movement of molecules is hindered, so that the thermal stability of the polyethylene naphthalate is improved, therefore, the PET and the polyethylene naphthalate in a certain proportion have a certain compatibility in melt blending, the PET molecules are influenced by the polyethylene naphthalate molecules acted with the PET molecules in the process of increasing the temperature, and the thermal stability of the polyethylene naphthalate is improved generally.

The present invention will be described in detail with reference to specific examples, but the embodiments of the present invention are not limited to these examples.