19. The use of finishes Flashcards
1
Q
Why are finishes used?
A
- prevent material from absorbing moisture
- protect against decay or corrosion
- protect against insect attack
- enhance the appearance of the final product
2
Q
What are the paper and board finishing processes?
A
- lamination via encapsulation
- lamination via surface coating
- embossing
- debossing
- varnishing
- UV varnishing
- spot varnishing
- foil blocking
3
Q
Why are paper and board finishing processes used?
A
- provide protection for the material
- enhance appearance
4
Q
What is lamination via encapsulation?
A
- sheet of paper is encapsulated by a polymer pouch or film roll
- desktop laminator
5
Q
What is lamination via surface coating?
A
- liquid lamination (for signage)
- film lamination (for menu cards)
6
Q
What is embossing?
A
- creates a raised design on the surface of paper or card
- gives a visual and tactile effect
7
Q
What is debossing?
A
produces an imprinted depression that sits below the surface of paper or cars
8
Q
What is varnishing?
A
- clear, non-pigmented ink used on pre-coated papers and boards to enhance the colour
- offers some protection against dirt, fingerprints and water
9
Q
What is UV varnishing?
A
- provides very smooth finish
- usually high gloss or matt
- abrasion and chemical resistant
- applied to a sheet via a set of rollers, then passed under a UV light to cure
10
Q
What is spot varnishing?
A
- applied in specific areas or spots
- rather than to the whole surface area
11
Q
What is foil blocking?
A
- heat and pressure applied to metallic paper (foil) to create areas of depth and texture
- add aesthetic impact
12
Q
Why are paper and board printing processes used?
A
- colours, text and images can provide aesthetic appeal
- information such as barcodes, safety warnings and product ingredients can be printed to communicate specific data to the consumer/retailer
- printing processes often use the term ‘substrate’
13
Q
What is the substrate?
A
the material on to which the print ink is applied
14
Q
What are the paper and board printing processes?
A
- screen printing
- flexographic printing
- offset lithographic printing
- digital printing
15
Q
What is screen printing?
A
- can be carried out in a workshop with minimal set up costs due to use of basic screens and printing inks
- screen has open areas for the ink to pass through
- different screen required for each colour
- quite a slow process with a reasonably high cost per product
- used for small print runs of items such as posters, display boards and textile T-shirts
16
Q
What is flexographic printing?
A
- use a four colour process (cyan, magenta, yellow and key black (CMYK))
- four colours are printed on top of one another in various quantities on to the substrate surface to create the print colour required
- colours must line up exactly to ensure a non-blurry image
- simple process
- least expensive due to fast drying water based inks
- used for newspapers, comics, catalogues, folding packaging cartons, labels, carrier bags and continuous patter products such as wallpaper and gift wrap
17
Q
What are the advantages of flexographic printing?
A
- high print speed
- ideally suited to long runs
- prints on a wide variety of substrate materials
- low cost of equipment and consumables
- low maintenance
18
Q
What are the disadvantages of flexographic printing?
A
- cot of the printing plates is relatively high, but last for millions of print runs
- takes a large amount of substrate to set up the job, so excess material may be wasted
- time consuming to change for any alterations to the print content
19
Q
What is offset lithographic printing?
A
- extremely versatile printing process
- capable of producing one colour (single roller)
- five colours (CMYK plus additional metallic colour on a five roller machine)
- ten feature machine (CMYK, metallic, varnishing, spot varnishing and duplex (both sides printed) on a ten roller machine)
- used for printing medium and long print runs of books, business forms and documentation, magazines, posters and packaging
20
Q
What are the advantages of offset lithographic printing?
A
- consistently high image quality
- suited to higher quality print runs of 1,000 or more
- quick and easy production of printing plates
- long life of printing plates because they only come into contact with the printing blanket, which is softer and less abrasive than the substrate
21
Q
What are the disadvantages of offset lithographic printing?
A
expensive set up and running costs for small quantities
22
Q
What is digital printing?
A
- widely utilised resource for printing products, due to its speed and efficiency
- digital printers produce full colour, highly detailed print runs with option of different designs on each page, both front and reverse sides
- can be used for both low and high volume print runs
- very popular for printing promotional materials such as business flyers and business cards
- ideal for mass customisation, due to fast drying inks
23
Q
What is polymer finishing?
