The use of finishes.
Technical principles
Paper and board finishes
Paper and Board Finishing
Finishing processes are used to protect the material from spills and dirt while enhancing its tactile and visual appeal.
Lamination
Encapsulation: The document is sealed entirely within a polymer pouch or film roll using a desktop laminator.
Surface Coating: *
Liquid Lamination: Often used for large-scale signage.
Film Lamination: Used for items like menu cards to provide a wipe-clean surface.
Physical Surface Effects
Embossing: Creates a raised design on the surface of the paper or card. It provides a premium visual and tactile effect, often seen on greetings cards and luxury packaging.
Debossing: The opposite of embossing; it produces an imprinted depression that sits below the surface of the paper.
Varnishing
Clear, non-pigmented inks applied to pre-coated papers to enhance color and offer protection against fingerprints and water.
UV Varnishing: Provides a very smooth finish (high gloss or matt). It is cured instantly under UV light, making it resistant to chemicals and abrasion.
Spot Varnishing: Applied only to specific spots or areas of a design to create a contrast between glossy and matt sections.
Foil Blocking
Heat and pressure are used to apply a metallic paper (foil) to the substrate. This adds depth, texture, and a high-end aesthetic impact.
Exam practice from my notes
15 Outline the factors that a manufacturer needs to consider before choosing a surface finish for a product. [6]
A manufacturer must consider how the surface finish will be applied. Large products may require spray application, while smaller components could be dip coated or powder coated. The material being finished also affects the method used, as some finishes are only suitable for metals, plastics or woods.
Performance requirements are important because the finish may need to protect the product from corrosion, moisture, UV light or abrasion. For example, galvanising may be used on steel to prevent rusting outdoors.
Durability must also be considered. A finish used on a frequently handled product should resist wear, scratching and impact to maintain the product’s appearance over time.
Aesthetics are another factor, as the finish contributes to the final appearance of the product through colour, texture and gloss level. A high-gloss finish may create a premium appearance, while a matte finish may reduce fingerprints.
Manufacturers should also consider maintenance requirements. Some finishes may need regular cleaning, reapplication or polishing, increasing long-term costs.
Cost and environmental impact are also important. Certain finishes may require specialist equipment, increase production time or release harmful VOCs, so manufacturers may choose more sustainable alternatives.
Printing processes
Paper and Board Printing Processes
Industrial printing involves applying graphics to a substrate (the material being printed on). Most processes use the CMYK (Cyan, Magenta, Yellow, and Key/Black) four-colour process.
Screen Printing
Setup: Uses basic screens and inks; low setup costs make it ideal for workshops.
Method: Ink is pushed through open areas in a mesh screen. A different screen is required for every color used.
Usage: Slow process with a high cost per unit. Best for small runs of posters, display boards, and T-shirts.
Flexographic Printing
Flexography uses flexible relief plates and fast-drying, water-based inks. It is common for packaging and continuous patterns.
Advantages:
Extremely high print speeds.
Perfectly suited for very long production runs.
Can print on a wide variety of substrates (plastics, films, paper).
Low cost of equipment, consumables, and maintenance.
Disadvantages:
The initial cost of printing plates is high (though they last a long time).
Setting up the job requires a large amount of substrate, leading to high initial waste.
Any changes to the print content are time-consuming and difficult.
Offset Lithographic Printing
A highly versatile process based on the principle that oil and water do not mix. It can handle up to 10 features (CMYK, metallics, varnishing, and double-sided printing).
Advantages:
Provides consistently high image quality.
Most cost-effective for high-volume runs (1,000+ units).
Printing plates are quick and easy to produce.
Plates have a long life because they only touch a soft "printing blanket" rather than the abrasive substrate.
Disadvantages:
Setup and running costs are too expensive for small quantities.
Digital Printing
Digital printing is the go-to for speed and efficiency, as it requires no physical plates.
Capabilities: Produces full-color, high-detail prints with the ability to change the design on every single page (front and back).
