Before proofing, it is necessary to clearly define the purpose: is it to "get the client's approval of the appearance", "test the packaging performance", or "verify the production feasibility"? The focus of different purposes is significantly different, and blindly conducting proofing will waste time.
01:Proofing instructions
• Appearance verification sample: The focus is on checking the patterns, colors, and text positions, such as whether the LOGO is centered, whether the gradient color is uniform, and whether the foil stamping/UV effect conforms to the design draft;
• Performance test sample: It is necessary to use the "real substrate" (such as PET/PE composite film, aluminum-plastic film) that has been finalized and mass-produced, rather than temporary substitute materials. Otherwise, the test results for barrier properties, temperature resistance, and load-bearing capacity will be invalid.
• Production verification sample: It is necessary to simulate the process parameters of batch production (such as printing speed, bonding pressure, and curing time), to prevent the sample from being qualified but problems such as inaccurate registration or wrinkling during batch production from occurring.
02:Material selection
• Clearly define the base material structure: For example, the commonly used "PET/AL/PE" (polyester/aluminum foil/polyethylene) for food bags, and "BOPP/CPP" (biaxially oriented polypropylene/flowable polypropylene) for daily chemical bags. During the proofing process, the material, thickness, and brand (if specified) of each layer must be consistent with the mass production.
Be vigilant against low-cost alternatives: Some factories, in an effort to cut costs, may use thinner substrates or niche brand films (for example, replacing 50μm PE with 30μm). Although the appearance is similar, during large-scale packaging, there may be leakage or bag rupture.
• Special substrate confirmation in advance: When it comes to functional substrates (high-temperature resistant cooking membranes, degradable membranes), it is necessary to confirm whether the factory has in-stock or needs to be customized to avoid sample production delays due to substrate shortages.
03:Color calibration: Data-based control to avoid visual errors
• Provide standard color charts: If the brand has specified colors, please provide the PANTONE color chart (such as PANTONE 186C). Avoid vague descriptions like "I want red".
• Control the observation environment: The color should be confirmed under a standard light box (D65 light source, simulating natural light), and it is necessary to avoid judging under incandescent lamps or sunlight to prevent incorrect judgments.
04:Quality testing
• Printing quality: Check if the text is interrupted (such as the character "口" lacking the stroke), whether the pattern registration is accurate (such as the edges of red and blue being misaligned), and if there are any ink spots/bubbles (which may be caused by the quality of the ink or the printing pressure issues);
• Compressive strength: Conduct a hand-tear test on the sample (not a finished product) to check for any layering.
• Sealing and cutting: The sealing should be smooth without any wrinkles.
05:Accuracy control
Dimension accuracy: Managed to the millimeter level, suitable for automated production
Size deviations may cause bag jams or missed installations in the automated production line, and therefore, strict control of accuracy is necessary.
• Provide detailed size diagrams: Clearly indicate key parameters such as the width, height, sealing width, and folded edge width of the bag, for example, "Three-sided sealed bag, width 100mm × height 150mm, sealing width 10mm", avoiding vague expressions like "about 10 centimeters wide".
06:Performance test:
• Barrier test: Food bags (such as milk powder, nuts, etc.) need to undergo tests for oxygen permeability and water vapor permeability (using professional equipment like the MOCON instrument) to ensure the extension of product shelf life;
• Temperature resistance test: For high-temperature sterilization products (such as cooked foods), the samples need to be tested in water at the corresponding temperature (e.g., 121°C for 30 minutes) to check for any deformation, delamination, or cracking of the seal.
• Sealing test: After inflating or filling with water, squeeze to check for any leaks - if the sealing of the liquid bag (such as laundry detergent, juice, etc.) is not up to standard, it will directly result in leakage.
07:File integration:
• Provide vector files: The design draft should be in vector formats such as AI, CDR (avoid JPG, PNG which may become blurry when enlarged), and indicate the bleed area (usually 3mm to prevent the cutting edge of the pattern from being cut off during the cutting process);
• Detailed process description: For special processes (such as foil stamping, embossing, window opening, label application), the position, size, and material (e.g., "The foil stamping area is 20mm x 30mm, located 5mm above the LOGO") must be specified to avoid ambiguity in verbal descriptions.
08:Sample retention and archiving: Establishing standard reference materials to ensure batch consistency
• Sample retention quantity: At least retain 1-2 qualified samples
• Mark key information: The sample bag should be labeled with the sample production date, order number, substrate structure, process requirements, and the person who confirmed it, etc., to facilitate subsequent verification.
• Batch first-piece verification: Before starting mass production, the factory is required to provide a first-piece sample for comparison with the retained sample (in terms of color, size, and process). Only after confirming that there are no errors can production commence, thus avoiding the generation of a large number of defective products.
Summary: The core of sample testing for soft packaging bags is to verify production risks through samples. Spending an extra 1-2 days to control the details is much more cost-effective than the cost loss from rework during mass production. It is recommended to choose factories with ISO certification and their own laboratories (where performance tests can be conducted). During communication, clearly define the data requirements (such as color difference ΔE, composite strength, size tolerance), rather than relying on "it looks similar" - professional factories will understand and meet these requirements, while unprofessional factories may simply give a cursory response.