阅读说明：本技术 一种提高聚乙烯醇光学薄膜拉伸性能的方法 (Method for improving tensile property of polyvinyl alcohol optical film ) 是由 唐成宏 向学毅 柳巨澜 徐学斌 刘密密 欧阳孔波 吴云柱 季逸飞 于 2019-09-16 设计创作，主要内容包括：本发明公开了一种提高聚乙烯醇光学薄膜拉伸性能的方法,其特征在于：该光学薄膜是将聚乙烯醇水溶液自挤出模头的模口流延至辊筒表面,受热蒸发水分后成型、剥离,再经其它辊筒的加热干燥,收卷获得；其中,通过调整模头唇口的开度,可以提高聚乙烯醇光学薄膜的拉伸性能。本发明通过对模口开度的定量设置,可以有效提高薄膜拉伸性能,且本发明的方法操作难度小、经济可行。(the invention discloses a method for improving the tensile property of a polyvinyl alcohol optical film, which is characterized by comprising the following steps: the optical film is obtained by casting a polyvinyl alcohol aqueous solution onto the surface of a roller from a die orifice of an extrusion die head, forming and stripping after heating to evaporate moisture, and then heating, drying and rolling the optical film by other rollers; wherein, the stretching performance of the polyvinyl alcohol optical film can be improved by adjusting the opening degree of the die head lip. The invention can effectively improve the tensile property of the film by quantitatively setting the opening of the die orifice, and the method has small operation difficulty and is economical and feasible.)

1. a method for improving the tensile property of a polyvinyl alcohol optical film is characterized by comprising the following steps:

The preparation method of the polyvinyl alcohol optical film comprises the following steps: casting a polyvinyl alcohol aqueous solution onto the surface of a roller from a die orifice of an extrusion die head to form a solution layer with a certain thickness, rotating along with the roller, heating to evaporate water, stripping after molding, heating and drying other rollers, and rolling to obtain a finished polyvinyl alcohol optical film;

Order: the opening degree of the die head lip is D, the thickness of a finished product of the polyvinyl alcohol optical film is D, the mass percentage concentration of a solute in a polyvinyl alcohol aqueous solution is C, and D, D and C satisfy a multiple relation: d ═ a × (D ÷ C);

then: the stretching performance of the polyvinyl alcohol optical film is improved by adjusting the value of a, namely, the opening degree of the die lip.

2. the method of claim 1, wherein the step of stretching the optical film comprises: when the polyvinyl alcohol optical film is prepared, the opening D of the die head lip is controlled by a being more than or equal to 1.2 and less than or equal to 2.1, so that the polyvinyl alcohol optical film with excellent tensile property can be obtained.

Technical Field

The invention relates to a method for improving the tensile property of a polyvinyl alcohol (PVA) optical film, in particular to a preparation method of the PVA optical film for producing a polaroid.

Background

The polarizer, which polarizes natural light, is a key component of a liquid crystal display device, and combines it with liquid crystal to form a component having a display function. The polaroid is formed by washing and swelling a polyvinyl alcohol optical film, dyeing by iodine, longitudinally stretching and attaching the polyvinyl alcohol optical film to a cellulose triacetate film, the cellulose triacetate film mainly plays a role in protecting moisture and humidity, the dyed and stretched polyvinyl alcohol optical film has a polarization performance, and the quality of the film determines the performance of liquid crystal display.

At present, the common production method of the polyvinyl alcohol optical film is to utilize the water solubility of polyvinyl alcohol, mix the polyvinyl alcohol with other auxiliary agents, prepare an aqueous solution with a certain concentration, extrude, cast, dry and form through a die head. Unlike other plastic films, the polyvinyl alcohol optical film does not need to be stretched in the drying and forming stage, and the aim of the polyvinyl alcohol optical film is to maintain the stretching performance of the film so as to ensure that the maximum stretching ratio can be obtained when downstream manufacturers dye and stretch the film. The higher the stretching ratio, the stronger the orientation of the polymer material constituting the film, and the better the polarizing performance of the obtained polarizer.

