JP2002348403A - Recovering method of cellulose ester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of recovering a high quality cellulose ester from a polarizing plate to reuse it. SOLUTION: In the recovering method, the cellulose ester-containing polarizing plate is crushed or cut, and soaked in an aqueous solution containing calcium compounds or polyols.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recovering a cellulose ester from a polarizing plate.

[0002]

2. Description of the Related Art Conventionally, waste plastics have been disposed of by landfilling or incineration. However, with the increase in environmental awareness in recent years, it has become difficult to secure landfill sites and increase the number of incineration plants, and it is necessary to change the processing method. ing. Further, depletion of petroleum resources and reduction of carbon dioxide emissions are required from the standpoint of resource protection and environmental conservation, and as a result, the recycling and reuse of used articles is no longer essential.

[0003] Cellulose ester is originally a plastic obtained by chemically treating linter or pulp from wood, which is a natural resource, but its reuse has been an issue from the standpoint of forest protection. Linter pulp tends to rely on wood pulp because of the small amount of linter pulp that can be obtained from the linter part of the cotton, the production amount is easily affected by the weather, and the cost.

A cellulose triacetate film is used for a polarizing plate for a liquid crystal image display device, a silver halide photographic light-sensitive material, and the like because it is transparent and mechanically strong.

[0005] A film laminate including a polarizing plate for a liquid crystal display device comprises a cellulose triacetate film as a protective film for a polarizing film, the surface of which is saponified in advance with an alkali solution, on both sides or one side of a uniaxially stretched polyvinyl alcohol-based polarizing film. The polarizing plate is laminated, and a surface protective film of a polyester film, an adhesive layer, an antiglare layer, an antireflection layer, a hard coat layer, an antistatic layer, and the like are further laminated on both sides of the polarizing plate. With silver halide photographic light-sensitive materials, the yield in the production of cellulose triacetate film is quite good, and the produced cellulose triacetate film is not so much waste as most of it remains at the photographer. On the contrary,
For a cellulose triacetate film for a liquid crystal display device, a polarizing plate in which a highly hygroscopic uniaxially stretched polarizing film is laminated, and the above-mentioned constituent layers are further laminated on both surfaces thereof, etc. At present, the final yield is considerably low because a large area is used to avoid dust and defects, and the waste film is discarded in each of these work processes.

Conventionally, as a technique for recovering a cellulose triacetate film for a silver halide photographic light-sensitive material, for example, Japanese Patent Application Laid-Open No. Hei 5-281686 discloses a method of treating with hypochlorous acid and then treating with an aqueous solution. 688,6
No. 14 describes an acidic treatment containing potassium permanganate, British Patent 1,087,038 discloses an alkaline treatment containing an oxidizing agent, and Japanese Patent No. 26403.
Nos. 94 and 2817020 describe a cellulase treatment and a water-soluble organic solvent treatment, respectively. Further, in the silver halide photographic light-sensitive material, there is no mixture which is mostly composed of a polyethylene terephthalate film and a cellulose triacetate film separately as a support, but when discarded, it is composed of a polyethylene terephthalate film. And a film composed of a cellulose triacetate film may be mixed. In the case of such coexistence, methods for separating and recovering each film by the underwater floating separation method are disclosed in JP-A-50-87469, JP-A-50-87470 and JP-A-50-87470.
No. 2-97738.

[0007] With the spread of liquid crystal display devices in recent years, there has been a growing demand for collecting cellulose acetate films used as protective films for polarizing films from polarizing plates. However, since the cellulose acetate film used as a protective film for a polarizing film has a different form of use from a photographic film, it has been found that the same collection method as that for a photographic film cannot always be diverted.

The cellulose acetate film used for the protective film for the polarizing film is mainly made of cellulose triacetate having a relatively high hydroxyl substitution degree, for example, having an acetylation degree of 58 or more, from the viewpoint of optical properties, physical properties and productivity. Have been.

In the manufacturing process of a polarizing plate, generally, the surface of a cellulose acetate film is saponified in advance with an alkali solution to improve adhesiveness, and then bonded to a polarizing film containing polyvinyl alcohol as a main component to form a polarizing plate. It is a plate.

