In-Mold Labeling(IML): Enhancing Durability and Aesthetics in Plastic Products

In-Mold Labeling (IML) is a sophisticated manufacturing process that integrates labels into plastic products during the molding process. This technique has revolutionized the plastic packaging industry by enhancing both the durability and aesthetics of the final product. By embedding the label within the plastic during molding, IML ensures that the label becomes an integral part of the product, offering superior resistance to wear and tear compared to traditional labeling methods.

What is In-Mold Labeling(IML)?

In-Mold Labeling (IML) is a technique used in the manufacturing of containers through processes such as blow molding, injection molding, or thermoforming. This method involves the integration of paper or plastic labels directly into the container during its formation. The label becomes an integral part of the final product, eliminating the need for separate labeling processes after production. This integration not only enhances the aesthetics of the container but also offers several practical advantages.

IML involves placing a pre-printed decorative film into the mold before the plastic container is shaped. Plastic pellets or resin are then heated and injected into the mold, where they merge with the label to create a unified product. This process ensures that the label becomes seamlessly fused with the container, providing a durable and visually appealing finish.

Initially developed by Owens-Illinois in collaboration with Procter & Gamble, IML was introduced to supply pre-labeled bottles that could be directly filled on the product filling line. One of the early applications of IML was seen in Head & Shoulders shampoo bottles.

This labeling method is commonly used for thin-walled disposable items such as consumer packaging, which typically have a shorter shelf life. Companies in industries such as food, personal care, household products, and cosmetics often utilize IML to brand their packaging due to its efficiency, durability, and aesthetic appeal.

Benefits of In-Mold Labeling

In-Mold Labeling (IML) offers several significant benefits across various industries. Here are some of the key advantages:

• Enhanced Durability: Labels become an integral part of the product, resulting in excellent resistance to wear, tear, and fading. Unlike traditional labels, IML labels are less prone to peeling, scratching, or damage during handling, transportation, and use.
• Superior Aesthetics: High-resolution printing allows for intricate designs, vibrant colors, and photographic images on the labels. The labels seamlessly integrate with the product’s surface, providing a premium and professional appearance without visible edges or wrinkles. This enhances brand perception and product appeal on the shelf.
• Cost Efficiency: By combining the labeling process with the molding process, IML reduces the need for separate labeling equipment, materials, and labor. This streamlines production, lowers overall injection manufacturing costs, and improves operational efficiency. Additionally, IML reduces the risk of label misalignment or errors, minimizing wastage and rework.
• Increased Production Speed: IML eliminates the need for secondary labeling operations, such as applying adhesive labels post-production. This results in faster production cycles and shorter lead times, allowing manufacturers to meet market demands more effectively. Additionally, since the label is applied during molding, there is no additional curing or drying time required.
• Design Flexibility: IML offers versatility in label design, allowing for complex shapes, textures, and finishes that may not be achievable with traditional labeling methods. Manufacturers have the freedom to customize labels according to brand requirements, product specifications, and consumer preferences. This flexibility enhances brand differentiation and product innovation.
• Environmental Sustainability: IML promotes sustainability by reducing material waste and energy consumption. Since the label is integrated into the product, there is no need for additional adhesives or packaging materials, minimizing environmental impact. Furthermore, IML products are often made from recyclable materials, supporting circular economy initiatives and reducing landfill waste.
• Consistent Quality: The automated nature of the IML process ensures consistent label placement, alignment, and adhesion across every product. This results in uniform product appearance and branding, enhancing brand recognition and consumer trust. Additionally, IML reduces the risk of label tampering or counterfeiting, ensuring product authenticity and integrity.

While In-Mold Labeling (IML) offers many benefits, such as enhanced durability and aesthetics, it also has some drawbacks. Here are the primary disadvantages of IML:

• High Initial Investment: Implementing IML requires significant investment in specialized equipment and custom molds. This high upfront cost can be a barrier for smaller manufacturers and is increased further by any necessary design changes.
• Complex Process: The IML process is technically complex, requiring precise integration of the labeling and molding steps. This increases setup time and operational complexity, making it less suitable for short production runs.
• Limited Flexibility: IML offers limited flexibility in terms of design and product variability. Changes in design require new molds, which are costly and time-consuming. The need for material compatibility further restricts options.
• Quality Control Issues: Ensuring precise label placement and adhesion within the mold is critical. Misalignments can lead to injection molding defects, necessitating stringent and costly quality control measures to maintain consistent, high-quality results.

