1.5 The Use of Finishes Flashcards
1
Q
METALS
cellulose & acrylic paints
A
- colour (& textured) finish
- barrier against corrosion
- used on low-cost metals (eg steel)
- surface must be cleaned & degreased before application
- primer coat used
- applied w/ brush/spray
- specialist paints add texture or special graphic effects (eg pearlescence)
2
Q
METALS
electroplating
A
- uses electrolysis to coat base metal in another metal (usually more expensive)
- protective layer & greater aesthetic appeal
- current passed through solution with the 2 metals)
- anode & electrolyte made up of plating metal (anode replenishes metal in solution)
- +ly charted ions attracted to cathode (-ly charged) & deposit on cathode forming plating
- because +ly charged ions gain electrons at cathode
- atoms in the anode lose electrons & dissolve into solution (oxidation)
3
Q
METALS
polymer dip coating
A
- metal product heated then dipped into tank of fine polymer powder
- tank has air blowing through it (fluidisation bath) to help get an even coating
- heat from product allows powder to melt over product
USES: wire hangers, dish drainers, dishwasher racks, outdoor play equipment
4
Q
METALS
metal dip coating
A
- product is dipped into tank of molten donor metal
- used for cheap metals (eg low carbon steel)
- protects against corrosion
- usually 2 types:
> tin plating (eg food cans)
> zinc plating (galvanising) (eg car bodies, gates, animal pens)
5
Q
METALS
powder coating
A
- product is statically (-ly) charged
- sprayed with (+ly) charged thermoset polyester resin through airgun
- charge causes strong attraction between powder & product
- product baked in oven- heat melts powder over product & gives even coat
USES: domestic white goods (fridge, dishwasher, etc), coloured finish to metal gates, fences etc
6
Q
METALS
varnishing
A
- clear finish
- used on expensive metals (protects but allows colour to show)
- eg brass, copper
- applied with spray/fine brush
7
Q
METALS
sealants
A
- tough polymer-based
- protect polished surfaces from decay & tarnishing
- silicon-based cheap sealants used on cars to protect bodywork from weathering, insect attack, road salts, etc
- applied using cloth/machine pad
- produces film that is left to cure before buffed
8
Q
METALS
preservatives
A
- can be temporary in-process or medium to long-term protection
- used on moulds/dies to prevent fingerprints, minor atmospheric corrosion or condensation build up
- applied by wiping on with cloth/spray/immersion
9
Q
METALS
anodising
A
- commonly used on aluminium
- enhances natural oxide layer> increased hardness & toughness
- can also provide colour
- similar to electroplating
> electric current passes through sulphuric acid electrolyte solution from anode (part to be treated) to cathode
> aluminium oxide builds up on treated part producing finish
> can be finished with clear lacquer/varnish to seal and prevent scratches
USES: outer casings of phones, hard drive covers etc
10
Q
METALS
cathodic protection
(basic info)
A
- all metals have a natural voltage
- when 2 different metals are joined together there is an electric current
- if water is present at the join an electrochemical cell is formed & one of the metals will corrode
- current flows through the water from the anode (more actively corroding metal) to the cathode (less actively corroding metal)
- eg aluminium sheets held together with brass screws in presence of rainwater- aluminium will corrode around joint
- cathodic protection used to control the rate of corrosion
- the anode is a sacrificial metal which protects the cathode
- main use: protect steel structures buried in soil/underwater (eg pipelines, ship hulls, offshore platforms)
11
Q
METALS
cathodic protection
(impressed current)
A
- component to be protected is connected to electrical power supply
- impressed direct current flows from an inert electrode through any liquid to the component to be protected
- EG burned pipeline recipes direct current from electrode buried in the ground. pipe = anode, electrode = cathode, cathode corrodes over time and is monitored
12
Q
METALS
cathodic protection
(sacrificial anodes)
A
- uses a sacrificial metal to protect the metal product of more value
- more electrochemically active metal is wrapped around/joined to the less active metal to provide corrosion resistance
- on large structures the sacrificial metal is monitored for signs of corrosion and replaced when needed
13
Q
POLYMERS
advantages of polymer finishing (4)
A
- polymers are self-finishing
- surface textures are produced from the mould
