What is the water absorption rate of eva hot melt adhesive film?
Jul 16, 2025
As a provider of EVA hot melt adhesive film, I often encounter questions from customers regarding various properties of our product. One of the frequently asked questions is about the water absorption rate of EVA hot melt adhesive film. In this blog post, I'll delve into what the water absorption rate of EVA hot melt adhesive film is, why it matters, and how it can impact the performance of the adhesive in different applications.
Understanding EVA Hot Melt Adhesive Film
Before we discuss the water absorption rate, let's briefly understand what EVA hot melt adhesive film is. EVA, or ethylene - vinyl acetate, is a copolymer that is widely used in the production of hot melt adhesive films. EVA hot melt adhesive film offers several advantages such as good adhesion to a variety of substrates, flexibility, and relatively low melting points, which make it suitable for many industries including textile, packaging, and automotive.
What is the Water Absorption Rate?
The water absorption rate of a material is defined as the amount of water that the material can absorb under specific conditions, usually expressed as a percentage of the material's original weight. For EVA hot melt adhesive film, the water absorption rate is determined by exposing the film to a controlled environment with a certain level of humidity and temperature for a set period.
The test typically involves weighing the dry EVA hot melt adhesive film sample first. Then, the sample is placed in a chamber with a defined relative humidity (e.g., 90% relative humidity) and temperature (e.g., 23°C) for a specified time, often 24 hours or 48 hours. After the exposure period, the sample is removed from the chamber, quickly wiped to remove any surface - adsorbed water, and then re - weighed. The difference in weight before and after the exposure is used to calculate the water absorption rate using the following formula:
Water Absorption Rate (%) = [(W₂ - W₁) / W₁] × 100
Where W₁ is the initial weight of the dry sample, and W₂ is the weight of the sample after water absorption.
Factors Affecting the Water Absorption Rate of EVA Hot Melt Adhesive Film
Composition of EVA Copolymer
The ratio of ethylene to vinyl acetate in the EVA copolymer significantly affects the water absorption rate. Generally, as the vinyl acetate content increases, the polarity of the EVA copolymer also increases, which leads to a higher water absorption rate. Vinyl acetate has a greater affinity for water molecules due to its polar groups, so EVA hot melt adhesive films with a higher vinyl acetate content will absorb more water compared to those with a lower content.
Additives
Additives are often incorporated into EVA hot melt adhesive films to enhance certain properties such as adhesion, flexibility, or heat resistance. Some additives can increase the water absorption rate, while others can reduce it. For example, hydrophilic additives will increase the film's ability to absorb water, while hydrophobic additives can create a barrier that reduces water absorption.
Film Thickness
Thicker EVA hot melt adhesive films generally have a higher water absorption capacity. This is because a thicker film has more material volume that can potentially absorb water. However, the water absorption rate per unit mass may not necessarily increase proportionally with thickness, as the diffusion of water through the film may be affected by factors such as the density and structure of the film.
Importance of Water Absorption Rate in Different Applications
Textile Industry
In the textile industry, EVA hot melt adhesive film is used for bonding fabrics, such as in the production of sportswear, underwear, and shoe linings. A high water absorption rate can be a disadvantage in this context. If the adhesive film absorbs too much water, it may lose its adhesion strength, causing the bonded fabrics to separate. Moreover, water absorption can lead to the growth of mold and mildew on the adhesive, which is not only unsightly but also can cause health problems. On the other hand, in some cases where breathability is required, a slightly higher water absorption rate may be acceptable as long as it does not compromise the adhesive's performance. You can learn more about fabric - related adhesive products like Flannel Fabric Adhesive Tape.
Packaging Industry
For packaging applications, the water absorption rate of EVA hot melt adhesive film can also have a significant impact. If the adhesive is used to seal packages that may be exposed to moisture during storage or transportation, a high water absorption rate can lead to the weakening of the seal. This can result in the ingress of moisture into the package, potentially damaging the contents. Therefore, in the packaging industry, EVA hot melt adhesive films with low water absorption rates are often preferred.
Automotive Industry
In the automotive industry, EVA hot melt adhesive films are used for interior trim bonding, such as attaching headliners, door panels, and seat covers. The interior of a vehicle can be exposed to various environmental conditions, including high humidity. A high water absorption rate can cause the adhesive to swell and lose its adhesion over time, leading to loosening of the interior components. Thus, automotive manufacturers require EVA hot melt adhesive films with low water absorption rates to ensure long - term durability.
Controlling the Water Absorption Rate
To meet the requirements of different applications, manufacturers can take several measures to control the water absorption rate of EVA hot melt adhesive films.
Adjusting the EVA Copolymer Ratio
By carefully selecting the ratio of ethylene to vinyl acetate in the EVA copolymer, manufacturers can tailor the water absorption rate. For applications where low water absorption is crucial, a lower vinyl acetate content can be used.
Using Hydrophobic Additives
Hydrophobic additives can be incorporated into the EVA hot melt adhesive film formulation. These additives create a hydrophobic layer on the surface of the film or within the polymer matrix, which reduces the film's affinity for water. For example, some silicone - based additives can effectively reduce the water absorption rate of EVA hot melt adhesive films.
Surface Treatment
Surface treatments can also be applied to the EVA hot melt adhesive film to reduce water absorption. For instance, a thin layer of a hydrophobic coating can be applied to the film surface, which acts as a barrier to prevent water from penetrating into the film.
Our Offerings
As a leading provider of EVA hot melt adhesive film, we offer a wide range of products with different water absorption rates to meet the diverse needs of our customers. Our Hot Melt Adhesive Film With Modified Properties For Stick The Pp Board And Steel Board is designed with a low water absorption rate to ensure reliable adhesion even in humid environments. We also have TPU Hot Melt Adhesive Film for Fabric which can be customized according to the specific water absorption requirements in the textile industry.
If you are looking for high - quality EVA hot melt adhesive film and need to select the most suitable product based on the water absorption rate and other properties, we are here to assist you. Our team of experts can provide professional advice and guidance to help you make the best choice for your application. We welcome you to contact us for further details and to start a procurement negotiation. We are committed to providing excellent products and services to meet your business needs.
References
- ASTM D570 - 98(2018) Standard Test Method for Water Absorption of Plastics.
- "Handbook of Adhesives and Sealants", Second Edition, edited by Andrew Pizzi and K. L. Mittal.
- Research papers on the properties of EVA copolymers and their applications in adhesive films published in polymer science and engineering journals.