JPH01245031A - Oriented high polymer thin film and production thereof - Google Patents

Abstract

PURPOSE:To obtain a thin film in which molecular orientation properties are readily and homogeneously imparted to a film having a thickness of submicrons or less, by taking off a thin film at a high speed and orienting molecules in developing a high polymer solution on the surface of water. CONSTITUTION:A thin film in which a high polymer material is molecularly oriented and dichroic ratio at a specific infrared wavelength is >=1.05 in a thin film of 0.003-0.1mum thickness thereof obtained by a water surface developing method. A polyamic acid expressed by formula I or polyamide expressed by formula II [R1 is aromatic tetracarboxylic acid residue; R2 is H, 1-30C aliphatic, alicyclic or aromatic monofunctional group or Si(R4)3; R4 is 1-6C aliphatic, alicyclic or aromatic group; R3 is aromatic diamine residue] is used as the high polymer material. In the water surface developing, a high polymer solution is continuously fed to the water surface and formed into a film at a spontaneous developing speed or more.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a polymer thin film having molecular orientation.

[Conventional technology]

Orientation treatment of polymer films is an important means for increasing mechanical strength and imparting electrical and optical anisotropy. For thermoplastic resins such as polyester, the desired orientation process can be performed by stretching the film uniaxially or biaxially under heating, and for hydrophilic polymers such as polyvinyl alcohol, the film can be swollen by absorbing water. A molecularly oriented film can also be obtained by stretching the film in the same state. However, the orientation treatment by these stretching methods is a method that can be used for films with a thickness of 1 μm or more, but cannot be used for films or coated products with a thickness of submicron or less. On the other hand, rubbing treatment is a method for efficiently orienting only the surface of a plastic film. This is a simple method of rubbing the film surface in one direction with a cloth such as rayon. For example, in a liquid crystal display cell, in order to align liquid crystal molecules in a predetermined direction, polyimide etc. The objective is achieved by rubbing the surface with a thin layer of coating. In this way, rubbing treatment is an alignment treatment that can be used for films on smooth substrates, regardless of their thickness. However, it is difficult to quantitatively evaluate this rubbing treatment, and it is completely unclear how deep from the surface the orientation is, or how much the orientation is occurring.

Furthermore, since the treatment is performed only in the vicinity of the surface, it is not possible to impart orientation and anisotropy to the entire film.

[Problem that the invention seeks to solve]

As described above, it is difficult to uniformly impart molecular orientation to a film having a thickness of submicron or less using conventional stretching methods and rubbing treatments.

By the way, as a method for forming an ultra-thin film of polymer,
A water surface spreading method is known in which a polymer solution is spread on a water surface, the solvent is removed, and then the polymer solution is attached to a substrate. Conventionally, this method uses polymethylpentene (Japanese Unexamined Patent Publication No. 55-41808), silicone polymer (Japanese Unexamined Patent Publication No. 57-107204) to obtain a thin skin layer of an oxygen-enriched membrane.
It is used in polymers such as On the other hand, from the viewpoint of molecular orientation in thin films, in the conventional water surface development method, the polymer solution only spreads spontaneously on the water surface, removes the solvent, and forms a film, and does not impart molecular orientation. could not.

The present invention was made in view of the above circumstances, and an object of the present invention is to apply a water surface spreading method to provide a polymer thin film with uniform thickness and molecular orientation, and a method for easily manufacturing the same. It is something.

[Means for solving problems]

In the present invention, when a polymer solution is spread on a water surface to form a thin film, the thin film is continuously drawn off at a faster rate than the solution spontaneously spreads on the water surface, thereby forming a thin film. It imparts molecular orientation.

[Effect]

Until now, continuous production of thin films by the water surface spreading method has been achieved by supplying a polymer solution on the water surface, spontaneously spreading the supplied polymer solution, evaporating the solvent and solidifying it, thereby forming a thin film. This was done by transferring a thin film onto the surface of a substrate. The present inventors focused on the fact that the thin film obtained by this water surface spreading method is floating independently on the water surface, and that it exists as a gel-like layer with a high solid content on the water surface during the solvent removal process, and conducted intensive studies. As a result, they discovered that molecular orientation can be imparted to a formed thin film by drawing it off at a speed faster than the spontaneous expansion speed of the polymer solution, and the present invention was achieved.