However, since cellulose acetate having a high degree of substitution is susceptible to alkali and easily saponified, if the cellulose acetate film processed as a protective film for a polarizing film is directly recovered and regenerated, the cellulose acetate film is substituted. There is a problem in that cellulose acetate having a low degree is mixed in and becomes a raw material of a quality that cannot withstand reuse as a protective film for a polarizing film if it is used as it is. Further, there is a problem that storage stability is deteriorated.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for recovering and reusing a cellulose ester having high storage stability from a polarizing plate.

[0012]

The above object of the present invention has been attained by the following constitutions.

1. A method for recovering a cellulose ester, comprising crushing or cutting a polarizing plate containing a cellulose ester and immersing the polarizing plate in an aqueous solution containing at least one selected from a calcium compound and a polyol.

2. A method for recovering a cellulose ester, comprising crushing or cutting a polarizing plate containing a cellulose ester and then immersing the polarizing plate in an aqueous solution containing an amine compound.

[0015] 3. 3. The method for collecting a cellulose ester according to the above 1 or 2, further comprising a step of removing polyvinyl alcohol (PVA).

4. After crushing or cutting a polarizing plate containing a cellulose ester, the cellulose is characterized by being immersed in a mixed solution of water and a water-miscible organic solvent containing at least one selected from calcium compounds, polyols and amine compounds. Ester recovery method.

5. After crushing or cutting a polarizing plate containing a cellulose ester, it contains at least one selected from calcium compounds, polyols and amine compounds,
A method for recovering a cellulose ester, comprising immersing the cellulose ester in an aqueous solution containing a buffer.

6. 6. The method for recovering a cellulose ester according to the above item 5, wherein the buffer is a carbonate.

[7] 7. A method for recovering a cellulose ester, comprising: crushing or cutting off a scrap or returned material of a polarizing plate containing a cellulose ester, and then recovering the material by the recovery method according to any one of the above items 1 to 6.

8. 8. A method for recovering a cellulose ester, comprising a step of dissolving the cellulose ester treated by the method for recovery according to any one of the above items 1 to 7 with an organic solvent capable of dissolving the cellulose ester.

The present invention will be described in more detail. The object of recovery of the present invention is a cellulose ester used for a polarizing plate.

The cellulose ester to be recovered in the present invention is obtained by subjecting a hydroxyl group of cellulose to an acylation reaction of a lower fatty acid. Cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate and cellulose acetate proteate are used. It is at least one selected from pionate butyrate. The substitution degree of the acyl group substituted by the hydroxyl group of cellulose is preferably 2.4 to 3.0, and the degree of polymerization is 3
It is preferably at least 00, more preferably at least 400.

The cellulose ester film used in the polarizing plate according to the present invention is obtained by dissolving a cellulose ester in a solvent, for example, methylene chloride to form a dope.
It is formed by a solution casting method such as a usual cellulose triacetate film. The surface is further saponified with an alkali solution and treated so that the polarizing film is easily adhered. An example of the saponification treatment conditions of the cellulose ester film according to the present invention is as follows: 2 mol of 40 to 60 ° C.
/ L of NaOH aqueous solution for about 30 to 150 seconds, washed with water at room temperature for about 30 to 60 seconds, and further added with 1 to 5% by mass HCl.
And neutralize for about 30-60 seconds, then with normal temperature water for about 30-60
The condition is that it is washed with water for 2 seconds and dried at about 80 ° C., but is not limited thereto.

The polarizing film is made of, for example, polyvinyl alcohol,
An aqueous solution of a polyvinyl alcohol-based polymer such as an ethylene-vinyl alcohol copolymer is formed into a film, and the film is uniaxially stretched and dyed with iodine or a dichroic dye. Water-resistant treatment was carried out with an agent.

As described above, the polarizing plate according to the present invention is obtained by laminating a cellulose ester film having a saponified surface on both sides of the polarizing film.

