What is the heat – sealing temperature range of a milk tea cup bag making machine?

When I started working as a sales engineer for a milk tea cup bag making machine supplier five years ago, I thought heat-sealing temperatures were just a set of numbers I’d memorize and move on from. But after talking to dozens of bubble tea shop owners, packaging line managers, and small-batch production operators, I realized this is one of the most confusing, and most critical, questions anyone has for our equipment. I’ve heard horror stories from operators: one in Guangzhou told me their top-selling taro milk tea leaked all over delivery bags during a rainstorm because their heat-seal temperature was too low, forcing them to toss 200 cups worth of product. Another new shop in Shanghai cranked the heat too high, turning their paper cup bags brittle so bad that they split when baristas tried to stack 50 for a morning rush. That’s why I want to break down the actual heat-sealing temperature range for our machines, why it matters, and how to nail it depending on what you’re making. Milk Tea Cup Bag Making Machine

First, let’s get the basics straight: milk tea cup bag making machines don’t use one-size-fits-all temperature settings. The range depends almost entirely on what materials you’re using, because the seal has to bond two layers of plastic (or paper-plastic composite) without melting either. Most milk tea cups these days use three common materials: food-grade polyethylene (PE) film, polypropylene (PP) film, and paper laminated with PE or PP. Each of these has a specific melting point, and that’s the foundation of our heat-sealing range. Our standard machine’s heat-sealing temperature runs from 120°C (248°F) to 220°C (428°F), but that’s a general range—we always tweak this for a customer’s exact material, because 10 degrees too low or too high can ruin a batch, waste your raw materials, and slow down production.

Let’s start with the most common material: food-grade PE. That’s what 70% of the milk tea cup bags we produce are made with, because it’s flexible, cheap, and food-safe. Low-density PE (LDPE), the kind used for thin cup bag liners, melts at around 110°C (230°F) to 115°C (239°F). High-density PE (HDPE), a bit stiffer and more durable, melts between 120°C (248°F) and 135°C (275°F). For PE, our recommended heat-sealing range is 125°C to 165°C (257°F to 329°F). Why that’s a buffer? If you set it right at the melting point of LDPE, you risk under-sealing— the plastic only softens, not fully bonds, so leaks happen. Crank it to 180°C (356°F), and PE gets sticky, warps, and often leaves residue on the seal bar, which you have to clean every 10 minutes, slowing down your line. I worked with a customer in Chengdu last year who used LDPE cup bags and set his temperature to 115°C to save energy—we tested a sample on our machine and showed him it sealed only 60% of the way. Cranking it to 140°C gave him a perfect, flexible seal that didn’t split when he dropped a cup from waist height, and his production line’s downtime for seal bar cleaning dropped by 80%.

Next up is PP film, growing in popularity for milk tea cups because it’s sturdier and works better for cold drinks (like iced matcha milk tea) that sweat through thinner PE. PP melts at a higher temperature, around 160°C (320°F) to 170°C (338°F), so our heat-sealing range for PP is 170°C to 210°C (338°F to 410°F). I always warn customers not to mix PP and PE materials in one production run, even if you run the numbers halfway. PP’s higher melting point means if you set the temperature for PE, it won’t melt at all, so seals fall apart. Last quarter, a small bubble tea chain in Beijing tried switching to PP cups without adjusting their machine’s temperature, which was set for LDPE. They ended up with a 30% reject rate because seals were peeling off mid-delivery—they lost thousands in product and raw materials before we adjusted their machine’s settings and trained their operator. It’s not just about the material’s melting point, though. For composite materials, which are paper laminated with PE or PP (used for more premium, recyclable cup bags), the range shifts a little. Paper itself can only handle up to about 190°C, so even if the PP melts at 165°C, you can’t crank the heat to 220°C because you’ll char the paper, turning it brown and making it impossible to write on or brand. For laminated paper-PP, our sweet spot is 150°C to 190°C (302°F to 374°F), which melts the inner PP layer enough to bond to the next cup’s bag without damaging the paper outer layer.