Types of In-Mold Labeling Processes

There are three methods for in mold labeling: injection molding, blow molding, and thermoforming, with injection molding being the most commonly used IML method.

Injection Molding

Using injection molding machines and molds, by heating and liquefying plastic or polymer and injecting it into the mold, the plastic can cool and solidify, seamlessly integrating the label into the final product. Injection molding is widely used in the manufacturing of plastic containers, butter or ice cream boxes, cosmetic packaging, plastic paint buckets, and other products. Below are the detailed steps of the injection molding process:

Injection Molding Process

The injection molding process for in-mold labeling (IML) and labels can be briefly explained in four steps:

1. Label Inserted:
   • Before the molten plastic is injected into the mold, the pre-printed label is inserted into the mold. The labels are typically made from the same or similar material as the plastic substrate (such as polypropylene) to ensure they can firmly bond during the molding process.
2. Plastic Injected:
   • Molten plastic is injected into the mold cavity. At this point, the high temperature and high pressure of the plastic allow it to perfectly fill every corner of the mold while encapsulating the label.
3. Plastic & Label Merged:
   • During the molding process, the label fuses with the plastic part. As the molten plastic cools and solidifies, it embeds the label firmly into the product’s surface, making it an integral part of the product.
4. IML Product:
   • The finished plastic product with the label is ejected from the mold. At this stage, the label is fully integrated into the plastic product, forming a smooth, seamless surface without the issues of edge lifting, peeling, or wear associated with traditional labels.

Blow Molding

Blow molding is a manufacturing process used to create hollow plastic products by inflating a heated plastic tube (preform) until it fills a mold and forms the desired shape. This process is particularly suitable for producing containers, bottles, and similar items. Blow molding is also an effective technique for in-mold labeling (IML), allowing labels to be seamlessly integrated into the surface of the molded products. Here are the detailed steps of the blow molding process:

Blow Molding Process

The blow molding process for in-mold labeling (IML) can be described in four steps:

1. Label Inserted:
   • Before the preform is introduced into the mold, the pre-printed label is placed inside the mold cavity. The labels are typically held in place by static charge or mechanical holding devices to ensure precise positioning.
2. Preform Inserted:
   • A heated plastic preform, which is a tube-like piece of plastic, is inserted into the mold. The preform is usually made from the same type of plastic as the final product to ensure compatibility and proper bonding.
3. Plastic Blown and Merged:
   • The mold closes around the preform, and air is blown into the preform, causing it to expand and take the shape of the mold. As the preform expands, it presses against the mold walls and the label, embedding the label into the surface of the plastic. During this process, the high pressure and heat ensure that the label fuses with the plastic.
4. IML Product:
   • The molded product is cooled and solidified within the mold. Once the plastic has hardened, the mold opens, and the finished product with the label seamlessly integrated into its surface is ejected. The resulting product has a smooth, durable surface with the label as an integral part, eliminating issues like label peeling or abrasion.

Thermoforming

Thermoforming is a manufacturing process where a plastic sheet is heated to a pliable forming temperature, formed to a specific shape in a mold, and trimmed to create a usable product. This process is commonly used for creating a variety of products, including packaging, trays, and containers.

Here’s a detailed explanation of the thermoforming process:

Thermoforming Process

Thermoforming involves several key steps:

1. Preparation of Plastic Sheet:
   • A plastic sheet, typically made from materials like polyethylene (PE), polypropylene (PP), or polystyrene (PS), is loaded into the thermoforming machine.
2. Heating:
   • The plastic sheet is heated to its forming temperature using radiant heaters, infrared heaters, or convection ovens. Heating softens the plastic and makes it pliable for forming.
3. Forming:
   • Once the plastic sheet reaches the appropriate temperature, it is transferred to the forming station. A mold, typically made from aluminum or composite materials, is used to shape the heated plastic sheet.
   • Vacuum, pressure, or a combination of both is applied to draw the softened plastic sheet into the mold cavity, forming it into the desired shape.
   • The formed plastic sheet is held in the mold until it cools and solidifies, taking on the shape of the mold.
4. Trimming:
   • After cooling, excess plastic (flashing) around the formed part is trimmed off using cutting tools or automated trimming equipment.
   • Trimming ensures that the final product has clean edges and meets the desired specifications.
5. Additional Processing (Optional):
   • Depending on the product requirements, additional processing steps such as drilling, punching, or printing may be performed after trimming.
6. Product Removal:
   • Once trimming and any additional processing are complete, the formed products are removed from the mold. Automated systems or manual labor may be used for product removal.
7. Quality Control:
   • Formed products undergo quality checks to ensure they meet dimensional accuracy, cosmetic standards, and other specified criteria.