Mass Customisation: Ideal for "Print on Demand" (e.g., personalized names on bottles) because it uses fast-drying inks and requires zero setup time between different designs.
Usage: Popular for both low- and high-volume runs, especially promotional materials like flyers and business cards
Polymer finishes
Polymer Finishing
Polymers are generally considered self-finishing materials. This means that once they are removed from the mould or manufacturing process, they require no additional surface treatments to be functional or aesthetically pleasing.
Overmoulding
Overmoulding involves moulding a second polymer (often TPE - Thermoplastic Elastomer) over specific parts of a base product to provide grip, texture, or color contrast.
Method | Process Description | Best For... |
|---|---|---|
Two-Mould Process | The main product is injection moulded in one machine. It is then manually or robotically moved to a second mould where the overmoulding polymer is injected onto it. | Lower volume production or complex parts. |
Twin-Shot Injection | A high-speed, continuous process. The machine uses a rotating mould (180°) with two cavities. The main body is shot, the mould rotates, and the overmould is shot immediately. | High-volume mass production (e.g., toothbrushes, power tool grips). |
Acrylic Spray Paints (A-level Only)
While polymers are self-finishing, acrylic paints are sometimes applied for specific functional or aesthetic reasons.
Properties: Fast-drying, water-soluble when liquid, but water-resistant and UV-resistant once dry.
Protection: Provides a barrier against UV light and weathering, which can prevent polymers from becoming brittle.
Mass Customisation: Used extensively in the automotive industry (e.g., wing mirrors and bumpers).
Efficiency: It is more cost-effective to spray-paint small batches of different colors than to stop an injection moulding machine to change the color of the polymer granules (which causes downtime and waste).
Adding Pigments
Pigments are the primary method for coloring polymers. They are integrated into the material rather than sitting on the surface.
Application: Pigments can be added during the initial manufacture of the polymer stock form or mixed into the granules during the injection moulding/extrusion process.
Smart Pigments:
Thermochromic: Changes color based on temperature (e.g., baby spoons).
Phosphorescent: Glows in the dark (e.g., emergency exit signs).
GRP (Glass Reinforced Plastic): Pigments are added to the gel coat (the outer layer) during the lay-up process to provide a high-quality color finish.
Functional Coding: Using colors to categorize products, such as color-coded kitchen chopping boards to prevent cross-contamination
Metal finishes
Metal Finishing
Most metals naturally form an oxide layer when exposed to oxygen. However, the effectiveness of this layer as a barrier varies significantly between metals.
Copper: Forms a green patina. This layer is stable and protective, preventing further corrosion of the metal underneath.
Mild Steel: Forms a porous oxide layer (rust). Because it is porous, moisture and oxygen can penetrate the layer, causing the metal to continue corroding until it fails.
Stainless Steel: Forms a stable, non-porous chromium oxide layer. This creates an airtight seal that prevents any further corrosion.
Exam Tip: Never refer to a paint finish simply as a “spray.” Spraying is the method of application; the finish is the paint itself (e.g., cellulose or acrylic).
Metal Finish | Method of Application | Purpose / Typical Use |
|---|---|---|
Cellulose & Acrylic Paints | Metal is cleaned and degreased. A primer (often red oxide) is applied to create a "keyed" surface. Undercoat and top coats are applied via brush or spray. | Adds color and texture. Provides a barrier against corrosion. Low-cost finish for steel. |
Electroplating | Component and donor metal are placed in an electrolyte solution. A direct current is applied, depositing metal ions from the donor onto the component. | Improves corrosion resistance. Hardwearing and decorative (e.g., chrome, zinc, nickel). |
Polymer Dip Coating | Metal is heated and dipped into a fluidized bed of polymer powder. The powder melts on contact, forming an even plastic coating. | Tough, impact-resistant. Used on wire products (dish racks) and outdoor equipment. |
Metal Dip Coating | Cleaned metal is dipped into molten metal. Includes tin plating and galvanizing (zinc). | Excellent corrosion protection. Tin for food cans; galvanizing for structural steel. |
Powder Coating | Component is electrically charged. Charged thermoset powder is sprayed on, then baked in an oven to melt and cure the finish. | More durable than paint. Used on white goods (fridges), gates, and railings. |
Metal Varnishing | Metal is polished and degreased. A clear coat is applied by brush or spray. | Protects the surface while keeping the natural metal color visible. Used on brass and copper. |
Anodizing (A-level) | Aluminium acts as the anode in an acid electrolyte. A controlled oxide layer forms, which can then be dyed. | Increases hardness and corrosion resistance. Used on high-end electronics and flashlights. |
Cathodic Protection
Cathodic protection is an electrochemical technique used to prevent corrosion. When two different metals are in contact in the presence of moisture, they form an electrochemical cell. The more reactive metal becomes the anode (and corrodes), while the less reactive metal becomes the cathode (and is protected).
