JPH0420659B2 - - Google Patents

Description

[Detailed Description of the Invention] As lifestyles change, the distribution and processing of food products has changed significantly. A variety of new packaging formats have been created with the aim of making food packaging more functional. Vacuum packaging and gas exchange packaging are one of these, and have become widely popular with the development of gas barrier films/sheets. Gas-barrier packaging has been particularly useful in preventing food deterioration in freshness due to oxygen, and in preserving the shelf life of food during transportation to remote consumption areas.

However, some foods generate gas by themselves through respiration or fermentation, and packaging using gas barrier materials may cause the package to blister or break. Examples include cheese and roasted coffee beans, and the gas generated is carbon dioxide. (“Packaging Technology” 18 (No.
4)'82, P4-7) Carbon dioxide gas is also known to inhibit the respiration of some vegetables and fruits, causing discoloration and deterioration. (``PACKS'' 26 (No. 12) '82, P96-102) Promptly absorbing and removing the carbon dioxide gas generated by food helps to preserve the shelf life of the product and maintain its freshness. The present invention was obtained as a result of research aimed at developing a carbon dioxide absorbing material that can quickly absorb and remove carbon dioxide gas generated from foods and the like that are hermetically packaged with gas barrier materials.

Since carbon dioxide gas is an acidic gas, it can be neutralized and absorbed by alkaline solids. Powdered slaked lime is known as a carbon dioxide absorbent. However, slaked lime is strongly alkaline and is highly irritating to the skin, mucous membranes, and eyes. Especially if it comes into contact with the eye, it will damage the cornea. Slaked lime powder is difficult to handle and cannot be used as part of food packaging. In addition, inventions already disclosed (Japanese Patent Application Laid-Open No. 55-59825, JP-A No. 55-158933)
There is a sheet in which a thermoplastic resin is filled with calcium hydroxide, as disclosed in Japanese Patent Laid-Open No. 15894/1983). According to this invention, a maximum of about 15 c.c. of carbon dioxide gas can be absorbed per gram of slaked lime, which is only 5% of the theoretical value. Also, from the slope of the absorption curve, the absorption of carbon dioxide gas approaches saturation and appears to be at its limit.

In our additional tests, we found that simply filling thermoplastic resin with slaked lime did not show any effective ability to absorb carbon dioxide gas. Therefore, the present inventors conducted extensive research in an effort to develop a carbon dioxide absorbing material with high activity close to the theoretical value and long life, and as a result, they came up with the present invention.

The present invention 1) enables mass filling of slaked lime into resin by surface treating it with a titanium coupling agent, and 2)
The surface of the slaked lime was renewed through boiling treatment, and its activity was dramatically increased by adsorbing trace amounts of water onto the surface. Furthermore, by vacuum packaging with gas barrier material, it is possible to maintain the highly active surface until it is actually used. The present invention will be explained in more detail below.

In order to improve the compatibility between an inorganic filler and a thermoplastic resin, it is generally effective to change the hydrophilic surface of the filler to a lipophilic surface, and various additives, commonly called coupling agents, are used for this purpose. What is known is known. Among these types of additives, titanium coupling agents are known to be effective for inorganic fillers other than silicate-based fillers. (“Polymer Digest” 30 (No.10)’78,
P49-65, 30 (No. 11)'78, P57-71) Titanium coupling agents are also effective in the present invention, are compatible with resins, and have good moldability.
It is preferable to add the titanium coupling agent to 0.5% of the slaked lime. Since the amount of slaked lime to be filled is directly related to the amount of carbon dioxide gas absorbed, it is desirable to be able to fill as much as possible, but it is preferably in the range of 50 to 100 parts by weight from the viewpoint of moldability and strength of the resulting molded product.

As shown in the following equation, stoichiometrically, 1 g of slaked lime absorbs about 324 c.c. (20°C, 1 atm) of carbon dioxide gas.

Ca(OH) ₂ +CO ₂ →CaCO ₃ +H ₂ O However, when the present inventors investigated the carbon dioxide absorption ability of powdered slaked lime, it was found that approximately 30% of the theoretical amount was absorbed in 120 hours.
It was found that only ~40% was absorbed. When the slaked lime was analyzed, it was found that about 6% was calcium carbonate. This is thought to be because the calcium hydroxide on the surface is converted to calcium carbonate by carbon dioxide gas in the air, and the surface has already lost its activity.
Further, possible reasons include that the gas-solid reaction is slower than the liquid-liquid reaction, and since it is an ionic reaction, ionization is necessary, and the reaction rate is extremely slow in the absence of water. From the above considerations, in order to increase the activity of slaked lime, it is essential to remove the calcium carbonate layer covering the surface and the presence of a trace amount of water. Some of the inventions already disclosed include a method of adding a third component such as an oxide to prevent water from being contained, but the carbon dioxide absorption capacity is still extremely low compared to the theoretical value.