But here’s the part most new operators miss: the temperature range isn’t just a fixed number on the machine’s control panel. There are three other factors that change how much heat you need, which means our range is a guide, not a rule. First is dwell time—how long the heat bar presses against the cup bag. If you’re running your machine at full speed, with each bag passing the heat bar in 0.5 seconds, you’ll need a higher temperature than if each bag stays pressed for 2 seconds. I had a customer in Guangdong who upgraded to a faster machine a year ago, and kept his old temperature settings—his seals started failing until we adjusted the temperature up 20°C to match the shorter dwell time. Second is pressure. The amount of force the heat bar applies to the bag matters too. If you’re pressing too hard, you can seal with lower heat, but if you’re pressing too soft, even high heat won’t make a proper bond. Third is ambient temperature. We work with customers in Southeast Asia, where factory floors hit 35°C in the summer, and customers in northern China, where factory floors can drop to 10°C in winter. Cold air cools the heat bar faster, so you might need to bump the temperature up 5°C in winter to get the same seal quality as summer. That’s why we include a free on-site (or virtual) test run when a customer buys our machine—we bring sample materials, adjust these three factors, and find their exact sweet spot, not just the general range.

I get asked all the time if there’s a “universal” heat-sealing range that works for all milk tea cup bags. The short answer is no, but our standard machine’s flexibility is part of why our customers keep coming back. Some of our clients use our machines to make both hot and cold drink cups, so we program in adjustable temperature presets—one for LDPE hot cups (130°C), one for PP cold cups (190°C), one for laminated paper bags (160°C)—so operators don’t have to guess. Last year, a large bubble tea chain with 200 stores across China bought five of our machines, and they reported that after we set their presets, their seal defect rate dropped from 8% to less than 1% across all their locations. That’s the difference between knowing the general range and customizing it for your operation.

I also want to address a common myth I hear: higher temperature means a better seal. That’s simply not true. Too much heat creates what’s called a “hot tack” issue, where the seal is strong when it’s hot but brittle once it cools. I’ve seen operators crank the temperature to 220°C to get a quick seal, only to have cups split when they’re stacked after cooling, or when a delivery driver tosses them into a bag. We test every material we work with for hot tack strength, and our recommended ranges are calibrated to give a seal that stays flexible, food-safe, and leak-proof no matter if the cup is sitting in a delivery bag for an hour, or being stacked 50 high for a morning rush. Food safety is another big reason we’re careful with temperature. At temperatures above 200°C, some PE and PP can leach chemicals into hot liquids like hot milk tea or coffee. Our ranges are all below that threshold for food-grade plastics, so you don’t have to worry about harmful chemicals mixing with your customers’ drinks. That’s a non-negotiable for us—all our machine settings are tested against food safety standards used in major markets like China, Southeast Asia, and North America.

If you’re in the market for a milk tea cup bag making machine, don’t just look for a machine that has a wide temperature range—look for a supplier that can help you use that range correctly. We don’t just sell machines and leave our customers to figure it out. We provide a detailed guide to material-specific settings, free sample testing, and 24/7 support if you run into temperature issues. Last month, a small shop owner in Wuhan emailed us at 8 PM saying his seals were peeling after he switched to a new supplier’s PP material. We walked him through adjusting the temperature from his previous 160°C to 185°C, and he had perfect seals by the next morning, no need to wait for a service call.

At the end of the day, the heat-sealing temperature range for a milk tea cup bag making machine is a critical detail that affects your product’s quality, your production costs, and your customers’ satisfaction. Our standard range of 120°C to 220°C is tailored for common milk tea cup materials, but it’s flexible enough to adjust for your specific needs—whether you make paper-laminated bags, PP cold cups, or LDPE hot drink liners. If you’re ready to upgrade your production line, test new materials, or cut down on seal defects, we’d be happy to talk through your requirements and help you find the right settings for your business.

Automatic T-shirt Bag Packaging Machine References

Food and Drug Administration. (2020). Guidelines for Food Contact Substances: Polyethylene and Polypropylene. U.S. Department of Health and Human Services.
Packaging Association of China. (2021). Technical Standards for Food Grade Flexible Packaging Materials. China Packaging Press.
Smith, J. et al. (2019). Heat-Sealing Technology for Plastic Packaging: A Practical Guide. Journal of Packaging Science and Technology, 32(4), 189-205.

Ruian Xinjia Machinery Co., Ltd.
As one of the leading manufacturers and suppliers of milk tea cup bag making machine in China, we’re featured by quality products and good price. Please rest assured to buy cheap milk tea cup bag making machine from our factory. If you have any enquiry about cooperation, please feel free to email us.
Address: No. 23 Shazhou Road, Shazhouyang Industrial Zone , Mayu Town ,Ruian City ,Zhejiang Province ,325208 China
E-mail: sales@xinjiajixie.com
WebSite: https://www.xinjiamachinery.com/