One example of the preparation of the polarizing film and the method of bonding the polarizing film to the polarizing film is shown below. One surface of each of two saponified cellulose ester films is coated with an aqueous solution of polyvinyl alcohol as an adhesive solution, Then, a uniaxially stretched polyvinyl alcohol film is immersed in an iodine solution, and then a uniaxially stretched polarizing film is sandwiched and bonded. Examples of the adhesive solution include a polyvinyl alcohol-based adhesive solution such as a polyvinyl alcohol aqueous solution and a polyvinyl butyral solution, and a vinyl polymerized latex such as butyl acrylate. A completely saponified polyvinyl alcohol aqueous solution is preferable.

At present, there are two different manufacturers of cellulose ester films, one for laminating the polarizing film and the other for laminating the waste separately. By doing so, the recovery amount is increased, the recovery rate is improved, and the cellulose ester can be advantageously reused.

In the present invention, the polarizing plate at the time of recovery can be conveniently formed into an amorphous or small rectangular chip by grinding or cutting, and the size is the minimum to maximum length of the chip. About 0.1 to 20 mm is suitable for the treatment, and particularly preferably 0.5 to 10 mm.

The cellulose ester recovery method of the present invention comprises:
The cellulose ester film and the polarizing film are separated and separated by washing the chip having the above size with an aqueous solution.

The aqueous liquid contains at least one selected from calcium compounds, polyols and amine compounds. However, when two or more compounds are used, they may be the same or different types of compounds.

Examples of the calcium compound that can be preferably used in the present invention include calcium chloride, calcium bromide and calcium hydroxide, and examples of the polyols include glycerin and gluconic acid. Examples of the amine compound include sulfanilic acid, sulfamic acid, polyethyleneimine, urea, guanidine hydrochloride, (NH ₄ ) ₂ SO _{3 and the} like.

As the solvent of the aqueous liquid used in the present invention,
Water alone may be used, or a mixture of water and a compound having at least one hydroxyl group and having compatibility with water having 1 to 6 carbon atoms. Examples of the compound having at least one hydroxyl group and having compatibility with water having 1 to 6 carbon atoms include methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, and s- Butanol, t-butanol, ethylene glycol, 1,3-trimethylene glycol, 1,4-tetramethylene glycol, diethylene glycol, glycerin, trimethanolethane, trimethanolpropane, pentaerythritol, cyclohexanol, glucose, pentose, xylitolose, xylitol And the like, but are not limited thereto. The content of the above compound in the aqueous liquid is 0.1 to 99.9% by mass, preferably 10 to 90% by mass, and more preferably 30 to 80% by mass. However, these values may vary depending on the solubility of these compounds in water.

The treatment temperature in the aqueous liquid treatment of the present invention varies depending on the type and mixing ratio of water and the above compound.
-100 ° C is preferred, and 35-80 ° C is more preferred.
The treatment pH of the aqueous solution is preferably neutral to weakly alkaline. Further, the aqueous liquid preferably contains a buffer. Any buffer can be used as long as the buffer maintains pH 7 or more, but carbonate, phosphate, glycine,
Tris (2-amino-hydroxymethyl-1,3-propanediol) and the like are preferred. A buffer in an ethanol / water system does not precipitate in ethanol, and any buffer capable of maintaining a pH of 7 or more is possible.
s, glycine and the like. Preferred buffers include carbonates.

The state in which the polarizing film is separated from the cellulose ester film by the aqueous liquid treatment of the present invention is various, such as a state in which the polyvinyl alcohol film is dissolved, swollen, or not swollen. In particular, in the case where a compound having at least one hydroxyl group and having compatibility with water having 1 to 6 carbon atoms is used, in many cases, separation is performed without almost swelling.

Since the polarizing film is dyed with iodine or a dichroic dye, when treated with the above-mentioned aqueous solution, coloring may remain on the cellulose ester film side. It is preferred to use The reducing agent can be used without limitation as long as it can be decolorized, and examples thereof include sodium thiosulfate, ascorbic acid, ferrous chloride and the like. The amount used is 0.1 to 100 g, preferably 1 to 20 g per 1 kg of the aqueous liquid.
g, more preferably 4 to 10 g.

