Drierite干燥剂在保存和包装中的应用

包装建议

种常用的存储容器是瓦楞纸箱或木箱。除非它们被蜡涂层或树脂处理过，否则水蒸气很容易通过这些容器渗透。标准做法是使用塑料薄膜(如聚乙烯)对其进行覆盖。尽管这种塑料薄膜能够阻隔液态水，但水蒸气却可能从中穿过。例如，1-mi聚乙烯的透水蒸气速率约为1.5克平方英尺/24小时，而4mil聚乙烯在75°F和100%相对湿度下仅能透过约0.05克/平方英尺/24小时的量。我们通常建议您至少使用4密尔聚乙烯材料，或与之相当的其他材料，以确保其具备良好的水蒸气透过率。

对于短期储存——两到四周——我们建议每20平方英尺4密尔聚乙烯使用8盎司DRIERITE，并补充足够的DRIERITE以去除袋子或容器中水分。中期储存（一到三个月）时，每块10平方英尺的防潮层使用8盎司。如果是长期储存——三个月或更久——每五平方英尺的防潮层使用八盎司DRIERITE。在后面两种情况下，必须加入足够的额外的DRIERITE，以去除容器内的水分。

上述推荐的DRIERITE剂量是基于相对稳定的储存条件得出的。如果存在较大的日温差波动或需应对极端高温与高湿度环境，则DRIERITE的用量应加倍。

需要多少干燥剂？

密封容器或包装内水污染源有四种：包装内空气中的水蒸气、包裹内材料中吸附的水、容器壁上的水，以及水蒸气渗透到容器内。为了保护容器或包装内的内容物免受水的破坏，必须使用足够的DRIERITE来去除这些水源中的全部水分。

密封容器在正常环境下密封，每10立方英尺的自由体积约需4盎司DRIERITE，以烘干容器内空气。在更极端的条件下（100°F和100% R.H.），需要8盎司的DRIERITE。容器里任何吸附着水的东西都需要额外的DRIERITE。木材和纸制品中吸附水量可达10%。泡沫塑料和某些橡胶制品的吸附水量可能仅为0.5%。一旦估算出容器中材料中的水分量，你可以通过将吸附水的重量除以0.06来计算出额外的DRIERITE量。保护密封容器所需的总DRIERITE量是干燥空气体积所需的DRIERITE量与干燥容器内材料所需DRIERITE量的总和。

如果使用密封良好的容器，如带密封盖的55加仑桶，所需DRIERITE的计算与密封容器相同，只是每10立方英尺体积额外加4盎司DRIERITE，以补偿密封层的水分渗透。为了保护箱体，如保险箱、工具箱或无垫圈的套筒，需要每5立方英尺体积约8盎司的DRIERITE，外加去除箱内水分所需的DRIERITE。上述DRIERITE的数量基于环境储存条件相对稳定，且每日温度波动不大的假设。如果未密封容器存放在温度每天波动30华氏度的区域，该容器每月可能呼吸其自由体积的200%。如果是这样，需要额外的DRIERITE来吸收因容器呼吸而进入的水。

Packaging Suggestions

A commonly used storage container is a corrugated carton or a wooden box. Unless they are wax-coated or resin-treated, water vapor is transmitted through them quite readily. Standard practice is to line them with a plastic film, such as polyethylene. While the plastic film will hold liquid water, water vapor may pass through it. For instance, 1-mil polyethylene will pass water vapor at the rate of 1.5 grams/sq. ft./ 24 hrs, while 4-mil polyethylene will only pass about 0.05 grams/sq. ft./24 hrs at 75° F and 100% RH. We normally recommend that you use a minimum of 4-mil polyethylene, or something equivalent to it in water vapor transmission rate.

For short term storage - two to four weeks - we suggest that you use eight ounces of DRIERITE for every 20 sq. ft. of 4-mil polyethylene, plus sufficient DRIERITE to remove the water in the contents of the bag or container. For medium term storage - one to three months - use eight ounces for each 10 sq. ft. of vapor barrier. For long term storage - three months or longer - use eight ounces of DRIERITE for every five square feet of vapor barrier. Enough extra DRIERITE will have to be added in the last two cases to remove the water in the contents of the container.

The quantities of DRIERITE recommended above are based on relatively stable storage conditions. If there are large daily fluctuations in temperature or if extremely high temperatures and high humidity are to be encountered, the amount of DRIERITE should be doubled.

How Much DRIERITE Is Required?

There are four sources of water contamination in a closed container or package: the water vapor in the air inside the package, the water adsorbed in the materials inside the package, the water adsorbed on the walls of the container, and the permeation of water vapor into the container. In order to protect the contents of a container or package from the destructive effects of water, enough DRIERITE must be used to remove all the water from these sources.

A hermetically sealed container, closed in a normal ambient atmosphere, would require approximately four ounces of DRIERITE for every 10 cubic feet of free volume to dry the air in the container. At more extreme conditions (100° F and 100% R.H.) eight ounces of DRIERITE would be required. Anything in the container that has water adsorbed in it would require extra DRIERITE. Wood and paper products can have as much as 10% by weight adsorbed water. Styrofoam and some rubber products may have as little as 0.5% adsorbed water. Once the amount of water in the material in the container has been estimated, you can calculate the amount of extra DRIERITE required by dividing the weight of the adsorbed water by 0.06. The total amount of DRIERITE required to protect a hermetically sealed container would be the sum of the amount of DRIERITE required to dry the air volume plus the amount of DRIERITE required to dry the materials in the container.

If a well-sealed container, such as a 55 gallon drum with a gasketed lid, is being used, the amount of DRIERITE required is calculated the same as for a hermetically sealed container, except that an additional four ounces of DRIERITE per ten cubic feet of volume is used to compensate for moisture permeation through the seal. To protect an enclosure such as a safe, tool box or a slip cover can, where there is no gasket, requires about eight ounces of DRIERITE per five cubic feet of volume plus the DRIERITE required to remove the water from the contents of the enclosure. The quantities of DRIERITE suggested above are predicated on the assumption that the ambient storage conditions are rather stable, and there are not large temperature fluctuations daily. If an unsealed container were stored in a area where the temperature could fluctuate 30° F daily, the container may possibly breathe 200% of its free volume per month. If this were the case, additional DRIERITE would be needed to absorb the water entering due to the breathing of the container.