How to do screen printing on PE and PP?

Screen printing on PE and PP., The process isn't simply about transferring paint to a plastic surface. Due to the low surface energy of polyethylene and polypropylene surfaces, the production additives used, and mold release residues, the paint may not adequately wet the surface. As a result, even if the print looks smooth initially, it may peel off during tape testing, rub off, or crack when the product is bent.

For successful production, the correct type of plastic must be determined, the surface cleaned, and, if necessary, activated with corona, plasma, controlled flame, or a suitable primer. Then, only screen printing inks whose compatibility with PE or PP is clearly stated in the technical documentation should be used; the mesh, emulsion, squeegee, machine, and drying conditions should be adjusted according to this ink system.

Those who want to first examine the general principles of screen printing, including the mold, paint, and squeegee, From the guide on how to do screen printing can begin. Other material groups that can be printed on are: Guide to products that can be screen printed They are being compared.

Short answer: Screen printing is possible on PE and PP; however, direct application of ordinary plastic paint will not yield reliable results. First, the type of plastic and surface energy must be determined, surface treatment applied if necessary, and then a sample print should be made with paint whose compatibility with PE or PP has been verified by the manufacturer.

Contents

1. The difference between PE and PP
2. Why doesn't the paint adhere?
3. Pre-press surface inspection
4. Corona, plasma, flame and primer
5. Paint selection for PE and PP.
6. Mold, mesh and emulsion selection
7. Machine, fixture and squeegee adjustment.
8. Step-by-step printing process
9. Drying and curing
10. Adhesion and durability tests
11. Errors and solutions table
12. Transition to mass production control
13. Supply of materials and equipment
14. Frequently Asked Questions

How does the difference between PE and PP affect printing?

PE is an abbreviation for polyethylene, and PP is an abbreviation for polypropylene. Although both belong to the polyolefin group, they are not the same plastic. Density, flexibility, crystalline structure, thermal behavior, additive package, and surface characteristics can vary depending on the product formulation. Therefore, a paint and surface treatment that works on one PP container may not yield the same result on another PP sheet. The same applies to HDPE, LDPE, and other types of polyethylene.

PE can be used in bottles, canisters, caps, flexible packaging, bags, sheets, and various industrial parts. PP, on the other hand, is frequently seen in food containers, storage products, injection molded parts, buckets, lids, automotive parts, folders, and promotional products. Simply defining a product as "plastic" is not sufficient for paint selection.

The trade name of the plastic, its production method, surface treatment history, and additives should be obtained from the supplier. If a material technical data sheet is not available, at least different batches should be tested separately. It should not be assumed that parameters that worked in a previous batch will be used unchanged in the new batch.

Short answer: PE and PP belong to the same polyolefin family; however, they are not interchangeable in terms of printing. The plastic formula, additives, product geometry, and previously applied surface treatments can alter paint adhesion. A suitability test must be performed for each new product or raw material batch.

Briefly

• PE and PP are different types of plastic.
• Simply describing the product as "plastic" is not enough.
• Additives and mold release agents can alter paint adhesion.
• Each new combination of materials and paints should be tested on a sample.

Why doesn't screen printing ink adhere to PE and PP?

For a screen printing ink to adhere to a surface, it must first spread evenly over the plastic. On plastics with low surface energy, such as PE and PP, the ink may collect in droplet form, retract, or fail to fully wet the surface. In this case, sufficient contact between the ink and the plastic does not occur.

The purpose of surface treatment is to improve the wettability of the plastic and its interaction with paint, coating, or adhesive. Enercon's corona treatment technical description states that for effective wetting, the plastic's surface energy must be higher than the surface tension of the applied liquid; a safety margin is generally beneficial as a practical approach. The actual target value should be determined according to the technical documentation of the paint to be used. Corona treatment and surface energy technical document. This explains the basis of the relationship. 

Other important factors that can reduce paint adhesion include:

• Presence of oil, dust, fingerprints, or mold release agents on the surface.
• Migration of lubricant additives within the plastic to the surface over time.
• Inadequate or irregular application of surface treatment.
• An excessively long time elapsed between surface treatment and printing.
• Using PP instead of PE, or using paint formulated for a different plastic instead of PP.
• Incorrect paint-hardener ratio preparation.
• Adding unsuitable thinner or retarder
• Incomplete drying or failure to complete chemical curing.
• The product should not be bent, impacted, or exposed to chemicals after the paint has dried.

