JPH0432699B2 - - Google Patents

Description

[Detailed description of the invention]

As lifestyles change, food distribution and processing patterns have 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. Cheese, roasted coffee beans, etc. generate carbon dioxide gas. ("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 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 eliminate 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 Application Laid-open No. 158934/1983). 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) treats the surface of slaked lime with a titanium coupling agent to enable mass filling into the resin and improves moldability, and (2) renews the slaked lime surface through boiling treatment, allowing a small amount of moisture to flow onto the surface. The activity was dramatically increased by adsorption. Furthermore, (3) the absorption capacity was further increased by stretching the sheet. 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 fill a thermoplastic resin with a large amount of filler, it is generally effective to change the hydrophilic surface of the filler to an lipophilic surface, and various additives, generally called coupling agents, are used for this purpose. Are 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) The titanium coupling agent is also effective in the present invention, and even when filled in an amount equal to or more than the resin, it has good dispersibility and extrusion processability. It is preferable to add the titanium coupling agent to 0.5% of the slaked lime. The amount of slaked lime to be filled is directly related to the amount of carbon dioxide absorbed, so it is desirable to be able to fill as much as possible, but due to issues such as extrusion processability and the strength of the resulting sheet, it is
A range of 200 parts by weight is preferred. 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, they 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, 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 necessary to remove the calcium carbonate layer that covers the surface.
The presence of trace amounts of moisture is essential. 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 sheet 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 directly reaches the active surface of the slaked lime is immediately ionized 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. During stretching, microvoids generated between the filler and matrix resin during stretching help absorb moisture and diffuse carbon dioxide gas, further enhancing the effectiveness of boiling treatment. Stretching may be uniaxial or biaxial stretching, and is not particularly limited. Appropriate conditions can be selected depending on the use of the sheet and the filler filling amount. Although the stretching temperature is not particularly limited, if the stretching temperature is as low as possible,
The surface will be rough, but the boiling effect will be enhanced. Particularly in the case of polyethylene, stretching near the melting point or below the melting point is preferred. The stretching ratio in the uniaxial direction is preferably in the range of 1.1 to 4 times, more preferably in the range of 1.2 to 2.0 times. If it is less than 1.1 times, no effect of stretching can be observed, and if it is more than 4 times, it is difficult to stretch it and the sheet shape cannot be obtained, and both are unsuitable. The thermoplastic resin used as the matrix is
Any thermoplastic resin may be used as long as it can be kneaded with slaked lime and extruded. In the slaked lime-filled sheet, it can be assumed that carbon dioxide gas may react with directly exposed slaked lime or diffuse through the resin and react with slaked lime, but the amount of directly exposed slaked lime is thought to be extremely small. Therefore, as the matrix resin, a resin having a large permeability coefficient for carbon dioxide gas is preferable, and from this point of view, polyethylene, particularly low density polyethylene, is preferable. Polyvinyl chloride is also desirable because it can be filled with a large amount of slaked lime and has good processability. Considering the actual usage of activated slaked lime-filled sheets, it would be rare for them to be used 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. After removing the water adhering to the surface of the boiled sheet by blowing it away with compressed air,
80°C, more preferably 55-65°C, for 5-30 minutes,
More preferably, it is dried for 5 to 15 minutes. For applications where it is a problem for the sheet to contain excess moisture, a longer drying time is recommended, and for applications where the moisture content is not so great, a shorter drying time is recommended. However, within the above range, no difference is observed in the effectiveness of the boiling treatment. As the gas barrier packaging material, aluminum/polyethylene laminate sheets and EVAL/polyamide multilayer sheets are preferable. The present invention will be explained in more detail with reference to Examples below. The material used is low density polyethylene (LDPG): Sumikasen F101
-1 (manufactured by Sumitomo Chemical Co., Ltd.) Polyvinyl chloride (PVC): Sumiritz SX-11F
(Same as above) Slaked lime: Specially selected slaked lime (manufactured by Tagen Lime Industry Co., Ltd.) Titanium coupling agent: Blen Act TTS (manufactured by Ajinomoto Co., Inc.) Carbon dioxide absorption capacity was measured using dry ice as a carbon dioxide gas source and a nylon/EVAL multilayer film. (Sumito Bakelite Co., Ltd., Sumilite CEL) bag together with a sheet of the test material, and quantified using a gas chromatograph. Surface treatment of slaked lime was carried out by stirring slaked lime and 0.5% titanium coupling agent in a super mixer for 10 minutes. Example 1 0.5% titanium coupling agent (Plenact
100 parts by weight of slaked lime treated with TTS) and 100 parts by weight of low density polyethylene (Sumikasen F101-1) were kneaded in an MS pressure kneader manufactured by Moriyama Seisakusho, and then
A T-die sheet with a thickness of 1 mm was produced using a 40 mm extruder. The sheet was boiled in water for 20 minutes, then taken out of the water and blown with compressed air to remove moisture. Furthermore, air dry in a hot air dryer at 60℃ for 15 minutes.
It was used as a sample. 12g of this sample (6g as slaked lime)
was sealed in the aforementioned bag with 3 g of dry ice, and the amount of carbon dioxide gas absorbed was measured after 120 hours (5 days) had elapsed.
The results are shown in Table 1. Example 2 The extruded sheet of Example 1 was uniaxially stretched 2 times, but otherwise treated in the same manner as in Example 1. Results first
Shown in the table. Example 3 100 parts by weight of polyvinyl chloride (Sumirit SX-11F), 100 parts by weight of plasticizer DIDP (manufactured by Sekisui Chemical Co., Ltd.), and 3 parts of stabilizer were kneaded in the same manner as in Example 1, and then a press sheet was prepared. The rest of the process was carried out in the same manner as in Example 1. The results are shown in Table 1. Comparative Example 1 6 g of slaked lime itself was sealed in a bag with 3 g of dry ice in the same manner as in Example 1, and the carbon dioxide absorption capacity was compared. The results are shown in Table 1. Comparative Example 2 The carbon dioxide absorption capacity of 6 g of slaked lime treated with the titanium coupling agent used in Example 1 was compared. The results are shown in Table 1. Comparative Example 3 The carbon dioxide absorption capacity of the extruded sheet produced in Example 1 was measured without subjecting it to boiling treatment. The results are shown in Table 1. Comparative Example 4 The carbon dioxide absorption capacity of the uniaxially stretched sheet produced in Example 2 was measured without subjecting it to boiling treatment. The results are shown in Table 1.

