JP3421165B2 - Composition for film formation - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a film-forming composition, particularly
The present invention relates to a film-forming composition containing chitosan.

[0002]

2. Description of the Related Art A film made of a film-forming composition using a synthetic resin, for example, a coating film made of a paint, is said to be less likely to spontaneously decompose and to contribute to environmental pollution after disposal. For this reason, studies have been made on this type of membrane, for example, to impart natural degradability (biodegradability) by microorganisms to enhance environmental adaptability. By the way, in the case of imparting spontaneously degradability to a film such as a coating film, it is conceivable to adopt the same method as that for realizing a biodegradable plastic. Specifically, it is considered effective to use a natural polymer such as starch or chitosan as a main element or an auxiliary element in a film-forming composition for forming the film.

However, a film made of a film-forming composition containing a natural polymer has lower mechanical strength than a film made of a normal film-forming composition containing no natural polymer, and has good solvent resistance. Not. The object of the present invention is to expect biodegradability,
Moreover, it is to form a film having good mechanical strength and solvent resistance.

[0004]

The composition for film formation of the present invention comprises a solution of chitosan having an amino group and an aqueous polyamide resin having a functional group capable of forming a covalent bond with the amino group. This composition is, for example, 1 g of chitosan
Amine equivalent (A) per 1 g of water-based polyamide resin
The ratio with the epoxy equivalent (B) per unit is A: B = 1:
It contains a solution of chitosan and a water-based polyamide resin so as to be 1.5 to 1: 2.5.

Chitosan is a low molecular weight chitosan having a weight average molecular weight of 5,000 to 100,000, for example. Furthermore, the water-based polyamide resin has, for example, an epoxy group as a functional group capable of forming a covalent bond with an amino group. This type of water-based polyamide resin is, for example, polyamide-epichlorohydrin-based resin or epoxy-modified polyamide resin.

Chitosan Solution The chitosan used in the present invention has a structure similar to that of cellulose. It is obtained by acetylation. Therefore, such chitosan has an amino group. Deacetylation of chitin can be achieved, for example, by treating chitin with an alkali. Examples of the alkali used here include an aqueous solution of sodium hydroxide,
A potassium hydroxide aqueous solution etc. are mentioned.

The chitosan used in the present invention preferably has a weight average molecular weight of 5,000 to 100,000.
It is more preferably from 50,000 to 50,000. When the weight average molecular weight is less than 5,000, it is difficult to form a film having sufficient mechanical strength. On the other hand, when the weight average molecular weight exceeds 100,000, the compatibility with the water-based polyamide resin decreases, and it becomes difficult to obtain a uniform film.

In order to obtain chitosan having a weight average molecular weight within the above range, it is usually necessary to lower the molecular weight of commercially available chitosan (the weight average molecular weight is usually several hundreds of thousands to several millions). . It is also possible to use a commercial product of an aqueous chitosan solution having a low molecular weight and dissolved in an organic acid such as dilute acetic acid. However, commercially available products are often discolored to blackish brown due to side reactions such as addition of preservatives and sugar-amino group-induced Maillard reaction, and therefore it is not suitable to use when forming a colored film. . Therefore, when forming a colored film or the like, it is preferable to use a commercially available chitosan having a low molecular weight, instead of using a commercially available low molecular weight chitosan.

The method for reducing the molecular weight of chitosan is not particularly limited, and a conventionally known method, for example, a method using hydrogen peroxide, nitrous acid, phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid or an enzyme can be used. Can be adopted. Among these methods, the method using hydrogen peroxide is preferable from the viewpoint of easy post-treatment. Examples of the method using hydrogen peroxide include the method disclosed in JP-B-56-33401. However, this method is slightly difficult to carry out because the reaction conditions are heterogeneous, alkaline environment and high temperature. Therefore, a novel method including the following steps can be adopted.

Step 1: An aqueous acetic acid solution (about pH 3) in which 5% by weight chitosan is uniformly dissolved is prepared. Step 2: Hydrogen peroxide is added to the aqueous acetic acid solution obtained in Step 1 so that the reaction concentration becomes 2% (v / v). Step 3: Stir for a predetermined time at room temperature (about 20 ° C.) to react. Step 4: After completion of the reaction, the mixture is neutralized with a 2N aqueous sodium hydroxide solution, and the resulting white solid precipitate is suction filtered with a G2 glass filter. Step 5: Wash the white solid with deionized water until the filtrate is neutralized. Step 6: The white solid is freeze-dried to obtain a white powder (chitosan having a reduced molecular weight). By such a method, the weight average molecular weight is 590,00.
Table 1 shows the results of measuring the molecular weight of the low molecular weight chitosan obtained by lowering the molecular weight of 0 chitosan (trade name: SK-50: manufactured by Koyo Chemical Co., Ltd.).