Polyolefin surfaces can be activated by processes such as corona or flame treatment, but the resulting effect may diminish over time. Plastic Coatings Network corona technical note This is explained as well. Therefore, the information that "the product has been exposed to corona at the factory" is not sufficient on its own; the existing surface condition must be re-measured before printing. 

Short answer: The primary reason for paint peeling on PE and PP is often low surface energy. However, the problem isn't solely due to the type of plastic. Mold release agents, lubricant additives, incorrect thinner, insufficient curing, and excessive waiting time after surface treatment can also impair print adhesion.

Briefly

• The paint must first wet the surface, then bond with the plastic.
• Plastic that looks clean isn't necessarily ready for printing.
• The effectiveness of the surface treatment may diminish over time.
• Paint and surface treatment should be evaluated together.

How to inspect PE and PP surfaces before printing?

Selecting paint without performing a surface inspection before mass production increases the risk of waste. The first inspection involves determining the type of plastic and the product manufacturing method. Whether the product is manufactured by injection molding, extrusion, or blow molding can affect mold marks, additives, and geometric tolerances on the surface.

1. Verify the type of plastic.

Information regarding raw material type, material grade, additives used, and surface treatment (if any) should be requested from the product supplier. Recycled content, colorant masterbatch, or surface additives can alter print behavior. General plastic markings on packaging may be helpful; however, technical data sheets and print tests are more reliable for final dye selection.

2. Perform a visual surface inspection.

The surface should be examined for glossy and oily areas, mold release marks, scratches, high static electricity, dust, or hand contact marks. The printing area should not be touched with bare hands. Samples should be handled with clean gloves, and the printing surface should be stored in a protected manner.

3. Try cleaning with a compatible cleaner.

Not every solvent is suitable for every plastic. Aggressive cleaners can dull, crack, cause stress cracking, or alter the product's color. The cleaner to be used should first be tested on a small, inconspicuous area; the paint and plastic manufacturer's recommendations should be followed.

4. Evaluate surface energy.

Dyne pens or suitable test fluids can provide a quick preliminary check on the production site. However, the dyne test is not a substitute for the final adhesion test. The age of the test fluid, application method, temperature, humidity, surface contamination, and operator interpretation can all affect the result. The measurement method should be recorded and documented in the production records.

5. Create a sample printing plan.

On the same product, uncleaned, cleaned, surface-treated, and, if necessary, primed areas can be compared. This allows us to see which process truly contributes to the result. Not only should the print look aesthetically pleasing be tested, but also post-drying adhesion, friction, bending, and operating conditions.

Short answer: Pre-press quality control should consist of plastic type verification, surface contamination examination, compatibility cleaner testing, surface energy control, and sample printing. A single dyne measurement or visual inspection is not sufficient for mass production approval.

Briefly

• Verify the plastic grade with the supplier.
• Do not touch the printing area with your bare hands.
• Test the cleaner on a small area.
• Support the Dyne measurement with an adhesion test.

Corona, Plasma, Flame, and Primer Applications for PE and PP.

Although the methods used to prepare PE and PP surfaces for printing serve the same principle, their application methods differ. The correct method should be selected according to whether the product is flat or round, the production quantity, the surface area, heat sensitivity, the desired print durability, and the ink manufacturer's specifications.

Corona procedure

The corona system alters the chemical properties of the plastic surface and increases wettability using high-voltage electrical discharge. The success of the process doesn't depend solely on the device being switched on. Parameters such as line speed, power density, electrode structure, material thickness, and the side of the surface facing the electrode all influence the outcome.

Plasma treatment

Atmospheric plasma can be used, especially in localized printing areas or on shaped parts. It may be possible to process only the area to be printed, rather than the entire surface. However, if the nozzle distance to the part and its movement speed are not standardized, some parts of the printing area may receive sufficient activation while others remain insufficient.

Flame surface treatment

Flame application should not be considered as random heating with a household blowtorch. It requires a controlled oxidizing flame, a suitable air-gas mixture, a constant distance, processing speed, and a safety system. Excessive application can cause melting, gloss changes, or deformation of the surface; insufficient application can lead to uneven paint adhesion.

Primer application

Some paint systems recommend a special wiping primer or adhesion enhancer for PP. It is safer to evaluate the primer within the same manufacturer's system as the paint. Uncontrolled mixing of primers, paints, hardeners, and thinners from different brands can lead to unpredictable chemical reactions and loss of adhesion.

