JPH08259706A - Production of cellulose acylate film - Google Patents

Abstract

PURPOSE: To obtain a process for forming, using a halogen-free solvent not causing environmental pollution, a cellulose acylate film useful as a photographic film and a protective film for polarizing plates. CONSTITUTION: From a solution comprising 15-250 pts.wt. solvent comprising at least 60wt.% 1,3-dioxolane and 10 pts.wt. cellulose acylate dissolved therein, a film is cast with microwave heating to efficiently obtain the film excellent in transparency, homogeneity, and optical isotropy and reduced in residual solvent content.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for forming a cellulose acylate film using a non-halogen solvent. More specifically, it is possible to produce a cellulose acylate film having excellent surface properties, transparency and homogeneity from a cellulose acylate solution composition mainly containing 1,3-dioxolane which is a non-halogen solvent that does not cause environmental pollution. It relates to a good manufacturing method.

[0002]

BACKGROUND OF THE INVENTION Cellulose acetate plays an important role in various fields including photographic base film and packaging. In recent years, it has been put to practical use as a protective film for polarizing plates in liquid crystal display devices and the like. The properties of cellulose acetate differ considerably depending on the degree of polymerization and the degree of acetylation. Generally, the larger the degree of acetylation and the degree of polymerization, the higher the mechanical properties,
It has excellent physical properties such as heat resistance, moisture absorption and dimensional stability, but poor processability and solubility. At present, high molecular weight cellulose triacetate is said to be the only one that can be dissolved in methylene chloride at a high concentration, and is cast from a methylene chloride solution. However, in recent years, methylene chloride has been banned from the viewpoint of environmental pollution including carcinogenicity.

The problem is that the solvent has a low boiling point (boiling point 40
Due to the fact that the temperature is ℃, the environmental pollution is doubled by volatilizing in the manufacturing process. There is also a problem that methylene chloride decomposes to generate hydrochloric acid, which corrodes the manufacturing equipment. From such a viewpoint, the appearance of a solvent replacing methylene chloride is awaited.

[0004]

In view of the above-mentioned prior art, the object of the present invention is to obtain excellent surface properties, transparency and optical isotropy by casting from a cellulose acylate solution composition using a non-halogen solution. And to form a film with less residual solvent.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that 1,3-dioxolane is a good solvent for cellulose acetate, and even if it is dissolved at a high concentration, a solution ( It was found that the dope) is excellent in stability and that a dry film can be easily formed from this solution.

Generally, hot air heating, electric heating, infrared heating or the like is used as a means for drying the film. In addition, microwave heating has been proposed. The principle of microwave heating is based on shaking the dipoles contained in the body to be heated by microwaves. Therefore,
The microwave absorption efficiency depends on the magnitude of the dipole moment and the ease with which the molecule follows the period of the microwave. Water is a typical substance that satisfies both,
It has been put to practical use as a so-called microwave oven and is industrially used for drying products containing water. However, it is not always effective for general organic substances. The present inventors have found that 1,3-dioxolane has two oxygen atoms of negative atoms in the molecule and the molecular structure is asymmetric, and therefore the dipoles involved in the two oxygen atoms do not cancel each other out. I focused on. That is, paying attention to the fact that a large dipole moment can be expected, the present invention was applied to the film drying from the 1,3-dioxolane solution of cellulose acylate in the present invention. As a result, it was found that the solvent can be efficiently evaporated from the inside of the cast film, and a film having a small amount of residual solvent and a very excellent surface smoothness can be obtained.

That is, according to the present invention, a cellulose acylate solution composition having 10 parts by weight of cellulose acylate dissolved in 15 to 250 parts by weight of a solvent containing 1,3-dioxolane in an amount of 60% by weight or more is provided on a supporting substrate. A method for producing a cellulose acylate film, characterized in that microwave heating is used in the step of evaporating and drying the solvent when the film is cast into a film to produce a film.

The cellulose acylate used in the present invention is a generic term for a part or all of the hydroxyl groups of cellulose acylated. Here, examples of groups that are preferably used as the acyl group include an aliphatic acyl group such as an acetyl group, a propionyl group, and a butyryl group, and an alicyclic acyl group such as a cyclohexanecarbonyl group. More preferred are cellulose acetate, cellulose propionate and cellulose butyrate whose acyl group corresponds to acetyl group, propionyl group and butyryl group, and most preferred is cellulose acetate. Further, the acyl group may be a single kind or two or more kinds.