The thickness of the thin film produced by the water surface spreading method varies depending on the type of polymer, solvent, additives, and developing conditions, but the film thickness is generally 30 μm to 1 μm. Generally, the orientation of polymer films is evaluated by measuring X-ray diffraction, birefringence, etc., but these measurement methods cannot be easily applied to such ultra-thin films. Therefore, the present inventors determined that infrared dichroism evaluation is convenient as a measure of the orientation of such ultra-thin polymer films in terms of operability and accuracy, and used this evaluation. In particular, to explain the evaluation of dichroic ratio using an infrared spectrometer FT-IR, a polarizer is set between the sample film and the incident infrared light, and its polarization axis is set at 0 with respect to the orientation axis direction of the sample. 90° and observe the absorption spectrum. Figure 1 shows a model spectrum. In the figure, curve A shows absorbance Abs//, and curve B shows absorbance Abs±. The ratio of the above absorbances obtained at a specific absorption wavelength (A b s ///A b
s) is the infrared dichroic ratio. This value is 1 for a non-oriented film. Regarding this point, since the film actually produced by casting a polymer solution is non-oriented, a value of accuracy <1.00 was obtained for the above-mentioned infrared dichroic ratio. Regarding the evaluation of dichroic ratio, measurement of dichroic ratio using ultraviolet light can also be used; however, in general, there are more peaks with higher quantitative properties in the infrared light region, and FT
-Infrared light is advantageous because it allows use of a highly sensitive and highly accurate evaluation device called IR. In the present invention, from this viewpoint, the value of the infrared dichroic ratio is used as a measure of the molecular orientation of the thin film. However, this value is only a relative value, and it is difficult to compare values between different types of polymers.

It is believed that the present invention can be applied to all systems that can be made into thin films by the water surface development method. That is, when a certain developing solution is supplied to the surface of water by an appropriate solution supplying means, it will develop spontaneously and at a certain speed (Am
/m1n), the thin film solidified moves forward. Generally, the produced thin film is brought into contact with a film-like base material and pulled up from the water surface, and at this time, the moving speed of the base film is approximately the same as the speed A above.
m1n and controlled so that there is no stress or sag in the thin film (for example, Japanese Patent Laid-Open No. 58-3831).

In reality, a uniform thin film laminate can be obtained even if the moving speed of the base film is set to Am/min or higher, as the present inventors have done. At this time, as a matter of course, the faster the moving speed, the thinner the thin film becomes, and an effect that appears to be that of an upper stretching process is also expected. However, as can be seen from the solution development pattern shown in Figure 2, it is thought that the stress of pulling is mainly relaxed in the solution region a, and an orientation effect similar to that produced by stretching a solid film cannot be considered in common sense. do not have.

In FIG. 2, l is a nozzle, 2 is a water surface, 3 is a discharged polymer solution, 4 is a take-up roller, a is a solution area of the polymer solution, b is a gel-like area, and C is a solid film area. It is. However, the present inventors did not follow such common technical knowledge and changed the moving speed of the base film to A m /
Considering that molecular orientation occurs in the thin film when it is m l n or more, the above-mentioned infrared dichroic ratio values were determined for thin films produced by varying the take-up speed. At this time, the sample for infrared spectrum measurement is scooped with an infrared sample holder (window frame shape) while keeping the solidified film (area C in Figure 2) in tension as it moves continuously on the water surface. I took it and submitted it for evaluation. As a result, surprisingly, the dichroic ratio of the thin film wound at a rate other than the spontaneous unfolding speed of the solution was l.

Values other than OO group were shown. FIG. 3 shows typical results, and the dichroic ratio increased almost linearly as the take-up speed increased, and showed values such as 1.2 and 1.4, for example. This indicates that the constituent molecules of the thin film are highly oriented.

The details of why a thin film developed on a water surface that is rolled up at high speed exhibits an infrared dichroic ratio due to its molecular orientation are unknown, but the stress at the time of taking it off causes the unevaporated part of the developing solution (second Stress is applied to the gel-like layer (area b in Figure 2, which can be visually confirmed by a change in interference color), which cannot be relaxed only in area a) of the figure, and has a high solid content concentration due to partial solvent volatilization. It is thought that the effect of stretching the molecular chains in the winding direction worked.

