Low-humidity indicator and application method thereof
By using moisture-sensitive polymers containing specific groups as low humidity indicators, the polymer is heated after hygroscopic absorption to generate bubbles, solving the problem that the prior art cannot effectively indicate a low humidity environment, and achieving efficient humidity indication at lower cost and complexity.
Patent Information
- Application Number
- CN202411986147.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-31
- Publication Date
- 2025-04-11
AI Technical Summary
The existing humidity indicators cannot effectively indicate low humidity environments, and the commonly used equipment is costly and the detection methods are complex, making it difficult to meet the indication requirements in large-scale production processes.
A moisture-sensitive polymer containing an amide group, a carbamate group, and an ester group is used as a low humidity indicator. After the polymer absorbs moisture, bubbles are generated when heated above 120°C to indicate the ambient humidity.
The humidity indication in the range of relative humidity 3.3% to 90% is achieved, and the cost is low and is suitable for low humidity environment indication in large-scale production processes.
Smart Images
Figure CN119798585A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of humidity indicators, and in particular to a low humidity indicator and an application method thereof. Background Art
[0002] Humidity indicators are widely used in daily life. They indicate the humidity of the environment by absorbing moisture in the environment and producing a series of changes. Silica gel humidity indicators are currently the most widely used humidity indicators. The color-changing principle is that CoCl2 absorbs moisture in the air to become CoCl2·6H2O, and then the color changes from blue to pink. Limited by its color-changing principle, CoCl2 can only produce obvious color changes when it absorbs enough moisture and a sufficient proportion of molecules change, so it can only be used for humidity indication in high humidity environments (for example, humidity greater than 10%). Other common humidity indicators, such as ferric chloride, generally have a lower limit of 10% for humidity indication. Therefore, for the indication of low humidity environments, the common humidity indicators on the market cannot meet the application requirements.
[0003] In order to solve the humidity indication in low humidity environment, it is generally necessary to use professional humidity sensors or analytical instruments, but the cost investment is large, the detection method is complicated, and the detection time is long. It is more suitable for small-batch research analysis, but not for indication in large-scale production processes. Summary of the invention
[0004] The technical problem to be solved by the present invention is to provide a low humidity indicator and an application method thereof, so as to solve the technical problem raised in the background technology.
[0005] In order to solve the above technical problems, the technical solution of the present invention is:
[0006] In a first aspect, the present invention discloses a low humidity indicator, which includes a polymer, wherein the polymer is a moisture-sensitive polymer, and when the polymer absorbs moisture and is heated above 120° C., bubbles are generated inside the polymer.
[0007] As an embodiment, the polymer has a glass transition temperature greater than 90°C.
[0008] As an embodiment, the low humidity indicator is used in a relative humidity range of 3.3% to 90%.
[0009] As an embodiment, the thickness of the indicator is greater than 0.1 mm. Preferably, the thickness of the indicator is 0.3-0.7 mm.
[0010] As an embodiment, the polymer contains any one or more of an amide group, a carbamate group, and an ester group. For example, it can be thermoplastic polyurethane, polyester, polycarbonate, or microcrystalline nylon. In some implementation examples, the polymer is Covestro Makrolon 3108 polycarbonate, Evonik CX 7323 microcrystalline nylon, GrecoIsothane 8101B thermoplastic polyurethane, Lanxcess B 1600 polyester or Lubrizol Isoplast2530ETPU thermoplastic polyurethane.
[0011] As an embodiment, the light transmittance of the indicator is greater than 80%.
[0012] As an embodiment, when the indicator absorbs moisture and is heated at a temperature of 120 to 250° C., bubbles are generated inside the indicator.
[0013] As an embodiment, when the indicator absorbs moisture and is heated at a temperature of 160 to 220° C., bubbles are generated inside the indicator.
