Production method of BOPET (Biaxially Oriented Polyethylene Terephthalate) optical base film with improved surface performance

Abstract

The invention discloses a production method of a BOPET (Biaxially Oriented Polyethylene Terephthalate) optical base film with improved surface performance. The outer surface layer is PET (Polyethylene Terephthalate); the middle core layer is composed of PET, PBT, talcum powder and GMA grafted SEBS; and the inner surface layer is PET. PET and PBT of the middle core layer have good compatibility and mutually form eutectic, talcum powder is added to serve as a nucleating agent, so that the middle core layer is good in heat resistance and impact resistance, and the impact strength can be further improved through added GMA grafted SEBS; in addition, the surface performance of the film can be obviously improved, and the film can be widely applied to liquid crystal display back plate film groups.

Description

Technical Field

[0001] The invention relates to the technical field of optical films, in particular to a production method of a BOPET optical base film. Background Art

[0002] An optical film refers to a film that has been processed on an optical base film through secondary processes such as coating, evaporation, compounding, and pressing, so that when a light beam propagates through its cross section, it can reflect, transmit, and polarize the light beam to meet specific functions. According to the properties of the optical film, it is mainly divided into: reflective film, anti-reflection film (also called anti-reflection film), spectroscopic film, filter film, brightening film, diffusion film, polarizer (full name polarizer), etc. BOPET optical base film is a common optical base film. BOPET film has many characteristics such as chemical corrosion resistance, low air permeability, transparency, non-toxicity, folding resistance, high mechanical strength and good temperature resistance. It is widely used in liquid crystal display backplane film groups. At present, the requirements for BOPET optical base film are getting higher and higher, such as how to improve the surface properties of the film substrate. Therefore, if a BOPET optical base film with improved surface properties is developed, it is the research direction that the staff in this field want to study. Summary of the Invention

[0003] In view of the above-mentioned defects of the prior art, an object of the present invention is to provide a method for producing a BOPET optical base film with improved surface properties.

[0004] To solve the above problems, the technical solution of the present invention is: a method for producing a BOPET optical base film with improved surface properties, the base film comprising an outer surface layer, an intermediate core layer and an inner surface layer; The outer layer is PET; The middle core layer is composed of PET, PBT, talc, and GMA grafted SEBS; The inner surface is PET; The production method comprises the following steps: (1) Weigh the raw materials according to the proportions of the outer layer, middle core layer and inner surface layer; (2) The raw materials of the outer layer, the middle core layer and the inner surface layer are mixed separately and sent into respective extruders for mixing and plasticizing; (3) The molten melts are fed into the die heads respectively, and the melts are combined in the die heads and then pass through the flat die head mouth to form a molten sheet; (4) Using an air knife to attach the sheet to a chilled roller, the sheet is quenched to form an unshaped sheet, and then cooled in a water bath to form a cast sheet; (5) The cast sheet is stretched to form a film; (6) The film thickness is detected by infrared and the corresponding thickness deviation is fed back to the die head. The heating power of the corresponding bolt is slightly adjusted to correct the film thickness deviation. (7) Grafting a fluorinated styrene copolymer onto the outer surface of the film; (8) Laser pretreatment of the outer surface to increase the laser damage threshold of the film; (9) Roll up the film.

[0005] Furthermore, the components of the outer layer, the middle core layer and the inner layer are as follows by mass: outer layer 20%, middle core layer 60%, inner layer 20%.

[0006] Furthermore, the components of the middle core layer are as follows by mass ratio: PET 80%, PBT 10%, talc 0.5%, and GMA grafted SEBS 9.5%.

[0007] Furthermore, step (7) includes the following steps: (71) The film surface was hydrolyzed and oxidized to produce hydroxyl groups, which were then converted into acyl chloride groups using phosphorus pentachloride. Diethanolamine with a branched structure was then added to obtain a high-density initiator. 2-Bromoisobutyryl bromide was then used to fix the atom transfer radical polymerization initiator on the film surface. (72) The catalyst CuCl, 2,2'-bipyridine and the initiator prepared in step (71) were added to a dry container, evacuated, filled with argon three times, and sealed; the solvent N,N-dimethylformamide, monomer 4-fluorostyrene, styrene, and free initiator α-bromoisobutyrate were added in sequence, and then placed in a constant temperature oil bath and stirred for 14 hours. After the reaction was terminated, the film was ultrasonically washed with tetrahydrofuran and acetone in sequence, and dried in a vacuum drying oven.

