The selection of packaging bags plastic requires matching material properties to specific application demands including load weight environmental exposure and closure method. Packaging bags plastic are available in hundreds of combinations of thickness material type and additive packages. Shenlong Packaging Products Co., Ltd. presents this guide to help engineers and procurement professionals specify the correct packaging bags plastic based on measurable performance criteria.
Commercial packaging bags plastic fall into four material families LDPE for flexibility HDPE for stiffness PP for heat resistance and PET for clarity and barrier. The following table compares key performance metrics across these four types of packaging bags plastic
| Property | LDPE | HDPE | PP | PET |
|---|---|---|---|---|
| Tensile strength MPa | 10 to 16 | 20 to 30 | 30 to 40 | 50 to 75 |
| Maximum service temperature C | 80 | 90 | 120 | 150 |
| Minimum service temperature C | -50 | -50 | -20 | -60 |
| Clarity percent haze | 10 to 20 | 30 to 70 | 5 to 15 | 2 to 5 |
| Moisture barrier WVTR g/m²/day | 15 to 20 | 5 to 12 | 5 to 10 | 20 to 40 |
| Oxygen barrier OTR cm³/m²/day | 1800 to 2200 | 1500 to 2500 | 1500 to 2000 | 50 to 100 |
LDPE packaging bags plastic dominate the flexible packaging market with 48 percent share due to their balance of cost flexibility and impact resistance. HDPE packaging bags plastic represent 32 percent of the market and are the standard for retail grocery bags and trash can liners. PP packaging bags plastic at 12 percent market share are growing fastest due to demand for microwaveable and hot fill packaging. PET packaging bags plastic hold 8 percent market share primarily in premium food and medical packaging.
Retail packaging bags plastic for lightweight merchandise such as clothing or small electronics require 15 to 25 micron HDPE or 30 to 40 micron LDPE. At these thicknesses packaging bags plastic provide adequate strength while minimizing material cost. The burst strength for 20 micron HDPE packaging bags plastic is 25 to 35 pounds per square inch when tested by the Mullen method.
Grocery produce packaging bags plastic for fruits and vegetables use 10 to 15 micron LDPE to allow moisture venting. Ventilation holes of 2 to 3 millimeter diameter are added at a density of 5 to 10 holes per 100 square centimeters. Ventilated packaging bags plastic extend produce shelf life by preventing condensation while maintaining 70 to 80 percent relative humidity inside the bag.
Industrial packaging bags plastic for chemical powders and granules require 80 to 120 micron LDPE with UV stabilizers. The UV stabilizer package adds 0.02 to 0.05 USD per kilogram of resin but extends outdoor storage life from 6 months to 24 months. For packaging bags plastic storing product outdoors for more than 30 days UV stabilized material is essential to prevent embrittlement.
Medical grade packaging bags plastic for sterile devices require 50 to 75 micron LDPE or 40 to 60 micron PP with Tyvek or breathable membrane seals. Medical packaging bags plastic must pass microbial barrier testing per ASTM F1608 showing no microbial penetration after 24 hours of challenge. The cleanroom manufacturing environment for medical packaging bags plastic must maintain ISO Class 7 or better with particle counts below 352000 particles per cubic meter at 0.5 micron.
Heat seal closures for packaging bags plastic provide the lowest cost and highest reliability for single use applications. Heat seal strength for packaging bags plastic should exceed 18 newtons per 15 millimeter width to ensure bag integrity during filling and transport. Heat sealing parameters for LDPE packaging bags plastic are 140 to 160 degrees Celsius at 2 to 4 bar pressure for 0.3 to 0.8 seconds dwell time.
Zipper closures for recloseable packaging bags plastic add 0.03 to 0.06 USD per bag depending on zipper width and profile design. The zipper closure on packaging bags plastic must withstand 500 open close cycles without failure for consumer grade applications. Medical grade recloseable packaging bags plastic require 1000 cycle testing with no loss of seal integrity.