The important point is this: surface treatment does not replace paint selection. If a paint incompatible with PP is printed on a corona-treated PP surface, reliable results cannot be obtained. Similarly, even if the correct paint is used, the print may fail if mold release agents are present on the surface.

Short answer: The most suitable surface treatment for PE and PP varies depending on the product geometry and paint system. Corona treatment is suitable for films and sheets; plasma treatment for localized areas; controlled flame treatment for appropriately molded parts; and primers where recommended by the paint manufacturer. The treatment result must be measured and verified by printing.

Briefly

• Coronavirus, plasma, flame, and primary are not the same thing.
• Flame treatment should only be performed using a controlled, professional system.
• The time between surface treatment and printing should be kept under control as much as possible.
• Surface treatment does not eliminate the need to choose the right paint.

What type of ink is used for screen printing on PE and PP?

When selecting paint for PE and PP, it is not sufficient for the product name to simply state "plastic paint". The applicable surfaces must be clearly checked in the technical data sheet. It should be determined whether the document uses the terms "pre-treated PE", "pre-treated PP", "untreated PP" or "polyolefin".

For example, the Spinks 700ST technical data sheet states that the paint system can be used on pre-treated PE and PP, but due to different plastic formulations, suitability testing under real-world conditions is required before production. The same document also explains that antistatic, mold release, and lubricant additives can negatively affect adhesion. Sample technical data sheet for PE and PP compatible paints., This shows why reading technical documentation is necessary when selecting a product. 

The Pröll product documentation shows that, in addition to systems designed for pre-treated PE and PP, there are separate dye series developed for use on untreated PP. This demonstrates that both extreme approaches—"PP must always be treated" or "all PP products can be printed directly if a special dye exists"—are flawed. The dye, plastic formula, and usage conditions must be verified together. Proll screen printing paint selection document based on surface type. It compares different systems. 

Single-component paints

Single-component systems can offer ease of application. When preparing the paint for use, no additives other than the thinner or retarder recommended by the manufacturer should be added. Being a single-component system does not mean it will adhere directly to every PE or PP surface.

Two-component paints

In two-component paints, the hardener ratio, mixing order, holding time, and pot life are critically important. Adding too much or too little hardener can impair curing instead of increasing strength. The mixed paint should not be revived by adding solvent after the usage time specified in the technical data sheet has expired.

UV-cured paints

UV paint only cures correctly when the appropriate wavelength, energy dose, and surface compatibility are achieved. The paint appearing dry on the surface does not guarantee that the substrate is fully cured. The surface treatment and energy requirements for UV systems intended for use on PE and PP must be clearly checked in the technical documentation.

Can PVC paint be used on PE or PP?

Paints developed for PVC should not automatically be considered suitable for PE or PP. (From OkanGökhan's website) PVC screen printing paint options These are PVC-focused products. If PE or PP application is planned, product compatibility must be further verified through the paint manufacturer's technical data sheet and sample testing.

To examine the general distinctions between paint types. A guide to ink types in screen printing., to decide based on different surfaces What type of paint is used in screen printing? and to understand the basis of paint structure What is screen printing paint? Guide available.

Short answer: The technical data sheet for paints to be used on PE and PP must clearly state the type of plastic. Simply stating "plastic paint" or "PVC paint" is insufficient. Pretreatment requirements, hardener ratio, thinner, drying time, and final strength conditions must all be evaluated within the same technical system.

Briefly

• The paint technical data sheet must clearly indicate whether it is made of PE or PP.
• Different systems may be available for pre-treated and untreated PP.
• PVC paint should not be assumed to be compatible with PE and PP.
• Testing on a real part before production is mandatory.

Mold, Mesh, and Emulsion Selection in PE and PP Printing

Mesh selection is not based solely on the type of plastic. The viscosity of the paint, the pigment structure, the intended paint layer, the detail of the print, the thickness of the lettering, and the product surface are all considered together. A lighter mesh generally allows for greater paint transfer, while a denser mesh facilitates a more controlled and thinner paint layer. However, the final choice should be made in consultation with the paint manufacturer's technical recommendations.

If an excessively loose mesh is used for fine lettering and lines, the paint may spread. If an excessively dense mesh is chosen, the paint may not pass through sufficiently, may dry inside the mold, or the opacity may decrease. The general principle behind mesh selection is... In the screen printing silk number selection guide It is explained in detail.