[0008] Furthermore, in step (8), the outer layer surface is irradiated multiple times with laser light of gradually increasing intensity.

[0009] The beneficial effects of the present invention are as follows: the PET and PBT of the middle core layer have good compatibility and form a eutectic with each other; the addition of talc as a nucleating agent makes the middle core layer heat-resistant and has good impact resistance; and the addition of GMA grafted SEBS can further improve the impact strength; Grafting a fluorinated styrene copolymer onto the outer surface of the film significantly improves the film's surface free energy and hydrophobicity. Because the grafted copolymer contains hydrophobic styrene and strongly hydrophobic 4-fluorostyrene, the film's surface hydrophobicity is enhanced. The presence of 4-fluorostyrene significantly reduces the film's surface free energy, as the fluorine element in the fluorinated polymer reduces the surface tension of the PET film, increases the contact angle, and improves its hydrophobicity. Laser pretreatment is performed on the outer surface to increase the laser damage threshold of the film. The pretreatment process can gradually eliminate defects and form stable, slight damage, avoiding defects that are instantly triggered by laser and cause large-scale damage to the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Schematic diagram of the structure of the optical base film of the present invention.

[0011] As shown in the figure: 1 - outer surface layer, 2 - middle core layer, 3 - inner surface layer. DETAILED DESCRIPTION

[0012] In order to more intuitively and completely understand the technical solution of the present invention, a non-limiting description of the features of the present invention is now provided below in conjunction with the accompanying drawings: like Figure 1 As shown, a method for producing a BOPET optical base film with improved surface properties, the base film includes an outer surface layer 1, an intermediate core layer 2 and an inner surface layer 3; The outer layer 1 is PET; The middle core layer 2 is composed of PET, PBT, talc, and GMA grafted SEBS; The inner surface layer 3 is PET; The production method comprises the following steps: (1) Weigh the raw materials according to the proportions of the outer layer, middle core layer and inner surface layer; (2) The raw materials of the outer layer, the middle core layer and the inner surface layer are mixed separately and sent into respective extruders for mixing and plasticizing; (3) The molten melts are fed into the die heads respectively, and the melts are combined in the die heads and then pass through the flat die head mouth to form a molten sheet; (4) Using an air knife to attach the sheet to a chilled roller, the sheet is quenched to form an unshaped sheet, and then cooled in a water bath to form a cast sheet; (5) The cast sheet is stretched to form a film; (6) The film thickness is detected by infrared and the corresponding thickness deviation is fed back to the die head. The heating power of the corresponding bolt is slightly adjusted to correct the film thickness deviation. (7) Grafting a fluorinated styrene copolymer onto the outer surface of the film; (8) Laser pretreatment of the outer surface to increase the laser damage threshold of the film; (9) Roll up the film.

[0013] The components of the outer layer, the middle core layer and the inner surface layer are as follows by mass: outer layer 20%, middle core layer 60%, inner surface layer 20%.

[0014] The components of the middle core layer are as follows by mass ratio: PET 80%, PBT 10%, talc 0.5%, and GMA grafted SEBS 9.5%.

[0015] Step (7) includes the following steps: (71) The film surface was hydrolyzed and oxidized to produce hydroxyl groups, which were then converted into acyl chloride groups using phosphorus pentachloride. Diethanolamine with a branched structure was then added to obtain a high-density initiator. 2-Bromoisobutyryl bromide was then used to fix the atom transfer radical polymerization initiator on the film surface. (72) The catalyst CuCl, 2,2'-bipyridine and the initiator prepared in step (71) were added to a dry container, evacuated, filled with argon three times, and sealed; the solvent N,N-dimethylformamide, monomer 4-fluorostyrene, styrene, and free initiator α-bromoisobutyrate were added in sequence, and then placed in a constant temperature oil bath and stirred for 14 hours. After the reaction was terminated, the film was ultrasonically washed with tetrahydrofuran and acetone in sequence, and dried in a vacuum drying oven.

[0016] In step (8), the outer layer surface is irradiated multiple times with laser light of gradually increasing intensity.

