JPH06157794A - Coating type anti-fogging agent having excellent durability - Google Patents

Abstract

PURPOSE:To obtain an anti-fogging agent readily applicable to agricultural covering film, having excellent adhesiveness, hardly being washed away with condensed water on the inner face of the film, having excellent durability, containing a specific amount of a polyvinyl acetal resin. CONSTITUTION:This anti-fogging agent contains 0.5-5wt.% polyvinyl acetal resin obtained by acetalizing (A) a polyvinyl alcohol having 200-4,500 (preferably 500-4,500) average polymerization degree with (B) an aldehyde (preferably aromatic aldehyde) such as butylaldehyde. The degree of acetalization is preferably 2-40mol%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antifogging agent for a covering film for agriculture, such as polyethylene and polyvinyl chloride, which is used for greenhouse cultivation and tunnel cultivation of crops, and more particularly has excellent sustainability. The present invention relates to a coating type antifogging agent.

[0002]

2. Description of the Related Art Agricultural coating films such as polyethylene and polyvinyl chloride that make up greenhouses and tunnels for crop cultivation adhere to the inside of the greenhouses and tunnels as water droplets by condensing on the film surface. Anti-fogging property is imparted for the purpose of preventing the light transmission of the film and preventing adverse effects on crops due to water drops falling from the coating film.

Conventionally, as a method of imparting such anti-fogging property, a surfactant is kneaded into the coating film to bleed the water on the surface so that the attached water droplets flow down the inner surface of the coating film to ensure the light transmission. The method of improving the water wettability has been adopted. The surfactant used for this kneading is N, N-bis (2-hydroxyethyl) alkylamine, polyoxyethylene alkylamine or its fatty acid ester, glycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester. And so on.

[0004]

However, since all of the above-mentioned surfactants are of low molecular weight, they easily bleed out from the film, and the surfactant is washed away by the condensed water on the inner surface of the film, and the surfactant is short-lived. There was a drawback that the antifogging effect disappeared.

In view of the above points, an object of the present invention is to provide a coating type antifogging agent which is made of a substance which is difficult to be washed away by condensed water on the inner surface of the film and which is excellent in sustainability.

[0006]

The antifogging agent according to the present invention has been devised in order to achieve the above-mentioned object, and contains a polyvinyl acetal resin in an amount of 0.5 to 5% by weight and has excellent durability. It is an antifogging agent.

The polyvinyl acetal resin is obtained by acetalizing polyvinyl alcohol with butyraldehyde, and usually has an acetal group, an acetyl group and a hydroxyl group in the ethylene group of the main chain. The preferred acetyl group content is 2-40 mol%.

The reason for using the polyvinyl acetal resin having an acetalization degree of 2 to 40 mol% is that the acetalization degree is 2
When it is less than mol%, the antifogging layer has good water absorption but poor water resistance. On the contrary, when the degree of acetalization is more than 40 mol%,
This is because the antifogging layer has good water resistance but poor water absorption, so that sufficient antifogging property cannot be obtained.

As a method for acetalizing polyvinyl alcohol, known methods such as a precipitation method using an aqueous medium in the presence of an acid catalyst and a dissolution method using a solvent such as alcohol are adopted. It is also possible to use a polyvinyl acetate resin as a raw material and perform saponification and acetalization in parallel to obtain a polyvinyl acetal resin.

Polyvinyl alcohol generally has an average degree of polymerization of 200 to 4500, preferably 500 to 45.
No. 00 is used. If the average degree of polymerization is less than 200, it is difficult to synthesize polyvinyl alcohol, and conversely, if the average degree of polymerization exceeds 4,500, the solution viscosity becomes too high, and the practicality in this application is lowered. The higher the average degree of polymerization, the better the water resistance and water absorption.

The degree of saponification of polyvinyl alcohol is generally 75 to 99,8 mol%. Saponification degree is 7
If it is less than 5 mol%, the solubility during the reaction is insufficient,
On the contrary, if it exceeds 99.8 mol%, it becomes difficult to synthesize polyvinyl alcohol. The lower the degree of saponification, the better the water absorption.

Aldehydes to be condensed with polyvinyl alcohol include aliphatic aldehydes such as formaldehyde, acetaldehyde, butyraldehyde, hexyl aldehyde, octyl aldehyde and decyl aldehyde;
Benzaldehyde, 2-methylbenzaldehyde, 3-
Aromatic aldehydes such as methylbenzaldehyde, 4-methylbenzaldehyde, other alkyl-substituted benzaldehydes, chlorobenzaldehydes, and other halogen-substituted benzaldehydes; having a substituent such as a hydroxy group, an alkoxy group, an amino group, or a cyano group on the aromatic ring Aromatic aldehydes, such as aldehydes having a condensed aromatic ring such as naphthaldehyde and anthralaldehyde.

Aromatic aldehydes are particularly preferable in that a resin having excellent water absorption, water resistance and transparency can be obtained.

In the antifogging agent according to the present invention, alcohol such as isopropyl alcohol or ethyl alcohol or an aqueous solution thereof is preferably used as a solvent for dissolving the polyvinyl acetal resin.

The concentration of the polyvinyl acetal resin in the solution is 0.5 to 5% by weight. If the concentration of the polyvinyl acetal resin is less than 0.5% by weight, the antifogging effect will not be sufficiently exhibited, and if the concentration exceeds 5% by weight, the viscosity will be too high and the coating amount will be uneven. There are cases. A particularly preferable concentration of the polyvinyl acetal resin is 1 to 3% by weight.