- addition of pigments during manufacture adds colour making polymer self colouring
- polymers are considered finished and ready to use when manufacture is complete
14
Q
POLYMERS
overmoulding
(summary)
A
- moulding a second polymer over specific parts of a product
- TPE often used
- primarily used to provide different areas of grip/texture or highlight different colours for different component parts
- eg toothbrush handle
15
Q
POLYMERS
overmoulding
(using two injection moulding moulds)
A
- one mould is made for the product & one for the grip areas
- product body is injection moulded then placed into second mould
- overmoulding is injection moulded onto the body
16
Q
POLYMERS
overmoulding
(twin shot injection moulding)
A
- mould has two separate component cavities
- can rotate 180° to line up with twin injection points
- main body is made first
- then mould opens up slightly and rotates to secondary position
- mould closes again & second injection applies overmould
- twin shot injection moulding is a continuous process- a new part made while another being overmoulded
17
Q
POLYMERS
acrylic spray paint
A
- fast-drying, water-soluble paint, becomes water resistant when dry
- enhances aesthetics, protects against UV & weathering
- allows for mass customisation (eg cars)
- polymers can be pigmented during manufacture instead but not cost effective to keep changing granules in machine
18
Q
POLYMERS
pigments
A
- added during manufacture process
- pigment particles can be added to hopper during injection moulding but more commonly bought as pre-pigmented stock forms
- smart pigments (eg thermochromic etc) can be added in the same way
19
Q
POLYMERS
gel coat & lay up process
A
- pigment can be added during lay up process for GRP
- polyester resin bought pre-pigmented then applied to mould before GRP matting
- eliminates need to add individual pigments to resin
- no need for additional finishing
- eg boat hulls
20
Q
WOOD
general purpose of wood finishing (4)
A
- protect against absorbing water
- protect against decay
- protect against insect attack
- enhance appearance
21
Q
WOOD
wet rot
(summary)
A
- occurs when moisture content of wood is very high (above 50%)
- black fungus may grow on timber
- wood fibres break down & fungus grows
- timber feels soft & spongy
22
Q
WOOD
wet rot
(treatment)
A
- cause of moisture identified & stopped
- wet rot treated with fungicide
- sometimes affected area has to be removed & replaced
23
Q
WOOD
dry rot
(summary)
A
- caused by fast-spreading fungus
- leaves cracks deep in the grain
- white sheets of fungus (mycelium growth) can sometimes be seen
- timber can become dry, soft and powdery
- can spread throughout timber and cause significant structural damage
24
Q
WOOD
dry rot
(treatment)
A
- dry rot treatment used to eradicate moisture
- infected timber is replaced
25
WOOD
insect attack
(summary)
- often known as wood worm
- insects (eg furniture beetles) lay eggs in cracks in the wood
- hatched larvae eat through wood forming tunnels
- leaves tiny holes visible on surface of wood
26
WOOD
insect attack
(treatment)
- permethrin-based wood treatment applied to affected area with brush/spray
- alternatively, it can be injected into the wood
27
WOOD
| preparing surface for finishing
- surfaces made smooth by planing/sanding (progressively finer glass paper)
- sanding should be done in direction of wood grain (avoid scratching)
- cloth used to wipe away remaining dust
- finish applied
28
WOOD
| polyurethane/acrylic varnish
- 3 types: gloss, shear, matt
- clear or coloured
- APPLICATION: thin coat applied with brush, several coats applied in between glass paper to smooth surface
- SURFACE FINSH/DECAY PREVENTION
> hard, tough, heat proof, waterproof
> clear finish allows wood grain to be seen
29
WOOD
| water-based paints
- different finishes: gloss, matt, metallic, satin
- mostly used for softwoods
- knots must be treated before to prevent resin seeping out
APPLICATION: primed & undercoated, paint applied with brush/roller
SURFACE FINISH/DECAY PREVENTION:
> provides protection & colour
> can be used inside & outside
> surfaces more aesthetically pleasing
> harder, tougher, water resistant
30
WOOD
| stains
- many different colours & types (eg mahogany, antique)
- water/spirit based
- surfaces need to be grease free before application
APPLICATION: applied with brush/roller/spray
SURFACE FINISH/DECAY PREVENTION:
> helps colour, enhances grain
> can be used to make cheap woods look more expensive
> adds colour but allows grain to show
> no protective properties
31
WOOD
| colour wash