[0011]

[Table 1]

The molecular weight measurement results were obtained using high performance liquid chromatography and pullulan as a standard sample for calibration. From Table 1, it can be seen that the low molecular weight chitosan usable in the present invention can be obtained by an easier method than the method described in the above-mentioned publication.

The degree of deacetylation of chitosan is not particularly limited, but is preferably 30 to 100%, 60
-100% is more preferable. The degree of deacetylation is
Concentration of alkali used when deacetylating chitin,
It can be adjusted to a desired value by appropriately adjusting the processing temperature or the processing time.

The solution of chitosan used in the present invention is the above-mentioned chitosan dissolved in an acid. The acid used for dissolution may be either an inorganic acid or an organic acid. A preferable acid is acetic acid in terms of prevention of deterioration of chitosan, prevention of corrosion of the apparatus and economy. Generally, the concentration of the solution is preferably set to 1 to 10% by weight. If it is less than 1% by weight, the solid content concentration becomes small,
It takes a long time to dry. On the contrary, if it exceeds 10% by weight,
Although it depends on the average molecular weight of chitosan, the viscosity is often high, which makes handling difficult.

Aqueous Polyamide Resin The aqueous polyamide resin used in the present invention has a functional group capable of forming a covalent bond with the amino group of chitosan described above. An epoxy group is mentioned as such a functional group. Examples of the water-based polyamide resin having an epoxy group include polyamide-epichlorohydrin resin and epoxy group-modified polyamide resin.

Polyamide epichlorohydrin resin is
It is a water-soluble polyamide resin treated with epichlorohydrin. In the present invention, the solubility in water is good,
Further, those having a viscosity of 30% by weight of 20 to 120 centipoise, preferably 30 to 80 centipoise are preferably used. Specific examples of such a polyamide epichlorohydrin resin include Polyfix 105, 202, 301 and 3 manufactured by Showa High Polymer Co., Ltd.
02 and the like.

As the epoxy group-modified polyamide resin,
An alcohol-soluble or water-soluble polymer in which a hydrogen atom of an amide group of a polymer having a main chain formed by repeating acid amide bonds is partially substituted with a methoxymethyl group is used.
In particular, it is preferable to use, as a base material, 8-nylon in which a part of amide bond hydrogen is methoxymethylated, and a glycidyl group-containing monomer is graft-polymerized thereto by a known method. The glycidyl group-containing monomer can be exemplified by glycidyl acrylate.

Here, the 8-nylon as the substrate preferably has a number average molecular weight of 10,000 to 100,000, more preferably 30,000 to 50,000. When the number average molecular weight is less than 10,000, the water resistance of the obtained coating becomes small. On the other hand, when it exceeds 100,000, compatibility of the composition of the present invention tends to be impaired.

The grafting ratio is preferably set to 5 to 40%, more preferably 10 to 30% based on the weight of the glycidyl group-containing monomer.
If it is less than 5%, good solvent resistance cannot be obtained. On the contrary, if it exceeds 40%, it is difficult to obtain a uniform film. Specific examples of such an epoxy group-modified polyamide resin include respective resin-based prepolymers manufactured by Teikoku Chemical Industry Co., Ltd. The water-based polyamide resin is
Usually, it is used as an aqueous solution having a concentration of 20 to 30% by weight.

Mixing Ratio The mixing ratio of the above chitosan solution and the water-based polyamide resin was calculated based on the deacetylation degree of chitosan,
The ratio A: B between the amine equivalent (A) per 1 g solid content of chitosan and the epoxy equivalent (B) per 1 g solid content of the water-based polyamide resin is set to be 1: 1.5 to 1: 2.5. Preferably. If the ratio is out of this range, it is difficult to obtain a uniform and smooth film. In addition to the above-mentioned essential components, the composition of the present invention may contain various additives such as extender pigments and coloring pigments, as long as the object of the present invention is not impaired.

Utilization of Film-Forming Composition The film-forming composition of the present invention can be used not only as a paint but also as various protective, packaging, separating or agricultural films. In the film formed by the composition of the present invention, the functional group of the water-based polyamide resin and the amino group of chitosan react to form a covalent bond, whereby chitosan forms a crosslinked structure between the water-based polyamide resin. It is considered to be a thing. Therefore, such a film can be expected to be biodegradable, has high mechanical strength, and has good solvent resistance.

[0022]

Example 1 Commercially available 10% chitosan solution (acetic acid aqueous solution, molecular weight = about 1)
8,000, Deacetylation degree = 85%: 4 parts by weight of Koyo Chemical Co., Ltd., and epoxy modified polyamide resin solution (trade name = Toresin UN-1, 29% (w / w) water-methanol solution, Molecular weight = about 40,000, epoxy equivalent = estimated 488: Teikoku Chemical Industry Co., Ltd.) 8.9 parts by weight to prepare a mixed solution. This was spread on a glass plate using a doctor blade (No. 9, 225 μm) and dried by heating at 80 ° C. for 1 hour.