A
polymers are self-finishing materials as they require no additional finishing process once manufactured
24
Q
What do polymer finishes do?
A
- enhance aesthetics
- improve product function
25
Q
What are the polymer finishes?
A
- overmouldings
- acrylic spray paints
- addition of pigments
26
Q
What is overmoulding?
A
- moulding a second polymer over specific parts of a product
- TPE (thermoplastic elastomer) is often used
- provide areas of grip or texture
- can highlight different colours for different component parts on products
- two methods
- two injection moulding moulds
- twin-shot injection moulding
27
Q
What is two injection moulding moulds?
A
- one mould for the product
- one mould for the grip areas
- product is injection moulded, then placed in second mould where overmoulding polymer is injection moulded onto the body
28
Q
What is twin-shot injection moulding?
A
- injection moulding machine has a mould designed to product the product in one cycle
- mould has two sepaprate component cavities, and can be rotated 180 degrees so they line up with the twin injection points
- main product part is created in first mould cavity
- mould opens slightly and rotates 180 degrees to secondary position
- mould closes and second injection applies the overmould
29
Q
What are acrylic spray paints?
A
- enhance aesthetics
- fast drying
- water soluble paint that becomes water resistant when dry
- can provide additional protection against effects of UV light and weathering
- often used for mass customisation
- used in automotive industry
- could be pigmented, but impractical and not cost effective for manufacturer
30
Q
What is adding pigments?
A
- provides colour
- pigment particles can be added during manufacturing process or during manufacture of polymer stock form
- smart pigments can be added the same way, producing ready finished smart polymer products
- pigments can be added to gel coats when laying up GRP
- can be used for kitchen chopping boards to identify different ones for different foods
31
Q
What is metal finishing?
A
- most metals have oxide layer (except steels), which provides barrier against environmental effects
- steels (not stainless steel) have an oxide layer, which is porous, allowing moisture to penetrate the metal, leading to rust
32
Q
What are the metal finishes?
A
- cellulose and acrylic paints
- electroplating
- polymer dip coating
- metal dip coating
- powder coating
- metal varnishing
- sealants
- preservatives
- anodising
33
Q
What are cellulose and acrylic paints?
A
- paints primarily used on low cost metals such as steel
- surface of metal is cleaned and degreased, which ensures the primer coat has a sound surface to ‘key’ / grip to
- red oxide primer often used, followed by undercoat in a similar colour to the final top coats
- paints can be applied by brush or spray
34
Q
What is the purpose of cellulose and acrylic paints?
A
- provide colour and textured finish
- provide barrier against corrosion
- specialist paints provide texture or special graphic effects such as pearlescence
35
Q
What is electroplating?
A
- metals for electroplating include silver, gold, zinc, copper and tin
- product and donor material are placed in a container with an electrolyte solution
- as direct current is applied, the product attracts the donor metal and the product is electroplated
36
Q
What is the purpose of electroplating?
A
- protective layer
- more hardwearing finish
- enhanced aesthetics
37
Q
What is polymer dip coating?
A
- metal product is heated to approx. 230 degrees
- then dipped into a tank of fine polymer powder, which has air blowing through it to provide an even coating on the product
- the retained heat from the product melts the polymer powder over the product
- then air cooled to allow the coating to set evenly
38
Q
What is the purpose of polymer dip coating?
A
used on products such as wire coat hangers, kitchen dish drainers, coat hooks, dishwasher racks and outdoor play equipment
39
Q
What is metal dip coating?
A
- metals are coated by dipping the product into a tank of molten plating metal (donor metal)
- metals must be clean and degreased
- tin plating
- pass sheets of steel through a tank of molten tin at approx. 320 degrees
- zinc plating (galvanising)
- dipping steel into molten zinc at approx. 460 degrees
40
Q
What is the purpose of metal dip coating?
A
- provides barrier against corrosion
- tin plating is often used to provide a non-corrosive coating to food cans
- zinc plating is used for many industrial and agricultural applications
- beams, gates and animal pens
- zinc plating is also used as the first protective layer in car bodies made from low carbon steel
41
Q
What is powder coating?
A
- product to be coated is statically charged (negatively)
- thermoset polymer resin (positively charged) is then sprayed through an airgun
- the use of charge results in a strong attraction between the powder and product
- the product is then baked in an oven
- the heat melts the powder over the product to give an even coating
42
Q
What is the purpose of powder coating?
