HOW TO CONTROL THE MATERIAL PROPERTIES DURING THE PRODUCTION PROCESS OF SELF-ADH

  

I. Key Points and Methods for Controlling Core Material Properties

Self-adhesive labels are composed of face materials, adhesives, and backing papers. Their key properties (such as shrinkage rate, adhesion, and peel force) need to be controlled respectively, which is the foundation for stable production.

1. Control of Face Material Properties: Focus on "Shrinkage Deformation" and "Printing Adaptability"

The shrinkage rate, surface flatness, and temperature resistance of face materials (such as paper, PET, PE) are key factors affecting label dimensions and printing effects. Control should be implemented from both the source and during production.

Control of Shrinkage Rate (especially for film-type face materials)

Source selection: Prioritize the purchase of face materials that have undergone "pre-shrinkage treatment" (such as pre-shrunk PET, stable PE). These materials have had internal stresses eliminated through heating and stretching processes before leaving the factory, and their shrinkage rate can be controlled to ≤0.5% (unprocessed face materials may have a shrinkage rate of 1%-2%).

Production pretreatment: If using non-pre-shrunk face materials, they should be left to acclimatize in the workshop for 24 hours ("moisture and temperature adjustment") before production to adapt to the workshop's temperature and humidity (suggested 20-25℃, humidity 50%-60%), reducing subsequent shrinkage due to environmental changes.

Process control: Use a "constant tension control system" during printing and die-cutting to prevent excessive tension from stretching the face material (for film-type face materials, tension should be controlled at 5-10N, and for paper face materials, at 3-8N). Tension fluctuations should be ≤±1N.

Ensuring surface adaptability (printing / adhesion)

Surface cleanliness: Before production, use compressed air to blow off the surface of the face material to remove dust and oil (especially for film-type face materials, as oil can affect ink adhesion and adhesive stickiness). If necessary, wipe with alcohol and dry.

Surface tension (for film-type face materials): The surface tension of PET, PE, etc. is low and needs to be increased to ≥38dyne through "corona treatment" to ensure that ink or adhesive can adhere firmly. After treatment, use a surface tension pen for spot checks, testing every 100 meters to avoid uneven treatment.

2. Control of Adhesive Properties: Focus on "Unstable Adhesion" and "Scene Adaptability"

The adhesion (initial adhesion, holding adhesion), temperature resistance, and water resistance of adhesives directly affect the label's adhesion effect. Selection and control of their stability should be based on the usage scenario.

Ensure adhesion matches the scenario

Source selection: Choose the appropriate adhesive based on the carrier (such as plastic, glass, paper) and environment (such as normal temperature, freezing, humid) - select "low-temperature adhesive" for freezing scenarios (-20℃ still maintains adhesion), "waterproof adhesive" for humid scenarios, and "removable adhesive" for temporary labeling. Suppliers should provide adhesion test reports (such as initial adhesion ≥10N/25mm, holding adhesion ≥24h/1kg).

Process spot checks: During production, randomly select 10 labels from each batch and test the initial adhesion according to GB/T 4852 standard (using the rolling ball method) and the holding adhesion according to GB/T 4851 standard (hanging a 1kg weight and observing the detachment time). If the adhesion does not meet the standards, immediately stop using the batch of adhesive.

Control the uniformity of adhesive application

Equipment calibration: Before application, check the gap of the adhesive roller (error should be ≤±0.01mm) to ensure uniform adhesive thickness (typically dry adhesive thickness 5-15μm), avoiding local over-thickness (causing label wrinkling) or under-thickness (resulting in insufficient adhesion). Process Observation: During production, visually inspect the coated surface material. If "stripes, bubbles, or missed coating" are found, immediately stop the machine to clean the coating roller (possibly clogged with impurities) and adjust the coating speed (too fast a speed can lead to uneven coating, it is recommended to control it at 30-50m/min).

  

3. Control of Backing Paper Characteristics: Focus on solving "unstable peel force" and "flatness"

The peel force and flatness of backing paper (such as glassine paper, PET release paper) can affect label peeling and die-cutting accuracy. It is necessary to avoid production delays caused by backing paper issues.