The plate size should be determined to leave sufficient working space from the printing area. Frame and mesh options. in the screen printing plates categoryThis can be examined. When selecting a mold according to the printing area, the mold clamping capacity of the machine should also be checked.

Emulsion resistance

If solvent-based or two-component paint is to be used, the emulsion must be resistant to paint and cleaning solvents. An unsuitable emulsion may swell, deform at the edges, or create pinholes on the plate during printing. For the relevant product group... mask and emulsion options It can be examined.

Exposure and mold quality

Underexposed paint can quickly deteriorate when exposed to solvent-based paint. Overexposure, on the other hand, can make it difficult to reveal fine details. To determine exposure parameters... Screen printing exposure time calculation And Exposure time adjustment guide They can be evaluated together. Businesses that will prepare the mold in their own workshop. screen printing exposure machines And Exposure camera selection criteriacan examine.

Short answer: There is no single standard mesh number for PE and PP printing. The flow of the paint, the desired layer thickness, and the design detail are the determining factors. The emulsion must be resistant to the paints and cleaning chemicals used; the exposure time must be verified with a test plate.

Briefly

• The mesh number depends on the type of plastic as well as the paint composition.
• Excessively open mesh can spread the print.
• Overly dense mesh can reduce dye transfer.
• For solvent-based paints, a solvent-resistant emulsion should be used.

How to Choose a Printing Machine, Fixture, and Squeegee?

PE and PP products can be in the form of sheets, films, containers, bottles, caps, or injection molded parts. Therefore, machine selection should be based not only on the printing dimensions but also on the product geometry. Machine options generally include: in the screen printing machines categorycomparable.

Flat and rigid parts

For flat PE or PP sheets, the material must not move during printing. vacuum manual screen printing machine, It can help to fix flat pieces of appropriate size. However, excessively high vacuum levels in thin films or easily deformable sheets can cause wrinkling or deformation. The vacuum level and hole distribution must be adjusted according to the sample.

Small and medium-sized businesses

For samples, prototypes, or low-volume plain products screen printing desktop printing apparatus This can be evaluated. To reduce operator-induced pressure and speed variations when production volume increases. semi-automatic screen printing machine Solutions like these can be compared.

Bottles, tubes and cylindrical products

PE or PP bottles, tubes, and jars must be rotated during surface printing. Manually rolling the product on a flat table will not yield repeatable results. This applies to cylindrical products. semi-automatic circular printing machine A custom-made fixture can be used for the product. Diameter, printing circumference, product taper, and printing area should be measured before purchasing.

Ragle selection

Squeegee stiffness, edge sharpness, angle, speed, and pressure all affect paint transfer. Controlled paint release is important on hard and smooth plastic surfaces. A squeegee that is too soft can transfer too much paint; excessive pressure can warp the plate and damage the printing edges. screen printing squeegee category, Squeegee rubber options, ready-made screen printing squeegee And screen printing squeegee rubber It can be evaluated according to the printing area.

Squeegee pressure should not be used to force the print onto the surface. If the paint is not adhering to the surface, applying more pressure will not resolve the underlying mismatch; it will only alter the paint layer and print geometry.

Briefly

• Flat parts require a table, while cylindrical products require a rotary fixture.
• Excessive vacuum can cause deformation in thin PE and PP materials.
• Squeegee pressure does not compensate for surface incompatibility.
• Machine selection should be based on the printing area, product geometry, and production quantity.

Steps for Screen Printing on PE and PP

1. Describe the product: The type of plastic, product geometry, usage environment, and expected durability from the print are clarified.
2. Choose your paint system: Paints, hardeners, thinners, and auxiliary products are selected together, provided that the relevant PE or PP surface is clearly specified in the technical data sheet.
3. Clean the surface: The manufacturer-approved cleaner removes grease, dust, mold release agents, and fingerprints.
4. Check the surface energy: The current transaction level is measured and recorded using an appropriate method.
5. Apply the necessary surface treatment: Corona, plasma, controlled flame, or primary treatment is performed with specified parameters.
6. Prepare the mold: A solvent-resistant emulsion is used with a mesh suitable for the paint and detail level.
7. Adjust the fixture: The part is secured so that it will not move during printing; however, it will not deform due to excessive compression or vacuum.
8. Prepare the paint: The mixing ratio is applied by weighing. Thinner and hardener are not added by eye.
9. Get a test print: Squeegee angle, pressure, speed, and mold ejection distance are adjusted in small increments.
10. Complete the drying or curing process: The time, temperature, UV energy, or waiting conditions specified in the paint technical data sheet are applied.
11. Perform an adhesion test: Printing is evaluated not only in terms of image quality, but also in terms of tape, friction, scratching, bending, and the chemicals used.
12. Record the production parameters: The plastic batch, surface treatment, paint lot, mixing ratio, mesh, squeegee, and drying conditions are added to the work order.