Depending on the manufacturer, the polarizing film may be a polyvinyl alcohol-based polymer cross-linked with a cross-linking agent such as boric acid, or a polyvinyl alcohol having a high degree of saponification. May be difficult to dissolve in liquid. In such a case, in the present invention, it is preferable to add a polyvinyl alcohol degrading enzyme capable of decomposing the polyvinyl alcohol-based polymer to the aqueous liquid. Further, the polyvinyl alcohol film peeled off by the aqueous liquid treatment is dissolved or swelled in the aqueous liquid, and if discharged as it is, there is a risk of polluting the river, and an enzyme capable of decomposing the polyvinyl alcohol-based polymer is used for the waste liquid treatment. Is preferred. The degrading enzyme for polyvinyl alcohol is described in Section 7, Polyvinyl Alcohol Degrading Enzyme (p. 466 to 476) edited by Yoshiharu Dohi, “Biodegradable Plastic Handbook”, edited by Biodegradation Study Group (NTS Inc.). Degradative enzymes that have been used can be used. Conditions suitable for the decomposition of polyvinyl alcohol by the decomposing enzyme vary depending on the decomposing enzyme, but the temperature is 30 to 65 ° C and the pH is 6.5 to 9.5.
0. As polyvinyl alcohol to be decomposed,
A wide range of polyvinyl alcohols can be easily decomposed, from those having a high degree of polymerization to those having a low degree of polymerization, and those having complete saponification to those having a low degree of saponification.

A surfactant may be used in order to allow the aqueous liquid to quickly permeate the interface between the cellulose ester film and the polarizing film of the polarizing plate. The surfactant may be any of anionic, cationic, amphoteric and nonionic. Examples of the anionic surfactant include an alkyl carboxylate, an alkyl sulfonate, an alkyl benzene sulfonate, an alkyl naphthalene sulfonate, an alkyl sulfate, an alkyl phosphate, and an N-acyl-N-alkyltaurine. , Sulfosuccinates, sulfoalkylpolyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl phosphates, etc., which have a carboxy group, a sulfo group, a phospho group, a sulfate group, a phosphate group, etc. Compounds are preferred. Examples of the cationic surfactant include alkylamine salts, aliphatic or aromatic quaternary ammonium salts, heterocyclic quaternary ammonium salts such as pyridinium and imidazolium, and phosphonium or sulfonium salts containing an aliphatic or heterocyclic ring. Is preferred. As the amphoteric surfactant, for example, amino acids, aminoalkyl sulfonic acids, aminoalkyl sulfates or phosphoric esters, alkyl betaines, amine oxides and the like are preferable. Nonionic surfactants include, for example, saponins (steroids), alkylene oxide derivatives (eg, polyethylene glycol, polyethylene glycol / polypropylene glycol condensates, polyethylene glycol alkyl ethers or polyethylene glycol alkyl aryl ethers, polyethylene glycol esters, polyethylene) Glycol sorbitan esters, polyalkylene glycol alkylamines or amides, silicone polyethylene oxide adducts), glycidol derivatives (eg, alkenyl succinic acid polycerides, alkylphenol polyglycerides), and alkyl esters such as polyhydric alcohol fatty acid esters. preferable.

The treated and recovered cellulose ester may be washed with water, dried and then dissolved in a solvent capable of dissolving the cellulose ester, followed by filtration, film formation, precipitation, purification, re-dissolution, etc. Examples of the organic solvent having a dissolving ability for a cellulose ester include methylene chloride, methyl acetoacetate, ethylene chloride, chloroform, methyl acetate, 1,3-dioxolan, 1,4-dioxane,
Examples thereof include nitromethane, epichlorohydrin, N-methylpyrrolidone, dimethylsulfoxide, and fluoroalcohol.

[0039]

The present invention will be described in detail with reference to the following examples.
It is not limited to this.

Example 1 Treatment 1) Crushing Treatment A polarizing plate (manufactured by Sumitomo Chemical Co., Ltd.) having a three-layer laminated structure of a polarizing film substrate film layer of polyvinyl alcohol and a protective film of triacetyl cellulose was prepared for about 0.5. ~ 1.0cm
Crushed into corners.

Treatment 2) Washing treatment (warm water washing method) 80 g of the crushed polarizing plate was placed in 2000 ml of an aqueous solution containing the additives shown in Table 1, and was placed at 75 ° C for 1 hour.
After the heating / stirring treatment, the liquid was removed, the same solution was newly added, and the same treatment was performed. This was repeated three times. Further, this solution was removed, and hot water of 75 ° C.
Then, the mixture was washed by stirring for 30 minutes. This hot water was removed, hot water was newly added, and the same treatment was performed. This was repeated three times.