Materials Used for In-Mold Labeling

In-Mold Labeling (IML) involves integrating labels directly into plastic products during the manufacturing process. To ensure successful integration and durability, specific materials are used for both the labels and the plastic products. Here are the primary materials used for In-Mold Labeling:

Label Materials:

1. Polypropylene (PP):
   • PP is one of the most commonly used materials for IML labels due to its excellent printability, durability, and compatibility with various plastic substrates used in manufacturing. PP labels offer good resistance to moisture, chemicals, and abrasion, making them suitable for a wide range of applications.
2. Polyethylene (PE):
   • PE labels are also popular for IML applications, offering similar properties to PP. PE labels are flexible, lightweight, and cost-effective, making them ideal for high-volume production of disposable packaging and containers.
3. Polyethylene Terephthalate (PET):
   • PET labels are known for their high clarity, gloss, and stiffness, making them suitable for applications where visual appeal is critical. PET labels offer excellent printability and dimensional stability, making them ideal for branding and promotional packaging.
4. Polystyrene (PS):
   • PS labels are lightweight, rigid, and offer good printability, making them suitable for a wide range of applications. PS labels are commonly used for packaging of food and beverage products, cosmetics, and consumer goods.
5. Biaxially Oriented Polypropylene (BOPP):
   • BOPP labels offer excellent tensile strength, clarity, and printability, making them suitable for high-quality IML applications. BOPP labels are commonly used for premium packaging of cosmetics, personal care products, and specialty foods.

Plastic Product Materials:

1. Polypropylene (PP):
   • PP is a widely used plastic material for IML applications due to its versatility, durability, and compatibility with IML labels. PP offers good chemical resistance, stiffness, and impact strength, making it suitable for various packaging, containers, and consumer products.
2. High-Density Polyethylene (HDPE):
   • HDPE is known for its high strength-to-density ratio, chemical resistance, and moisture barrier properties. HDPE is commonly used for IML applications in industries such as food packaging, pharmaceuticals, and industrial containers.
3. Polyethylene Terephthalate (PET):
   • PET is a clear, lightweight, and durable plastic material commonly used for IML applications where transparency and visual appeal are important. PET is widely used for packaging of beverages, personal care products, and household items.
4. Polystyrene (PS):
   • PS is a versatile plastic material known for its clarity, rigidity, and affordability. PS is commonly used for IML applications in packaging of food, cosmetics, and consumer goods.
5. Polyvinyl Chloride (PVC):
   • PVC is a versatile plastic material known for its durability, chemical resistance, and cost-effectiveness. PVC is commonly used for IML applications in packaging of pharmaceuticals, household products, and industrial containers.

Related resources: PVC Injection Molding: Process, Advantages and Disadvantages

Application of In-mold Labeling

In-mold labeling (IML) finds extensive application across various industries due to its numerous benefits. Here are some common applications of in-mold labeling:

1. Food Packaging: In-mold labeling is widely used in food packaging for products such as yogurt containers, butter tubs, ice cream tubs, and margarine tubs. The labels seamlessly adhere to the packaging during the molding process, providing vibrant graphics and product information directly on the container.

2. Personal Care Products: IML is commonly utilized in the packaging of personal care items like shampoo bottles, conditioner bottles, lotion containers, and cosmetic jars. The labels enhance the aesthetics of the packaging and withstand the harsh conditions often encountered in bathrooms.

3. Household Products: Various household products benefit from in-mold labeling, including detergent bottles, cleaning product containers, and air freshener packaging. The labels provide durability and resistance to moisture, ensuring the branding remains intact throughout the product’s lifespan.

4. Paint Buckets and Pails: In the paint industry, IML is employed for labeling paint buckets, pails, and other containers. The labels endure exposure to chemicals and abrasion, maintaining their appearance even in demanding environments such as construction sites.

5. Automotive Parts: In the automotive sector, in-mold labeling is used for interior and exterior parts such as dashboard trims, door panels, and center consoles. The labels can withstand temperature variations, UV exposure, and mechanical stresses, ensuring long-lasting branding.

6. Medical Devices: In-mold labeling finds application in the medical industry for labeling devices such as syringe casings, medicine containers, and surgical instrument trays. The labels are resistant to sterilization processes and provide essential product information for healthcare professionals.

7. Industrial Containers: Industrial containers, including lubricant drums, chemical barrels, and industrial packaging, often utilize in-mold labeling for branding and product identification. The labels offer excellent chemical resistance and durability in harsh industrial environments.