- many different colours
APPLICATION: using wet sponge
SURFACE FINISH/DECAY PREVENTION:
> adds colour but grain still shows through
> can be used to make wood more aesthetically pleasing/give vintage style while grain still shows
32
WOOD
| wax
- clear & coloured
- for indoor use
APPLICATION: with brush/stockinet cloth, once dry buffed with lint-free cloth
SURFACE FINISH/DECAY PREVENTION:
> can be buffed for high gloss finish
> increases surface hardness & toughness
> clear- shows wood grain
33
WOOD
| pressure treating
APPLICATION:
- wood placed in a pressure vessel containing solution of copper sulphate & other preservatives
- vacuum & pressure control to force solution into wood
- wood is steam dried
DECAY PREVENTION:
> protects for up to 50 years from rot, insect & fungal attack & weathering
USES: decking, cladding, bridges, overhead cable poles
34
WOOD
| yacht varnish
- high gloss or satin
APPLICATION: with brush/spray
SURFACE FINISH/DECAY PREVENTION:
> increases hardness, toughness & weather resistance
- for woods outside year round (eg doors, window frames, boat parts)
35
WOOD
| danish oil
- clear or coloured tints
APPLICATION:
- with lint-free cloth, oil is rubbed into wood, in direction of grain
- left for 5 mins to soak in, then excess wiped off
- lightly sanded/rubbed with wire wool between coats to open up grain
SURFACE FINISH/DECAY PREVENTION:
> maintains natural appearance of timber
> enhances grain
> not very hardwearing finish but regular application builds up matte, water resistant finish
36
WOOD
| teak oil
- clear tint
APPLICATION:
- with lint-free cloth, oil is rubbed into wood, in direction of grain
- left for 5 mins to soak in, then excess wiped off
- lightly sanded/rubbed with wire wool between coats to open up grain
SURFACE FINISH/DECAY PREVENTiON:
> mostly for outdoor use to improve weather resistance & resistance to insect & fungal attack
> enhances grain
37
PAPER & BOARD
| laminating (encapsulation)
- sheet of paper encapsulated in polymer pouch/film roll
- paper is fed through desktop laminator & heat sealed leaving polymer sheet cover on both sides & border
- polymer pouch is usually PET and EVA mix
38
PAPER & BOARD
| lamination (surface coating)
```
- liquid or film lamination
LIQUID:
- applied with roller/spray
- protects from moisture, dirt, UV light
- eg for signage
FILM:
- usually PP with adhesive
- can be done with hot or cold processes
- laminate is fed from roller & pressure applied as paper fed through
- eg for menu cards, business cards
```
39
PAPER & BOARD
| embossing
- creates a raised design on the surface of the paper
- visual & tactile effect
- uses 2 dies- male & female
- dies can be cold or heated
- substrate placed between the two dies & held under pressure until embossed design formed
- embossed area can have ink/foil applied or left as is (blind emboss)
- decorative technique- eg for cards, business cards, packaging
40
PAPER & BOARD
| debossing
- same as embossing but produces imprinted depression
41
PAPER & BOARD
| foil blocking
- application of heat & pressure to apply metallic foil to create areas of depth & texture
- adds aesthetic impact
- uses machine with heated die, design is stamped onto material through foil which is transferred as it sticks to paper
- requires accuracy & consistency- too hot/pressure held for too long foil will bubble & peel, too cool/not enough pressure foil will not adhere
- eg business cards, letterheads
42
PAPER & BOARD
| varnishing
- clear, non-pigmented ink used on pre-coated paper/board to enhance colour & protect against dirt, fingerprints, water
- gloss, matte, satin, tinted
- applied as flood coat
- only suitable for pre-coated papers because they won't soak up ink and swell/bleed colour
43
PAPER & BOARD
| uv varnishing
- very smooth finish
- ink must be completely dry before application
- specific machinery used that instantly cures UV varnish to provide high quality finish
- usually gloss or matte
- chemical & abrasion resistant
- applied via set of rollers then passed under UV light to cure
44
PAPER & BOARD
| spot varnishing
- varnish applied in specific areas of paper rather than whole surface
- plate/set of plates presses onto surface & applies varnish
- can be both varnish & UV varnish
45
PAPER & BOARD
offset lithographic printing
(summary)
- extremely versatile
- one colour (single roller), 5 colours (CMYK + metallic), 10-feature (CMYK + metallic + varnishing + sports varnishing + duplex [both sides printed])
- medium to long print runs (eg magazines, books, packaging)
- uses principle that oil & water do NOT mix
