Basic knowledge of desiccant

1. Adsorbent raw materials

2. Desiccant packing material

3, Bagged desiccant sealing method

1. Adsorbent raw materials

Adsorbent is a kind of material that can absorb water vapor. It inhales and locks the water vapor in the external environment through physical or chemical means to achieve the purpose of drying and moisture-proof. Currently widely used in dry moisture-proof adsorbent are: montmorillonite, activated clay, silica gel, molecular sieve, calcium chloride, etc.

Molecular sieve is generally used for insulating glass, not widely used for other industries, calcium chloride and lime desiccant belong to the chemical moisture absorption, they can not be used for some products such as circuit boards, general circuit boards usually copper (Cu), iron (Fe) and other metal components, calcium chloride containing halogen ions (chloride ions Cl). The solution containing halogen ion has strong conductivity and will promote the corrosion of metal elements by oxygen absorption.

A. Montmorillonite

1.Introduction: 

Montmorillonite, also known as microcrystalline kaolinite, is the target mineral of bentonite ore. The montmorillonite around the world has different colors such as white, light gray, pink and light green due to the genetic type, metallogenic environment and origin. It is mainly irregular and can form a spherical state after processing. Due to its crystal structure and molecular composition, non-toxic and harmless, can be degraded naturally, with strong adhesion and cation exchange properties, is widely used in dry adsorbent. 

2. Features: 

a. Natural bentonite is made of drying, crushing and screening, which can be naturally degraded, natural environmental protection, non-toxic and harmless 

b. At relative humidity below 20%, the adsorption capacity is better than silica gel, and the cost is lower. Montmorillonite has certain dust, can not be paired with ordinary non-woven packaging, will leak powder.

B. Silica gel

Silica gel can be divided into large pore silica gel, coarse pore silica gel, B type silica gel, fine pore silica gel, because of the different pore structure, so their adsorption performance has its own characteristics. Coarse pore silica gel has a higher adsorption capacity in the case of high relative humidity, fine pore silica gel in the case of low relative humidity adsorption capacity is higher than coarse pore silica gel, and B type silica gel due to the pore structure between coarse and fine pore silica gel, its adsorption capacity is also between coarse and fine pore. Therefore, different varieties should be selected according to different uses. 

1. Introduction: 

Silica gel, the main component is amorphous silica, transparent or milky white irregular granular or spherical solid. With open porous structure, strong adsorption, can absorb a variety of substances, is a kind of high performance active adsorbent. 

2. Features: 

a. Non-toxic and tasteless, stable chemical properties, except strong alkali, hydrofluoric acid does not react with any substance. It is a desiccant adsorption material approved by FDA that can be directly contacted with medicine and food, safe and reliable 

b. Silica gel has a strong adsorption capacity under various conditions 

c. silica gel can be reused; After absorbing water, it can be regenerated by exposure, baking, air drying and other methods.

Indicating silica gel

1. introduction:

Indicating silica gel mainly includes blue silica gel and orange silica gel, color-changing silica gel has the same performance as white silica gel, after hygroscopic, color change, more easy to observe hygroscopic state.

Orange silica gel is the update of blue silica gel products, blue silica gel contains a small amount of cobalt chloride, toxic, should avoid contact with food and inhalation in the mouth, orange silicone does not contain cobalt chloride, so it is also known as cobalt-free silica gel.

2. The color changing silica gel not only plays a hygroscopic role, but also its color changes with the hygroscopic growth to show the humidity change of the space medium of the sealed packaging. 

a. Generally used for the drying of sealed packaging items, mainly used for moisture absorption and rust prevention of instruments, meters and equipment under sealed conditions, and can directly indicate the relative humidity of the environment through the color change after moisture absorption. 

b. Use with ordinary silica gel desiccant to indicate the degree of moisture absorption and determine the relative humidity of the environment. As a packaging silicone desiccant, widely used in precision instruments, instruments, leather, shoes and hats, clothing, arts and crafts, food, medicine and household appliances such as color-changing silicone is much more expensive than white silicone, can be used with white silicone, so that there is an indication of the role and can reduce the cost. Collocation ratio can be customized, generally 3%.