Systems that can exhibit the effects of the present invention are all systems that can form a thin film by a water surface spreading method. Examples of polymers include olefin polymers such as polybutene, polypentene, polymethylpentene, and polyhexene, cellulose derivatives such as cellulose acetate and nitrocellulose, fluorine-containing polymers such as polyvinyl fluoride and polyvinylidene fluoride, polymethyl methacrylate, and polyethyl. Acrylic polymers such as methacrylate, various polyimides, and their precursor polyamic acids can be used. As the developing solvent, almost any organic solvent that dissolves the above polymer can be used. However, if sufficient water surface developability cannot be obtained with the -type of solvent, it is also effective to add a second organic solvent as a development aid. Such developing aids include aliphatic, cycloaliphatic or aromatic ketones, esters, alcohols, amines, aldehydes, peroxides and mixtures thereof.

In the present invention, the polymer that can be particularly effectively oriented is a material with a relatively rigid molecular structure of the skeleton, and aromatic polyimide and its precursor polyamic acid can be suitably used. Typical examples of such polymers are - polyamic acid represented by formula (1) and polyimide represented by formula (■).

In this system, it is preferable to use a solution containing IwL% or more of the above-mentioned developing aid.

In the present invention, the concentration of the polymer solution used for continuous film formation on a water surface is 0.5 to 30 wt%, preferably 1 to 20 wt%.
t%. If the polymer concentration is too low, it will be difficult to obtain a uniform continuous film, whereas if it is too high, the spreadability of the solution on the water surface will decrease, which is not preferable.

In the present invention, the above-mentioned polymer solution is spread on a water surface to form a thin film, and the thin film is adhered and integrated onto the surface of a substrate at a winding speed higher than the spontaneous spreading speed of the formed thin film.

The formation of the above-mentioned thin film or its attachment to the surface of the base material can be achieved by, for example, the fourth
As shown in the figure, the polymer solution is poured into the water tank 1 from the nozzle 11.
The thin film 14 generated on the water surface 13 is discharged onto the water surface 13 in the first container. Second. By the third rolls 15 to 17,
This is carried out by a method of attaching it to the surface of the sheet-like base material 18 that is continuously transferred. As such a continuous film forming method, various methods (Japanese Unexamined Patent Publication No. 56-92926,
No. 57-107204, No. 57-10704, No. 5B-3829, No. 5B-3831, No. 60-102907, No. 60-156508
Publication No.) is known. Also in the present invention, in addition to the method shown in the drawings, any suitable method among the various continuous film forming methods described above can be used.

Examples of the base material to which the above water surface spread thin film is attached and integrated include plastic films, nonwoven fabrics, metal foils, membranes, inorganic crystals, ceramic plates, glass, and paper. The thin film may be attached (layed) onto the base material in a single layer or in multiple layers.

In the case of multiple layers, it is preferable to completely dry the moisture adhering to the previously laid thin film before laminating the layers.

The polymer thin film of the present invention is obtained as described above, and is a single layer oriented thin film with a thickness of 0.003 to 1.0 μm and an infrared dichroic ratio of 1.05 or more, for example,
It can be effectively used as an ultra-thin layer that requires optical and electrical anisotropy, such as a liquid crystal alignment film. In particular, when the polymers of the above-mentioned formulas (1) and (II) are used, the above-mentioned oriented thin film can be smoothly obtained.

〔Effect of the invention〕

As described above, in the present invention, when forming a polymer thin film by the water surface spreading method, the produced thin film is closely laminated on a supporting substrate at a take-up speed that is higher than the spontaneous spreading speed of the polymer solution on the water surface. This has an excellent effect in that an ultra-thin film with molecular orientation having an infrared dichroic ratio of 1.05 or more can be formed satisfactorily. The obtained thin film exhibits excellent performance as a liquid crystal alignment film etc. due to its molecular orientation.

Next, the present invention will be explained based on Examples along with Comparative Examples.

