What are the factors affecting the heat sealing strength of composite film bag making?
Some of the most common things that affect the heat sealing strength of composite film bags are heat sealing pressure, heat sealing time, heat sealing speed, the bag’s contents, and so on.
The purpose of heat sealing pressure is to make the heat sealing layer of the composite film flow in a viscous state so that there is effective molecular mutual penetration and diffusion between the heat sealing interfaces at the heat sealing temperature. Heat sealing pressure also helps gas escape from the surface of the film, which shortens the distance between molecules on the surface of the heat sealing material and increases the force between molecules, which makes the heat sealing stronger. To get the best heat sealing strength, the right amount of pressure must be used. The heat sealing pressure depends on how well the composite film works, how thick it is, and how wide the heat seal is.
The speed of heat sealing, which shows how well the bag making machine makes bags, is also an important factor that affects the strength and appearance of the heat seal. The faster the heat sealing speed, the higher the heat sealing temperature should be to make sure that the heat sealing strength and heat sealing state reach the right level. Under the same heat sealing temperature and pressure, the slower the heat sealing speed, the more sufficient and firm the fusion of heat sealing materials will be, but it can’t cause root breakage.
The impact of the contents of the composite bag
Some products come in powder form, which makes it easy for the seal to get dirty while the product is being filled. For example, the seal is easy to break when LDPE is used as the inner layer. This is because LDPE doesn’t do a good job of keeping things inside it from moving around when it gets hot. The heat sealing strength needs to be improved by either changing the material of the inner film or making the film thicker.
Also important are how long the heat-sealing film stays in place and how well it seals. If the heat sealing temperature and pressure are the same and the heat sealing time is long, the heat sealing layer will be fused and bonded more fully and strongly. But if the heat-sealing time is too long, it’s easy for the heat-sealing joint to get wrinkled and misshapen, which changes how flat and nice it looks. At the same time, if you heat seal for too long, the plastic will break down and the sealing performance of the sealing interface will get worse.
Application of plastic film heat sealing instrument
In general, testing the heat sealing performance of a plastic composite film means finding out how strong the heat sealing is when the heat sealing part is still hot and hasn’t cooled to room temperature yet, and how strong it is after the heat sealing part has cooled and stabilized. Obviously, the most important thing for manufacturers is the strength of the heat seal after the heat seal part has completely cooled. This is because the strength of the heat seal is directly linked to the quality of the product and affects how well the product works over time.
At the moment, the biggest problems with plastic composite films on the market are too much heat sealing, not enough heat sealing, and not enough thermal viscosity. Many businesses don’t know the heat sealing strength and thermal viscosity of the packaging materials they use, or even the quality of the packaging materials they use, so they set the equipment parameters like heat sealing temperature, heat sealing time, and heat sealing pressure by guesswork, which causes problems.
The plastic film heat sealing instrument, which is also called the film heat sealing tester, can be used to test the heat sealing of different types of film, such as plastic film, plastic composite film, paper plastic composite film, extrusion film, aluminum coating film, aluminum foil, aluminum foil composite film, and so on, in order to cut down on economic losses.
Application of flexible plastic packaging
Different materials have different properties when it comes to heat sealing, and the way they are heat sealed is also very different. Most of the time, the temperature at which the heat seals the film is higher than the temperature at which the material flows. This is done to ensure a good connection at the point on the film where the heat seals. In a certain range of temperatures, as the heat sealing temperature goes up, the flow state of the film sealing part gets better, and the pressure-made seal gets stronger. But if the heat sealing temperature is too high, the sealing platform’s strength reaches its limit and won’t get any stronger.
Also, if the heat is too high, the film can easily soften and warp, and the mouth of the bag can even catch fire. For food that needs to be sterilized at a high temperature after heat sealing, pay more attention to finding the right temperature for heat sealing to make sure the seal is strong. The packaging material heat sealing testing machine uses the rigid hot pressing sealing method to measure the heat sealing performance parameters of plastic film and flexible packaging materials, such as heat sealing temperature, heat sealing pressure, and heat sealing time, so that more heat sealing performance indexes can be found.
Sealing film for canned fruit
Businesses and customers have always been interested in how well canned fruit opens. For a product to have good opening performance, the cover film of a can of fruit must be easy to open and the product must also have good sealing performance. The key to meeting this requirement is to adjust the heat sealing parameters, such as the heat sealing temperature, heat sealing pressure, and heat sealing time, so that the bonding between the cover film and the cup body stays within a reasonable range.
Setting the heat sealing temperature, heat sealing pressure, and heat sealing time on the heat sealing tester, then heat sealing the cover film and cup body of the fruit can under heat sealing conditions, and then testing the overall sealing performance and opening force of the cover film after heat sealing, is the basic process for figuring out the above controls. If the test results aren’t perfect, the process of “adjusting the heat sealing parameters, heat sealing, testing the sealing performance, and opening force” is repeated until the right heat sealing conditions are found so that the sample results meet the requirements.
Test principle
The heat sealing tester adopts the hot pressing sealing method, places the sample to be sealed between the upper and lower heat sealing heads, and completes the sealing of the sample under the preset temperature, pressure, and time.
How to use the heat sealer?
