Docstoc

The pad printing process

Document Sample
The pad printing process Powered By Docstoc
					                        The pad printing process

During the past forty years, the
                                                    Pad printing
pad printing process has gone
through a period of rapid deve-                  Origins of pad printing
lopment. An important factor in
this development was the imple-              The origins of the pad printing process
mentation of silicone rubber as the          are rooted in the Decalcier Process
                                             which was primarily used in the Swiss
method for ink transfer. Silicone is
                                             watch making industry. In this process,
used because it can be easily mol-
                                             a gelatine pad was used to add ink to
ded into a variety of shapes, and
                                             the watch face.
because it is resistant to colour
                                                                                         Teca-Print was founded 1973 in
absorption. The pad printing pro-            In the late 1960's, the implementation      Thayngen, Switzerland and belongs
cess is a direct marking process             of several technological advance-           now to the worlds best pad printing
that provides a high-quality deco-                                                       machine manufacturers. Our compa-
                                             ments such as the introduction of
ration or mark on any product.                                                           ny’s philosophy focuses strongly on
                                             silicone pads and more efficient
                                                                                         quality, reliability and dynamical furt-
                                             machinery and the development of            her development of the products,
                                             new applications provided the perfect       which include next to a big number of
            Introduction                     opportunity for the development of the      pad printing machines, peripherals
                                             pad printing process.                       and accessories like inks and printing
It is surely the colour of nature that has                                               plates. Many well-known costumers
inspired man to add colour and deco-                                                     all over the world are attended by a
ration to their immediate environment.                                                   dense staff of field service and sales
                                                  What is pad printing?                  personnal. Points of special interests
As a result, there is hardly a product
                                             Pad printing is an indirect photogravu-     are our own subsidiaries in USA
currently manufactured that does not
                                                                                         (Boston and Chicago), France
have some colour or embellishment to         re process. Depressions are etched
                                                                                         (Paris),       Germany        (Baden-
make it stand out in the market.             into a flat plate or printing block, and    Württemberg           and   Nordrhein-
                                             then they are filled with ink. A smooth     Westfalen) and Hungary (Miskolc).
                                             silicone pad is used to pick up the ink     Since 2002 Teca-Print AG is a self-
When considering decoration, manu-
                                             of the plate.                               dependent part of the Machines
facturers must not only find a process
                                                                                         Dubuit SA enterprises, that works in
that will be effective in their marketing                                                the silk screen process worldwide.
                                             Silicone is used because it is ink repel-
and advertising activities, but must
                                             lent, and as a result will not absorb any
also be cost-effective. Manufacturers,       of the ink.
when choosing a marking process,
must also consider if the process is
flexible and reliable.

The process that incorporates all of
these characteristics, cost effective-
ness, flexibility, and reliability, is the
pad printing process.
The pad printing process


                                                                                                                                             pad
                                                                                                blade holder



                                                                                                                          blade
                                                                                                                                              a
                                                                                                                                     plate
                                                                                                                           spatula


                                                                                                    inking slide
                                                                                                               ink well
                                                                                                                                              b




                                                 Fig. 2:
                                                 Pad printing makes it possible to simulta-                                                   c

                                                 neously print on all sides of an object, at
                                                 different heights or in cavities.
Fig. 1:
The pad printing machine TPE 150 is desi-                                                      Fig. 3:
gned for plate sizes from 100 x 100 mm to                                                      a) The starting position of the ink slide
                                                             Ink transfert
150 x 100 mm. Print capacity: 1800 cycles                                                          before the plate is flooded with ink
per hour.                                        Pad printing also allows for ink transfer     b) The plate is flooded with ink before the
                                                 to occur to a sloping or vertical surfa-         printing cycle has begun
     What materials can be                                                                     c) The doctor blade draws the ink back
                                                 ce. Tilt-head machines can be used
                                                                                                  into the reservoir
          printed ?                              for these fields of application.

