Explore humidity conditioning procedures before paper testing (below)

Relative Humidity RHRH Allowable Differential Temperature Temperature Tolerance Difference

Preconditioning atmosphere

10-35%

no

22-40°C

no

Conditioning atmosphere

50.0%

±2%

23°C

±1°C

Testing Environment Testingat mosphere

50.0%

±2%

23°C

±1°C

The requirements of the international standards for paper test procedures for the environmental control of chart 1 are less than 50% RH before the paper samples are humidified. The humidity adjustment process will increase the weight of the sample until it reaches a state of equilibrium with the environment RH. At this time, the weight of the sample is not There will be significant fluctuations and changes in humidity adjustment time (point B)

Determine the humidity adjustment time (point C) of the sample based on the average humidity conditioning curve and the X-axis.

When we test the data against the physical properties of the paper (such as tensile strength, stiffness, etc.); or require more accurate data to compare with the data tested elsewhere, we will find that humidity alone The procedure is not enough. In fact, the relative humidity of the storage environment before the humidity adjustment will directly affect the water content of the humidity-controlled sample and the accuracy of the test results. For example: If we have two identical test samples from the areas with relative humidity higher than 50% and lower than 50%, the deviation of paper water content can reach as high as 1.6% to 6% after the humidity adjustment is completed. The deviation to the physical property test data is as much as 5 to 25%. This kind of error caused by the history of paper storage relative humidity, we call it "Hysteresis" (Figure 2). Since we cannot completely rule out the occurrence of this phenomenon, nor can we accurately predict the range of fluctuations in water content caused by it, and the error in test results, we must take some steps to minimize its impact.

Paper water content %15Q P 0050100B C Reducing RH Increasing RH Relative Humidity (RH) % (Figure 2) Paper's "Hysteresis" Phenomenon

When the paper is stored in a place with less than 50% RH, move it to 50% RH to adjust humidity. The paper water content will change according to curve C, and the final water content is P

When the paper is moved from a storage location higher than 50% RH to 50% RH, humidity is adjusted. Paper water content will change according to curve B, and the final water content is Q

History of water content before humidity adjustment (storage relative humidity) will cause uncertainty in the water content of the humidity-controlled paper - Uncertainty (distance between Q and P in the figure), causing errors in the test data.

Experiments have found that if the paper is stored in a place where the relative humidity is lower than 50% for a period of time before the paper is moistened, it is helpful to control the fluctuation of the sample water content within 0.15%, so we call this a processing procedure. For preconditioning. As for the temperature and humidity requirements of pre-conditioning, we can refer to the previous period, and the time required is generally 24 hours. If we want more accurate pre-conditioning time, we can also refer to some of the recommendations in the test standard for pre-conditioning (Table 3).

Paper type Standard Recommended time Paper (single) Less than 1 hour Lightweight cardboard 1 to 2 hours Heavyweight cardboard or corrugated cardboard 5 to 10 hours Cardboard or corrugated board finished product 12 to 16 hours Water-resistant treated paper Or paperboard no less than 24 hours

Table III Standard Recommends the time required for pre-conditioning the paper

In the actual paper testing process, you may find it very difficult to control the environment in three stages. But in fact, in addition to the humidity conditioning process may encounter a little less trouble, basically the general household equipment can cope with, here are some environmental control suggestions, we may wish to use as a reference:

1. Pre-Humidification - Due to the relatively loose requirements on the ambient temperature and relative humidity, we just use air-conditioning devices and carefully control the paper storage environment.

2. Humidification - Due to the strict requirements and long storage time, it is recommended to use a constant temperature, constant humidity storage equipment.

3. Test Environment - As the testing time is short, we only need to properly use the air conditioning equipment and dehumidifier equipment to control the temperature and humidity of the environment during the test time.

Source: Graphic Art 260, 261
Author: Deng Hongyuan