High Adhesion TIJ Coding on PE and PP Bottles for Personal Care Manufacturers

High-adhesion TIJ coding on PE and PP bottles means using thermal inkjet (TIJ) printheads to print batch numbers and date information directly onto polyethylene (PE) and polypropylene (PP) bottles. The goal is a code that stays legible for as long as the consumer uses the product. PE and PP are commonly used for shampoo, body wash, lotion and hand soap bottles.

Among the specialty applications covered in the Complete TIJ Printing Applications for Manufacturing, Logistics, E-Commerce and Specialty Industries, PE and PP bottles have some of the stricter adhesion requirements. When personal care brands adopt TIJ, the problem is rarely whether the code prints. The problem is whether it is still legible after long exposure to moisture, cleaning agents and repeated rubbing.

Why Do Codes Rub Off PE and PP Bottles?

PE and PP have low surface energy, which makes them common hard-to-adhere plastic substrates. Surface energy describes how readily a material surface lets a liquid wet and spread across it. When a substrate's surface energy is low, poor wetting can limit ink spreading and interfacial contact with the substrate, and the dried ink is easier to peel off. How well the ink actually wets the surface also depends on the ink's surface tension and on the condition of the bottle surface.

Personal care bottles are difficult for two reasons:

• The material itself: PE and PP are polyolefins. Their molecular structure lacks polar groups, so an untreated surface does not hold ink well.
• How the product is used: shampoo and body wash bottles are repeatedly exposed to water and surfactants and rubbed by wet hands. Codes therefore face a higher risk of wearing off than on most packaging. Product that spills onto the outside of the bottle during filling may also weaken the ink layer.

The bottle-making process can also make results vary. Two potential factors are:

• Additive migration: some bottle resins contain slip or antistatic additives. These can migrate from inside the material to the surface during storage. The same bottle may therefore show different adhesion straight from the molder and after a few weeks in the warehouse.
• Mold release residue: if an external mold release agent is used during blow molding, residue may remain on the bottle surface and interfere with ink adhesion.

Coding Content and Labeling Rules for Personal Care Bottles

In Taiwan, general cleansing products such as shampoo and body wash are regulated as cosmetics. Under Article 7 of the Cosmetic Hygiene and Safety Act, the outer packaging or container of a cosmetic must show a batch number and one of three date combinations:

• Manufacturing date and period of validity
• Manufacturing date and shelf life
• Period of validity and shelf life

The format and method of labeling follow the labeling regulations for cosmetic outer packaging, containers, labels and leaflets (in Chinese) issued by Taiwan's Ministry of Health and Welfare, in force since July 1, 2021. Two points relate directly to coding:

• Marking method: date information must be applied to the outer packaging, container or label by embossing, or by printing or coding with non-fading ink.
• Small packages: when the largest surface of the outer packaging or container is smaller than 40 cm², the required information may go on a label, leaflet, card, tag or instruction sheet. The outer packaging, label or container must still keep the product name, intended use, manufacturer or importer name and date information, so not everything can be omitted.

Actual labeling still depends on each product's packaging, and later amendments follow the most recent announcements from Taiwan FDA.

For products exported to the EU, Article 19 of the EU Cosmetics Regulation (EC) No 1223/2009 sets date and batch requirements that differ from Taiwan's:

• Dates: products with a minimum durability of 30 months or less must show the date of minimum durability. For products above 30 months, that date is not mandatory. They generally show a Period After Opening (PAO) instead, except where the concept of durability after opening is not relevant.
• Batch number: the batch number of manufacture, or a reference that identifies the product, must be shown. Where this is impossible for practical reasons because the product is too small, it need only appear on the outer packaging.

Requirements for content, position and exceptions differ between markets. The brand's regulatory owner should confirm what goes on the bottle for each market during packaging design.

Many shampoo and body wash bottles have no outer carton, so the bottle is the main labeling surface. Once a code rubs off during use, consumers and retailers can no longer identify the batch on their own, and traceability relies more heavily on the brand's internal production records. This is why bottle adhesion should be judged over the product's period of use.

