JPH032281B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polarizing film comprising a hydrophobic resin and a dichroic organic dye. Polarizing films are used as important elements of liquid crystal display elements, and as the field of display applications expands, polarizing films are also required to have durability such as moisture resistance and heat resistance. recently,
Polarizing films based on hydrophobic resins are being considered in place of conventional polarizing films based on polyvinyl alcohol resins, but the optical properties and
In particular, the current situation is that a practical product has not yet been obtained in terms of polarization performance. Conventionally, as a method for manufacturing polarizing films, it has been known to stretch an unstretched film in one direction to as high a ratio as possible, but crystalline polymer films such as polyolefin, polyester, and polyamide are stretched using conventionally known stretching methods. Although the thickness is reduced by an amount corresponding to the stretching ratio, the length in the direction perpendicular to the stretching is hardly reduced, and as a result, sufficient polarizing performance is not exhibited. Furthermore, in order to maintain the heat-resistant dimensional stability of a polarizing film, it is common to carry out a so-called heat setting (annealing) operation after stretching, but there is also the problem that the polarizing performance deteriorates in this case. As a result of intensive studies to obtain a polarizing film with excellent polarizing performance, heat resistance stability, and optical uniformity, the present inventors found that there are differences in polarizing performance even at the same stretching ratio, and in particular, the thickness before and after stretching and the stretching It was discovered that an excellent polarizing film can be obtained by stretching the polarizing film with a specific relationship between the actual length in the direction perpendicular to the polarizing film, and after further study, the present invention was finally achieved. That is, in the production of a polarizing film made of a hydrophobic resin and a dichroic organic dye, the present invention provides that when an unstretched film is stretched 2.5 times or more in at least one direction, R determined by the following formula is at least 0.5. This is a method for manufacturing a polarizing film, characterized in that: R=(d×L)/(D×l) () (D: Actual thickness of unstretched film L: Actual length of unstretched film in the direction perpendicular to the stretching direction d: Actual thickness of the film after stretching l: The hydrophobic resin used in the present invention is a thermoplastic resin that can be processed into a transparent film and can be stretched, and includes polyester, polyamide, polyolefin, etc. , polyvinyl, polyether, polysulfone, ethylene vinyl alcohol copolymer, etc., among which polyester, polyamide, and polyolefin are particularly preferred. The photo dichroic organic dye used in the present invention can be selected from organic dyes and pigments known to have photo dichroism, and examples of the dye include direct dyes, disperse dyes, threne dyes, ionic dyes, and reactive dyes. (For example, JP-A-53-106743, JP-A-49-3944). Among these, those that can be dispersed and dissolved in hydrophobic resins or dyed are suitable.
The amount added varies depending on the degree of coloring of the polarizing film to be obtained, but is usually 0.001 to 10% by weight, preferably 0.01 to 3% by weight. The unstretched film used in the present invention is a resin composition obtained by blending a dichroic organic dye with the above-mentioned hydrophobic resin, or a resin composition prepared by blending the above-mentioned hydrophobic resin with a dichroic organic dye, or a film formed from the resin as it is by a conventional extrusion melt molding method, solvent casting method, etc. It is something. If the dye is not blended into the resin in advance, the dye can be incorporated into the film before and after stretching by a method such as dyeing. In the present invention, the unstretched film is
Stretch in at least one direction at 2.5 or higher. As the stretching method, known tension stretching, roll rolling stretching, etc. can be adopted, but a stretching ratio of less than 2.5 is not suitable because sufficient polarizing performance as a polarizing film is not imparted. The higher the stretching ratio, the better the polarizing performance, but if it exceeds 10, the workability usually deteriorates due to stretch breakage, etc., so the preferred stretching ratio is 3 to 10. In the present invention, during stretching, R determined by the following formula must be 0.5 or more, preferably 0.7 or more. R=(d×L)/(D×l) () In the above formula, D and d are the actual thicknesses of the film before and after stretching, respectively, and mean the substantial thickness of the resin layer. Further, L and l are the actual lengths of the film in the direction perpendicular to the stretching direction before and after stretching, respectively, and mean the actual dimensions of the film at the portions that are substantially stretched. This can be measured by stamping a straight line in the direction perpendicular to the stretching on a flat, unstretched film approximately in the center, and measuring the length before and after stretching. In formula (1), the relationship between L, D, d, and l changes depending on the stretching method. For example, in a region that has been uniformly stretched by a conventionally known method, the length in the length direction in the case of horizontal uniaxial stretching and the width direction in the case of longitudinal uniaxial stretching do not substantially change. That is,
l/L≒1. Therefore, the change in thickness d/D
If the stretching ratio is n, then d/D≈1/n. Therefore, when the stretching ratio n is 2.5 times or more, the R value can be roughly estimated from equation (1) as follows. When the stretching ratio n=2.5, R=0.40 When n=3.0, R=0.33 When n=4.0, R=0.25 When n=6.0, R=0.17 When n=8.0, R=0.13 In other words, conventionally known In the regions uniformly stretched by the above method, the R values are all 0.50 or less, which does not satisfy the R value of 0.50 or more, which is a feature of the present application. If R is less than 0.5, good polarizing performance cannot be obtained no matter how high the stretching ratio is. There is no particular upper limit, but
1.0 in order not to impair the flatness of the film.