Control Peel Force (Peeling Smoothness)

Source Selection: Choose the peel force based on the labeling method - "medium peel force" (5-10g/25mm) for automatic labeling (for easy machine peeling), and "low peel force" (3-5g/25mm) for manual labeling (for easy hand tearing), and require the supplier to provide a peel force test report.

Process Testing: During production, take 1 section of backing paper every 500 meters and test the peel force with a tensiometer. If the peel force fluctuates by more than ±2g/25mm (e.g., suddenly drops from 8g to 5g), check if there is batch mixing of the backing paper to avoid "label adhesion" or "backing paper breakage" during subsequent labeling.

Ensure Backing Paper Flatness

Source Inspection: When receiving backing paper, visually inspect for "wrinkles, creases, or curled edges". If such problems exist, immediately return it to the supplier (uneven backing paper can cause inaccurate positioning during die-cutting and label size deviations).

Production Support: During die-cutting, use a "backing paper support roller" (with a smooth surface and high hardness) to support the backing paper to prevent it from sagging due to its own weight and stretching. At the same time, control the die-cutting pressure (adjust according to the backing paper thickness, for example, for 80g glassine paper, the pressure should be controlled at 0.3-0.5MPa) to prevent the backing paper from being punctured.

II. Common Control Measures for the Entire Production Process

In addition to controlling the characteristics of individual materials, it is also necessary to manage the entire process to reduce material characteristic fluctuations and ensure stable production.

Establish Material Inbound Inspection Standards (IQC): After all materials (surface material, adhesive, backing paper) arrive, conduct inspections at a sampling ratio of ≥3‰, fill out the "Material Inbound Inspection Report", and prohibit the entry of unqualified materials. Inspection items include:

Surface Material: Thickness (using a thickness gauge, error ≤±5%), elongation (simulated production temperature and humidity test), surface tension (for film types).

Adhesive: Adhesion (initial adhesion, holding adhesion), coating uniformity (visual + thickness gauge).

Backing Paper: Peel force (tensiometer), flatness (visual + ruler), thickness (error ≤±5%).

Stable Production Environment Temperature and Humidity: Install a constant temperature and humidity system in the workshop, control the temperature at 20-25℃ (fluctuation ≤±2℃), and the humidity at 50%-60% (fluctuation ≤±5%) to avoid significant changes in temperature and humidity causing material characteristic fluctuations - for example, high temperature can reduce the adhesion of adhesives, and high humidity can cause paper-based surface materials to absorb water and deform. Record the temperature and humidity data daily, and if they exceed the range, immediately adjust and suspend production.

Batch Management and Traceability: Number each batch of materials and record "material type - supplier - inbound time - usage batch". If quality issues occur during production (such as label elongation, insufficient adhesion), quickly trace back to the corresponding material batch, analyze the cause (such as whether it is due to batch differences in materials), and promptly replace with qualified materials.

Regular Calibration of Production and Testing Equipment: Calibrate equipment related to material characteristics monthly:

Tension Control System: Calibrate with a standard tensiometer to ensure the display value has an error of ≤±5% from the actual value.

Coating Roller Gap: Calibrate with a feeler gauge, with an error of ≤±0.01mm. Calibration tools (digital calipers, tensiometer, surface tension pen): Send to a third-party institution for calibration to ensure the accuracy of the test data (calibration cycle ≤ 1 year).

III. Emergency Handling of Common Material Property Issues

If abnormal material properties are found during production, the cause must be quickly identified and addressed to prevent batch nonconformities:

Sudden expansion of the surface material: Immediately stop the machine, check if the temperature and humidity in the workshop exceed the standard. If normal, trace whether the batch of surface material has been changed (the new batch may not have been pre-shrunk). Replace with pre-shrunk surface material or let it stand for 24 hours before use.

Insufficient adhesive viscosity: Check if the thickness of the applied adhesive is too thin. If normal, test if the adhesive has expired (adhesive shelf life is usually 6-12 months). Replace with unexpired adhesive and retest the viscosity.

Unstable release force of the backing paper: Check if there is batch mixing. If so, isolate the nonconforming batches and replace with the same batch of backing paper. At the same time, increase the frequency of release force spot checks (once every 200 meters).

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