The antifogging agent according to the present invention is polyethylene,
It is applied to at least one side of an agricultural coating film such as polyvinyl chloride by a known method such as roll coating, spraying or brush coating.

[0017]

[Action]

1) Polyvinyl acetal resin is a high molecular weight polymer having both a hydrophobic group and a hydrophilic group. Therefore, when it is applied to an agricultural coating film, it exhibits the following characteristics.

That is, the hydrophobic group of the polyvinyl acetal resin exerts good adhesiveness to the surface of the synthetic resin film and prevents the polyvinyl acetal resin from being washed off by water.

On the other hand, the hydrophilic group of the polyvinyl acetal resin imparts good wettability to the agricultural coating film and imparts antifogging property. In this way, it is possible to form an antifogging film that is hard to flow out with water on the surface of the synthetic resin film.

2) Since the polyvinyl acetal resin is easily dissolved in an alcohol / water-based solvent, the antifogging agent solution thus prepared has a low viscosity and is easy to apply.

[0021]

EXAMPLES Next, the present invention will be specifically described by way of examples.

Example 1 A polyvinyl butyral resin (“ESREC KXI” manufactured by Sekisui Chemical Co., Ltd.) was added to an alcohol / water solvent (isopropyl alcohol / water = 60/40 weight ratio) at a concentration of 2.6% by weight.
To prepare a coating type antifog agent.

This antifogging agent was applied to a low-density polyethylene film (Mitsubishi Polyethylene LD F131, 0.05 mm thick).
Melt flow rate = 1.3, density = 0.924, manufactured by Mitsubishi Kasei Co., Ltd.) and air dried to prepare a sample film. The coating amount of the antifogging agent was adjusted so that the polyvinyl butyral resin content was 3 g / m @ 2 film surface.

Example 2 A sample film was prepared in the same manner as in Example 1 except that the concentration of polyvinyl butyral resin was changed to 1.3% by weight.

Comparative Example 1 A sample film was prepared in the same manner as in Example 1 except that the polyvinyl butyral resin concentration was changed to 7.7% by weight.

Comparative Example 2 Low-density polyethylene film having a thickness of 0.05 mm (Mitsubishi Polyethylene LD F131, melt flow rate = 1.
3, density = 0.924, manufactured by Mitsubishi Kasei) 99.3% by weight
And glycerin fatty acid ester (manufactured by Riken Vitamin Co.)
A mixture with 0.7% by weight was formed into a film by a usual inflation extrusion film forming method to prepare a sample film having a thickness of 0.05 mm.

Antifogging Performance Test Each sample film of Examples and Comparative Examples was tested for coating property, accelerated antifogging property and outdoor tunnel antifogging property by the following evaluation methods.

Evaluation method 1) Applicability The uniformity of the finish of the brush coating is visually observed to judge the quality.

2) Accelerated antifogging property A lattice film sticking frame is set on the water surface of a constant temperature water tank, each film is stuck, and the water drop adhesion state is observed with the water surface sealed. The environmental temperature is room temperature, the water temperature is 40 ° C., and the film inclination angle is 0 °.

Evaluation points 5: No water droplets 4: Water droplets within several pieces, but thin water droplets 3: Many water droplets grown, water droplets are independent and flow down vigorously 2: There are many grown water droplets and they are continuously connected. 1: Water droplets are on the entire surface and do not flow at all.

3) Open-air tunnel anti-fog property Location: Upland field in Omiya City, Saitama Prefecture Date: July-September 1992 Tunnel size: Frontage 40 cm x Height 30 cm x Depth 4
0 cm, Film spreading: Each sample film has dimensions of 90 cm x 120
For each cm, spread in a tunnel shape and seal the hem with soil.

Evaluation points 5: No water droplets 4: Water droplets within several pieces, but thin water droplets 3: Many water droplets grown, water droplets are independent and flow down vigorously 2: There are many grown water droplets and they are continuously connected. 1: Water droplets are on the entire surface and do not flow at all.

Table 1 shows the test results of these test items.

[0034]

[Table 1] As can be seen from Table 1, it is recognized that the sample films of the examples have a better coating property than that of the comparative examples and have an excellent antifogging effect with long lasting property.

[0035]

【The invention's effect】

(I) The polyvinyl acetal resin, which is the main constituent of the antifogging agent according to the present invention, is a high-molecular polymer having both a hydrophobic group and a hydrophilic group. Show the effect.

A) The hydrophobic group of the polyvinyl acetal resin exerts good adhesiveness to the surface of the synthetic resin film and prevents the polyvinyl acetal resin from being washed off by water.

(B) On the other hand, the hydrophilic group of the polyvinyl acetal resin imparts good wettability to the agricultural coating film and imparts antifogging property. In this way, it is possible to form an antifogging film that is hard to flow out with water on the surface of the synthetic resin film.

(Ii) The polyvinyl acetal resin is
The antifogging agent solution thus prepared has a low viscosity and is easy to apply because it is easily dissolved in an alcohol / water solvent.

Claims (1)

[Claims] 1. A polyvinyl acetal resin is added in an amount of 0.5-5.
A highly durable coating type anti-fog agent that contains 10% by weight.