[0014] On the other hand, the present invention discloses an application method of the above-mentioned low humidity indicator, the application method comprising: placing the polymer in an environment for a period of time (>10 minutes); heating the polymer, and if bubbles appear inside the polymer, it indicates that the relative humidity of the current environment is 3.3% and above. When the polymer is placed in the environment, it absorbs moisture from the air. After absorbing moisture for a certain period of time, the polymer is heated. After being heated to a certain temperature, bubbles will be generated inside the polymer. The bubbles in the polymer are used to indicate the humidity in the environment, and humidity indication is completed in a low humidity environment. Specifically, the temperature is heated to above 120°C, such as 120-250°C, 160-220°C.
[0015] Compared with the prior art, the present invention has the following beneficial effects:
[0016] The working range of the low humidity indicator of the present application is 3.3% to 90% relative humidity. The relative humidity span is large and the practicability is strong. It can complete humidity indication under humidity conditions as low as 3.3% relative humidity. Compared with the existing technology, it has lower cost and can be used under low humidity conditions. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:
[0018] Figure 1 This is a photo of bubbles generated after heating in Example 1;
[0019] Figure 2 This is a photograph of Example 6 showing that no bubbles were generated after heating. DETAILED DESCRIPTION
[0020] The specific embodiments of the present invention are further described below. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other.
[0021] As a component of air, moisture is everywhere in life and production, and it also affects life and production from time to time. Many products are affected by environmental humidity and interact with moisture, which in turn affects the physical properties of the products. For example, products such as potato chips will lose their crisp taste after absorbing moisture in a high humidity environment. If freeze-dried collagen absorbs moisture in a high humidity environment, it will affect the subsequent dissolution. In the storage process of some electronic, military and special materials, they are more sensitive to environmental humidity and need to strictly control the environmental humidity to an extremely low state, and can indicate low humidity. .
[0022] Silica gel humidity indicator is the most widely used humidity indicator at present. Its color-changing principle is that CoCl2 absorbs moisture in the air to become CoCl2·6H2O, and then the color changes from blue to pink. Limited by its color-changing principle, CoCl2 can only produce obvious color changes when it absorbs enough moisture and a sufficient proportion of molecules change, so it can only be used for humidity indication in high humidity environments (for example, humidity greater than 10%). Other common humidity indicators, such as ferric chloride, generally have a lower limit of 10% for humidity indication. Therefore, for the indication of low humidity environments, the common humidity indicators on the market cannot meet the application requirements.
[0023] In order to solve the humidity indication in low humidity environment, it is generally necessary to use professional humidity sensors or analytical instruments, but the cost investment is large, the detection method is complicated, and the detection time is long. It is more suitable for small-batch research analysis, but not for indication in large-scale production processes.
[0024] Many polymers contain amide, carbamate, ester and other groups, which can easily form hydrogen bonds with hydrogen atoms in water molecules and bind water molecules in the polymer, which is commonly known as water absorption or moisture absorption. Due to the thermal motion of molecules, water molecules in the polymer and water molecules in the air are constantly moving and exchanging, and water molecules on the surface of the polymer also move into the polymer and reach equilibrium after a certain period of time. When the temperature is low, the thermal motion of water molecules is slow, and the tendency to form hydrogen bonds with polymers is strong; when the temperature rises, the thermal motion of water molecules increases. When the temperature rises above the boiling point of water, the thermal motion of water molecules increases sharply, and the hydrogen bonds between the polymer and the polymer will be destroyed. The water molecules change from a bound state to a free state, that is, they are vaporized and expand. According to the ideal gas equation PV = nRT, an internal pressure of expansion is formed, but because they are in the polymer, the polymer chain will resist the expansion of the gas. When the polymer is in a glassy state, the internal pressure of the gas formed by the vaporization of water molecules is often less than the cohesive force of the polymer chain segment. Only when the polymer is in a highly elastic state can the vaporized molecules expand and produce bubbles.