Experimental operation process:
- Sample preparation: prepare two layers of packaging material base materials with a width of 330mm and a length of 200mm, stack them together and put them on the heat sealing tester. On the side, back, top, and bottom of the plastic film packaging bag,
Take any sample perpendicular to the hot sealing part, as the hot sealing samples are on the side, back, top, and bottom of the packaging bag. The width of the cut sample is (15 ± 0.1) mm and the developed length is (100 ± 1) mm. If the developed length is less than (100 ± 1) mm, the same material as the bag can be bonded with adhesive tape as shown in the figure to make the developed length of the sample meet the requirements of (100 ± 1) mm.
- Put the part that was heat-sealed in the middle of the prepared sample, open it up at an angle of 180 degrees, and clamp the two ends of the sample to the two clamps on the electronic tensile testing machine. The sample’s axis should be in the middle of the upper and lower clamps, and the clamps should be tight enough to keep the sample from moving around or breaking before the test. The distance between the clamps is 50 mm, and the speed of the test is (300 ± 20) mm/min. When the sample is broken, you can see how much weight it can hold. If the sample breaks in the fixture, it will be thrown away and another sample will be taken to fix it.
- The test results take the arithmetic mean value of 10 samples as the heat sealing strength of this part, expressed in N/15mm, and take three significant figures. Through professional equipment testing, we can find the appropriate temperature, pressure, and time to make the technical index of product sealing strength more standard, reduce unnecessary losses caused by sealing strength, and maximize the benefits of products.
Steps:
1) Prepare samples.
2) Turn on the power and navigate to the startup interface.
3) Navigate to the test interface.
4) Use the pressure regulating handle to adjust the pressure of the heat sealing knife, and the instrument interface will display the test pressure in real time.
The specific operation is: pull out the pressure regulating handle, turn right to increase the pressure, and turn left to reduce the pressure. After you’ve set the pressure, press the handle to the host side to secure the air pressure. The pressure is usually set at 0.2 mpa-0.4 MPa. The actual pressure depends on the customer’s sample.
5) Click “Set” to set the heat sealing time and the temperature of the upper and lower sealing knives.
6) Click “Test” to return to the main test interface. Click the upper heat sealing knife and the lower heat sealing knife to start temperature control. When the upper and lower heat sealing knives reach the set temperature, click “manual,” and the heat sealing stops at one time according to the set heat sealing time; click “automatic,” according to the set heat sealing time, stop for 3 seconds after heat sealing once, and then cycle the heat sealing to stop. The heat sealing will not end until the manual stop point stops.
How to calibrate the heat sealing instrument?
1) Turn on the power; Click “correction” in the lower left corner to enter the test result correction system.
2) After entering the calibration interface of the heat sealing instrument, set the temperature of the upper and lower sealing knives and observe the “current temperature” value displayed by the instrument. After the display is stable, fill in the difference between the set temperature and the current temperature in “temperature correction,” and the instrument will automatically calibrate. When the “current temperature” and “setting” displays are consistent, the calibration is completed.
FAQ：
What is the effect of heat sealing temperature on heat sealing strength?
The heat sealing strength is very much affected by the temperature at which the seal is made. How well the heat sealing layer works depends a lot on how thick the film used in it is.
When it’s cold, the heat seal layer melts. The heat seal layer’s top is also melted. This means that the contact temperature is low.
When the temperature is too high, it can melt the films of the heat seal layer or cause the heat seal layer to peel away from the base layer. This means that the base layers of both the upper and lower films will be part of the heat seal, which will weaken it. So, when we heat seal a film, we have to pick the right heat sealing temperature, which can’t be too high or too low.
What is the effect of heat sealing time on heat sealing?
The speed of an automatic packaging machine or an old bag making machine determines how long it takes for the heat seal to set. When the temperature and pressure of heat sealing don’t change, the longer the heat sealing time, the stronger the bond between the layers. But if the heat sealing time is too long, the part of the composite film where the heat sealing happens will be wrinkly and uneven, which will have a big effect on how the product looks.
What is the effect of heat seal pressure on heat seal?
The speed of the machine determines how long the heat seal takes on an automatic packaging machine or an old bag making machine. When the heat sealing temperature and pressure don’t change, the longer the heat sealing time, the stronger the bond between the heat sealing layers. But if the heat sealing time is too long, the part of the composite film where the heat sealing happens will be wrinkled and uneven, which will have a big effect on how the product looks.
What are the reasons for the uneven heat sealing pressure?
The knife for heat sealing is bent: Most heat sealing knives are made of aluminum or copper, which are good at moving heat. Both of these materials are pretty soft. So, when you put the heat sealing knife in place, if you don’t tighten the fixing screws the right way, the force on the heat sealing knife will be uneven, and if you change tools a lot, the heat sealing knife will get bent.
The heat sealing cutter is not made with a high level of precision: The heat sealing knife will have an uneven surface because the machine that makes it isn’t very good at what it does. This will make the heat-sealing pressure uneven, which will affect the strength of the heat-sealing on the composite packaging bag.
The heat sealing knife is dirty or has damage on its surface: There is dirt or bumps and scratches on the surface of the heat sealing knife, which will also cause uneven heat sealing pressure. Also, the melted resin that sticks to the surface of the heat sealing knife isn’t cleaned quickly enough, which also weakens the heat sealing.