As a comparative example, instead of the aqueous solution in Table 1,
The result of treatment with pure water is shown. Treatment 3) Drying treatment: The film pieces collected by the above treatment were dried in a dryer at 105 ° C.

Treatment 4) Film-forming step The cellulose ester obtained as described above was dissolved in a 5 times by mass amount of a solution of methylene chloride: ethanol (9: 1). This solution was filtered through a filter and then reprocessed into a cellulose ester film by a solution casting method.

Evaluation of Storage Stability (Deterioration Prevention Effect) A 2.0 g sample was placed in a 50 ml glass container, and
After humidity control for 24 hours at 90 ° C. and a relative humidity of 90%, the container was sealed and subjected to a thermal heat treatment at 80 ° C. and a relative humidity of 90% for 400 hours.

The sample after the treatment was immersed in a 50 ° C. methanol bath for 30 minutes. Repeat this three times to rinse,
The additive components other than cellulose triacetate contained in the sample were removed, and after the removal, the sample was dried at 105 ° C. for 2 hours.

After the rinsing and drying operations, the obtained sample was
The acetylation degree was quantified using the acetylation degree determination method (dissolution method) of the JIS L1013 chemical fiber filament yarn test method.
The acetylation degree after deterioration was compared with the acetylation degree before deterioration to determine the degree of deterioration. Table 1 shows the results.

[0047]

[Table 1]

In Table 1, Tris is 2-amino-
Hydroxymethyl-1,3-propanediol.

Table 1 shows that the method of the present invention is excellent with little deterioration of the degree of acetylation. Example 2 Treatment 1) Crushing treatment: Same as in Example 1.

Treatment 2) Washing treatment (warm water washing method) A polarizing plate (80 g) subjected to the same treatment 1 as in Example 1 was placed in Table 2
In 2000 ml of an aqueous solution containing the additives shown in
The mixture was heated and stirred at 75 ° C. for 1 hour. During this one hour, the pH was monitored, and a Ca (OH) ₂ aqueous solution was added dropwise so that the pH always became as shown in Table 2. Thereafter, the liquid was removed, the same solution was newly added, and the same treatment as in the first time was performed. This was repeated three times. Further, this solution was removed, and 2,000 ml of 75 ° C.
It was washed by stirring for 0 minutes. This hot water was removed, hot water was newly added, and the same treatment was performed. This was repeated three times.

Process 3) Drying process: Same as in Example 1. Process 4) Film forming process: Same as in Example 1.

The storage stability was evaluated in the same manner as in Example 1, and the results are shown in Table 2.

[0053]

[Table 2]

Example 3 Treatment 1) Crushing treatment: Same as in Example 1.

Treatment 2) Washing treatment (warm water washing method) A polarizing plate 80g that had been subjected to the same treatment 1 as in Example 1 was placed in Table 3
The mixture was placed in 2,000 ml of an aqueous solution containing the additive shown in (1), heated and stirred at 75 ° C. for 1 hour, and then the liquid was removed. The same solution was newly added and the same treatment was performed. This was repeated three times. Further, the solution was removed, 2000 ml of hot water at 75 ° C. was added, and the mixture was washed by stirring for 30 minutes. This hot water was removed, hot water was newly added, and the same treatment was performed. This was repeated three times.

Treatment 3) Drying treatment: Same as in Example 1. Process 4) Film forming process: Same as in Example 1.

The storage stability was evaluated in the same manner as in Example 1, and the results are shown in Table 3.

[0058]

[Table 3]

From Table 3, it can be seen that the method of the present invention to which the polyol was added was excellent with less deterioration of the acetylation degree.

Example 4 Treatment 1) Crushing treatment: Same as in Example 1.

Treatment 2) Washing treatment (warm water washing method) 80 g of the polarizing plate subjected to the same treatment 1 as in Example 1 was placed in Table 4
The mixture was placed in 2,000 ml of an aqueous solution containing the additive shown in (1), heated and stirred at 75 ° C. for 1 hour, and then the liquid was removed. The same solution was newly added and the same treatment was performed. This was repeated three times. Further, the solution was removed, 2000 ml of hot water at 75 ° C. was added, and the mixture was washed by stirring for 30 minutes. This hot water was removed, hot water was newly added, and the same treatment was performed. This was repeated three times.

