Practical Tips for Choosing PVC Bags (Professional Guide to Avoiding Pitfalls)
PVC bags are widely used in retail, industry, agriculture and other fields due to their transparency, water resistance and controllable cost. However, the materials vary greatly and the manufacturing process is complex. When purchasing, it is necessary to make a precise judgment based on actual needs. The following shares practical purchasing tips that can be directly applied from dimensions such as material properties, process details, and usage scenarios to help you avoid “pitfalls”.
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First, material selection: Distinguish between “authenticity” and “quality”
Distinguish between “virgin materials” and “recycled materials”
Virgin material: High transparency (similar to cellophane), no odor, smooth to the touch, good resilience after stretching, suitable for food contact or high-value product packaging.
Recycled materials: Yellowish in color, with impurity spots, and a distinct odor. They are prone to cracking and aging. Long-term use may release harmful substances. Use with caution in direct contact with food or children’s products.
Judgment method:
Light transmission test: Observe the light source, and the virgin material should have no black spots or foggy impurities. Fine particles or color spots can be seen in the recycled materials.
Odor detection: If a newly opened PVC bag has a pungent chemical smell, it is highly likely to contain recycled materials or inferior plasticizers.
Pay attention to the type of plasticizer
Phthalate plasticizers (such as DEHP) : They are low in cost but toxic and may interfere with the endocrine system. They have been banned in regions such as the European Union and the United States and should not be used in children’s toys or food packaging.
Environmentally friendly plasticizers (such as DOTP, TOTM) : They are highly safe and comply with environmental protection standards such as REACH and ROHS. Such products are preferred.
Suggestion: Request the MSDS (Chemical Safety Data Sheet) from the supplier to confirm the composition of the plasticizer.
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Second, thickness and load-bearing capacity: Match the scene to avoid “thinness and brittleness” or “waste”
Thickness does not equal absolute strength
Under the same thickness, the density of PVC material and the production process (such as double-layer composite and thickened edge banding) have a greater impact on load-bearing capacity.
Reference case:
A 5-microns ordinary PVC bag containing 5kg of rice is prone to tearing, but a 5-microns double-layer composite PVC bag can bear more than 10kg of weight.
Purchasing tips:
Heavy load requirements: Choose styles with thickened edge banding (width ≥5mm), bottom “cross” reinforcement or four corner reinforcement.
Light load demand: Avoid blindly pursuing thickness. A thickness of 3 to 5 microns, combined with high-frequency heat sealing technology, can meet the daily retail packaging requirements.
Conversion of thickness units
In China, “丝” (1丝=0.01mm) is commonly used, while in Europe and America, “mil” (1 mIL =0.0254mm) is more frequently employed to avoid confusion.
Conversion formula:
10 microns ≈0.1mm≈3.94mil (for convenient and quick comparison of international purchasing demands).
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Third, process details: sealing performance, durability, and customization
Edge banding process: The core of preventing leakage and moisture
High-frequency heat sealing: By melting the PVC edge through high-frequency current, it has strong sealing performance and is suitable for liquid and powder packaging (such as seeds, feed).
Ultrasonic welding: It generates heat through ultrasonic vibration and friction, ensuring a smooth seal without glue overflow. It is suitable for food-grade or high transparency requirements.
Glue bonding: Low cost but prone to delamination, only suitable for temporary and low-value item packaging (such as promotional flyers).
Pit-avoiding point: If the edge banding is easily delaminated or cracked when torn by hand, it indicates that the craftsmanship is not up to standard.
Printing process: Durability of the LOGO/ pattern
UV printing: Bright colors, wear-resistant and scratch-resistant, suitable for long-term display (such as brand packaging, exhibition materials).
Screen printing: Low cost but prone to color fading, only suitable for one-time or short-term use scenarios (such as temporary promotional labels).
Notes:
The printing ink should be compatible with PVC material to prevent the bag from becoming brittle due to ink corrosion.
If large-scale printing is required, it is recommended to choose white base film PVC bags (with low light transmittance and better color rendering effect).
Opening design: Enhance user convenience
Self-adhesive strips (Velcro) : They are easy to open and close repeatedly and are suitable for scenarios where items are frequently taken out (such as stationery and cosmetic packaging).
Zipper head: It has stronger sealing performance and is suitable for items with high moisture-proof requirements (such as electronic components and medicines).
Tear design: It should be equipped with easy-to-tear dotted lines to prevent the bag body from being damaged due to violent tearing (commonly seen in express delivery bags).
