When it comes to packaging, there are many different types of cups to choose from. In this blog post, we will compare PP injection cups and PP blister cups. We will discuss the differences in printing processes, as well as the advantages and disadvantages of each type of cup. We hope that this information will help you decide which type of cup is best for your business!
PP Injection Cup VS PP Blister Cup: What are the Differences?
Injection molding and blister molding are both methods of fabricating plastic cups. Though they share the same material, there are several key differences between the two processes.
Injection molding cups are made by melting plastic particles into a fluid and injecting them into a mold. The injection cup is then cooled and ejected from the mold. Blister molding, on the other hand, uses a sheet of plastic that is heated to a soft but not melted state. The softened sheet is then molded into shape and cooled.
There are several advantages and disadvantages to both methods. Injection molding cups are generally harder and more durable than blister cups. However , blister cups are typically cheaper to produce. In terms of color printing, injection molding gives you more options and allows for more colors to be used. Blister cups, on the other hand, are limited to one or two colors.
What are the Differences in Printing Processes ?
When it comes to printing on plastic cups, there are two main methods: PP injection cup and PP blister cup. Each has its own advantages and disadvantages, so which one is right for your project?
Offset printing, also known as lithographic printing, is a simple printing method that involves transferring ink from an adhesive surface to a paper surface. This type of printing produces high-quality prints with rich colors and tones. Also low cost of plate making, the printed products are full of layers, rich tone and soft colors.
Flexographic printing is a direct printing method that uses a flexible, raised image plate. This type of printing is often used for plastic bags, labels, and corrugated paper. Flexographic printing has the advantage of being able to print on a wide range of media types. However, the plates are not as precise as offset printing and the contrast is not as great.
UV printing uses a screen as a base plate and creates graphics through a photographic process. This type of printing is closest to our everyday life printing method and is widely used for plastic, wood, metal, textile, and leather products. UV printing has the advantage of being able to print on any substrate size or shape. However, it can be expensive and time-consuming to produce UV plates.
So, which printing method is right for your project? It all depends on your needs and budget. If you need high-quality prints with rich colors and tones, then offset printing is the way to go. If you need a quick turnaround time and don’t mind sacrificing some print quality, then flexographic printing may be the right choice. If you need to print on any substrate size or shape, then UV printing is the best option. However, keep in mind that all of these printing methods can be expensive and time-consuming. So, make sure you consider all your options before making a final decision.
What are the Advantages and Disadvantages of PP injection cup?
Advantages: lightweight, hand pinch will be deformed, recovery is also better, can withstand high temperature 110 degrees, low temperature resistance can reach -20 degrees, do not have to worry about what harmful substances will be released
Disadvantages: general transparency, semi-permeable, hand pinch will be deformed, easy to squeeze or high drop deformation during transportation
solution: the transport process of the cup, for the cup high fall edge cracking or squeezing problems, you can wrap the bubble film outside the cup to prevent the cup from cracking.
What Problems Will be Encountered in the Production Process of PP injection Cup Mold?
1.Cracking: a more common defect of plastic products, the main reason is due to stress deformation. There are mainly residual stress, external stress and stress deformation caused by the external environment.
Cracking caused by residual stress: residual stress is mainly due to the following three cases, i.e. overfilling, mold release and metal inlay. As the cracking in the case of overfilling, the solution can be mainly in the following aspects:
Since the pressure loss in the straight gate is the smallest, if the cracking is mainly generated near the straight gate, consider using multi-point distribution point gates, side gates and shank gates instead.
On the premise of ensuring the resin does not decompose and deteriorate, properly increasing the resin temperature can reduce the melt viscosity and improve the fluidity, and also reduce the injection pressure to reduce the stress.
In general, when the mold temperature is low, it is easy to produce stress, and the temperature should be increased appropriately. However, when the injection speed is high, even if the mold temperature is low, it can reduce the generation of stress.
Injecting and holding time is too long will also generate stress, and it is better to shorten it appropriately or to make multiple holding pressure switching.
Non-crystalline resins such as AS resin, ABS resin, PMMA resin, etc. are more likely to produce residual stress than crystalline resins such as polyethylene, polyformaldehyde, etc. and should be noted. When the mold is launched, due to the small release slope, mold cavity and convex mold roughness, so that the launch force is too large, resulting in stress, and sometimes even in the launch rod around the phenomenon of whitening or rupture. The cause can be determined by carefully observing the location where the cracking occurs.
Cracking caused by external stress: Here the external stress is mainly caused by unreasonable design and stress concentration, especially in the sharp corners need more attention.
Cracking caused by external environment: chemicals, water degradation caused by moisture absorption, and excessive use of recycled materials can cause physical deterioration and cracking.
2.Insufficient filling-The main reasons for insufficient filling:
- Insufficient resin capacity.
- Insufficient pressurization in the cavity.
- Insufficient resin fluidity.
- Poor exhaust effect.
As improvement measures, we can mainly start from the following aspects:
- Lengthen the injection time, to prevent the molding cycle is too short, resulting in the gate curing before the resin backflow and difficult to fill the cavity;
- Improve the injection speed;
- Improve the mold temperature;
- Improve the resin temperature;
- Improve the injection pressure;
- Expand the gate size, the general height of the gate should be equal to the product wall thickness of 1/2 to l/3;
- Set the gate in the product wall thickness;
- Set the exhaust slot (average depth 0.03mm, width 3-5mm) or exhaust rod, more important for smaller workpieces;
- Leave a certain buffer distance between the screw and injection nozzle;
- Choose low viscosity grade material;
- Add lubricant.
3.Wrinkles and pockmarks: the cause of this defect is essentially the same as underfilling, only the degree is different. Therefore, the solution is also basically the same as the above method. Especially for the resin with poor flowability (such as polyformaldehyde, PMMA resin, polycarbonate and PP resin, etc.) it is necessary to pay more attention to the appropriate increase of gate and appropriate injection time.
4.Shrinkage pit: The cause of shrinkage pit is also the same as underfilling, in principle, can be solved by overfilling, but there is a risk of stress, attention should be paid to the design of uniform wall thickness, should be as far as possible to reduce the wall thickness of the reinforcement ribs, convex columns and other places.
5.Overflow edge: the focus of the treatment of overflow edge should be mainly on the improvement of the mold. And in the molding conditions, it can start in reducing the liquidity. Specifically, the following methods can be used:
① reduce the injection pressure;
② reduce the resin temperature;
③ use high viscosity grade material;
④ reduce the mold temperature;
⑤ grind the mold surface where the overflow occurs;
⑥ use harder mold steel;
⑦ improve the clamping force;
⑧ adjust the exact mold bonding surface and other parts;
⑨ increase the mold support column to increase rigidity;
⑩ determine the size of different exhaust slots according to different materials.
6.Fusion marks: fusion marks are produced by the front part of the molten resin from different directions being cooled and not completely fused at the bond. In general, it mainly affects the appearance and has an impact on painting and plating. In severe cases, it affects the strength of the product (especially in the case of fiber-reinforced resins). It can be improved by referring to the following items:
- Adjust the molding conditions to improve the flowability. For example, increase the resin temperature, mold temperature, injection pressure and speed, etc.;
- Add a venting tank, and set a push rod at the place where the melt marks are produced is also conducive to venting;
- Minimize the use of mold release agent;
- Set the process overflow and use it as the place where the melt marks are produced, and then cut it off after molding;
- If it only affects the appearance, change the gate position to change the position of the melt marks. Or the part where the melt marks are produced can be treated as a dark glossy surface and so on to be decorated.