A
- protection from corrosion
- aesthetic appeal
- more hardwearing than paint
- used on washing machine bodies and refrigerator bodies, metal gates, fencing and railings
43
Q
What is metal varnishing?
A
- metal is polished to a shine and any surface grease removed
- varnish then applied by either a spray or with a fine brush
44
Q
What is the purpose of metal varnishing?
A
- protects metal
- allows colour of base metal to show through
- used on aluminium, brass and copper
45
Q
What are sealants?
A
- sealant applied with a cloth or machine pad to produce a film
- film then allowed to cure for up to 15 mins
- then buffed with a cloth to a shine
46
Q
What is the purpose of sealants?
A
- tough polymer-based sealant coatings to protect polished surfaces from decay and tarnishing
- often used in automotive industry against effects of weathering, road salts and insect attack
47
Q
What are preservatives?
A
- applied by wiping on with a cloth, spray or immersion of the product
- silicon sealants can also be classed as preservatives
- can be used on machine bed to provide a smooth, snag-free surface to allow materials to be pushed across the bed more easily and safely
48
Q
What is the purpose of preservatives?
A
- can provide temporary in-process or final post-processing, medium to long-term protection for metal surfaces
- often used on moulds and dies for preventing fingerprints showing on surfaces, minor atmospheric corrosion or condensation build up
49
Q
What is anodising?
A
- electric current passes through the sulphuric acid electrolyte solution from the part to be treated to a negative cathode
- as the current flows from the part to be treated (positive anode) to the negative cathode, the aluminium oxide layer builds up on the treated part, producing the anodised finish
- anodised products can then be finished with a clear lacquer or varnish to seal the finish and provide further protection against surface scratches
50
Q
What is the purpose of anodising?
A
- commonly used for aluminium products to enhance the natural oxide layer, resulting in increased hardness and toughness
- can also provide colour
- used in outer casings of torches, external hard drive covers, and casings for mobile phones or digital music players
51
Q
What do all metals have?
A
a natural voltage
52
Q
What happens when two different metals join, and if water is present?
A
- there is an electrical current
- if water present at the join, this results in an electrochemical cell and one of the metals will corrode
53
Q
What is the reaction?
A
current flow through the water from the anode (more actively corroding metal) to the cathode (less actively corroding metal)
54
Q
What is cathodic protection?
A
- method used to control the rate of corrosion
- makes the metal the cathode of an electrochemical cell
- the anode is a sacrificial metal which is more easily corroded
- the anode corrodes while the base metal is protected
55
Q
What is the main use of cathodic protection?
A
- to protect steel structures buried in soil or immersed in water
- e.g. pipelines, ship hulls, jetties and offshore platforms
56
Q
What are the two methods of cathodic protection?
A
- impressed current
- sacrificial anodes
57
Q
What is the impressed current method?
A
- component to be protected is connected to an electrical power supply
- the impressed direct current flows from an inert electrode through any liquid to the component to be protected
58
Q
Give an example of how impressed current works.
A
- a buried pipeline receives direct current from an electrode buried in the ground
- the pipe becomes the anode
- the electrode is the cathode
- the cathode corrodes over time and such corrosion is monitored so the pipeline stays intact
59
Q
What is the sacrificial anodes method?
A
- more basic because it uses a sacrificial metal to protect the metal product of value
- a more electrochemically active metal is wrapped around or joined to the less active metal to provide resistance to corrosion
- on large structures, the sacrificial metal is monitored for signs of corrosion and replaced when the base metal is no longer protecteed
60
Q
What is the purpose of finishing wood?
A
- prevent absorption of moisture
- protect against decay
- protect against inset attack
- enhance appearance of final product
61
Q
How does natural wood degrade?
A
- wet rot
- dry rot
- insect attack
62
Q
What is wet rot?
A
- alternating wetness and dryness means moisture is absorbed
- though the surface may dry out, moisture remains below the surface
- leads to breaking down of the wood fibres
- fungus spreads through
- wood becomes soft, wet and crumbly
63
Q
What is dry rot?
A
- different, fast spreading fungus causes dry rot
- quickly turns wood into a dry, soft, powdery state
64
Q
What is insect attack?