Block bottom packaging bags plastic feature a rectangular bottom created by folding and sealing the bag base. Block bottom packaging bags plastic stand upright on shelves without external support. The design requires 15 to 20 percent more material than flat bags of the same volume but reduces display fixture costs. Shenlong Packaging Products Co., Ltd. produces block bottom packaging bags plastic with bottom seal strength of 25 to 30 newtons per 15 millimeter width.
Handle reinforcement for retail packaging bags plastic adds a patch of thicker film or a laminated cardboard insert. Patch handle packaging bags plastic increase the maximum safe load from 5 kilograms to 10 kilograms. The reinforcement patch covers 40 by 80 millimeters around the handle hole and adds 0.01 to 0.02 USD per bag.
Surface printing on packaging bags plastic uses flexographic plates with line screens of 100 to 150 lines per inch. Surface printed packaging bags plastic have ink applied directly to the bag exterior where it can be scratched or rubbed off. For packaging bags plastic that will see abrasion during shipping surface printing requires an overprint varnish added at 0.001 to 0.002 USD per bag.
Reverse printing for packaging bags plastic places the ink between two layers of film. Reverse printed packaging bags plastic have the ink protected from abrasion by the outer film layer. The lamination process for reverse printed packaging bags plastic adds 0.005 to 0.010 USD per bag compared to surface printing. Reverse printing is recommended for packaging bags plastic that will be used in dusty environments or that require high durability graphics.
Digital printing on packaging bags plastic is available for short runs below 10000 units. Digital printing on packaging bags plastic has no plate costs and setup time of 24 to 48 hours. The cost per bag for digitally printed packaging bags plastic is 0.15 to 0.35 USD for runs of 1000 bags decreasing to 0.08 to 0.15 USD for runs of 10000 bags. For runs above 50000 units flexographic printing is more economical than digital.
All packaging bags plastic should be tested for tensile strength following ASTM D882. The test uses 15 millimeter wide strips pulled at 500 millimeters per minute. Minimum acceptable tensile strength for LDPE packaging bags plastic is 10 megapascals in the machine direction and 8 megapascals in the transverse direction. For HDPE packaging bags plastic minimum tensile strength is 20 megapascals machine direction and 18 megapascals transverse direction.
Seal strength testing for packaging bags plastic follows ASTM F88 using a 15 millimeter wide seal sample pulled at 300 millimeters per minute. The seal strength of packaging bags plastic should be reported as the average of 10 specimens with the lowest individual value not less than 70 percent of the average. Packaging bags plastic with seal strength below 12 newtons per 15 millimeter width are rejected for food or medical applications.
Impact resistance for packaging bags plastic is measured by the dart drop test per ASTM D1709. A dart with specified weight is dropped from 0.66 meters onto the film. The value reported is the weight at which 50 percent of tested packaging bags plastic samples fail. For 40 micron LDPE packaging bags plastic the dart drop impact is 80 to 120 grams. For the same thickness HDPE packaging bags plastic the value drops to 40 to 60 grams due to higher stiffness and lower elongation.
Tear resistance for packaging bags plastic follows ASTM D1922 using the Elmendorf pendulum. A pendulum swings through the sample tearing it over a fixed distance. For 40 micron LDPE packaging bags plastic tear resistance is 100 to 300 grams. For the same thickness HDPE packaging bags plastic tear resistance is 20 to 50 grams indicating that once torn HDPE bags propagate the tear easily.
Question 1 What is the difference between LDPE and HDPE packaging bags plastic
LDPE packaging bags plastic have lower density 0.910 to 0.925 g/cm³ resulting in more flexible film with higher impact resistance. HDPE packaging bags plastic have higher density 0.941 to 0.965 g/cm³ resulting in stiffer film with higher tensile strength but lower puncture resistance. For the same thickness LDPE packaging bags plastic stretch 200 to 600 percent before breaking while HDPE stretches only 10 to 120 percent. Choose LDPE for irregular shaped items and HDPE for flat uniform products.