[Example 1] Nitrocellulose with a viscosity of 3.0 and 4.9 seconds was dissolved in cyclohexanone to prepare a developing solution as a 10 wt % solution. This solution is pumped through the nozzle of the continuous film forming apparatus shown in Fig. 4 at a rate of 1 mj! The formed thin film was brought into contact with a polyethylene terephthalate film (PET film) as a base material while moving at a speed of 15 m/n+in to adhere and integrate, thereby obtaining an oriented thin film laminate. Ta. At this time, when the thin film on the water surface was sampled and the film thickness was measured, it was 0.05 μm, and the infrared dichroic ratio (2920
cm-') showed a value of 1.10.

[Example 2] Polyvinyl chloride with an average degree of polymerization of 800 was used in place of Nido0 cellulose. Otherwise, an oriented thin film laminate was obtained in the same manner as in Example 1. The thickness of the obtained thin film part is 0.03
In μm, the infrared dichroic ratio (2900 cm-') was 1.15.

[Example 3] Equal amounts of 3.3',4.4'-biphenyltetracarboxylic dianhydride and 4,4'-di(p-aminophenoxy)diphenylhexafluoropropane were mixed with N,N-dimethylacetamide. (DMAc) Polyamic acid was synthesized by reacting under the middle chamber. Acetophenone was added to this polyamic acid solution so that the polyamic acid solution was 5% and the ratio of DMAc/acetophenone was 1/1 (by weight). This solution was pumped through the nozzle of the continuous film forming apparatus shown in Figure 4 at 0°92
ml/min onto the water surface, and the formed thin film was used as a base material for PET film at 15 m/min.
They were brought into contact with each other while moving at a speed of 100 to form an adherent body, thereby obtaining an oriented thin film laminate. The thickness of the obtained thin film part is 0.01
In μm, the infrared dichroic ratio (1500 cm-') was 1.35.

[Comparative example]

A polyamic acid thin film was developed in the same manner as in Example 3, and adhered and integrated with the PET film at a speed of 5 m/min. The spontaneous development speed of this solution is about 5 m/win, the thickness of the obtained thin film part is 0.015 μm, and the infrared dichroic ratio (15
00co+-') was 0.98, indicating a non-oriented state.

[Brief explanation of the drawing]

Figure 1 is an infrared two-color measurement spectrum of an oriented thin film measured by FTIR, Figure 2 (A) is a schematic plan view showing the development of a polymer solution on the water surface, and Figure 2 (B) is its outline. FIG. 3 is a diagram showing changes in the infrared dichroic ratio of oriented thin films produced by varying take-up speeds, and FIG. 4 is a configuration diagram of an example of a continuous film forming apparatus. Patent Applicant Nitto Electric Industry Co., Ltd. Agent Patent Attorney Yukihiko Nishifuji Figure 1 Condolence Figure 1

Claims (4)

[Claims] (1) Film thickness 0.003 to 0.1μ obtained by water surface development method
An oriented polymer thin film having a dichroic ratio of 1.05 or more at a specific infrared wavelength, in which the polymer material forming the thin film has molecular orientation. (2) Claim 1, wherein the polymer material is composed of at least one of a polyamic acid represented by the following general formula (I) and a polyimide represented by the general formula (II). oriented polymer thin film. ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(II) [In formulas (I) and (II), R_1 is aromatic tetracarboxylic acid It is a residue. R_2 is H, an aliphatic, alicyclic, or aromatic monovalent group having 1 to 30 carbon atoms (these may be combined with each other), and Si(R_4)_
3 (R_4 is an aliphatic, alicyclic, or aromatic monovalent group having 1 to 6 carbon atoms), and may be the same or different. R_3 is an aromatic diamine residue. ] (3) In continuous water surface spreading film formation, in which a polymer solution is continuously supplied onto the water surface and the resulting thin film is laminated in close contact with a supporting substrate, the film is formed at a rate higher than the spontaneous spreading speed of the polymer solution on the water surface. A method for producing an oriented polymer thin film characterized by: (4) The method for producing an oriented polymer thin film according to claim 3, wherein the supporting substrate is a plastic film, nonwoven fabric, metal foil, membrane, inorganic crystal, ceramic plate, glass, or paper.