A
- furniture beetle (woodworm) attacks softwood and hardwood
- deathwatch beetle attacks hardwood
- both lay their eggs in cracks in the wood
- the hatched larvae eat into the wood, creating tunnels
- when the beetle forms, it eats its way out of the wood via a flight hole
65
Q
What should you ensure before applying a wood finish?
A
- make the surfaces smooth
- by planing and/or sanding with glass paper in the direction of the grain using progressively finer grades
- remove all dust with a cloth before the finish is applied
66
Q
What are the methods of wood finishing?
A
- polyurethane varnish / acrylic varnish
- water based paints
- stains
- colour wash
- wax
- yacht varnish
- danish oil
- teak oil
- pressure treating
67
Q
How is polyurethane varnish / acrylic varnish applied?
A
- available in gloss, satin and matt, clear or colours
- apply a thin coat with a brush in the direction of the grain
- several thin coats can be applied, rubbing down between coats with fine grade glass paper
68
Q
How does polyurethane varnish / acrylic varnish enhance appearance or prevent decay?
A
- provides a hard, tough, heatproof, waterproof finish
- clear finish allows the grain of the wood to be seen through the finish
69
Q
How are water based paints applied?
A
- available in gloss, satin, matt and metallic effects
- applied with a brush, roller or spray
- wood knots should be treated with knotting solution to prevent the resin oozing out and spoiling the finish
- the surface should then be primed and an undercoat applied prior to the paint finish
70
Q
How do water based paints enhance appearance or prevent decay?
A
- paint provides both protection and colour
- can be applied for both indoor and outdoor use
- predominantly used for softwoods
- paint makes surfaces more aesthetically pleasing, tougher, harder and resistant to moisture
71
Q
How are stains applied?
A
- available in many different colours and types
- applied with a brush, roller or spray
- surfaces should be grease free prior to application
72
Q
How do stains enhance appearance of prevent decay?
A
- help colour and enhance the grain
- can be used to colour an inexpensive wood to make it look more expensive, or to add colour
- do not have any specific protective properties
73
Q
How is a colour wash applied?
A
- available in many different colours
- applied with a wet sponge
74
Q
How do colour washes enahnce appearance or prevent decay?
A
- used to help colour the wood to make it more aesthetically pleasing, or to add a vintage style
- allows the grain to show
75
Q
How is wax applied?
A
- available in clear and coloured waxes for indoor use
- applied with a brush or a stockinet cloth
- then once dry, buffed with a clean lint free cloth
76
Q
How does wax enhance appearance or prevent decay?
A
- can be buffed to provide a high gloss finish
- increases surface hardness and toughness
- clear finish allows grain to be seen
77
Q
How is yacht varnish applied?
A
- available in high gloss and satin
- applied with a brush or sprayed directly on to the wood
78
Q
How does yacht varnish enhance appearance or prevent decay?
A
- suitable for woods that are outside all year round, such as doors, window frames or boat parts
- increases toughness, hardness and weather resistance
79
Q
How is Danish oil applied?
A
- available in clear or colour tints
- apply with a lint free cloth
- rub the oil into the surface of the wood in the direction of the grain
- leave to absorb for 5 mins, then rub away excess with a clean cloth
- lightly sand or rub with wire wool to open up the grain between coats
80
Q
How does Danish oil enhance appearance or prevent decay?
A
- maintains natural appearance of timber
- soaks into the wood and enhances the grain
- not a hardwearing finish
- regular application and subsequent coats build up a matt, water resistant finish
81
Q
How is teak oil applied?
A
- available in clear tint
- apply with a lint free cloth
- rub the oil into the surface if the wood in the direction of the grain
- leave to absorb for 5 mins, then rub away excess with a clean cloth
- used for naturally oily woods
82
Q
How does teak oil enhance appearance or prevent decay?
A
- mainly used for outdoor wood products to improve weather resistance and resistance to fungal and insect attack
- aesthetically pleasing as grain is enhanced
83
Q
How is wood pressure treated?
A
- wood placed in pressure vessel containing a solution consisting of copper sulphate and other preserving salts
- vacuum and pressure are controlled to force the preservative deep into the fibres of the wood
- the wood is then steam dried
84
Q
How does pressure treating enhance appearance or prevent decay?
A
- helps protect wood for up to 50 years from rot, insect and fungal attack and weathering
- suitable for products such as decking, overhead cable poles, harbour or bridge construction