The cellulose acylate may be selected from cellulose diacylate or cellulose triacylate having a desired acylation rate depending on the purpose of use, but in the present invention, the average repeating unit is 2.0 or more, preferably 2. It is 2 or more. If it is less than 2.0, the solubility decreases as the proportion of hydroxyl groups increases, which is not preferable. Cellulose triacylate having an acylation rate of more than 2.8, particularly cellulose triacetate, has low hygroscopicity and excellent mechanical strength, and is suitable for a photographic film, a protective film for a polarizing plate used for liquid crystal display, and the like. The upper limit of the acylation rate is 3.0 because the number of hydroxyl groups replaced by the acyl group in the repeating unit is 3.

The molecular weight of the cellulose acylate used in the present invention is such that the value of η _sp / c measured at 25 ° C. using a 0.5 g / dl 1,3-dioxolane solution is 0.1.
3 to 10.0 dl / g, preferably 0.5 to 8.0 dl
Those in the range of / g are used. The value of η _sp / c is 10.
If it exceeds 0 dl / g, not only the solubility decreases, but even if it dissolves, it becomes a high solution viscosity at a low concentration, which is not preferable for the purpose of film formation.

The solvent used in the present invention comprises 1,3-dioxolane in an amount of 60% by weight or more, preferably 70% by weight or more, and 1,3-dioxolane alone solvent is particularly preferable. The solvent may contain a small amount of water,
When it is present in a large amount, the gelling of the cellulose acylate solution occurs, it is difficult to obtain a film having a smooth surface, and it is difficult to sufficiently dry the film due to the interaction between the hydroxyl groups of the cellulose acylate and water. Therefore, it is preferable that such a solvent is substantially free of water. Other solvents that can be used at 40% by weight or less may be used in consideration of the effects. The effect here is due to mixing the solvent in a range that does not sacrifice solubility and stability. For example, improvement of surface property (leveling effect), adjustment of evaporation rate and viscosity of system. The kind and the addition amount of the mixed solvent may be determined depending on the degree of these effects, and one kind or two or more kinds may be used as the mixed solvent. Other solvents preferably used include toluene, hydrocarbon solvents such as xylene, acetone, methyl ethyl ketone, ketone solvents such as cyclohexanone, ethyl acetate, ester solvents such as butyl acetate, ethylene glycol dimethyl ether, 1,4- Dioxane, tetrahydrofuran, 1,2
Examples thereof include ether solvents such as dioxolane, aliphatic alcohol solvents such as methanol, ethanol and isopropanol, and halogenated hydrocarbon solvents such as methylene chloride and 1,2-dichloroethane.

The solution composition in the present invention comprises a solvent of 15 to
10 parts by weight of cellulose acylate is contained with respect to 250 parts by weight. If necessary, additives such as a plasticizer may be contained. The amount of solvent exceeds 250 parts by weight,
That is, if the solution concentration is less than 3.8% by weight, the stability of the solution is not a problem, but the amount of the solvent removed in the drying step is large because the effective concentration of cellulose acylate is low, which is not economically preferable. Further, when a film is formed by using the solution composition by a solution casting method or an extrusion method, the solution viscosity is low, but external disturbance is likely to occur and surface smoothness is difficult to obtain, which is not preferable because of the low solution viscosity. On the contrary, if the amount of the solvent is less than 15 parts by weight, it is difficult to obtain a stable fluid solution, which is not preferable. These concentrations are determined mainly in consideration of the stability of the solution and the viscosity of the solution. The amount of the solvent in the solution composition of the present invention is preferably 15 to 120 parts by weight, more preferably 35 to 110 parts by weight, still more preferably 45 to 10 parts by weight.
It is desirable to contain 10 parts by weight of cellulose acylate with respect to 5 parts by weight.

In the present invention, the solution composition (dope) obtained by dissolving cellulose acylate in a solvent mainly containing 1,3-dioxolane is cast on a supporting substrate,
The film is obtained by heating and evaporating the solvent.
The industrial continuous film forming process generally includes a casting process and a drying process. The casting step is a step of smoothly casting the dope, and the drying step is a step of evaporating and removing the solvent from the cast dope.

In the casting process, a method of extruding from a die, a method of using a doctor blade, a method of using a reverse roll coater, etc. are used. Industrially, the most common method is to continuously extrude a dope from a die onto a belt-shaped or drum-shaped supporting substrate. The supporting substrate used is not particularly limited, but a glass substrate, a metal substrate such as stainless steel or a ferro type, a plastic substrate such as polyethylene terephthalate, or the like is used. However, a mirror-finished metal substrate is most commonly used in order to industrially obtain a homogeneous film having a highly excellent surface property, which is the main subject of the present invention.