[0025] The present application has discovered a low humidity indicator, including a polymer, which is a moisture-sensitive polymer. When the polymer absorbs moisture and is heated above 120°C, bubbles will be generated inside the polymer, wherein the polymer contains any one or more of an amide group, a carbamate group, and an ester group, and the glass transition temperature of the polymer is greater than 90°C. The humidity range of the low humidity indicator is 3.3% to 90% relative humidity, which solves the problem that the prior art can only be used when the humidity is greater than 10%, or the problem that professional equipment costs are high when the humidity is less than 10%; the thickness of the indicator is greater than 0.1mm, and the preferred thickness of the indicator is 0.3 to 0.7mm to obtain better results; the light transmittance of the indicator of the present application is greater than 80%; preferably, the temperature range of the indicator of the present application after absorbing moisture is 120 to 250°C, and more preferably, the temperature range of the indicator of the present application after absorbing moisture is 160 to 220°C. See the following embodiments:
[0026] Example 1
[0027] The constant temperature and humidity chamber was set to 25°C and 20% humidity, and the low humidity indicator of the present application (made of Lubrizol Isoplast 2530ETPU thermoplastic polyurethane, thickness 0.1 mm) was placed in the oven. After 24 hours, it was taken out and placed on a 150°C heating plate. After 2 minutes, check whether there are bubbles.
[0028] Example 2
[0029] The constant temperature and humidity chamber was set to 25°C and 10% humidity. The low humidity indicator of the present application (produced by Lanxcess B 1600 polyester, thickness 0.5mm) was placed in an oven for 24 hours and then taken out and placed on a 180°C heating plate. After 2 minutes, it was checked for bubbles.
[0030] Example 3
[0031] The constant temperature and humidity chamber was set to 25°C and 3.3% humidity, and the low humidity indicator of the present application (made of GrecoIsothane8101B thermoplastic polyurethane, thickness 0.7 mm) was placed in the oven, and after being placed for 24 hours, it was taken out and heated to 200°C to check whether there were bubbles.
[0032] Comparative Example 1
[0033] A constant temperature and humidity chamber was set to 25°C and 20% humidity, and 5 g of color-changing silica gel produced by Sinopharm Chemical Reagent Co., Ltd. was placed in the oven. After 24 hours, the color was observed to see if it changed.
[0034] Comparative Example 2
[0035] A constant temperature and humidity chamber was set to 25°C and 10% humidity, and 5 g of color-changing silica gel produced by Sinopharm Chemical Reagent Co., Ltd. was placed in the oven. After 24 hours, the color was observed to see if it changed.
[0036] Comparative Example 3
[0037] The constant temperature and humidity box was set to 25°C and 10% humidity. A 6-point humidity indicator card was placed in the oven. The 6-point humidity indicator card was produced by Kunshan Weisheng Desiccant Co., Ltd., and observed for color change after 24 hours.
[0038] The results are shown in Table 1 below:
[0039] Table 1
[0040] Example / Comparative Example Phenomenon Is it possible to detect moisture? Comparative Example 1 Color changes from blue to pink yes Comparative Example 2 Blue color fades no Comparative Example 3 10% humidity indicator point changes from blue to pink yes Example 1 Produce bubbles (such as Figure 1 ) yes Example 2 Generate bubbles yes Example 3 Generate bubbles yes
[0041] Since both Comparative Example 1 and Example 1 were compared under a relative humidity of 20%, both Comparative Example 1 and Example 1 were placed under the same ambient humidity, and after 24 hours, both had color changes or bubbles generated, indicating that the ambient humidity was relatively high.
[0042] When the humidity further drops to 10% relative humidity, since silica gel needs to absorb a certain amount of moisture before color change occurs, and the color change process is gradual, under low humidity conditions, the granular silica gel indicator can no longer clearly indicate the ambient humidity. Comparative Example 2 shows the failure of the silica gel indicator.
[0043] Under the same 10% relative humidity condition, the 6-point humidity card, because the indicator cobalt chloride is printed on the surface of the card, the cobalt chloride content is relatively small, and the product color change will not be affected by insufficient water absorption. In comparative example 3, the environmental humidity can still be indicated by color change.
[0044] The lower limit of humidity that a conventional constant temperature and humidity chamber can reach is 10%. It is difficult to achieve a lower humidity through a constant temperature and humidity chamber. In order to obtain stable air with low relative humidity, the design uses compressed air that has been freeze-dried.
