Factors affecting heat seal strength

Heat sealing temperature, heat sealing pressure and heat sealing time are important factors for the adjustable heat-sealing process towel. Reasonably setting or adjusting the size between the three parameters can achieve a good heat sealing effect.

Sealing temperature

The role of the heat seal temperature is to heat the adhesive film layer to an ideal viscous state. It is found that the polymer has no definite melting point and is a melting temperature range, ie, there is a temperature zone between the solid phase and the liquid phase. When heated to this temperature zone, the film enters a molten state. In the melt-viscous state, the polymer molecules deform under the action of the sealing pressure and come close to each other, generating enough attractive forces between the molecules to seal the heat sealing surfaces to each other.

Heat sealing temperature is not fixed, first, according to the characteristics of the heat sealing material is not fixed, and second, according to the thickness of the film is not set, the third is based on the number of heat sealing hot pressure and the sealing area is not fixed. In non-automated pouching, the heat seal temperature is largely determined by the characteristics of the heat seal material and the thickness of the material.

The heat seal temperature directly affects the heat seal strength of the composite packaging material. In the process of packaging or bag making, if the heat sealing temperature is not properly set or improperly adjusted, the following two situations will occur.

When the heat sealing temperature is too high, it exceeds the heat shrinkage temperature of the composite film surface material, causing the composite film to shrink and deform, resulting in adhesion between the composite film and the heat sealing knife, and the heat sealing edge material is melt extruded to reduce the material's Heat seal strength. When the heat-seal temperature is too low, the polymer may not be melted due to melting, and the two films may adhere to each other with poor heat sealing. It also affects the heat seal strength and sealability. Therefore, in the actual production, different heat sealing temperatures should be selected or set for different heat seal layer materials. Also make the heat sealing temperature and heat sealing pressure and time adjust and cooperate with each other to achieve the best heat sealing effect. For example, when the thickness and heat-resistance of the composite film surface material limit the heat-sealing temperature so that it can no longer rise and the heat sealing phenomenon occurs, it can be compensated by increasing the heat-seal pressure and prolonging the heat-sealing time.

Sealing pressure

The role of heat sealing pressure is to make the polymer in the viscous flow state produce effective macromolecules to infiltrate and diffuse between the sealing interfaces. Applying proper pressure during heat sealing can promote the adhesion and mutual melting of the thermal cover material, and play a positive role in the improvement of the heat sealing effect. If the heat seal pressure is not enough or uneven, it will cause air bubbles in the heat seal area and cause the false weld, resulting in poor heat sealing. However, if the heat sealing pressure is too high, the material in the molten state will be squeezed out, causing the brittle edge of the heat seal to be brittle and easy to crack, thereby affecting the heat sealing effect and reducing the heat seal strength. After the general material is heat-sealed, the strength loss of the sealing part shall not be greater than 10%-15%.

Changes in pressure can change the heat seal properties. When the pressure decreases, the heat sealing temperature can be increased or the heat sealing time can be increased to achieve the same heat sealing effect. Conversely, when the pressure increases, the heat-sealing temperature can be appropriately reduced or the heat-sealing time can be shortened. This can increase the output by shortening the heat-sealing time, but requires a high temperature, and the operation is more difficult, so it can be done according to actual production conditions. Adjustment.

Sealing time

Heat sealing time refers to the time the film stays under the hot knife. The heat sealing time is related to the heat sealing temperature and the heat sealing pressure. When the heat sealing temperature is low, the heat sealing time needs to be increased, the heat sealing pressure is small, and the heat sealing time is also increased. However, the automatic sealing and bag-sealing and heat-sealing time determine the production efficiency of the heat-sealing equipment. At the same time, the heat-sealing time is also related to the characteristics of the heat-seal material. For example, for heat-sensitive high-polymer materials (PVC, PAV, PP) and various heat-sealable shrink films, the heat-sealing time cannot be too long, so as to avoid degradation, and the temperature should be high. Short-term heat seal.

Heat sealing material

The characteristics of the material and the thickness of the material are the key factors affecting the heat sealing effect

Material characteristics: Different kinds of polymer heat sealing temperature range greatly different, for the same kind of material, the lower the density, the lower the sealing temperature; molecular weight, the melt index is small, the heat sealing temperature is high.

