Plastic Shrink film heat seal normal issues in auto shrink wrap machine
In auto shrink wrap machine, we normally use POF PVC PE shrink film to pack goods.
When sealing, there may have some issues during the heat seal, below is detailed introduction:
Heat sealing uses the external conditions to make shrink film sealing parts into a sticky flow state, with the knife tool pressure to melt the film together, after cooling to maintain a certain strength. Heat sealing process has three factors:heat sealing temperature, pressure and time, especially the temperature. According to the different materials and different material bag movement states require different heat sealing conditions, these three factors must be coordinated to get a good heat sealing quality.
What is the effect of heat sealing temperature on heat seal strength?
Heat sealing temperature on the heat sealing strength has a very important impact, heat sealing layer involved in heat sealing film thickness of the effect of heat sealing play a decisive role.
- When the temperature is relatively low, the heat sealing layer surface is melted, involved in heat sealing film thickness is relatively thin, resulting in lower contact temperature.
- When the temperature is too high, the heat sealing film may be melted or the heat seal layer has the risk of stripping the base layer, resulting in the upper and lower layers of the film involved in heat sealing, which will inevitably lead to decreased heat sealing strength. So when sealing, we must choose the appropriate heat sealing temperature, not too high or too low.
What is the effect of Heat sealing time on the heat sealing?
The heat sealing time of the automatic packaging machine or the old bag machine is determined by the speed of the machine. When heat sealing temperature and heat sealing pressure keep invariability, the longer the heat sealing time, the stronger the bonding between the heat sealing layers. However, if the heat sealing time is too long, the heat seal part will appear wrinkles, uneven phenomenon, seriously affect the appearance quality of the product.
What effect of the heat sealing pressure on the heat sealing?
In order to ensure the plastic composite flexible packaging heat sealing strength, a certain heat sealing pressure is essential. Therefore, in the heat sealing process requires heat sealing pressure is moderate and uniform. If the heat sealing pressure is not enough or uneven, will make the heat sealing parts have bubble and Weld, resulting in poor heat sealing.If the heat sealing pressure is too large, the heat sealing parts will appear sealing deformation, if with the high heat sealing temperature, it also squeeze part of the composite material, resulting in the edge of the heat sealing brittle, easy to crack, while leading to heat sealing strength decreased.
What caused the uneven of heat sealing pressure?
- Heat sealing knife deformation.
Heat sealing knife is generally made of good heat transfer properties of aluminum or copper, these two materials are relatively soft material. So during the installation of the heat sealing knife, if the method of tightening the screw is not correct, will cause heat sealing knife force is not Evenly, after frequent tool change, it causes heat sealing knife deformation.
- Heat sealing knife processing accuracy is low.
Heat sealing knife processing accuracy will cause the heat sealing knife surface uneven, so in the heat sealing process, it will cause the heat sealing pressure is not uniform, thus affecting the composite bag heat sealing strength.
- Heat sealing knife surface sticky or injured.
Heat sealing knife surface sticky goods or surface bumps, scratches, the same will cause the heat sealing pressure is not uniform, coupled with the molten resin gluing in the heat sealing knife surface is not cleaned in time, will also affect the heat sealing strength.
- silicone rubber hardness and strength.
The quality of silicone rubber is the most important conditions to ensure that the heat sealing pressure uniformity.