JP3063984B2 - Phase difference plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a novel retardation plate having excellent production stability and little variation in retardation.

[Prior Art] A retardation plate is a film or a sheet having birefringence. Light passing through the retardation plate has different refractive indexes in two directions orthogonal to each other, so that light beams orthogonal to each other after passing through the retardation plate. A phase difference occurs.

As a practical retardation plate, there is a so-called 1 / 4λ plate obtained by uniaxially stretching a cellulose acetate film, which serves as an interchangeable element between linearly polarized light and circularly polarized light. They are used in splitters or in combination with linear polarizers to form circularly polarizing plates.

As other base materials, polyvinyl alcohol, polyvinyl chloride, polystyrene, polyamide, polycarbonate and the like are known.

[Problems to be Solved by the Invention] However, in the production of the conventional film, it is not always easy to control the film thickness and the stretching ratio, and as a result, there is a variation in retardation, and thus there is a problem in terms of production efficiency. .

[Means for Solving the Problems] The present inventors have conducted intensive studies to solve such problems, and as a result, have found that the ethylene content of boric acid or borax containing 10
After forming a saponified ethylene-vinyl acetate copolymer having a saponification degree of at least 90 mol% of the vinyl acetate moiety,
The inventors have found that a retardation plate formed by uniaxial stretching can achieve the object, and have completed the present invention.

In the saponified ethylene-vinyl acetate copolymer used in the present invention, the ethylene content is 10 mol% to 55 mol%, preferably 15 mol% to 40 mol%, and the saponification degree of the vinyl acetate portion is advantageously 90 mol% or more. It is. Outside this range, the effects of the present invention are difficult to obtain. The saponified product further contains a small amount of propylene,
Α such as isobutene, octene, dodecene and octadecene
-Comonomers such as olefins, unsaturated carboxylic acids or salts thereof, partial alkyl esters, full alkyl esters, nitriles, amides, anhydrides and unsaturated sulfonic acids or salts thereof may be contained as copolymerization components. The saponified ethylene-vinyl acetate copolymer is molded into a film or a sheet by any molding method such as a melt molding method and a salivation molding method, and then uniaxially stretched about 1.2 to 2.5 times. As a stretching method, for example, a method in which the film is preheated by passing the film between a number of rolls, followed by stretching to a predetermined magnification by two pairs of stretching rolls, and a method in which the film is passed between the number of rolls. For example, a method is employed in which preheating and stepwise stretching are performed in parallel with each other and a predetermined magnification is achieved. Stretching is appropriately performed depending on the intended use of the retardation plate. That is, the difference in the refractive index between the main stretching (MD) direction and the perpendicular (TD) direction (II _MD −II _TD )
The retardation value (r), which is defined by the product of the thickness of the retardation plate and the thickness (d) of the retardation plate, and represents the phase difference of transmitted light when linearly polarized light having an orthogonal relationship is incident at the same phase, is the wavelength of the light beam used. For example, when the stretching treatment is performed so as to have a value of (/ 4) of / 4, a / 4 wavelength plate is obtained, and when the stretching treatment is performed so as to have a value of 、, A half-wave plate is obtained. When the light used is a visible light, the retardation value of the quarter-wave plate is in the range of 95 to 170 nm. Therefore, by combining a quarter-wave plate and a linear polarizer in this range, accurate circularly polarized light in a certain visible ray can be obtained. The retarder of the present invention may contain various additives such as an ultraviolet absorber and a stabilizer. Further, after the stretching operation, a treatment such as annealing is appropriately performed to make the molecular orientation permanent.

The retardation plate of the present invention is obtained by a method in which boric acid or borax is mixed with a saponified ethylene-vinyl acetate copolymer, the resulting film is formed, and the film is uniaxially stretched.

It is advantageous to add boric acid or borax to the saponified ethylene-vinyl acetate copolymer film in an amount of about 1 to 5% by weight in terms of boron.

In practical use, the retardation plate of the present invention is usually used by laminating optically non-oriented and transparent polymer films or sheets on both surfaces or one surface thereof using an adhesive. Examples of such a polymer film include cellulose films such as cellulose triacetate and cellulose diacetate, polycarbonate films, polymethyl methacrylate films, polystyrene films, polyester films such as polyethylene terephthalate, and polysulfone films. As the agent, urethane type, acrylic type,
Epoxy type is often used.

[Operation] The retardation plate of the present invention has little variation in retardation and is extremely excellent in production efficiency.
Since the plate and the λ plate can be easily manufactured, they are useful not only for the use of anti-glare materials but also for various optical uses such as optical filters and the field of liquid crystal displays.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 20% of a saponified ethylene-vinyl acetate copolymer (ethylene content: 20 mol%, saponification degree: 99.6 mol%) was added to water / n-propyl alcohol / boric acid (49.5 / 49.5 / 1.0, weight ratio).
Was dissolved to a concentration of A film was formed from the solution by a salivation method, dried at 70 ° C. for 10 minutes without air, and further dried at 90 ° C. for 10 minutes to obtain a transparent film. This film was uniaxially stretched twice at 90 ° C., and then heat-set at 150 ° C. for 30 minutes to obtain a 20 μm thick retardation plate. The retardation value of the retardation plate was 590 nm, and had a uniform quality.

Example 2 Ethylene content of 29 mol% (Example 2), 35 mol%
Using the saponified ethylene-vinyl acetate copolymer of Example 3, a retardation film having a uniaxial stretching magnification of 1.5 times and a film thickness of 15 μm was obtained. The retardation values were 298 nm and 293 nm, respectively, and had uniform quality.

[Effects] The present invention provides an ethylene content of 10 to 55 mol% containing boric acid or borax in advance, and a saponification degree of vinyl acetate of 90 mol%.
A novel retardation plate comprising a film or sheet uniaxially stretched after forming the saponified ethylene-vinyl acetate copolymer into a film is provided.

Continuation of the front page (51) Int.Cl. ⁷ identification code FI C08L 29/04 C08L 29/04 SB29K 29:00 B29L 11:00 (56) References JP-A-61-25105 (JP, A) JP-A-61-25105 JP-A-63-311203 (JP, A) JP-A-55-7735 (JP, A) JP-A-57-5001 (JP, A) JP-A-57-34148 (JP, A) JP-A-57-59940 (JP, A) JP-A-55-100510 (JP, A) JP-A-55-126202 (JP, A) JP-B-49-20615 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB G02B 5/30 C08L 29/04 C08L 23/26 C08F 8/00-8/44

Claims (1)

(57) [Claims] 1. A saponified ethylene-vinyl acetate copolymer having an ethylene content of 10 to 55 mol% containing boric acid or borax and a saponification degree of at least 90 mol% of a vinyl acetate portion is formed beforehand. A retardation plate characterized by being uniaxially stretched.