White ink transfer printing is a process where white ink is printed on a transfer film, and then heated and pressed onto the substrate (such as clothing, fabric, etc.) under high temperature and high pressure. Temperature and humidity, as key environmental factors, will affect the quality, efficiency and stability of white ink transfer printing in multiple aspects. The specific impacts are as follows:

I. Impact on the White Ink Printing Process
The first step in the white ink transfer printing process is to print the white ink on the transfer film (usually in combination with colored ink). The influence of temperature and humidity at this stage mainly manifests in the ink performance and printing effect:

⑴Ink fluidity and adhesion 
•Low temperature (below 15℃): The resin components in the white ink tend to solidify, resulting in decreased ink flowability. During printing, there may be ink breaks, disconnected lines, uneven ink layer distribution, and it may affect the fine details of the pattern.
•High temperature (above 30℃): The ink is prone to volatilize, which may cause the nozzle to get clogged (especially for white ink which contains pigment particles, after volatilization, the particles are likely to deposit). At the same time, the ink layer dries too quickly, and the adhesion to the transfer film decreases, resulting in "ink loss" during subsequent hot stamping.
•Low humidity (below 40% RH): The dry environment enhances the static electricity on the transfer film surface, causing it to adsorb dust or white ink particles, resulting in white spots or impurities on the printed pattern; at the same time, the ink volatilizes too quickly, and the ink layer is prone to crack.
•High humidity (above 60% RH): The transfer film is prone to absorb moisture, making the surface damp. After printing, the drying speed of the ink slows down, resulting in smudging, color bleeding, and it may occur when mixing colored ink with white ink (especially when the two are mixed), causing the pattern edges to become blurry. 
⑵The thickness of the white ink layer and its covering power
The main function of the white ink is to cover the base color of the substrate (such as dark fabric). Unstable temperature and humidity can cause uneven thickness of the white ink layer during printing: 
•In a low-humidity and high-temperature environment, the white ink dries too quickly, which may require multiple printing layers to be stacked together, resulting in overly thick ink layers, increased costs, and the possibility of "bubbling" during subsequent hot stamping.
•In a high-humidity and low-temperature environment, the white ink dries slowly, and the ink layer printed in a single instance is too thin, lacking sufficient coverage power. After hot stamping, the pattern will show through.

II. Impact on the Drying and Solidification of the Ink Layer
The transference film after printing needs to undergo drying (either natural air-drying or drying by a machine) to ensure the solidification of the white ink layer. Temperature and humidity directly affect the drying efficiency and the quality of solidification:
⑴Drying speed:
- In a high-temperature and low-humidity environment, drying is fast, but if it is too rapid, it may cause the surface of the ink layer to solidify prematurely, while the internal moisture cannot evaporate, resulting in "external dryness and internal wetness". This makes the ink layer prone to mold growth and delamination during subsequent storage or stamping; in a low-temperature and high-humidity environment, drying is slow, prolonging the production cycle, and it may also breed bacteria, contaminating the ink layer.
⑵Curing strength:
- The resin in white ink needs to complete cross-linking and curing under suitable temperature and humidity conditions. If the temperature is too low or the humidity is too high, the curing will not be complete, resulting in insufficient ink layer hardness, easy scratching, and a decrease in washability (the pattern is prone to fall off during water washing after stamping).

III. Impact on the Stamping Process
Stamping is the process of transferring the pattern on the transfer film to the substrate through high temperature (150-200℃) and high pressure. At this time, the environmental temperature and humidity (especially the temperature and humidity of the substrate) can affect the transfer effect:
⑴Printing substrate condition 
•If the printing material such as fabric absorbs moisture in a high-humidity environment, the high temperature during stamping will cause the moisture to evaporate, forming bubbles between the pattern and the fabric, resulting in local bulging and unevenness of the pattern, and even detachment of the pattern.
In a low-temperature environment, the fabric fibers are harder, and the adhesion between the fabric and the ink layer decreases. The stamping pressure is difficult to be evenly transmitted, and there may be partial missing of the pattern, unclear edges.
⑵Transfer efficiency of the ink layer
•The thermal fusion transfer of the white ink layer relies on the viscosity of the resin under high temperature. If the environmental temperature is too low, the actual working temperature of the stamping machine may fluctuate due to the influence of the environment (especially for small equipment), preventing the resin from fully softening and resulting in incomplete transfer, with the pattern remaining on the transfer film; if the environmental humidity is too high, the water vapor on the transfer film or the surface of the fabric will weaken the viscosity of the resin, also affecting the transfer effect.

IV. Impact on Product Quality and Weather Resistance
Temperature and humidity not only affect the production process, but also influence the storage and usage stability of the finished products:
•If the finished product is stored in a high-humidity environment, the white ink layer may absorb moisture, causing the pattern to become soft, sticky, and even stick to the packaging material;
•In a low-temperature and dry environment, the finished product (especially fabric) may crack due to fiber contraction, especially in areas with a thick white ink layer.

Summary: Appropriate temperature and humidity range

•Temperature: 20 - 25℃ (for printing and drying processes); The equipment temperature during stamping is set according to the process requirements (not affected by drastic fluctuations in ambient temperature).
•Humidity: 45 - 55% RH (stability maintained throughout the printing, drying, and storage processes).

By controlling the temperature and humidity, problems such as ink interruption, smudging, blistering and peeling can be effectively avoided, ensuring the clarity, covering power and wash-resistance of the white ink烫printing patterns.