The following is preferable. To give a specific example of the method of the present invention, a photodichroic dye is uniformly mixed with the hydrophobic resin, melt-extruded using an extruder equipped with a die slit such as a T-die, and then rapidly cooled to prevent crystallization as much as possible. A restrained unstretched film is produced. If this is to be stretched in the longitudinal (longitudinal) direction using a roll tension method, multi-stage stretching, long-range stretching while sliding the film on heated rolls or heating plates, or tension stretching in an oven with a temperature gradient is performed. In short, a good polarizing film can be obtained by stretching at a temperature that allows for stretching, avoiding local stretching as much as possible and allowing free contraction in the transverse (width) direction. When transverse stretching is carried out by the clip tenter method, it is preferable to carry out the stretching so as to cause free contraction in the longitudinal direction, such as by continuously narrowing the clip interval in the stretching section. Another preferred stretching method is to stretch an unstretched film that has been previously subjected to a folding process in a direction perpendicular to the stretching direction. For example, when vertical roll stretching is performed, at least a preheated roll immediately before the stretching roll is curved into a convex shape and the film is stretched using a flat stretching roll, or when horizontal stretching is performed, the film gripping surface of the clip is used. There are two methods, such as forming the film into a concave and convex wave shape and gripping the film in a curved manner, or stretching the film as an unstretched film by passing the film through gear-type mesh rolls and folding it in the longitudinal direction. The stretched film is preferably heat-set by heat treatment in order to improve thermal dimensional stability. Usually, it is carried out in a short time at a temperature above the crystallization temperature and below the melting point using a heating roll, hot air, infrared heater, etc. The polarizing film produced by the method of the present invention has a polarizing performance comparable to that of conventional polyvinyl alcohol-based films, and has optical uniformity and
It also has excellent thermal dimensional stability, moisture resistance, etc., and is incorporated into liquid crystal display elements, and is particularly suitable for use in fields where durability is required. Specific fields include display panels for vehicles, OA equipment, industrial instruments, etc. The present invention will be further explained below with reference to Examples. In addition, the physical property evaluation performed in the examples relied on the following method. Optical characteristics (light transmittance, degree of polarization) Self-recording spectrophotometer (Hitachi double beam type)
UV-200), calculate the light transmittance (To) of one polarizing film and the light transmittance (T〓 or T⊥) when two sheets are stacked so that their absorption axes are parallel or perpendicular to each other. Maximum absorption wavelength (λmax)
The degree of polarization () was determined from the following formula. Dimensional stability (thermal shrinkage rate) A sample cut into a 10cm length (1cm width) in the stretching direction was placed in boiling water at normal pressure, the dimensions were measured after 30 minutes, and the shrinkage dimensions were calculated as a percentage. Ta. Examples 1 to 6 Anthraquinone disperse dye Miketon in polyethylene terephthalate resin pellets (IV0.71)
Polyester “Blue M-34” (manufactured by Mitsui Toatsu Chemical Co., Ltd.)