After examining various methods to increase the activity of slaked lime, it was found that boiling the slaked lime-filled molded product was the most effective. Although this mechanism is not clear, it can be thought about as follows.

(1) The surface calcium carbonate layer is peeled off by boiling,
Or a crack enters and a new surface of calcium hydroxide is formed.

(2) Water adheres to the active calcium hydroxide surface,
It is thought that the carbon dioxide gas that diffuses through the resin layer covering the surface or reaches it directly is immediately ionized on the active surface of the slaked lime in the presence of water and reacts with the active calcium hydroxide. The preferred boiling time is about 20 minutes; if it is too short, it will not be effective.

The pores that exist between the filler and matrix resin help absorb moisture and diffuse carbon dioxide, further increasing the effectiveness of boiling treatment. Therefore, if the molding temperature is too high than the melting point of the resin, pores will not be formed, the contact area between slaked lime and carbon dioxide will become small, and the absorption capacity will decrease. Furthermore, if it is lower than the melting point, the matrix resin powder will not fuse and will not maintain its shape and will collapse. Therefore, it is desirable that the molding temperature T is in the range of Tm+30°C≧T>Tm−15°C with respect to the melting point Tm of the resin. It is more desirable that Tm+5°C≧T≧Tm, although it varies depending on the molding method and ease of melt flow of the resin. The molding method is not particularly limited, but from the viewpoint of product usage conditions and ease of handling, pellet or tapelet shapes are preferred, and press molding is also preferred.

The polyethylene resin used is not particularly limited, but
Resins with large MI are unsuitable, and ultra-high molecular weight polyethylene resin powder (Mitsui Petrochemical Industries, Ltd. HiZex Million, etc.) is most suitable.

The porosity of the molded article is determined from the difference between the bulk specific gravity d' and the reciprocal of the true specific gravity d.

P=(1/d'-1/d)×100 [%] The porosity is preferably 10 to 50%; if it is less than 10%, the absorption capacity is poor, and if it is more than 50%, the shape of the molded product cannot be maintained.

It would be rare to use it immediately after boiling.
Therefore, it is clear that unless there is a way to maintain and preserve the activity until it is actually used, the carbon dioxide absorption capacity will be lower than that of ordinary slaked lime. Therefore, the inventors of the present invention tried various preservation methods, and found that vacuum packaging using gas barrier packaging material was the most desirable.

The best way to remove moisture adhering to a boiled molded product is to use a centrifugal dehydrator, or to blow it off with compressed air. 50~80℃ after removing adhering moisture,
It is preferably dried at 35 to 65°C for 5 to 30 minutes, more preferably 5 to 15 minutes.

The gas barrier material is preferably an aluminum/polyethylene laminate sheet or an EVAL/polyamide multilayer sheet.

The present invention makes it possible to provide a carbon dioxide absorbent that is highly useful, has a long life, and is convenient to handle. The present invention will be explained in more detail with reference to Examples below.

Example 1 100 parts by weight of ultra-high molecular weight polyethylene (Hi-Zex Million 240L Mitsui Petrochemical Industries, Ltd.),
After mixing 100 parts by weight of slaked lime surface-treated with a titanium coupling agent (Plenact TTS, Ajinomoto Co., Inc.) in a super mixer for 10 minutes, it was mixed with a manual press.
It was molded into a 32 mm x 7 mm tablet at 140°C.
The porosity of this tablet was 28%. The tablets were boiled for 20 minutes, centrifugally dehydrated in a household washing machine, and air-dried at 60°C for 10 minutes. Figure 1 shows how this tablet absorbs carbon dioxide. To measure carbon dioxide absorption, the test material and dry ice were sealed and the carbon dioxide concentration was measured using gas chromatography.

Example 2 Immediately after drying the tablet of Example 1, aluminum/
Vacuum packed in polyethylene laminate sheet, 30
Figure 1 shows how carbon dioxide gas is absorbed after one day.

Comparative Example 1 Figure 1 shows how carbon dioxide gas was absorbed in Example 1 without the boiling treatment.

[Brief explanation of drawings]

FIG. 1 shows the relationship between the amount of carbon dioxide absorbed and time. ○ mark indicates Example 1, ● mark indicates Example 2, □ mark indicates Comparative Example 1, initial carbon dioxide concentration x _p and carbon dioxide concentration over time x _o .

Claims (1)

[Claims] 1. After mixing A: 100 parts by weight of powdered polyethylene resin and B: 50 to 200 parts by weight of slaked lime, the melting point Tm of the polyethylene resin is determined.
A pellet-like or tablet-like molded product is molded at a temperature T in the range of Tm+30°C≧T>Tm−15°C so that the porosity of the molded product is 10 to 50%, and then After boiling the molded product and removing the moisture attached to the molded product,
A method for producing a carbon dioxide absorbent characterized by drying at a temperature of 80°C.