Key Process Points For Ultrasonic Atomization Of Natural Latex

I. Key Points for Latex Stock Solution Preparation

Solid Content Control: The solid content of virgin natural latex is approximately 35%–40%, which must be diluted. Diluting to 10%–18% solid content is recommended. Too concentrated, and it will cause stringing, clogging of the transducer, and large droplets; too diluted, and the film will be too thin and prone to sagging.

Viscosity Control: The optimal viscosity for ultrasonic atomization is 60–150 mPa·s.

Use only deionized water for dilution; do not add organic solvents. If the viscosity is too high, add water slowly while stirring, and measure the viscosity continuously.

Stability and Anti-agglomeration: Natural latex is prone to demulsification and clumping; it needs to be maintained at a slightly alkaline state:
Add a small amount of dilute ammonia to control the pH at 8.0–9.0;
Vacuum filter through a 100–200 mesh screen to remove gel particles and impurities to prevent clogging of the atomization surface.

Excessive stirring is prohibited.
Stir at low speed to avoid introducing a large number of air bubbles, which will cause pinholes and pitting on the coating needle surface after atomization.

 

II. Key Points of Ultrasonic Equipment Parameters and Processes
**Working Frequency Selection:**
For micron-sized particles (1-5μm): Select 60-80kHz.
For conventional coating (3-10μm): 40kHz (general purpose).
Higher frequencies produce finer droplets, making them more suitable for ultra-thin and uniform coating of acupuncture needles.

Power Matching:
Power should not be at full throttle; medium to low power is sufficient for stable resonance.
Excessive power: Latex will be vibrated and splashed, producing large droplets; Insufficient power: Atomization will be intermittent and uneven.

Atomization Liquid Level Height:
Strictly control the immersion depth of the transducer/atomizing plate in the liquid; it should not be too deep or suspended.
Deviating from the optimal liquid level will immediately cause atomization interruption and large particle splashing, which is the most common cause of unstable atomization.

Liquid Supply Method: Prioritize a micro-peristaltic pump for uniform liquid supply to maintain a constant liquid level. Avoid manually filling the liquid level completely at once, as fluctuations in the liquid level directly lead to inconsistent droplet size and uneven coating thickness.

III. Atomization Environment and Airflow Process:
Carrier Gas Atmosphere: Use clean, dry, dust-free air/nitrogen with low-velocity laminar flow.
Excessive air velocity: Droplets are blown away, resulting in a thin coating; Insufficient air velocity: Droplets diffuse and settle, leading to excessive material accumulation on the needle body.

Ambient Temperature and Humidity:
Ambient temperature 20–28℃, humidity 50%–65%.
Too low humidity: Droplets dry prematurely and condense into powder; Too high humidity: Latex dries slowly, causing stickiness and dripping on the needle surface.

Dust-Free Environment: A Class 10,000/Class 100,000 cleanroom is required. Dust settling on the wet film will directly render the acupuncture needle coating unusable.

 

IV. Key Points for Pre-treatment of Workpieces (Acupuncture Needles)
**Thorough Degreasing and Oil Removal:** Ultrasonic cleaning with alcohol → drying. The surface must be free of oil stains; otherwise, the coating adhesion will be poor, leading to peeling and flaking.

Surface Activation: For precision coatings, plasma surface activation is recommended to improve the adhesion between the latex film and the needle, resulting in a denser, non-flaking film.

Placement Method: Needles should be arranged vertically/evenly, with low-speed rotation to ensure consistent circumferential coating thickness, eliminating dead angles and thickness variations.

 

V. Key Points for Atomized Coating & Curing:
**Atomization Spray Distance:** The distance from the atomizing head to the acupuncture needle should be fixed. Too far, and droplets will scatter, resulting in a thin film; too close, large particles will drip directly, causing lumps.

Deposition Time: Control the atomization deposition time according to the target film thickness. Micron-level thin films are suitable for short, intermittent atomization sessions, which are more uniform than a single, long spray.

Drying and Curing

Segmented Low-Temperature Drying After Atomized Coating:
First, pre-dry at 40-50℃ for surface drying, then fully cure at 60-75℃;

High-temperature rapid drying is strictly prohibited, as it easily causes film cracking, shrinkage, and wrinkling.

 

VI. Common Faults and Process Avoidance

Large droplets, with splashing: Viscosity too high, frequency too low, liquid level too deep, power too high

Uneven coating, thicker on one side than the other: Turbulent airflow, needle not rotating, unstable liquid supply

Peeling or flaking of the coating: Needle not degreased, no surface activation, latex ratio imbalance

Intermittent misting: Gel impurities in the raw solution, filter blockage, liquid level fluctuation