Question 2 Can packaging bags plastic be recycled
LDPE and HDPE packaging bags plastic are recyclable through store drop off programs that accept plastic film. Clean dry packaging bags plastic with no food residue can be recycled into new bags or plastic lumber. Packaging bags plastic with heavy printing or adhesives may be rejected by recyclers. Check with local recycling facilities as 91 percent of curbside programs do not accept packaging bags plastic. Shenlong Packaging Products Co., Ltd. offers take back recycling for industrial quantities of used packaging bags plastic.
Question 3 How do I prevent static in packaging bags plastic during filling
Add antistatic agent to packaging bags plastic at 1 to 3 percent loading. Antistatic packaging bags plastic have surface resistivity of 10^9 to 10^11 ohms per square compared to 10^14 ohms for untreated film. For temporary antistatic protection spray packaging bags plastic with isopropyl alcohol based antistatic solution immediately before filling. For permanent protection order packaging bags plastic with internal antistatic additive mixed into the resin before extrusion.
Question 4 What causes packaging bags plastic to become brittle with age
UV exposure causes photo oxidation that breaks polymer chains in packaging bags plastic. After 500 hours of accelerated UV testing LDPE packaging bags plastic lose 40 percent of original elongation. Heat aging above 50 degrees Celsius also embrittles packaging bags plastic with each 10 degree increase above 40 degrees Celsius doubling the rate of property loss. Store packaging bags plastic in cool dark conditions below 30 degrees Celsius for maximum shelf life.
Question 5 What are the standard width tolerances for packaging bags plastic
Industry standard tolerance for width of packaging bags plastic is plus or minus 2 millimeters for widths under 300 millimeters and plus or minus 3 millimeters for widths between 300 and 600 millimeters. Thickness tolerance across the width of packaging bags plastic is plus or minus 5 percent for quality manufacturers. Shenlong Packaging Products Co., Ltd. holds width tolerance to plus or minus 1.5 millimeters and thickness tolerance to plus or minus 4 percent for all packaging bags plastic orders.
Slip additives reduce the coefficient of friction on packaging bags plastic allowing bags to open easily and move smoothly on filling lines. A slip additive concentration of 500 to 1500 parts per million reduces COF from 0.5 to 0.6 down to 0.2 to 0.3. Too much slip additive in packaging bags plastic above 2000 parts per million prevents seals from forming properly as the additive migrates to the seal surface.
Antiblock additives prevent packaging bags plastic from sticking to each other in the roll. Without antiblock agents packaging bags plastic require up to 30 percent more force to separate individual bags. Silica based antiblock additives at 1000 to 3000 parts per million create microscopic surface roughness that reduces bag to bag adhesion. For clear packaging bags plastic the antiblock particle size must be below 5 microns to remain invisible to the naked eye.
Processing aids for packaging bags plastic include fluoropolymer based additives that reduce melt fracture during extrusion. Melt fracture appears as surface roughness or shark skin on the bag surface. Processing aids at 300 to 600 parts per million eliminate melt fracture and increase extrusion output by 15 to 25 percent. For printing on packaging bags plastic processing aid levels must stay below 500 parts per million or ink adhesion decreases.
Color masterbatch for packaging bags plastic is added at 2 to 6 percent by weight to achieve solid colors. White packaging bags plastic require 4 to 8 percent titanium dioxide masterbatch to reach 90 percent opacity. Black packaging bags plastic need only 2 to 4 percent carbon black masterbatch which also provides UV protection. Color matching for packaging bags plastic should use spectrophotometer measurement with tolerance of plus or minus 0.5 Delta E for non critical colors and plus or minus 0.2 Delta E for brand colors.
Shenlong Packaging Products Co., Ltd. formulates additive packages for packaging bags plastic based on specific end use requirements. Standard additive packages include slip and antiblock for automatic filling lines UV stabilizer for outdoor storage and antistatic for electronics packaging. Custom additive packages for packaging bags plastic are developed with a lead time of 10 to 15 days for lab testing before production.