Matching Surface Treatment With TIJ Ink

Adhesion on PE and PP bottles depends on both the bottle surface and the ink formulation, so the two need to be evaluated together. Adjusting only one of them may not solve an adhesion problem.

Corona, Flame and Plasma Treatment

Corona treatment is a pretreatment that raises the surface energy of plastics to improve adhesion. It is most common on films. Three-dimensional containers such as bottles and jars are often treated with flame or plasma instead. The effect depends on the material and the treatment energy, and may decline during storage at a rate that varies with the material and storage conditions.

The level of treatment can be checked by measuring wetting tension. ASTM D2578 is a test method for the wetting tension of PE and PP films. Because it was written for films, it can only serve as a reference for its principle on curved bottle surfaces, not as a claim that measurement was done to the standard. The standard itself also notes that wetting tension is not a complete measure of ink adhesion, so actual print testing is still needed.

Choosing TIJ Ink

PE and PP are low-surface-energy, non-porous substrates, so the ink needs to suit their surface characteristics. Solvent-based TIJ ink is a common choice, but actual adhesion still depends on the formulation, bottle resin, surface treatment and contamination. Even with the same HDPE or PP grade, different production lots should be evaluated for potential variations in adhesion and rub resistance. Suitability cannot be judged from the material name alone.

When evaluating ink, check four points against real conditions:

• Adhesion to the bottle resin: HDPE, LDPE and PP have different surface properties, so test on actual bottles.
• Drying speed: bottles soon reach guide rails, labelers or case packing after coding, so the code must dry before the next contact point.
• Decap time: personal care lines often stop for changeovers. Whether the printhead recovers smoothly after sitting idle affects the first few bottles after restart.
• Resistance to product contents: wipe tests with your own product, neat and diluted, are closer to real use than generic solvents.

For the positioning and suitable substrates of each Uniplus cartridge type, see the Uniplus TIJ industrial ink cartridge page.

TIJ Adhesion Testing on PE and PP Bottles

Before adopting TIJ coding on PE or PP bottles, always run adhesion tests on actual production bottles. The purpose is to confirm how durable the code is under real use conditions, not just how it looks right after printing.

Five Test Areas

A single tape peel or solvent wipe cannot represent bathroom humidity, surfactant contact, repeated squeezing and long-term storage. A complete test program should cover five areas:

• Initial adhesion: let the code dry completely, then check for ink removal with a tape peel.
• Rub and solvent resistance: test dry rubbing and solvent wiping under separately agreed conditions, then check whether the code remains legible.
• Wet durability: simulate a shower environment by rubbing repeatedly with wet hands or a damp cloth. Rub count, pressure, contact time and pass criteria must be agreed in advance; otherwise the result is only a quick screen.
• Product contact: wipe with your own product, neat and diluted, or leave the code in contact with the product for a period before checking.
• Squeeze and storage aging: squeeze bottles repeatedly and check for cracking in the ink layer; retest after a period of storage.

Reference Methods for Testing

Tape peel testing can follow the principle of ASTM D3359. That standard mainly covers coatings on metal substrates, so it cannot be treated as a complete validation standard for codes on plastic bottles. Wet rub, product contact, squeeze and aging tests should be defined separately to match the customer's actual use conditions.

Quick Screening vs. Formal Validation

A quick screen is not validation. Results change with the tape type, solvent, rubbing force and environment. If a customer requires formal data, the test method and pass criteria should be agreed in writing beforehand. For example, the agreement might specify how many rubs the code must survive while staying legible and keeping its barcode readable. Passing a single tape test does not support a claim that the code will last for the product's entire period of use.

Testing With Production Bottles and Real Product

Test on production bottles. If the bottle has been corona treated or coated, results will differ noticeably. Sample bottles can be used for initial screening but cannot replace formal validation on production bottles. Use your own product as the wiping liquid wherever possible. Shampoo and lotion contain different proportions of surfactants and oils, and they affect the ink layer differently.

Record the tape type, wiping solvent, rub count and force, drying time, ambient temperature and humidity, and bottle lot number for every test. Without these, the next comparison means little.

Because surface treatment effects can change during storage, Uniplus recommends testing bottles at different points after they arrive, for example on delivery and again after several weeks in storage. This checks whether adhesion drops noticeably under the chosen storage conditions.