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Fourth, usage scenarios: Match as needed to avoid “excessive packaging”
Retail scenario
Clothing/Accessories: 3-5 filament transparent PVC bags + self-adhesive strips, with gilded logos to enhance the texture.
Food/Medicine: Select food-grade PVC bags of 10 microns or more with high-frequency heat sealing to ensure sealing and moisture-proofing.
Hardware accessories: 6-8 thread thickened bags + four corner reinforcement to prevent sharp objects from piercing.
Industrial/agricultural scenarios
Fertilizers/seeds: PVC bags with a thickness of more than 10 microns and UV repellents added. Avoid long-term outdoor exposure to sunlight to prevent brittleness.
Aquatic product transportation: 12 microns or more, high-toughness bag body, combined with oxygen pump to achieve live transportation (such as shrimp fry, fish fry).
Heavy machinery parts: Double-layer composite PVC bags (total thickness ≥20 microns) + metal keyholes to ensure hoisting safety.
Special requirements
Low-temperature environment: Ordinary PVC is prone to becoming brittle below -10℃. Cold-resistant PVC formula (with toughening agent added) should be selected.
Anti-static requirement: Anti-static PVC bags (surface resistivity 10⁶-10⁹Ω) should be used for packaging electronic components.
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Fifth, Price and Cost Performance: Reject the “low-price trap”
Cost composition analysis
Material cost: virgin materials > recycled materials, environmentally friendly plasticizers > ordinary plasticizers.
Process cost: High-frequency heat sealing > ultrasonic welding > glue bonding; UV printing > Screen printing.
Customization costs: Special sizes, thickening treatments, multi-color printing, etc. will all increase the unit price.
Reference formula:
Reasonable unit price range = (material cost + process cost + management fee) × 1.2 (profit margin)
Example: The cost of a 5-micron ordinary PVC bag is approximately 0.1 yuan per piece, and a reasonable retail price range is 0.12 to 0.15 yuan.
Techniques for avoiding pitfalls
Beware of “ultra-low prices” : If the unit price is more than 30% lower than the industry average, it is highly likely that recycled materials or simplified processes will be used.
Require itemized quotations: Clearly define the costs of each link such as materials, processes, and printing to avoid hidden price hikes.
Small-batch trial orders: For the first cooperation, place an order of 500 to 1,000 units to test the quality. After confirming that there are no errors, make bulk purchases.
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Sixth, Supplier Selection: Dual guarantee of qualifications and services
Verification of core qualifications
Environmental protection certifications: ROHS (EU), REACH (EU), FDA (US Food Grade), GB 4806.7 (China Food grade).
Quality certification: ISO 9001 (Quality Management), ISO 14001 (Environmental Management).
Test report: Test data such as thickness, tensile strength, weather resistance, and heavy metal content issued by a third-party institution.
Service Capacity assessment
Sample-making speed: Regular manufacturers can provide samples within 3 to 5 days, and respond promptly to customized demands.
Delivery cycle: Regular inventory products will be dispatched within 1-3 days, and for customized products, a reasonable cycle is 10-15 days.
After-sales guarantee: The terms such as free replenishment for quality issues, redoing for printing errors, and compensation for logistics damage should be clearly written into the contract.
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Summary: The “Golden Rule” for Choosing PVC bags
Clarify requirements: Prioritize the determination of the usage scenario, load-bearing capacity, and environmental protection requirements to avoid the misconception that “the thicker, the better”.
Material is king: Virgin materials + eco-friendly plasticizers are the safety bottom line. We reject recycled materials and inferior inks.
Craftsmanship determines quality: High-frequency heat sealing, ultrasonic welding, and UV printing are standard equipment for high quality.
Compare prices among three options: Take into account the overall cost, quality and service, and choose the solution with the best cost performance.
Contractual constraints: Incorporate material standards, delivery times, and after-sales terms into the contract to safeguard your own rights and interests.
By using the above techniques, PVC bags that meet the requirements can be precisely screened out, avoiding losses caused by material, process or service issues.
We Committ To Serve All Kinds Of PVC/ EVA Bags, Cosmetic Bags, Canvas Bags And Paper Bags With Custom Service!
Shanghai Chenhuan Industrial is a manufacturer which is specialized in the research, development and production of all kinds of bags and packaging. Our products include PVC bags, EVA bags, TPU bags, PE bags, paper bags, cosmetic bags, canvas bags and tote bags. We provide OEM service to the material, the size, the style and the printing.Official website Address:https://www.chenhuanind.com/