Methods of Protection
Impressed Current
An external power supply provides a continuous flow of electricity to the structure.
Usage: Large-scale infrastructure like underground pipelines and storage tanks.
Sacrificial Anodes
A block of a more reactive metal (like zinc or magnesium) is attached to the main structure.
The sacrificial metal corrodes away entirely to save the main structure.
Usage: Ship hulls, offshore oil rigs, and underground pylons.
Wood finishes
Wood Finishing
Natural Wood Degradation
Wet rot: Alternating wetness and dryness means moisture is absorbed into the wood. Even if the surface dries, moisture remains below the surface, breaking down wood fibres. A fungus spreads, making the wood soft, wet, and crumbly.
Dry rot: A different, fast-spreading fungus that turns wood into a dry, soft, powdery state.
Insect attack: Furniture beetles (woodworm) attack softwood and hardwood; deathwatch beetles attack hardwood. Larvae eat into the wood creating tunnels and exit via "flight holes."
Methods of Wood Finishing
Wood Finish | Method of Application | How they enhance appearance or prevent decay |
|---|---|---|
Polyurethane / Acrylic varnish | Available in gloss, satin and matt, clear or colours. Apply a thin coat with a brush in the direction of the grain. Several coats can be applied, rubbing down with fine glass paper between coats. | Provides a hard, tough, heatproof, waterproof finish. Clear finish allows the grain to be seen. |
Water-based paints | Available in gloss, satin, matt and metallic. Applied with brush, roller or spray. Knots should be treated with knotting solution. Surface should be primed and undercoated first. | Provides protection and colour. Used predominantly for softwoods. Makes surfaces more aesthetically pleasing, tougher, and resistant to moisture. |
Stains | Available in many colours. Applied with brush, roller or spray. Surfaces must be grease-free. | Help colour and enhance the grain. Can make inexpensive wood look more expensive. Do not have specific protective properties. |
Colour wash (A-level only) | Available in many colours. Applied with a wet sponge. | Used to colour the wood for a "vintage" style while allowing the grain to show. |
Wax | Available in clear and coloured waxes. Applied with a brush or cloth; once dry, buffed with a lint-free cloth. | Can be buffed to a high-gloss. Increases surface hardness and toughness. Clear finish shows the grain. |
Yacht varnish | Available in high gloss and satin. Applied with a brush or sprayed directly onto the wood. | Suitable for woods that are outside all year (doors, window frames, boat parts). Increases toughness and weather resistance. |
Danish oil (A-level only) | Applied with a lint-free cloth in the direction of the grain. Leave for 5 mins, then rub away excess. Sand/wire wool between coats. | Maintains natural appearance; soaks into the wood. Not hardwearing, but regular coats build a water-resistant finish. |
Teak oil | Applied with a lint-free cloth. Leave for 5 mins, then rub away excess. Used for naturally oily woods. | Primarily for outdoor products to improve weather resistance and resistance to fungal/insect attack. Enhances grain. |
Pressure treating | Wood is placed in a pressure vessel with copper sulphate and preserving salts. Vacuum and pressure force it deep into fibres. | Protects wood for up to 50 years from rot, insects, and weathering. Used for decking, bridge construction, and cable poles. |