Businesses installing a new screen printing system should list the equipment sequence. Guide to getting started with screen printing And Guide to professional screen printing supplies You can plan it through this. For necessary paint, emulsion, squeegee and cleaning products. screen printing materials category with Screen printing auxiliary materials category They can be examined together.

Short answer: The correct sequence for PE and PP printing is: material identification, surface cleaning, surface energy control, activation if necessary, appropriate dye and plate selection, controlled printing, full curing, and durability testing. Skipping any of these steps can result in high waste in mass production.

Briefly

• First, the compatibility of the plastic and paint must be verified.
• Paint mixtures should not be prepared by guesswork.
• The test print should not be evaluated before it is fully cured.
• The approved parameters must be converted into a written production recipe.

Drying and Curing in PE and PP Screen Printing

“Dry to the touch” and “fully cured” are not the same thing. With solvent-based paint, the surface may feel dry after losing some of the solvent; however, solvent may remain in the substrate. Two-component paint may require additional time for chemical cross-linking to complete. With UV paint, even if the surface appears hardened, the substrate may be incompletely cured if sufficient energy is not received.

Paint that dries by air or solvent evaporation.

The printed parts should be placed so that they do not touch each other. For this purpose... screen printing drying systems, for small and medium-sized parts 50x70 paint drying rackor for different sized jobs screen printing paint drying rackThis can be considered. Using a shelf does not replace the curing conditions specified in the paint technical data sheet; it simply ensures that the products are stored neatly and without contact.

Systems that use heat

PE and PP parts can bend, shrink, or alter the fixture mark under heat. Therefore, standard fixing formulas used in textile dyes should not be applied directly to plastic parts. If an oven or hot air is to be used, the temperature, product thickness, and holding time permitted by the plastic manufacturer should be tested.

Waiting in two-component systems

In paints containing hardeners, achieving full chemical resistance may take time. If the tape test is performed too early, the paint may appear to fail; if tested too late, the manufacturing defect may go unnoticed until shipment. Therefore, separate time points should be determined for the initial adhesion test and the final strength test.

Stacking and blocking

Insufficiently cured prints can stick together or bleed paint onto the backing when stacked. Temperature, ventilation, shelf spacing, and stacking times in the drying area should be standardized.

Short answer: In PE and PP printing, drying can occur via air solvent removal, chemical curing, or UV curing, depending on the paint system. A dry surface does not necessarily mean full durability. Tests should be repeated after the final curing time specified in the technical data sheet has been completed.

Briefly

• Dryness to the touch is not the ultimate strength.
• Plastic surfaces are at risk of deformation due to heat.
• With two-component paints, a chemical curing time must be observed.
• Products should not be stacked before they are completely ready.

How to Test Adhesion and Durability in PE and PP Printing?

The decision to begin mass production should not be based solely on visual quality. The actual use conditions the print will encounter, such as friction, bending, impact, cleaning chemicals, water, oil, temperature, and external environmental factors, must be determined. The test plan should be prepared according to the product's usage scenario.

Tape and cut test

ASTM D3359 describes methods used to evaluate the adhesion of organic coatings to tape. While the standard notes that applications are also possible on non-metallic surfaces such as plastics, it also highlights limitations related to these surfaces. Therefore, the test method should be agreed upon in advance between the customer, the paint manufacturer, and the quality team. ASTM D3359 tape adhesion test standard It can be used as a reference. 

Friction test

The printing surface can be rubbed with a dry cloth using a specified load and a fixed number of repetitions. If the product is to be cleaned with detergent, alcohol, or another chemical during use, a separate test should be prepared with the relevant liquid. Using random cloths and unknown force makes it difficult to compare results.

Scratch and abrasion test

Scratching the print with a fingernail can provide a quick field inspection; however, it is not a standardized quality test. In professional production, a device or method with a defined tip geometry, applied load, and number of movements should be used.