Generally, the solution viscosity is an extremely important factor in forming a transparent and smooth film from a dope. Although the solution viscosity depends on the resin concentration, the molecular weight and the type of solvent, the viscosity of the solution composition used in the present invention is 500
~ 200,000 cps, preferably 1000-10
It is 10,000 cps. If it exceeds 200,000 cps, the fluidity of the solution may be lowered, so that a smooth film may not be obtained. On the other hand, if it is less than 500 cps, the fluidity is too high, and the surface is disturbed due to external disturbance, so that a uniform and smooth film may not be obtained.

In the present invention, the casting temperature is preferably in the range of 10 to 70 ° C, more preferably 15 to 50 ° C. If it exceeds 70 ° C, foaming due to evaporation of the solvent occurs at the same time as casting, which is not preferable. Also, 10
If the temperature is lower than 0 ° C, the casting dope is cooled to increase the viscosity, which makes it difficult to obtain smoothness and causes dew condensation, which is not preferable.

In the present invention, the drying step includes an initial drying step of evaporating and removing most of the solvent from the cast dope and peeling off the film on the substrate, and a post-drying step of removing the remaining solvent (heat treatment step). ) Can be implemented separately. Further, in the present invention, microwave heating may be used for all of the initial drying and heat treatment steps, or may be used for a part thereof. In addition, continuous method (conveyor oven method)
Or may be dried in a batch system. Furthermore, you may use together with hot air heating, electric heating, infrared heating, etc.

Ideally, the frequency of the microwave heating apparatus used in the present invention should be selected so that the molecules of both 1,3-dioxolane and cellulose acylate can move easily. However, in general, due to the restrictions of the Radio Law and the restrictions of microwave electron tubes, 2,450M
Heating devices with a frequency of Hz are common. However, 915 MHz can also be used as long as it does not interfere with other communications. In the present invention, the frequencies of 2,450 MHz and 915 MHz are preferably used because of such circumstances. The microwave intensity may be selected in consideration of conditions such as foaming of the film surface, citron skin, and waviness.

In the present invention, the cellulose acylate solution composition cast on the supporting substrate is dried in the initial drying step until the residual solvent amount becomes 5 to 30% by weight, preferably 10 to 20% by weight, and then, In the post-drying step, after peeling the film from the substrate, it is desirable to perform drying until the residual solvent amount becomes preferably 1% by weight or less, more preferably 0.5% by weight or less. If the amount of residual solvent is larger than this in the initial drying process, the film will be soft and will cause flow deformation of the polymer, and if the amount of residual solvent is small, stress adhesion will occur when peeling due to high adhesion to the substrate. Is not preferred. Further, if the residual solvent amount is larger than that in the post-drying step, deformation occurs with time, and if heat is applied in the post-processing step, dimensional change occurs, which is not preferable.

The thickness of the cellulose acylate film obtained by the present invention is not particularly limited, but is generally 5 to 5.
It is in the range of 500 μm, preferably 10 to 300 μm.

[0021]

According to the present invention, when a cast film is produced by using a high-concentration solution containing 1,3-dioxolane as a main solvent, the surface property, transparency and optical isotropy are obtained by drying by microwave heating. A cellulose acylate film having excellent properties and a small amount of residual solvent can be efficiently obtained in a short time with high productivity.

Such a film is useful as various films such as a base film for photography, a packaging film and a protective film for a polarizing plate.

[0023]

EXAMPLES The present invention will be described in detail below with reference to examples. However, the present invention is not limited to this.

The physical properties in the examples were measured by the following methods. Transmittance and haze value: Measured using an ultraviolet-visible spectroscope (UV-240) manufactured by Shimadzu Corporation. Measurement of solution viscosity: Tokyo Keiki Co., Ltd. B type viscometer BH type was used and it measured at 30 degreeC. Retardation: Automatic birefringence meter (K, manufactured by Kanzaki Paper Co., Ltd.)
OBRA-21AD) was used to measure the birefringence value in visible light of 590 nm. Amount of residual solvent: The film sample was dried at 150 ° C. for 16 hours, and the weight was determined before and after the measurement. Film thickness and thickness unevenness: Measured using a stylus type film thickness measuring instrument manufactured by Anritsu Corporation. Thickness unevenness corresponds to fine irregularities due to surface roughness. Here, 1 cm at any place on the film
It was defined as the difference between the highest value and the lowest value when the driver swept.