[0045] As the temperature decreases or the air pressure increases, the chances of water molecules colliding increase, making it easier for them to condense and change from gas to liquid. Therefore, by cooling and pressurizing, air with a lower water content can be obtained, and under the conditions of fixed temperature and pressure, the saturated water content in the air is also fixed. When the air that has been cooled and pressurized is restored to room temperature and 1 atmosphere, its water content remains unchanged. This method can be used to obtain constant low-humidity air. For example, the air is compressed to 0.7MPa and the compressed air is processed through a refrigerated dehumidification dryer with a freezing temperature of -23°C. At this time, the theoretical air water content is 761.7mg / m3 and the relative humidity is 3.30% (20°C).
[0046] Comparative Example 4
[0047] The constant temperature and humidity chamber was set to 25°C, and compressed air that had been freeze-dried at -23°C was introduced. A 6-point humidity indicator card produced by Kunshan Weisheng Desiccant Co., Ltd. was placed in the oven. After 24 hours, the card was observed to see if it changed color.
[0048] Example 4
[0049] The constant temperature and humidity chamber was set to 25°C, and compressed air that had been freeze-dried at -23°C was introduced. A low humidity indicator (made of Covestro Makrolon 3108 polycarbonate, 0.7 mm thick) was placed in the oven. After 24 hours, it was taken out and heated to 260°C to check for bubbles.
[0050] Example 5
[0051] The constant temperature and humidity chamber was set to 25°C, the humidity was set to 90%, and a low humidity indicator (manufactured by Evonik CX 7323 microcrystalline nylon, thickness 1.0 mm) was placed in an oven, left for 24 h, taken out and heated to 220 °C, and checked for bubbles.
[0052] Example 6
[0053] The constant temperature and humidity chamber was set to 25°C, and freeze-dried compressed air at -24°C was introduced, with a relative humidity of 3.0%. A low humidity indicator (made of Covestro Makrolon 3108 polycarbonate, 0.7 mm thick) was placed in the oven. After 24 hours, it was taken out and heated to 260°C to check for bubbles.
[0054] The results are shown in Table 2:
[0055] Table 2
[0056] Comparative Examples / Examples Phenomenon Is it possible to detect moisture? Comparative Example 4 6-point humidity card has no change no Example 3 Generate bubbles yes Example 4 Generate bubbles yes Example 5 Generate bubbles yes Example 6 No bubbles (such as Figure 2 ) no
[0057] Under the same low humidity environment, the conventional 6-point humidity card can no longer detect moisture, but the low humidity indicator of the present application can still indicate the change of environmental humidity through the generation of bubbles at high temperature.
[0058] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the protection scope of the present invention.
Claims
1. A low humidity indicator, characterized in that: The indicator comprises a polymer, which is a moisture-sensitive polymer. When the polymer absorbs moisture and is heated above 120° C., bubbles are generated inside the polymer.
2. The low humidity indicator according to claim 1, characterized in that The polymer has a glass transition temperature greater than 90°C.
3. The low humidity indicator according to claim 1, characterized in that The low humidity indicator is used in a relative humidity range of 3.3% to 90%.
4. The low humidity indicator according to claim 1, characterized in that The thickness of the indicator is greater than 0.1 mm.
5. The low humidity indicator according to claim 4, characterized in that The thickness of the indicator is 0.3-0.7 mm.
6. The low humidity indicator according to claim 1, characterized in that The polymer contains any one or more of an amide group, a carbamate group, and an ester group.
7. The low humidity indicator according to claim 1, characterized in that The light transmittance of the indicator is greater than 80%.
8. The low humidity indicator according to claim 1, characterized in that When the indicator is heated at 120-250° C. after absorbing moisture, bubbles are generated inside the indicator.
9. The low humidity indicator according to claim 8, characterized in that When the indicator is heated at 160-220° C. after absorbing moisture, bubbles are generated inside the indicator.
10. A method for using the low humidity indicator according to any one of claims 1 to 9, characterized in that: The polymer is placed in an environment for a period of time; the polymer is heated, and if bubbles appear inside the polymer, it indicates that the relative humidity of the current environment is 3.3% or above.