Bending test

On flexible PE or PP products, the print must be evaluated in conjunction with the actual movement of the part during use. If the print area is in a region of the product that is folded or constantly stretched, the paint must have sufficient flexibility. A rigid and thick paint layer may crack upon bending, even if it adheres well.

Chemical resistance test

The actual chemicals the product will come into contact with on the packaging or industrial part must be identified. The concentration of the test liquid, contact time, temperature, and wiping method should be recorded. Just because a paint is water-resistant does not mean it will also be resistant to oil, alcohol, or detergent.

Aging test

Some adhesion problems appear not immediately after printing, but days or weeks later. Strength may decrease due to migration of plastic additives to the surface or embrittlement of the paint film. For critical products, in addition to the initial test, retesting should be performed after specific waiting periods.

Briefly

• Visual quality alone does not indicate adhesion quality.
• Tests should be repeated after initial drying and complete curing.
• Flexible products should undergo bending tests.
• Chemical tests should be designed according to actual usage conditions.

PE and PP Screen Printing Errors and Solutions

If a comparison needs to be made between screen printing and digital methods in terms of PE and PP applications. Screen printing vs. digital printing guide This can be examined. Screen printing can be a strong option for repeated production of the same design; however, for low-volume or constantly changing designs, the total preparation time should be calculated separately.

Short answer: In PE and PP printing, paint peeling cannot be solved simply by using more hardener or increasing squeegee pressure. First, the plastic type, surface contamination, surface energy, paint compatibility, and curing time must be checked in that order. Changes made without identifying the source of the problem can create new defects.

Things to Check Before Mass Production Begin

While successful sample printing is important, it is not sufficient on its own. In mass production, hundreds or thousands of parts need to undergo the same surface treatment, be held in the same fixture, and go through the same curing conditions.

• Is the type of plastic and the raw material batch registered?
• Is the time elapsed from surface treatment to printing defined?
• Are the surface energy control method and acceptance criteria defined?
• Are the paint, hardener, and thinner lots being recorded?
• Is the mixture prepared with a scale?
• Is paint that has reached the end of its pot life removed from production?
• Are the mesh, emulsion, and mold numbers listed on the work order?
• Are the squeegee stiffness, angle, and pressure speed standardized?
• Does the fixture and vacuum deform the product?
• Is the drying area adequately ventilated?
• Are the initial part, intermediate check, and final part tests defined?
• Is a final quality control check performed after full curing?
• Are the test results linked to the product batch?
• Do operators have access to safety data sheets?
• Is there a quarantine area for separating unsuitable products?

Solvent and chemical safety

If solvent-based paints, thinners, cleaners, hardeners, or primers are used, the product's Safety Data Sheet must be consulted. Ventilation, personal protective equipment, control of fire sources, chemical storage, and waste management should be planned according to the actual conditions of the facility. IFC printing industry environmental, health and safety guide., It is an enterprise reference source for general risks in printing facilities, including screen printing. 

Mold cleaning and emulsion removal processes must be carried out in a controlled area. screen printing plate washing booth, for auxiliary chemicals Template helpers category This can be evaluated. The compatibility of the products to be used with the paint and emulsion system should be verified before purchasing.

Briefly

• The sample recipe must be converted into a written production standard.
• Raw material, dye, and auxiliary product lots must be monitored.
• The pot life and curing time should be monitored.
• Chemical safety is an integral part of production.

Supply of Materials and Equipment for PE and PP Printing

A workshop that will print on PE and PP needs to plan not only the paint but also the appropriate machinery, molds, mesh, emulsion, squeegee, drying and cleaning equipment for the surface. General product groups Screen printing materials homepage, The paint options are: screen printing paint categoryIt can be examined through this method.

Businesses that print on PE and PP packaging, plastic parts, and promotional products; Istanbul screen printing supplies, Screen printing supplies in Ankara., Screen printing supplies in Izmir., Screen printing supplies in Bursa. And Screen printing supplies in Kocaeli. You can browse product groups through their pages.

For workshops operating in Central Anatolia and other production regions Screen printing materials in Konya., Screen printing materials in Eskişehir., Adana screen printing supplies, Gaziantep screen printing materials, Screen printing materials in Tekirdağ., Balıkesir screen printing materials And Samsun screen printing materials The contents are available.