46
PAPER & BOARD
offset lithographic printing
(how/why it works)
- oil & water do not mix
- lithographic plates chemically treated to make image area oleophilic (easily absorbs oils) so receptive to oil-based ink
- non-image area hydrophilic (absorbs water)
- dampening solution applied to roller- mostly water based so attracted to non-image areas
- ink applied and attracted to image area
- ink and water don't mix so solution prevents ink entering non-image area
47
PAPER & BOARD
offset lithographic printing
(printing process)
- printing substrate fed into printing machinery
- printing plates produced by computer to plate (CTP) process using a laser to etch image onto plate
- plates attached to machine & dampened
- ink applied to printing plate, plate cylinder rotates onto blanket roller which is coated in ink
- as substrate fed through image on blanket roller is transferred to substrate
48
PAPER & BOARD
flexographic printing
(summary)
- uses CMYK- inks are printed on top of each other in various quantities to produce print colour
- colours must be precisely aligned to create accurate, non-blurry image- registration marks used
- least expensive printing process- simple, fast-drying inks
- rolls of substrate used rather than sheets to allow for continuous printing
- eg newspapers, carrier bags, wallpaper, gift wrap
49
```
PAPER & BOARD
flexographic printing
(printing process)
```
- flexible printing plate wrapped around rotating cylinders on web press
- water-based/UV curable ink fed from 1st roller to anilox roller
- anilox roller makes ink a uniform thickness and transfers ink to printing plate cylinder
- substrate moves between plate cylinder & impression cylinder
- impression cylinder applies pressure to plate cylinder to transfer image to substrate
- web (now printed) fed into overhead dryer so ink is dry before it goes to next print unit
50
PAPER & BOARD
screen printing
(summary)
- used for small print runs (eg posters, t-shirts, display boards)
- can be carried out in a workshop
- minimal set up costs- basic screens & printing inks
51
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PAPER & BOARD
screen printing
(printing process)
```
- substrate sits on machine base & is secured
- image is created on screen/stencil. this is a mesh held by the frame
- screen has 'open' areas for ink to pass through
- different screen required for each colour (can make process time consuming & increase production cost)
- screen placed over substrate
- pigmented printing ink placed on mesh
- squeegee used to force ink through mesh & onto substrate
- once each colour complete ink dries/cures
52
PAPER & BOARD
| digital printing
- becoming more popular & widely used because of speed & versatility
- full colour, highly detailed print runs
- option of different designs on each page, both front and reverse sides
- similar to laser printers- ink sits on top of substrate and allowed to dry/be laminated
- both low & high volume print runs
- ideal for mass customisation- use of fast drying inks
- uses: flyers, business cards etc
53
what does CMYK stand for?
Cyan
Magenta
Yellow
Key (black)
54
advantages of offset lithography (7)
- most common printing method
- consistent high quality
- fast
- prints onto paper well
- suitable for high print runs (1000+)
- quick & easy to produce printing plates
- long life of printing plates as they only come into contact with blanket roller which is less abrasive than substrate
55
disadvantages of offset lithography (3)
- expensive set up cost
- only suitable for porous substrate materials
- very expensive for small print runs
56
advantages of flexography (5)
- very fast
- suited to long print runs
- prints on wide variety of substrate (porous & non-porous)
- low cost of equipment & consumables
- low maintenance
57
disadvantages of flexography (5)
- expensive set up cost
- cost of printing plates very high (but last for millions of print runs)
- large amount of substrate needed to set up job
- excess material may be wasted
- time consuming to change for any alterations to print content
58
advantages of screen printing (2)
- good for short print runs
| - can print on absorbent surfaces (eg fabric)
59
disadvantages of screen printing (2)
- slow
| - not as high print quality as other methods
60
advantages of digital printing (3)
- allows for mass customisation
- fast
- highly detailed prints
61
disadvantages of digital printing (2)
- more expensive for longer print runs (usually fixed price per print)
- can't print lighter colours (eg white) on dark substrate