8. Electronics: In the electronics industry, IML is used for labeling products such as battery casings, electronic device enclosures, and appliance components. The labels provide a sleek, integrated appearance while offering resistance to scratches and abrasion.

9. Promotional Items: In-mold labeling is also employed for promotional items such as branded cups, mugs, and containers used in marketing campaigns and events. The labels enhance the visual appeal of the items and serve as effective advertising mediums.

10. Custom Packaging: IML allows for highly customizable packaging solutions tailored to specific brand identities and marketing strategies. The versatility of in-mold labeling enables the creation of unique, eye-catching designs that stand out on retail shelves.

Factors Influencing In-Mold Labeling (IML)

In-Mold Labeling (IML) is a sophisticated technique where labels are integrated into the plastic product during the molding process. Several key factors impact the effectiveness and quality of IML, including the labels, molds, robots, and injection molding equipment. Among these, the injection molding equipment is particularly crucial.

1. Labels

Labels play a critical role in the IML process, directly affecting the product’s quality. Poor label performance can lead to defects, particularly if the label’s adhesion or ink quality is subpar, causing contamination or inferior product quality.

Composition: Labels generally consist of three layers: a substrate (typically PET or polycarbonate), ink, and adhesive (often a specialized glue). Once injection molding is complete, the film and plastic merge into a single entity, with the film remaining on the exterior surface. This film is usually hardened for durability.

Sheet Forming: The sheet material is crucial for successful IML. Common materials include PET, PMMA, and polycarbonate, with PET being widely preferred due to its excellent molding properties, surface gloss, and wear resistance. The typical thickness for PET sheets used in IML is around 125μm. Precise temperature control during thermoforming is vital to prevent deformation and high scrap rates. The thermoforming machine maintains a constant temperature, and the sheet is preheated before molding to ensure it softens appropriately. The sheet size should be slightly smaller than the final part dimensions, typically by 0.02–0.03 mm on each side, to facilitate easy placement in the cavity and full expansion during molding.

Ink: Ink selection is critical for IML labels. It must adhere well to the label material, offer high scratch resistance, and withstand chemical exposure. Testing for these properties is essential before use. UV inks are preferred over solvent-based inks for IML due to their higher strength and suitability for the injection molding process. For injection molding labels, static charge is often used to hold the label in place within the mold because the high pressure during injection can displace labels if vacuum techniques are used.

2. Molds

Film Forming Mold Design: The dimensions of the forming mold must account for the injection mold size, thermal expansion of the injection mold (typically 60–80°C), and film shrinkage, minus the forming mold’s thermal expansion and film thickness. When using similar materials for both forming and injection molds, their thermal expansions can offset each other, simplifying the design.

Injection Mold Design: Typical shrinkage rates for materials like ABS and PMMA are around 0.5%, but for IML, where the product is covered with a PET film, a reduced shrinkage rate of 0.3% is more suitable. The PET film constrains the plastic, reducing shrinkage. To minimize issues like vibration and deformation during molding, high-rigidity materials like H-13 are used for mold construction, although they cost about 20% more than standard molds. Reinforcement ribs and thicker templates can also enhance mold rigidity.

3. Robots

Robots are essential for placing labels accurately within the mold, preventing misalignment. The synchronization between the robot and the injection molding machine is critical for efficiency and safety. Robots must place labels with a high degree of precision (±0.2 mm) and maintain stability to ensure consistent product quality.

4. Injection Molding Equipment

High-precision electric injection molding machines are preferred for their stability and low wear rates. Equipment like JSW’s specialized packaging injection molding machines meets these demands, offering high precision and stable operation. Unstable machines can lead to inaccuracies in mold opening positions, increasing defect rates. For IML containers with wall thicknesses typically below 1.0 mm, the injection molding machine must achieve injection speeds of at least 300 mm/s and injection pressures of 200 MPa.

5. Forming Processes

In-mold labeling (IML) can be achieved through three primary forming methods: blow molding, injection molding, and thermoforming. For injection molding IML, the process begins with an automated robotic arm that accurately places the pre-printed label onto the inner surface of the mold. Once the mold is closed, molten resin is injected into the cavity. The high temperature of the resin causes the adhesive on the back of the label to melt and bond with the resin, effectively fusing the label with the container. This method ensures that the label becomes an integral part of the molded product. Notably, approximately 80% of IML applications in Europe utilize the injection molding process due to its precision and efficiency.