[Example 1] Average acetyl group introduction ratio 2.8
5 parts / repeating unit, 10 parts by weight of cellulose triacetate having η _sp /c=3.9 dl / g, and 1 part by weight of triphenyl phosphate were dissolved in 90 parts by weight of 1,3-dioxolane while stirring to give a transparent viscous solution. Obtained. The solution viscosity was 7.5 × 10 ³ cps. The solution was cast on a glass substrate using a doctor blade,
50MHz, 300W in microwave heating device for 3 minutes,
It was dried at 500 W for 5 minutes. The residual solvent amount of the obtained film was 17.0% by weight. After peeling off the film, heat treatment was further performed at 135 ° C. for 40 minutes. The residual solvent amount of the obtained film was 0.4% by weight. Further, the film thickness was 65 μm and the thickness unevenness was 0.8 μm / cm, and the surface properties were very excellent. The transmittance of this film in the visible light region was 92%, the haze value was 0.4%, and the transparency was very excellent. Further, the phase difference at the wavelength of 590 nm (retardation, Re = Δn · d, Δn is the birefringence index, d is the thickness (μm)) was 10 nm or less, and the isotropy was extremely high.

Example 2 A film was formed according to Example 1 except that a mixed solvent of 1,3-dioxolane and acetone (weight ratio 9/1) was used instead of 1,3-dioxolane. The residual solvent amount of the obtained film was 0.4% by weight. Further, the film thickness is 66 μm and the thickness unevenness is 0.
It was 8 μm / cm, and the surface property was very excellent. The light transmittance of this film is 92%, and the haze value is 0.
The transparency was very excellent at 5%. The phase difference at a wavelength of 590 nm was 10 nm or less, which was extremely high in isotropy.

Example 3 Average Acyl Group Introduction Rate 2.85
Individual / repeating unit, η _sp /c=3.4 dl / g cellulose acetate butyrate (butyryl group content 26%) 1
5 parts by weight, 2 parts by weight of triphenyl phosphate in 1,3
-Dissolve in 85 parts by weight of dioxolane while stirring to obtain a transparent viscous solution. The solution viscosity is 30 ° C. and is 3.4.
It was × 10 ⁴ cps. The solution was cast on a glass substrate using a doctor blade, 2,450 MHz,
3 minutes at 300W in microwave heating device, 5 at 500W
Dried for minutes. The residual solvent amount of the obtained film was 14.
It was 5% by weight. This film is peeled off and 1k
Microwave heating was performed at W for 10 minutes, and further heat treatment was performed at 150 ° C. for 20 minutes. The residual solvent amount of the obtained film was 0.2% by weight. The film thickness is 70 μm,
The thickness unevenness was 0.7 μm / cm, and the surface property was very excellent. The light transmittance of this film is 92%,
The haze value was 0.6% and transparency was very excellent. The phase difference at a wavelength of 590 nm was 10 nm or less, which was extremely high in isotropy.

Example 4 Average Acetyl Group Introduction Rate 2.4
0 parts / repeating unit, 15 parts by weight of cellulose diacetate having η _sp /c=3.8 dl / g, and 2 parts by weight of triphenyl phosphate were dissolved in 85 parts by weight of 1,3-dioxolane with stirring to give a transparent viscous solution. Got The solution viscosity at 30 ° C. was 4.5 × 10 ⁴ cps. The solution was cast on a glass substrate using a doctor blade, and the temperature was 2,450 MHz and 300 in a microwave heating device.
It was dried at W for 3 minutes and at 500 W for 5 minutes. The residual solvent amount of the obtained film was 14.6% by weight. This film was peeled off, and microwave heating was further performed at 1 kW for 10 minutes, and heat treatment was further performed at 150 ° C. for 20 minutes. The residual solvent amount of the obtained film was 0.2% by weight. Further, the film thickness was 70 μm and the thickness unevenness was 0.7 μm / cm, and the surface properties were very excellent. Further, the light transmittance of this film was 92% and the haze value was 0.5%, and the transparency was very excellent. The phase difference at a wavelength of 590 nm was 10 nm or less, which was extremely high in isotropy.

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Claims (3)

[Claims] 1. A cellulose acylate solution composition having 10 parts by weight of cellulose acylate dissolved in 15 to 250 parts by weight of a solvent containing 60% by weight or more of 1,3-dioxolane is cast on a supporting substrate. A method for producing a cellulose acylate film, wherein microwave heating is used in the step of evaporating and drying the solvent in producing the film. 2. The method for producing a cellulose acylate film according to claim 1, wherein the cellulose acylate is cellulose acetate. 3. The method for producing a cellulose acylate film according to claim 2, wherein the cellulose acetate is cellulose triacetate.