Instead of simply stating "I will be printing on PP" to the OkanGökhan Screen Printing Machines team during product selection, it is essential to provide a photo of the product, its flat or round shape, print dimensions, estimated quantity, existing surface treatment, desired durability, and cleaning conditions. This will allow for a more informed selection of machinery and auxiliary equipment. Paint compatibility should be confirmed through the paint manufacturer's technical documentation and actual part testing.

Frequently Asked Questions About Screen Printing on PE and PP

1. Is screen printing possible on PE?

Yes, screen printing is possible on polyethylene surfaces. However, since PE generally has low surface energy, the paint may not adequately wet the surface directly. The type of PE, its additives, and the existing surface treatment must be determined. The paint technical data sheet should clearly state the relevant polyethylene type and pretreatment requirements. Corona, plasma, controlled flame, or the manufacturer's recommended primer can be applied. Before mass production, tape, friction, bending, and resistance to operating chemicals tests should be performed on fully cured samples.

2. Is screen printing possible on PP (polypropylene)?

Screen printing is possible on PP; however, not all polypropylene products behave the same way. Some paint systems require pre-treated PP, while some specialized products are designed to adhere to specific types of untreated PP. This information can only be verified from the paint manufacturer's technical data sheet. Mold release agents, lubricants, or antistatic additives can negatively affect adhesion. Therefore, surface cleaning, surface energy control, the correct paint system, full curing, and strength testing under actual usage conditions must be applied together.

3. Is corona treatment mandatory for PE and PP printing?

Corona treatment may be necessary or beneficial in many PE and PP applications; however, it cannot be defined as an absolute necessity for all products and all paints. Some plastics may have been treated during production, and some special PP paints may work without pretreatment on certain surfaces. Conversely, the existing corona level may decrease over time. The most accurate decision is made through surface energy measurement, paint technical data sheet, and actual part testing. Corona treatment does not eliminate the need for surface cleaning and correct paint selection.

4. Can PVC screen printing paint be applied to a PP surface?

It should not be assumed that a paint formulated for PVC will reliably work on PP. PVC and PP have different surface chemistry. Even if the paint appears smooth initially, it may peel off with tape or rub off after curing. The technical data sheet of the paint to be used must clearly state the appropriate terminology: PP, pre-treated PP, or untreated PP. If no technical documentation is available, mass production should not begin; written conformity information should be obtained from the paint manufacturer, and sample tests should be completed.

5. What mesh number should be used for PE and PP?

There is no single mesh number that suits all applications for PE and PP printing. The mesh size is selected according to the ink viscosity, pigment structure, print detail, intended ink thickness, and manufacturer recommendations. A lighter mesh allows more ink to pass through; a denser mesh provides a thinner and more controlled layer. Excessive ink spreading in fine lettering, and an overly dense mesh, can lead to insufficient transfer and in-mold drying. The most accurate method is to compare two or three mesh options on the same part, starting from the range specified in the ink technical data sheet.

6. Can flame surface treatment be done with a household blowtorch?

Uncontrolled application with a household blowtorch is not recommended. Professional flame treatment is performed with equipment that controls the air-gas mixture, flame characteristics, distance, speed of movement, part temperature, and safety systems. Random application can melt plastic, alter surface gloss, deform the product, or create irregular activation. Furthermore, it poses a serious fire risk in workshops containing flammable solvents and paints. If flame treatment is necessary, appropriate industrial systems, ventilation, fire safety measures, and a trained operator must be used.

7. Is measuring with a Dyne pen sufficient?

Dyne pens or test fluids provide a quick field indication of surface wettability; however, they do not alone prove ultimate paint adhesion. Pen age, surface contamination, application quantity, temperature, humidity, and operator commentary can all affect the result. Furthermore, even with the correct dyne level achieved, the print may peel due to incorrect paint or incomplete curing. Dyne measurement should be evaluated in conjunction with the paint manufacturer's target value, sample print, tape test, abrasion test, and actual use durability.

8. How long does PE and PP printing take to dry?

Drying time cannot be determined solely by the type of plastic. Single-component solvent-based, two-component reactive, and UV-cured paints have different curing processes. Ambient temperature, airflow, paint layer type, and the thinner and hardener used also affect the curing time. A surface being dry to the touch does not mean that final curing is complete. Tape, friction, or chemical resistance tests should be repeated after the full curing time specified in the paint technical data sheet. A fixed value should not be written in the production recipe without verifying the exact time with the paint manufacturer.