Treatment 3) Drying treatment: Same as in Example 1. Process 4) Film forming process: Same as in Example 1.

The storage stability was evaluated in the same manner as in Example 1. Simultaneously, the bright spot foreign matter was measured by the following method. The results are shown in Table 4.

Evaluation method for bright spot foreign matter: A polarizing film and a cellulose ester film are superimposed, and the bright spot (10 μm
Points of the above sizes) are visually counted. ：: 40 or less / 250 mm ² Δ: 41 to 80/250 mm ² ×: 81 or more / 250 mm ² .

[0065]

[Table 4]

From Table 4, it can be seen that the method of the present invention to which the amine compound was added was excellent, with less deterioration of acetylation degree and less bright spot foreign matter.

Example 5 Treatment 1) Crushing treatment: Same as in Example 1.

Treatment 2) Washing treatment (Water-soluble organic solvent washing method) 80 g of a polarizing plate treated in the same manner as in Example 1 was treated with 200 g of a 75% aqueous ethanol solution containing the additives shown in Table 5.
In 0 ml, the mixture was stirred at 60 ° C. for 2 hours to dissolve and remove additives and the like, and at the same time, the polarizing film (polyvinyl alcohol) was peeled off.

Table 5 shows that 75% ethanol
The buffer used in place of 5% pure water is shown.

As a comparative example, the results of a stirring treatment with a 75% aqueous ethanol solution (ethanol diluted with pure water containing no additive) are shown.

The aqueous solution was removed by filtration through a wire mesh, and hot water of 75 ° C. was directly added to the solution to dissolve the polarizing film and to remove the remaining TA.
The C film was collected with a wire mesh. In addition, the collected TAC
The film was washed by stirring in warm water at 75 ° C. for 30 minutes. (3 times) Treatment 3) Drying treatment: Same as in Example 1.

Treatment 4) Membrane forming step: The cellulose ester obtained as above was added with 10% by mass of triphenyl phosphate and dissolved in a solution of methylene chloride: ethanol (9: 1) 5 times the mass of the recovered product. did. After the solution was filtered through a filter, it was reprocessed into a cellulose ester film by a solution casting method, and the storage stability was evaluated.

[0073]

[Table 5]

From Table 5, it can be seen that the method of the present invention using ethanol is excellent with little deterioration of the degree of acetylation.

[0075]

According to the present invention, a method of recovering and reusing high quality cellulose ester from a polarizing plate can be provided.

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Claims (8)

[Claims] 1. A method for recovering a cellulose ester, comprising crushing or cutting a polarizing plate containing a cellulose ester and immersing the polarizing plate in an aqueous solution containing at least one selected from a calcium compound and a polyol. 2. A method for recovering a cellulose ester, comprising crushing or cutting a polarizing plate containing a cellulose ester, and immersing the polarizing plate in an aqueous solution containing an amine compound. 3. The method according to claim 1, further comprising a step of removing polyvinyl alcohol (PVA). 4. After crushing or cutting a polarizing plate containing a cellulose ester, the plate is immersed in a mixed solution of water containing at least one selected from calcium compounds, polyols and amine compounds and a water-miscible organic solvent. A method for recovering a cellulose ester. 5. After crushing or cutting a polarizing plate containing a cellulose ester, the polarizing plate is immersed in an aqueous solution containing at least one selected from a calcium compound, a polyol and an amine compound and containing a buffer. Method for recovering cellulose ester. 6. The method according to claim 5, wherein the buffer is a carbonate. 7. A method for recovering a cellulose ester, comprising: crushing or cutting off scraps or returned material of a polarizing plate containing a cellulose ester, followed by recovery by the recovery method according to any one of claims 1 to 6. Method. 8. A cellulose, which comprises a step of dissolving the cellulose ester treated by the recovery method according to any one of claims 1 to 7 with an organic solvent capable of dissolving the cellulose ester. Ester recovery method.