Why are Flat Bottom Zipper Bags Flat and Smoo

Why are Flat Bottom Zipper Bags Flat and Smooth

Flat Bottom zipper bags are more and more widely used because they are easy to carry and easy to store. But the zipper bag is prone to wrinkles and other problems, affecting the quality and beauty of the bag. Different materials of packaging bags, the production process of temperature, pressure requirements and tolerance are different, so flat bottom zipper bag production process, need to be adjusted according to the material.
According to the material, flat bottom zipper bags can be divided into flexible zipper bags with BOPP fabric and matte film fabric, rigid zipper bags with PET or NY material and PBAT fabric
Degradable material degradable flat bottom zipper bag, fabric for PE material zipper bag. The production control points of these 4 common materials and flat bottom zipper bags are as follows.

1.BOPP or Matte Film Flat Bottom Zipper Bag

flat bottom zipper bag

flat bottom zipper bag

flat bottom zipper bag

flat bottom zipper bag

Printing process: need to use temperature resistant ink, rather than ordinary light ink, layout design as far as possible to leave more than 2mm transparent edge, if the whole page design Map, as far as possible to design for a white design (that is, there is a white ink layer under the ink)
Composite process: whether the use of solvent-free or ordinary solvent-based glue, must be the need for temperature resistance, and cannot use ordinary light package material nature of the glue, otherwise, zipper head.
The location is prone to high temperature separation phenomenon.
Bottom material: Choose slightly low-temperature material, the same flat bottom zipper bag material also try to use low-temperature material, in order to better match the fabric material BOPP or matte OPP fabric itself
It’s not very heat resistant.

2.PET or NY steel material class flat bottom zipper bag

Because the fabric material belongs to the rigid material, itself belongs to the temperature resistant material, the edge temperature resistance is very good, but this is only the surface temperature resistance. For composite film, or the same need to choose temperature resistant ink and glue. Of course, due to the surface temperature resistance, the zipper’s thermal sealing temperature range will have a wider range of choice.

3.Flat bottom zipper bags made of PBAT and other degradable materials

The base material of this kind of flat bottom zipper bag should also match the material of PLA and other categories, and the zipper should also be PLA. At present, this kind of packaging is relatively few in the market circulation.
The main control point of this type of bag is the heat sealing of bag making.

With PLA material flat bottom zipper bag, if the heat-sealing fastness is relatively solid, this kind of flat bottom zipper bag is easy to be affected by high temperature, and it will be easy to embrittlement in a relatively short time. Therefore, in the heat sealing, it is necessary to seek suitable production process temperature, otherwise it will be very prone to high temperature embrittlement phenomenon.
On the other hand, the bite force of PLA zipper is easy to become very small or very large, so large that the flat bottom zipper bag can only be broken to open the bag, so it becomes a phenomenon of defective products.

Flat bottom zipper bags containing degradation materials have similar requirements for printing and composite as BOPP categories, which require that the temperature resistance is enough to meet the requirements of bag making heat seal. It is understood that there are relatively few flat bottom zipper bags made of degradable materials in the current market, and there are still many technological difficulties and stability to be developed and overcome.

4. The fabric is PE material flat bottom zipper bag

This type of ink glue requirements and fabrics for PET and other types of flat bottom zipper bag requirements are roughly the same.
PE fabric type of composite flat bottom zipper bag, in the bag-making process has a relative particularity. At the beginning, when everyone tried PE//PE material structure, there were great difficulties in the bag-making process, even if it was to make a three-sided sealing bag. Because of the tensile property and melting property of PE itself, the control difficulties of this kind of material bag-making process were caused. By modifying the surface layer PE, its temperature resistance, stiffness and high temperature shrinkage and other difficulties were improved, and the sub-surface layer PE at high temperature, can be similar to BOPP class of a temperature resistance level.

That is, the fabric PE is fused at high temperature as far as possible, and the PE melting temperature of the bottom hot cover is reduced to the minimum as far as possible. At the same time, the zipper is also used at low temperature, so that the three are better matched.
Once the three are not well matched, it is easy to produce the phenomenon of weak heat sealing or PE surface layer being crushed in the bag-making process, and even the inner PE layer will be crushed, and may lead to the stretching deformation of the bag-making edge.

5.The middle layer is made of VMPET, aluminum foil, NY, PET and other materials

This structure is the most special kind of flat bottom zipper bag, but also has a certain production difficulty. Whether it matches fabric BOPP or matte OPP, or NY or PET structure, this flat bottom zipper bag containing aluminum plated PET structure is very troublesome.
First of all, the composite effect of the same plane layer of aluminum plating layer is very challenging the production process. Once the composite strength is too high, the aluminized layer will produce transfer; If the compound strength is not enough, it will weaken the heat-sealing performance, and the position of the hot sealing zipper head is easy to wrinkle at high temperature. But this does not extend to high temperature separation. If the composite glue is too strong to produce aluminum plating transfer, only attributed to high temperature separation.

Therefore, for flat bottom zipper bags containing aluminized PET structure, we need to find a balance between the aluminized composite strength and the temperature resistance of the zipper position heat seal. It is not only required that aluminum plating will not produce transfer, but also can make the hot sealing zipper, especially the position of the zipper head, will not produce high temperature wrinkle phenomenon, also will not produce high temperature separation phenomenon.

At the same time, how we choose the glue is very important. At present, there are many special glues for aluminum plating on the market. Many glue manufacturers can provide very mature temperature resistant polyurethane glue, which is the glue with composite aluminum plating structure and temperature resistant properties.
At the same time, ripening is also very important. Ripening mainly depends on the conditions of the glue reaction. In general, it is generally decided to the relatively low temperature and the slightly longer time.

Another point to pay special attention to is that each supplier’s glue is different, so the enterprise can only analyze the problem on a case-by-case basis, not generalize.
At the same time, flat bottom zipper bag containing aluminum plated structure, mainly choose low-temperature zipper.

For more detailed types or questions about flat bottom zipper bag, please refer to: Food packaging film – China Packaging Bag & Film OEM Factory (kxpack.com)