Comparison of In-mold Labeling with Other Labeling Methods

This table compares In-Mold Labeling (IML) with other common labeling methods across various factors, highlighting the strengths and weaknesses of each approach.

Aspect	In-Mold Labeling (IML)	Pressure-Sensitive Labels (PSL)	Shrink Sleeve Labels	Heat Transfer Labels	Wet Glue Labels	Direct Printing
Durability	Highly durable; label becomes part of the product, resistant to wear, tear, and fading	Moderately durable; labels can peel or degrade over time	Durable; good resistance to moisture and abrasion	Durable; labels are bonded through heat, offering good resistance	Less durable; prone to peeling and damage when exposed to moisture	Varies; depends on the printing technique and surface material
Aesthetics	Seamless integration with high-quality graphics and no visible edges	High-quality graphics, but edges may be visible	360-degree coverage with high-quality graphics, but may have visible seams	High-quality graphics, but edges may be visible	High-quality graphics but can have visible edges and glue marks	Can offer high-quality graphics, but dependent on the substrate and printing process
Application Process	Integrated into the molding process; requires specialized equipment	Applied post-production using adhesive backing; relatively simple application	Applied post-production; involves heat shrinking the label to fit the product	Applied post-production; uses heat and pressure to transfer the image from a carrier film to the product	Applied post-production; labels are glued to the product manually or automatically	Printing is done directly on the product surface, requiring specialized printing equipment
Cost Efficiency	Cost-effective in high volumes; reduces the need for separate labeling steps	Moderate cost; cost increases with the complexity and volume of labels	Moderate to high cost; shrink sleeves and application equipment can be expensive	Moderate cost; heat transfer equipment and consumables can be expensive	Lower cost; simple application process but can be labor-intensive for high volumes	Varies; can be cost-effective but depends on the printing technology and volume
Production Speed	Integrated process can be slower initially but efficient for large runs	Fast application speeds, especially in automated lines	Moderate application speed; shrinking process adds time	Moderate application speed; heat transfer process adds time	Fast application speed, especially in automated lines	Varies; can be very fast with advanced printing technologies
Environmental Impact	Environmentally friendly; reduces waste by combining labeling and molding	Varies; adhesive-backed labels can generate waste	Moderate impact; uses significant plastic material but labels are recyclable	Varies; involves use of heat and chemicals, generating some waste	Less environmentally friendly; involves use of glue and paper	Varies; direct printing can reduce waste but depends on the type of ink and printing process used
Flexibility in Design	High flexibility; complex shapes, textures, and finishes are possible	High flexibility; can be used on a variety of shapes and materials	High flexibility; full-body coverage allows for intricate designs	Moderate flexibility; limited to the type of carrier film and the products they can adhere to	Moderate flexibility; can be applied to various shapes but design is limited by the glue application process	High flexibility; allows for complex designs and variations depending on the printing technology
Consistency in Quality	Very consistent; automated process ensures uniform label placement and adhesion	Consistent quality but dependent on adhesive performance	Consistent quality; uniform shrinkage ensures tight fit but dependent on precise application	Consistent quality but dependent on the heat transfer process and uniformity of heat application	Varies; dependent on the glue application process and environmental conditions	Varies; high consistency achievable with advanced printing technology
Suitability for Short Runs	Less suitable for short runs; high setup costs and longer setup times	Suitable for short runs; lower setup costs and flexibility	Less suitable for short runs; high cost of shrink sleeves and setup	Suitable for short runs but involves setup time for heat transfer equipment	Suitable for short runs; low setup costs and flexibility	Suitable for short runs but depends on the type of printing equipment and setup time
Adhesion	Excellent; label and product become one piece, no risk of peeling	Good adhesion but can vary with adhesive quality	Excellent adhesion; tight fit due to shrinkage	Excellent adhesion; heat bonding creates strong attachment	Moderate adhesion; dependent on glue quality	Excellent adhesion directly onto the product, assuming compatible materials are used

Conclusion

In summary, in-mold labeling (IML) stands as a favored choice across industries seeking lasting, robust, adaptable, and eco-friendly labeling solutions. With its various types and specifications, understanding the labeling process is crucial for determining its suitability for your project.

Are you in search of in-mold labeling services? Look no further than BOYI. Our plastic manufacturing services seamlessly integrate in-mold labeling, providing comprehensive solutions for your needs. Contact us today to explore how we can incorporate IML into your project and meet your labeling requirements effectively.

Resources:

https://www.sciencedirect.com/science/article/abs/pii/B9781845696757500142

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Catalog: Injection Molding Guide