There are many factors that affect the stretching performance of the optical film made of polyvinyl alcohol, such as the molecular weight, molecular structure, plasticizer type, solution formulation, and processing technology of polyvinyl alcohol. Therefore, the method for improving the tensile property of the polyvinyl alcohol optical film is significant.

Disclosure of Invention

The invention aims to provide a method for improving the tensile property of a polyvinyl alcohol optical film, and the invention finds out that the tensile property of the film can be effectively improved by reasonably adjusting the opening degree of a die orifice of an extrusion die head.

The invention relates to a method for improving the tensile property of a polyvinyl alcohol optical film, which is characterized by comprising the following steps:

The preparation method of the polyvinyl alcohol optical film comprises the following steps: casting a polyvinyl alcohol aqueous solution onto the surface of a roller from a die orifice of an extrusion die head to form a solution layer with a certain thickness, rotating along with the roller, heating to evaporate water, stripping after molding, heating and drying other rollers, and rolling to obtain a finished polyvinyl alcohol optical film;

Order: the opening degree of a die head lip (hereinafter referred to as a die opening) is D, the thickness of a finished product of the polyvinyl alcohol optical film is D, the mass percentage concentration of solute in a polyvinyl alcohol aqueous solution is C, and D, D and C satisfy a multiple relation: d ═ a × (D ÷ C);

Then: the stretching performance of the polyvinyl alcohol optical film is improved by adjusting the value of a, namely, the opening degree of the die lip.

As shown in fig. 1, the value of a, i.e. the opening of the die adjusting opening, has a great influence on the film stretching performance:

The value a is too small, the opening degree of the die orifice is smaller, the solution flows and delays from the die orifice, the rotating speed of the roller is relatively slow, the pulling strength of the roller to a film (in a solution state at this moment) is weaker, the pulling force and the fluid tension are not easy to balance, the casting form is unstable, liquid discharged from the die orifice is easy to stack and accumulate, and the forming is difficult. As shown in the left diagram of fig. 1.

the value a is too large, the opening degree of the die opening is far larger than the film thickness, the solution flows and delays from the die opening, and the rotating speed of the roller must be increased to thin the film (in the solution state at this time) by drawing, so that the pre-stretching effect is generated, and the stretching performance of the finished film is reduced. As shown in the right drawing of fig. 1.

the value a is moderate, when the liquid discharged from the die opening is cast on the surface of the roller, enough pulling force is provided to ensure the stability of the liquid discharged casting form, and simultaneously, the pre-stretching strength is reduced to the maximum extent. As shown in the middle diagram of fig. 1.

Repeated tests prove that when the polyvinyl alcohol optical film is prepared, the opening D of the die head lip is controlled by a being more than or equal to 1.2 and less than or equal to 2.1, and the polyvinyl alcohol optical film with excellent tensile property can be obtained.

Compared with the prior art, the invention has the beneficial effects that:

The invention can effectively improve the tensile property of the film by quantitatively setting the opening of the die orifice, and the method has small operation difficulty and is economical and feasible.

Drawings

FIG. 1 is a schematic view of a die casting state in the present invention, wherein the reference numerals: 1 is the arc surface of the casting roller; and 2 is a die lip.

Detailed Description

The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.

The following examples are presented to improve the tensile properties of polyvinyl alcohol optical films:

Casting a polyvinyl alcohol aqueous solution onto the surface of a roller from a die orifice of an extrusion die head to form a solution layer with a certain thickness, rotating along with the roller, heating to evaporate water, stripping after molding, heating and drying other rollers, and rolling to obtain a finished polyvinyl alcohol optical film;

Order: the opening degree of the die head lip is D, the thickness of a finished product of the polyvinyl alcohol optical film is D, the mass percentage concentration of a solute in a polyvinyl alcohol aqueous solution is C, and D, D and C satisfy a multiple relation: d ═ a × (D ÷ C);

Then: the stretching performance of the polyvinyl alcohol optical film is improved by adjusting the value of a, namely, the opening degree of the die lip.

The elongation at break (%) of the finished polyvinyl alcohol optical film obtained in the following examples was measured by the method specified in GB/T12683.