The obtained dried film was cut to a size necessary for measuring physical properties, immersed in a 2% sodium hydroxide aqueous solution for a short time, the peeled film was transferred to a Teflon plate and washed with deionized water. When this was air dried overnight at room temperature, a film having an average film thickness of about 40 μm was obtained.

Example 2 Chitosan (trade name = SK-50, weight average molecular weight = 59)
50,000: Koyo Chemical Co., Ltd.) was uniformly dissolved in 5% by weight to prepare an aqueous acetic acid solution (about pH 3). Hydrogen peroxide was added to this so that the reaction concentration was 2% (v / v), and the mixture was reacted by stirring at room temperature (about 20 ° C.) for 60 minutes. After completion of the reaction, the mixture was neutralized with a 2N aqueous sodium hydroxide solution to cause precipitation, and the resulting white solid substance was suction-filtered with a G2 glass filter, and this solid substance was washed with deionized water until the filtrate was neutralized. The solid matter after washing was lyophilized to obtain white powder chitosan (weight average molecular weight = 57,000) having a low molecular weight. The obtained chitosan was adjusted to 0.
It was dissolved in 5% (v / v) acetic acid to prepare a 5% (w / w) chitosan solution.

Next, 4 parts by weight of the obtained chitosan solution,
A mixed solution with 6 parts by weight of an epoxy-modified polyamide resin solution (21% (w / w) water-methanol solution, molecular weight = about 40,000, epoxy equivalent = estimated 1,435: manufactured by Teikoku Chemical Industry Co., Ltd.) was prepared. A free film having an average film thickness of 25 μm was obtained by the same method as in Example 1.

Comparative Example 1 The same 10% chitosan solution as used in Example 1 was cast on a glass plate and dried by heating at 80 ° C. for 1 hour. The film thus obtained was immersed in a 2% aqueous solution of sodium hydroxide and then washed with deionized water to obtain a film. When this film was transferred onto a polyethylene terephthalate resin film whose surface was hydrophilized with a silicon coat and air-dried, a free film having an average film thickness of 58 μm was obtained.

Comparative Example 2 The same epoxy-modified polyamide resin solution used in Example 1 was coated on a smooth Teflon plate and dried by heating at 80 ° C. for 1 hour. After cooling this to room temperature, peel it off,
A free film having an average film thickness of 39 μm was obtained.

Evaluation Young's modulus of the film obtained in each Example and Comparative Example,
The tensile strength, elongation at break, dynamic glass transition temperature (Tm) and gelation rate were evaluated. The evaluation method is as follows.
The results are shown in Table 2.

(Young's modulus, tensile strength and elongation at break) The tensile strength was measured using a constant-speed elongation type tensile tester (Tensilon manufactured by Toyo Baldwin Co., Ltd.). (Dynamic glass transition temperature) Vibron DDV-II-EA manufactured by Toyo Baldwin was used for measurement. (Gelization rate) The precisely weighed film was immersed in methanol for 2 hours, and then the residue was separated by filtration, and the dry weight thereof was evaluated by the weight% with respect to the initial charged weight.

[0030]

[Table 2]

According to Table 2, the film obtained in each of the examples has a higher dynamic glass transition temperature than the film obtained in each of the comparative examples, and has a significantly high gelation rate. Therefore, it is considered that not only a blended film structure of the chitosan component and the polyamide resin component, but a crosslinked structure of both components is formed.

[0032]

The film-forming composition of the present invention contains a solution of chitosan having an amino group and an aqueous polyamide resin having a functional group capable of forming a covalent bond with the amino group, and therefore is expected to have biodegradability. It is possible to form a film having good mechanical strength and good solvent resistance.

Claims (6)

(57) [Claims] 1. A film-forming composition comprising a solution of chitosan having an amino group and an aqueous polyamide resin having a functional group capable of forming a covalent bond with the amino group. 2. The ratio of the amine equivalent (A) per 1 g of the chitosan and the epoxy equivalent (B) per 1 g of the aqueous polyamide resin is A: B = 1: 1.5 to 1: 2.
The film-forming composition according to claim 1, which contains the chitosan solution and the water-based polyamide resin so as to be 5. 3. The chitosan has a weight average molecular weight of 5,0.
The composition for film formation according to claim 1 or 2, which is a low molecular weight chitosan of 00 to 100,000. 4. The film forming composition according to claim 1, 2 or 3, wherein the water-based polyamide resin has an epoxy group as a functional group capable of forming a covalent bond with the amino group. 5. The water-based polyamide resin is polyamide.
The film-forming composition according to claim 4, which is an epichlorohydrin-based resin. 6. The film-forming composition according to claim 4, wherein the water-based polyamide resin is an epoxy-modified polyamide resin.