C. Activated clay

1. Introduction: 

Active mineral desiccant is made of attapulgite after activation. Due to the presence of chloride ions, it is not allowed to directly contact with food, drugs, metals, etc. The shape of the gray ball, the most suitable for moisture absorption in the environment below 50℃. When the temperature is above 50℃, its "water" degree is greater than "water absorption" degree. But it has the advantage of being cheap. 

2 Features: 

high humidity moisture absorption ability is good mineral desiccant chlorine particles, moisture absorption ability is relatively poor, but the price is cheap, general used by clothing factory and shoe factory.

2, Desiccant packaging material 

Desiccant packaging material must have good breathable performance, strength and excellent heat sealing. Different packaging materials can be selected according to the application industry and grammage weight. At present, the widely used desiccant packaging materials mainly include: TYVEK, ordinary non-woven fabric, spunky non-woven fabric, Japanese non-woven fabric, breathable tissue(cotton) paper, OPP film, etc.

A. Material introduction and application scope

1. Composite paper: Composite paper is the composite of different characteristics of materials together, with good printing and decorative effects.

Scope of application: Suitable for 1g - 10g bag desiccant.

2. Breathable cotton paper: composed of fiber and heat seal layer. Can be used for small size silica gel desiccant packaging, for packaging montmorillonite strength is not enough and easy to leak powder, good air permeability.

Scope of application: less than 5g small packaging bag desiccant

3. Ordinary non-woven fabric: it is composed of oriented or random plastic fibers, is a widely used packaging material, it has a certain strength, and excellent air permeability, but used for packaging montmorillonite, easy to leak powder;

Scope of application: 2g-200g bag desiccant.

4. Mesh paper: high strength, good dust resistance, wide applicability, higher price than ordinary composite paper, but far lower than dupont paper, is the ideal choice of high-grade packaging materials.

5.Tyvek: It is the trademark of a series of sheet products of DuPont Company.Tyvek is made of high-density polyethylene fiber. It is an ideal material for all kinds of desiccant packaging, with high strength, folding resistance, tear resistance, anti-static, good air permeability and other characteristics, but also has excellent weather resistance and chemical resistance, dust-free design, used for packaging desiccant, both good air permeability, and has enough strength and beautiful printing effect, the only disadvantage is high price.

Scope of application: Suitable for 0.5g - 1000g bag desiccant.

6 spunlaced non-woven fabric: it is the high pressure micro water jet to a layer or multilayer fiber net, so that the fibers intertwined with each other, so that the fiber net to be reinforced with a certain strength.

Scope of application: more than 100g bag desiccant.

7. Japanese non-woven fabric: also known as Japanese fiber paper, is a kind of non-woven fabric, with high temperature resistance, high mechanical strength and other characteristics, high technical requirements, high cost.

Scope of application: 1g-1000g bag desiccant.

8.OPP film: composed of PP and PE film, it is a transparent packaging material, which can easily observe the state of adsorbent in the desiccant package. OPP itself does not have air permeability, need to be punched after can be used as a desiccant packaging material.

Scope of application: bag desiccant under 20g, low temperature environment

9. Aihua Paper: Aihua paper is an environmentally friendly non-woven fabric without toxicity. Made of special fiber textile, through the paper can clearly identify the internal packaging object, so it is also known as transparent Aihua paper. This material has strong tensile resistance, breathable uniformity, strong sealing degree, high transparency, and good thermal guyron performance. Aihua paper set transparent, beautiful, uniform and other advantages as one.

Aihua paper can be widely used in clothing, craft gifts, shoes, hats and food industries.

Scope of application: bag desiccant less than 20g.

B. How to choose desiccant packing material?

1. safety

The safety of packaging materials is mainly reflected in its own strength, anti-dust performance and sealing strength. In the application of desiccant, the role of packaging materials is to ensure that the adsorbent is isolated from the moisture-proof products as far as possible. The leakage of dry adsorbent caused by the defects of packaging materials may affect the product quality

a. Strength: The desiccant in the bag may be under pressure due to extrusion and twisting during moving or transportation of the packaged goods. If the desiccant packaging material is not very good strength, there will be a great possibility of breaking the package.

b. Sealing strength: The most vulnerable part of the desiccant bag is the sealing interface, so the packaging material is required to have a high sealing strength.

c. Dust prevention: All kinds of dry adsorbents have a certain amount of dust, and dust is very dangerous to some products. Of course, most common products are not sensitive to trace amounts of dust. Among all the desiccant packaging materials, DuPont Tyvek is the best anti-dust packaging material.