TIJ Printhead Setup on Bottle Lines

Coding stability on bottles is closely tied to where the printhead sits on the line.

Coding Before or After Filling

Two approaches are used for coding timing:

• Coding empty bottles before filling: the bottle surface is clean and free of product. Empty bottles are light and tend to wobble or tip over on the conveyor, so guiding and holding mechanisms are needed.
• Coding after filling and capping: filled bottles are stable and convey more smoothly. Before coding, confirm the print area is dry and free of product; clean or dry it if needed.

Curved Bottles and Throw Distance

Throw distance, the distance from the nozzles to the substrate surface, is generally short for TIJ. The allowable distance depends on the printhead, ink, resolution and speed. The more curved the surface, the greater the difference in distance between the top and bottom of the code, and edge characters tend to thicken or blur. Bottle wobble and printhead angle also affect the result. On round and oval bottles, place the code on a flatter area or reduce the code height.

Batch and date information usually takes two to three lines of text. A half-inch cartridge with a nominal print height of 12.7 mm is usually enough, but confirm the effective height for each model. When more lines are needed in the same position, consider a one-inch cartridge or a multi-printhead setup, and confirm the controller's capability and font layout at the same time.

For products sold in Taiwan, the printed batch and date information must also comply with applicable cosmetic labeling requirements, including minimum character dimensions. When selecting a half-inch or one-inch TIJ cartridge, verify not only the available print height and number of lines, but also the final character size and legibility required by the target market.

Drying Time and Downstream Contact Points

Any contact before the code is fully dry can cause smearing. For a rough estimate, divide the distance from the printhead to the next contact point (guide rail, labeler, shrink sleeve, case packer) by the line speed. The result is the drying time available under ideal conditions. This estimate does not account for acceleration, bottle rotation or safety margin, so whether the ink dries in time at real line speed must still be checked on site.

Changeover Stops and Decap Time

Personal care brands run many SKUs, so changeover stops are routine. Decap time is the length of time nozzles can be exposed to air after printing stops and still recover normal ink ejection. It varies with the environment and stop conditions. After a longer stop, follow the recovery procedure for the specific ink and equipment, such as cleaning or spitting, before resuming production. This helps reduce the risk of missing dots or broken characters on the first few bottles.

TIJ Coding Differences Between PET and PE/PP Bottles

Personal care packaging is not limited to PE and PP. Some clear shampoo and toner bottles use PET, and each material has different coding considerations:

Adhesion and fast-drying properties on PET bottles are covered separately in PET Bottle TIJ Coding: Adhesion and Fast-Drying Properties. If your brand also uses glass, acrylic or metal tube packaging, coding conditions differ again; see TIJ Coding on Glass, Acrylic and Metal Tube Packaging for Cosmetic Brands.

Evaluation Checklist Before Bottle Coding

Confirming the following items before adoption helps avoid discovering missing or smeared codes after production starts:

Beyond bottle codes, barcodes on shipping cartons follow GS1 size and quality rules; see High-Speed TIJ Barcode Coding on Logistics Carton Lines. Substrates and evaluation points for other industries are covered in the complete TIJ printing applications guide.

Uniplus TIJ Cartridges for PE and PP Bottles

Uniplus has manufactured thermal inkjet cartridges since 2002. Its industrial cartridges cover three ink types, solvent-based, water-based dye and water-based pigment, in half-inch (12.7 mm) and one-inch (25.4 mm) formats. For HDPE, LDPE and PP personal care bottles, solvent-based TIJ inks designed for non-porous substrates are the first option to evaluate. Actual adhesion, drying speed and resistance to product contents must still be confirmed by testing with the specific ink model, production bottle surface and use conditions. For compatible printers and specifications of each model, see the TIJ industrial ink cartridge page.

Uniplus provides compatibility verification services. If your equipment uses encrypted chips, share the printer model during discussions and we will help evaluate feasible options.

When evaluating bottle coding needs, we ask customers for four inputs: production bottle samples, print content, line speed and operating environment. With these, adhesion and drying tests can be arranged under conditions close to actual production. Contact Uniplus to discuss your bottle coding conditions.