[Table] 1 g of slaked lime absorbs approximately 220 c.c. of carbon dioxide gas. There are differences in carbon dioxide absorption depending on the storage method, and examples are given below. Example 4 The sample of Example 2 was vacuum packed in a bag made of an aluminum/polyethylene laminate sheet, and the carbon dioxide absorption capacity was measured after storage for 30 days. The results are shown in Figure 1. Comparative Example 5 A nylon/ionomer film (manufactured by Steel Chemical Co., Ltd.) coated with adhesive on both surfaces of the sample of Example 2.
CANS film) was laminated. The end face is exposed to the outside air. The carbon dioxide absorption capacity of this sample was measured after storage for 30 days. The results are shown in Figure 1. As shown in Comparative Example 5, since the end face is exposed to the outside air, the carbon dioxide absorbability is lower than in Example 2. As described above, differences in carbon dioxide absorption also occur depending on the storage method.

[Brief explanation of drawings]

Figure 1 shows the amount of carbon dioxide absorbed (residual amount of carbon dioxide)
This shows the relationship between and changes over time. ○ mark indicates Example 2 (carbon dioxide absorption amount was measured immediately after sheet creation), △ mark indicates Example 4, □ mark indicates Example 5, initial carbon dioxide concentration x ₀ , carbon dioxide concentration over time x _o Ta.

Claims (1)

[Claims] 1. A resin composition consisting of 100 parts by weight of a thermoplastic resin and B: 50 to 200 parts by weight of slaked lime is formed into a sheet, the sheet is boiled in water, and then the sheet surface is A method for producing a carbon dioxide absorbing sheet, which comprises removing attached moisture and drying at 50 to 80°C for 5 to 30 minutes. 2. Claim 1, wherein the slaked lime is slaked lime treated with a titanium coupling agent.
2. Method for manufacturing carbon dioxide absorbing sheet. 3. The method for producing a carbon dioxide absorbing sheet according to claims 1 and 2, wherein the thermoplastic resin is polyethylene or polyvinyl chloride. 4. Manufacture of a carbon dioxide absorbing sheet according to claims 1, 2, and 3, characterized in that the sheet is a uniaxially stretched sheet or a biaxially stretched sheet stretched 1.1 to 4 times in a uniaxial direction. Method.