JPH0261706B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an oxygen indicator that changes color depending on the presence or absence of oxygen. In recent years, in order to improve the shelf life of packaged foods, especially to prevent oxidation of oil-based foods, to prevent spoilage and mold growth of wet foods, and to exterminate pests of clothing and grains, vacuum packaging, nitrogen purge packaging, and deoxidizing packaging have been introduced. Oxygen inside the container is removed by sealing the agent together with the contents. However, in order to confirm the removal of oxygen when packaging the contents, or even after the contents have been packaged, the container may not be tightly sealed due to poor sealing, pinholes in the packaging container, or damage to the container during transportation. Since this may be sufficient, it has become considered desirable to encapsulate an oxygen indicator along with the contents so that the presence or absence of oxygen in the container can be easily determined during the product distribution process or by the end consumer. Conventionally, known oxygen indicators include aqueous oxygen indicators consisting of caustic soda, glucose, and methylene blue, and solid oxygen indicators containing specific dyes such as methylene blue, alkaline substances, and dithionites. ing. The water-based oxygen indicators mentioned above do not change color unless they are used as an aqueous solution, so even if they are used by soaking them into a water-containing base material, they cannot be used when the content is food that dislikes moisture; In some cases, there was a problem of contamination. Furthermore, since glucose, which is a reducing agent, is easily oxidized in the air, the biggest practical difficulty is that it cannot be stored in the air for a long period of time. The above solid oxygen indicator is published in Japanese Patent Application Laid-open No. 1983-
It is disclosed in Publication No. 117495. However, in order for the oxygen indicator to work, the presence of water or an alcoholic compound is required, and in this respect it cannot be said that the drawbacks of water-based oxygen indicators have been fully resolved. In addition, it is necessary to use the oxygen indicator by mechanically mixing it with a water-absorbing powder, or by molding the mixed powder into a tablet, making the oxygen indicator industrially extremely expensive. In particular, the high price has currently hindered the widespread use of this type of oxygen indicator. The present inventors have conducted intensive studies to overcome the drawbacks of the water-based and solid oxygen indicators and to develop an industrially very easy and inexpensive oxygen indicator, and as a result, they have arrived at the present invention. That is, the present invention provides bis(salicylaldehyde)-
3,3'-diiminodipropylamine cobalt (2
This is an oxygen indicator made by vapor-depositing a chemical compound or a derivative thereof on the surface of a substrate. In the present invention, bis(salicylaldehyde)-
3,3'-diiminodipropylamine cobalt (2
derivatives of halogen atoms, alkyl groups,
It has a substituent such as an alkoxy group or a nitro group. Bis(salicylaldehyde)-3 of the present invention,
3′-diiminodipropylamine cobalt (divalent)
Or a derivative thereof, for example, by refluxing salicylaldehyde or a derivative thereof with 3,3'-diaminodipropylamine and a cobalt salt such as cobalt acetate (divalent) or cobalt nitrate (divalent) in an alcoholic solvent such as ethanol. It can be easily obtained by Substrates that can be used in the present invention include plastic films such as polypropylene, polyethylene, polyester, polyvinylidene chloride, polyvinyl chloride, polybutadiene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polystyrene, and polyamide. , metal foil such as aluminum foil, paper, cloth, and composite films or sheets selected from these. It may also be made of plastic with a metal such as aluminum or tin or an inorganic material such as alumina deposited on it. Furthermore, metal powders such as aluminum powder and iron powder can also be used. After drying, the bis(salicylaldehyde)-3,3'-diiminodipropylamine cobalt (divalent) or derivative thereof obtained by the above method is vapor-deposited on the surface of the substrate, preferably under reduced pressure. The film or sheet can be cut and used as desired. Furthermore, it is also possible to use a film or sheet obtained by vapor deposition by laminating or coating a film with good oxygen permeability or a porous film on the vapor deposition surface, or by enclosing it in the film. Bis(salicylaldehyde)-3,3'-diiminodipropylamine cobalt (divalent) or its derivatives obtained as a powder exhibits a black color at room temperature and a yellowish brown color in an oxygen-free atmosphere. However, when used by vapor deposition on the surface of a substrate, the vapor deposition increases the activity against oxygen, resulting in extremely sensitive discoloration, especially when aluminum foil or white opaque film is used as the substrate rather than transparent film. The color change from bright yellow to black can be clearly seen depending on the oxygen concentration. The oxygen indicator of the present invention works solely with atmospheric oxygen and does not require water or other compounds. It also has excellent storage stability as it reversibly changes color any number of times. Examples will be described below. Example 1 Polyethylene terephthalate/aluminum foil/polyethylene/unstretched polypropylene The following bis(salicylaldehyde)-3,3'-diiminodipropylamine cobalt () was applied to the unstretched polypropylene surface of the composite film. An oxygen indicator was produced by vapor deposition under the following conditions. Equipment: Boat using EBH-6 type vacuum evaporation equipment manufactured by Japan Vacuum Technology Co., Ltd. Tungsten boat Boat material distance: 9 cm Degree of vacuum: 1×10 Torr Vapor deposition time: 10 seconds Film thickness: 100 Å Boat temperature: 300°C The prepared prototype piece was placed at 25°C. The samples were placed in atmospheres with different oxygen concentrations, and changes in hue were observed after 1 hour. Bis(salicylaldehyde) for comparison
-3,3'-diiminodipropylamine cobalt (bivalent) powder was also observed.

[Table] Example 2 Screws (3-
Ethoxysalicylaldehyde)-3,3'-diiminodipropylamine cobalt (divalent) () was deposited under the same conditions as in Example 1 to produce an oxygen indicator. The produced prototype piece was placed in an oxygen atmosphere for 1 hour to completely turn black, and then placed in a container with a commercially available oxygen scavenger to observe the color change at 25°C.

[Table] Example 3 Bis(3-fluorosalicylaldehyde)-3,3'-diiminodipropylamine cobalt (bivalent) () was vapor-deposited on the substrate used in Example 1 under the same conditions as Example 1. Then, an oxygen indicator was created. The same test as in Example 1 was conducted, and almost the same results were obtained. Example 4 An oxygen indicator was prepared by depositing bis(salicylaldehyde)-3,3'-diiminodipropylamine cobalt (divalent) () on the surface of a polyethylene terephthalate film on which aluminum was deposited under the following conditions. The same vapor deposition apparatus as in Example 1 was used. Boat used: Tungsten boat Boat distance: 9 cm Vacuum level: 5×10 Torr Deposition time: 50 seconds Film thickness: 3000Å Boat temperature: 300℃

Claims (1)

[Claims] 1. An oxygen indicator in which bis(salicylaldehyde)-3,3'-diiminodipropylamine cobalt (divalent) or a derivative thereof is vapor-deposited on the surface of a substrate.