Material thickness: The heat seal temperature and time range are less affected by the material. However, when the thickness of the material is increased, the temperature and time of the heat-sealing will also increase. If the heat-sealing temperature does not change, the heat-sealing time must be extended. Relevant data show that for every 25 μm increase in film thickness, the heat-sealing time increases by 50%.

When the thickness of the heat seal material is small, the required heat seal time and temperature decrease accordingly. Especially when heat-sealing a thin material, the heat-seal pressure must be very small. Excessive pressure can make the heat-sealing time and temperature smaller and difficult to control.

If the heat sealing material is thick, the heat sealing temperature and pressure should be properly adjusted. Obviously, the thicker the thickness, the higher the required sealing temperature and the corresponding increase in pressure.

envirnmental factor

Temperature and humidity in environmental factors are closely related to the properties of the material, such as tensile strength, breathability, moisture permeability, impact resistance, and so on. For composite materials, changes in temperature and humidity affect the material's interlayer peel strength and the physical properties of the material. Similarly, environmental factors have a direct impact on the heat seal strength of composite materials.

When the material is in a normally wet environment, the heat seal strength gradually decreases with time. This result has important implications for long-term storage of goods in a constant humidity environment. If the heat seal strength of the material does not meet the requirements of the package after a period of time, then this period of time is the storage period of the goods. Such as food, cement, sealed mechanical and electrical products. For such a product, the storage period will not affect the quality of the product, but it will affect the appearance of the package because of the strength of the sealing area, cracking, bag breakage, etc. during handling and stacking. For food, cement will also cause losses.

Under the same conditions of heat sealing, the heat-sealed material is called in the environment, and there is a significant difference in the heat-sealing performance of the two materials. In materials with relatively high relative humidity, the heat seal strength after the same period of time is significantly less than that in the normally wet environment. Therefore, when designing the overall packaging scheme, it is necessary to ensure that the relative humidity of the environment in which the inner packaging is placed is low during the storage period. It can be protected from two aspects: First, the waterproof material selected for the outer package is better than the waterproof material, and it must be able to prevent the moisture outside the package from penetrating. Second, the relative humidity of the internal environment of the inner packaging must also be small. The most important method to solve this problem is to put desiccant in the internal packaging. The amount of desiccant is calculated according to the formula provided by the national standard GB4879. Taking into account the possible problems in the transportation and storage environment of the goods, the safety factor can be appropriately enlarged, that is, the amount of desiccant can be increased.

When the material is in a high-humidity environment, the heat-sealing effect gradually decreases over time. At the same time, affected by the temperature and humidity of the environment, the extent of its decline will change.

It can be seen that the influence of temperature and humidity of the environment on the performance of the material cannot be ignored. Therefore, the change in the environment that packages may undergo during storage and transportation must be fully taken into account when designing the packaging of the packaging solution. The best security.

Vacuum packaging of export machinery mainly solves two problems: First, the mechanical products are fixed in the packaging box. The product should be well fixed without damaging the vacuum package or with minimal damage to the vacuum package so that it will not be damaged by impact, vibration, and drop during circulation. The choice of fixing method depends on the shape, weight and other factors of the packaged product. The second is the tightness of vacuum packaging materials. This involves the packaging process and the study of the properties of selected materials. It is necessary to determine the parameters of the packaging process by studying the properties of the packaging materials. This can not only achieve a good packaging effect, but also can provide targeted solutions to the factors that are not conducive to the sealing of the packaging. Only by fully implementing these two tasks can we propose better packaging solutions and achieve better packaging results. This is also the main direction of future research work.

(Author/Han Cuiyan Li Outline Wood Industry College, Nanjing Forestry University)
Source of information / China Packaging News

our acrylic Desk Organizer functions as both a file sorter and bookend. it's streamlined design allows you to beautifully display and effortlessly organize your work.
Make the most of your space and find urgent things effectively with this desk organizer. This storage organizer will resolve all isuues.

Acrylic Desktop Organizer

Acrylic Desktop Organizer,Desktop Organizer,Desk Organizer,Table Organizer

Shenzhen Apex Artcrafts Co,.LTD , http://www.apexdisplaycn.com