9. How to clean PE or PP products before printing?

The cleaning method must be compatible with the plastic, paint, and surface treatment. First, loose dust and dirt are removed; then, the cleaner recommended by the paint manufacturer can be applied with a clean, lint-free cloth. Not all solvents are safe for PE and PP. Some chemicals may cause dulling, discoloration, stress cracking, or deformation of the product. The cleaner should be tested on a small, inconspicuous area before proceeding with surface treatment or printing until it is completely removed. The cleaned printed area should not be touched again with bare hands.

Why does the 10th print run well on the first day but then disappear a few days later?

This situation can occur due to incomplete chemical curing, migration of plastic additives to the surface, inadequate surface treatment, or paint-plastic incompatibility. A simple nail test performed on the first day can be misleading. While some paint systems gain strength over time, adhesion weakens later in some unsuccessful combinations. Therefore, in addition to the initial inspection, tests should be performed after full curing and at the specified aging times. If the raw material batch, surface treatment, paint lot, and mixing ratios are not recorded, it becomes difficult to find the source of the problem.

11. Can thin PE film be fixed to a vacuum plate?

Thin PE film can be fixed to a vacuum bed; however, excessive vacuum can cause the film to be pulled towards the holes, wrinkled, or dimensionally altered. The vacuum level, hole diameter, and distribution should be adjusted according to the material thickness. If necessary, permeable backing paper, carrier plate, or product-specific masking can be used. In multi-color printing, registration stability should also be tested because the solvent and tension effects after the first color can alter the film dimensions. Successful single-color sampling does not guarantee problem-free multi-color production.

12. Is it possible to print on PP bottles and containers using a flat printing machine?

Printing on cylindrical PP bottles or containers requires controlled, simultaneous movement of the printing surface, mold, and product. Manually rolling the product on a flat table leads to variations in position, speed, and pressure. For repeatable production, a circular printing machine and product-specific fixtures should be used. The diameter, taper, printing circumference, surface treatment, and joints of the product must be measured. If the printing area coincides with the mold trace or seam line of the product, adhesion and image quality should be evaluated separately.

13. Is it necessary to use a primer in PE and PP printing?

Primer requirements depend on the paint system and plastic type. Some PP paints are used with the manufacturer's recommended wipe-off primer, while others require corona or plasma treatment. Primer does not mean applying any chemical to the surface. A product compatible with the paint and defined in the technical data sheet must be used. Application quantity, drying time, and the time between priming and printing should be controlled. Excess primer can leave residue on the surface; insufficient primer can create uneven adhesion. The final decision should be made by sample testing.

14. Are PE and PP printed materials resistant to water and detergent?

With the correct paint, appropriate surface treatment, and full curing, certain levels of water and detergent resistance can be achieved. However, the term "water-resistant" does not mean resistance to all detergents, hot water, dishwashers, or prolonged immersion. The actual use scenario of the product must be defined. Sample testing should be performed with the detergent to be contacted, the temperature, the dwell time, and the wiping method. In special applications such as food, cosmetic, or chemical packaging, relevant legislation and product conformity requirements should also be verified with experts.

15. How many samples should be printed before mass production?

There is no fixed sample count applicable to all projects. The risk level varies depending on order quantity, product cost, printing area, number of colors, and customer durability expectations. At least enough samples should be prepared to compare different surface treatments and paint parameters. Some samples should be set aside for initial adhesion, some for full curing, some for bending or chemical testing, and some for aging. In critical production processes, it is safer to prepare a pilot batch with actual machine speed and drying setup, rather than just a laboratory sample.

Conclusion: Success in PE and PP Printing is a Systems Effort

Screen printing is possible on PE and PP; however, the result does not depend solely on the paint brand or machine model. The plastic formulation, surface cleanliness, surface energy, corona or other activation methods, paint system, mesh, emulsion, squeegee, fixture, drying, and testing process must all work together.

The most common mistake is to accept the initial adhesion of a small sample to the surface as approval for mass production. Full curing is necessary for reliable results; adhesion, friction, bending, chemical, and aging tests must be performed. All approved parameters should then be translated into a written production recipe.

You can receive technical guidance from OkanGökhan Screen Printing Machines when selecting machinery, molds, squeegees, emulsion, and drying equipment for your PE or PP product. Before the consultation, preparing information about the plastic type, product dimensions, printing area, surface geometry, production quantity, and expected durability will help determine the right system more quickly. Paint suitability should be confirmed through a technical data sheet and actual product testing.