As the final polarizing film, adjust the amount added so that the single transmittance (To) is approximately 40% and mix uniformly.
The film was melt-formed (290°C) at φ), the take-up speed was adjusted so that the average thickness at the center of the film was 75 μm, 150 μm, and 300 μm, and the film was slit to produce an unstretched film with a width of 500 mm. After imprinting a 100 mm long mark in the lateral (width) direction approximately in the center of this film, it was introduced into a line drawing roll consisting of a pair of rubber rolls and a metal roll, and heated to 65°C, 69°C, and 74°C in order. After passing through three preheating rolls, the film was stretched in the longitudinal direction using a set of tension stretching nip rolls at the magnification shown in Table 1. At this time, it was confirmed that the film was being stretched while sliding on the surfaces of the three preheating rolls (chrome plating) and was shrinking in the lateral (width) direction. Furthermore, the film after passing through a stretching roll is heated to 180℃.
The film was brought into contact with a heated annealing roll (for a few seconds) and heat-set, resulting in a polarizing film. The thickness, mark length, optical properties (λmax: 640 mm), and thermal dimensional stability of each stretched film were measured. The results are shown in Table-1. Comparative Examples 1 to 2 Using the unstretched film with an average thickness of 150 μm obtained in Example 1, a rubber pinch roll was attached to the third preheating roll that rotates at the same speed as the line drawing roll, and the unstretched film was A polarizing film was obtained in the same manner except that the stretched film was stretched in close contact with the film. The thickness, mark length, and physical properties of this stretched film were measured. The results are shown in Table-1.

[Table] Example 7 Adding azo disperse dye Miketon Polyester “Orange” to polyethylene terephthalate resin (IV0.67)
3GSF" (manufactured by Mitsui Toatsu Chemical Co., Ltd.) was blended at 0.07% and extruded and melted to form a film with an average thickness of 150 μm. A 100 mm long mark was engraved in the vertical direction approximately in the center of this film, and a gear meshing mark was engraved in the vertical direction. An unstretched film was created by using a roll to form a wave shape in the longitudinal direction (pitch 10 mm, depth 8 mm).Next, this state was introduced into a clip-type tenter stretching machine, and the stretching section was
Transverse stretching was performed by 4.5 times at 75°C, and heat setting was performed through an annealing section at 190°C. At this time, the average thickness of the obtained stretched film is
At 76 μm, the mark length in the vertical direction had shrunk to 60 mm. (R≒0.84) This film had an excellent transmittance of 36% at the maximum absorption wavelength (460 mm) and a polarization degree of 82%. Comparative Example 3 A stretched film was prepared in the same manner as in Example 7, except that the film was produced in the same manner as in Example 7 with the added amount of dye being 0.12%, and was then introduced into a tenter and stretched. (R≒0.33), and although the transmittance was almost the same, the degree of polarization was inferior at 58%. Example 8 An unstretched film was formed (280°C) in the same manner as in Example 3 except that nylon-6 resin was used instead of polyethylene terephthalate resin, and three preheating rolls were heated at 95°C, 105°C, and 110°C. Vertical roll stretching was carried out in the same manner except that. R of the obtained film
was 0.91, the transmittance at λm640nm was 34%, and the degree of polarization was excellent at 89%.

Claims (1)

[Claims] 1. In the production of a polarizing film made of a hydrophobic resin, which is either polyester, polyamide, or polyolefin, and a dichroic substance, an unstretched film is stretched 2.5 times or more in one direction, and after stretching, A method for producing a polarizing film, which comprises stretching the film under stretching conditions such that R determined by Formula 1 is 0.5 or more. R=(d×L)/(D×l) (1) D: Actual thickness of unstretched film L: Actual length of unstretched film in the direction perpendicular to the stretching direction d: Actual thickness of the film after stretching l: Actual length 2 in the direction perpendicular to the stretching direction of the film after stretching The method for producing a polarizing film according to claim 1, wherein the film is stretched while being freely shrunk in the direction perpendicular to the stretching direction. 3. The method for producing a polarizing film according to claims 1 and 2, wherein the unstretched film is previously subjected to a folding treatment in a direction perpendicular to the stretching direction.