[0017] The PET and PBT in the middle core layer have good compatibility and form a eutectic with each other. The addition of talc as a nucleating agent makes the middle core layer heat-resistant and impact-resistant, while the addition of GMA grafted SEBS can further improve the impact strength. Grafting a fluorinated styrene copolymer onto the outer surface of the film significantly improves the film's surface free energy and hydrophobicity. Because the grafted copolymer contains hydrophobic styrene and strongly hydrophobic 4-fluorostyrene, the film's surface hydrophobicity is enhanced. Prolonging the grafting polymerization reaction time increases the grafting percentage on the film's surface. A large amount of grafted fluorinated polymer increases the surface hydrophobicity. When the grafting polymerization time is 14 hours, the contact angle can increase to nearly 98°. The presence of 4-fluorostyrene significantly reduces the film's surface free energy, because the fluorine element in the fluorinated polymer reduces the surface tension of the PET film, increases the contact angle, and improves its hydrophobicity. Laser pretreatment is performed on the outer surface to increase the laser damage threshold of the film. This process gradually eliminates defects, resulting in stable, minimal damage, preventing defects from being instantly triggered by the laser and causing extensive damage to the film. Multiple laser irradiations of the outer surface are performed with increasing laser intensity because achieving optimal results requires precise control of the laser's energy gain and time interval, and multiple irradiations are required.

Claims

1. A method for producing a BOPET optical base film with improved surface properties, characterized in that: The basement membrane includes an outer surface layer, a middle core layer and an inner surface layer; The outer layer is PET; The middle core layer is composed of PET, PBT, talc, and GMA grafted SEBS; The inner surface is PET; The production method comprises the following steps: (1) Weigh the raw materials according to the proportions of the outer layer, middle core layer and inner surface layer; (2) The raw materials of the outer layer, the middle core layer and the inner surface layer are mixed separately and sent into respective extruders for mixing and plasticizing; (3) The molten melts are fed into the die heads respectively, and the melts are combined in the die heads and then pass through the flat die head mouth to form a molten sheet; (4) Using an air knife to attach the sheet to a chilled roller, the sheet is quenched to form an unshaped sheet, and then cooled in a water bath to form a cast sheet; (5) The cast sheet is stretched to form a film; (6) The film thickness is detected by infrared and the corresponding thickness deviation is fed back to the die head. The heating power of the corresponding bolt is slightly adjusted to correct the film thickness deviation. (7) Grafting a fluorinated styrene copolymer onto the outer surface of the film; (8) Laser pretreatment of the outer surface to increase the laser damage threshold of the film; (9) Roll up the film.

2. The method for producing a BOPET optical base film with improved surface properties according to claim 1, wherein: The components of the outer layer, the middle core layer and the inner surface layer are as follows by mass: outer layer 20%, middle core layer 60%, inner surface layer 20%.

3. The method for producing a BOPET optical base film with improved surface properties according to claim 1, wherein: The components of the middle core layer are as follows by mass ratio: PET 80%, PBT 10%, talc 0.5%, and GMA grafted SEBS 9.5%.

4. The method for producing a BOPET optical base film with improved surface properties according to claim 1, wherein: Step (7) includes the following steps: (71) The film surface was hydrolyzed and oxidized to produce hydroxyl groups, which were then converted into acyl chloride groups using phosphorus pentachloride. Diethanolamine with a branched structure was then added to obtain a high-density initiator. 2-Bromoisobutyryl bromide was then used to fix the atom transfer radical polymerization initiator on the film surface. (72) The catalyst CuCl, 2,2'-bipyridine and the initiator prepared in step (71) were added to a dry container, evacuated, filled with argon three times, and sealed; the solvent N,N-dimethylformamide, monomer 4-fluorostyrene, styrene, and free initiator α-bromoisobutyrate were added in sequence, and then placed in a constant temperature oil bath and stirred for 14 hours. After the reaction was terminated, the film was ultrasonically washed with tetrahydrofuran and acetone in sequence, and dried in a vacuum drying oven.

5. The method for producing a BOPET optical base film with improved surface properties according to claim 1, wherein: In step (8), the outer layer surface is irradiated multiple times with laser light of gradually increasing intensity.

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