2. validity

The breathability of desiccant packaging material is the most important manifestation of its effectiveness. Desiccant DIN55473 German standard and MIL-D-3464E US military standard both require desiccant packaging materials to have good water vapor transmittance. The desiccant using poor steam permeable packaging materials will have four wet slow problem, which affects the effect of humidity control desiccant.

3. economy

Desiccant is mainly used for moisture-proof. On the basis of safety and effectiveness, it is very important to choose a desiccant packing material suitable for our own products, which requires us to select a desiccant product scheme suitable for our own products according to the requirements of safety and effectiveness, combined with price factors in the process of product selection, and discover the best product cost performance. It's easy to do this by comparison.

3, Bagged desiccant sealing method

Dry packaging materials to dry adsorbent packaging, should ensure that dry adsorbent does not leak, avoid dry adsorbent mixed into the product, so the desiccant sealing firm is very important, according to the different size of the package, the specific application, we can choose different sealing methods. The main sealing methods of desiccant are: back sealing, three side sealing, four side sealing, and hand sewing.

A. Comparison of sealing methods

1. Back seal

a. Features:

1) Compact bag, saving packaging materials

2) Sealing firm and stable, high safety

3) Harmonious proportion and beautiful appearance

4) The packaging desiccant has a wide range of gram weight

b. Gram weight range: 0.5g~1kg

2. Three-side seal

a. Features:

1) Fast packaging and production speed

2) Suitable for large batch production of small grams

3) The sealing of large gram heavy products is unstable and the appearance is not coordinated

b. Weight range: 1g to 100g

3. Four-side seal

a. Features:

1) Wide edge width, safe and reliable

2) The desiccant bag is flat and suitable for moisture-proof packaging with narrow space

b. Weight range: 2g~100g

4. Hand sew

a. Features:

1) Mainly deal with some packaging materials that can not be packaged by machine, and heavy weight desiccant.

2) Sewing bag is strong and durable, free in form, and can be easily added with hooks or lanyard.

3) Due to manual processing, the speed is relatively slow

b. Gram weight range: 1kg~2.5kg

B. Reasons affecting the sealing strength of desiccant bag

1. In the process of packaging production, there is adsorbent material in the sealing.

2. The coating strength of packaging materials is not enough. For example, the strength of the Tyvek bag after gelatinized heat seal is limited, and it is not suitable to pack bags of more than 500 grams.

3. Packaging machinery or packaging process adjustment is not in place, resulting in "unilateral", "virtual seal" and "short edge" and other problems.

C. Damage of broken/leaked desiccant bag

The desiccant used for packaging is usually in direct contact with or close to the product. If the desiccant bag is broken in the process of handling because the sealing strength is not enough, although the current mainstream silicone and montmorillonite will not corrode the product, but the scattered adsorbent will dirty the product and affect the product phase or other performance of the product.

D. Test desiccant bag strength with drop testing machine 

1. Drop testing machine to the specified height 

2. Drop the desiccant bag from the height 

3. If damaged, it is unqualified 

4. Test criteria: According to the "DIN 55473-2007)," "Mil-D-3464E >", "GJB2714-96" and other bag desiccant strength regulations, at 3m height positive and negative alternating drop rules do not break the bag, recorded drop times is the strength of the desiccant bag. 

We usually use grams to distinguish the specifications of desiccant, generally described as 1 gram, 2 grams, etc., and "unit" is commonly used as the desiccant adsorption unit abroad. According to the desiccant of "unit" under the condition of equilibrium temperature of 250 (RI -- 403), it can adsorb 6.0g water vapor. To be exact, a "unit" montmorillonite dryer is equivalent to 33g, and a "unit" silica gel dryer is equivalent to molecular sieve and molecular sieve is equivalent to 28g.