Because of the wide variety of inks available,                                                 The pad, regardless of size or hard-
                                                 Fig. 3 depicts the actual ink transfer
pad printing can be done on almost any                                                         ness, is cone shaped; that is the base
                                                 process. When a printing cycle is trig-
material.                                                                                      of the pad is wider than its point.
                                                 gered, the ink that is lying on the plate
                                                                                               This shape is necessary because
                                                 is drawn back into the ink reservoir by
Advantages of pad printing?                                                                    during the print cycle, the pad uses a
                                                 a doctor blade. The thinner that is in
                                                                                               rolling motion to eliminate the air that is
There are many advantages that pad prin-         the ink evaporates causing the ink to
                                                                                               between the surface of the plate and
ting has over other methods of marking.          become sticky. The pad is then lowe-
                                                                                               the ink. Eliminating the air between the
                                                 red onto the plate's surface and the ink
                                                                                               pad and the plate guarantees proper
The first advantage is the use of silicone as    is transferred from the plate to the pad.
                                                                                               image pick-up.
the means of transferring the ink. Silicone is   The ink on the pad is then transferred
a very flexible substance and can be mol-        to the component.
                                                                                               The only area of the pad that has direct
ded into a variety of shapes for any applica-                                                  contact with the ink is the area where
tion.                                            Silicone Pad as the Transfer
                                                                                               the image is placed on the pad. All
                                                          Mechanism
                                                                                               other areas of the pad remain free from
This flexible quality enables the pad to print                    (Fig. 4)
                                                                                               ink (Figure 4).
on uneven surfaces. Pad choice is depen-
dent upon the shape of the product, the          The printing pads Teca-Print use are
image size and its positioning. The use of       made of silicone and are available in a
height compensators, as shown in Figure 2,       variety of shapes and degrees of hard-
will allow for a simultaneous printing of an     ness. The pad that is selected for any
image at different heights.                      application must be chosen so that it
                                                 can conform to the component's
                                                 shape without causing any distortion in
                                                 the image during transfer.
                                                                         The pad printing process

                                                 damages the pad's surface and its
                                                 ability to transfer the ink.
                                                 The actual print life of a standard prin-
                                                 ting pad – under ideal conditions –
                   a                       b     would be between 20,000 and
                                                 500,000 printing cycles. The printing
                                                 life is dependent on a number of fac-
                                                 tors including:
                                                 – the type of ink used
                   c                       d     – pad shape, size and hardness
                                                 – the shape of the printed part
                                                 – the type of object surface

                                                 The printing quality of the pad deterio-
                                                 rates over time because the printing
                   e
                                                 surface (which needs to be smooth for
Fig. 4:                                          undistorted ink transfer) is in contact     Fig. 5:
Ink transfert process:                           with the ink and thinner that causes        Pad printing machine TPX 301 for multi-
a) The thinner evaporates from the surface       the pad's surface to become rough.          colour printing.
   of the ink in the plate and the ink beco-
   mes sticky.                                          Ink layer thickness
b) The pad sinks down on the surface of                                                      Although pad printing does have its
   the plate and the ink sticks to the pad.      The actual thickness of the ink that is     limitations, it is no different than other
c) The pad is then lifted up from the plate.     transferred from the pad to the com-        printing processes. Relief printing, for
   The ink layer is detached from the plate.     ponent is approximately four microns.       example, is able to provide excellent
d) The ink is carried by the pad to the surfa-                                               colour transfer because the ink sub-
                                                 The ink's thickness is dependent on
   ce of the component. The thinner eva-
                                                 the type of ink that is used, ink visco-    strate is welded film. This process is
   porates from the ink on the pad. The ink
                                                 sity, the etch depth of the plate, and      very expensive and most manufactu-
   becomes sticky. The ink is applied to
   the component’s surface and remains           atmospheric conditions such as heat,        rers are unable to use this process
   on the objekt.                                air temperature, and humidity.              profitably.
e) The pad is lifted off from the component
   and the ink layer detaches from the pad             Multi-colour printing                 Screen printing can be used to mark
   and stays on the component.                                                               large images, but it is not a flexible
                                                 Because of the rapid conditioning of        method and the squeegee cannot
             Pad quality                         the ink, it is also possible to use pad     adapt itself to the shape of the object.
                                                 printing for multi-coloured applications.
The quality of image printed on the
product is dependent upon the pad's              The accessories available for such
surface texture. When using a pad for            applications include:
the first time, the silicone oil must be         – The two-colour pad sliding device
washed off the pad's surface. This can           – Rotary tables
be accomplished by using ink thin-               – Displacement tables
ners.                                            – Transfer carrousels
                                                 – Linear indexing devices.
The actual surface of the pad that will
be used for printing must also be                Pad printing must be viewed as a
cleaned, but therefore only cleaning             separate and distinct method of prin-
tape is recommended. It is also impor-           ting, not just as a “refinement" of other
tant to understand that the pad surfa-           printing processes, specifically screen
ce should never be rubbed dry as this            printing and relief printing.
The pad printing process

                                                     general, the etch depths are 16            Fig. 7:
              Plates                                 microns for fine scripts, and 22           For large images, the doctor blade can
        Steel plates       (Fig. 6)                  microns for standard scripts.              sag, scrape the plate and remove too
                                                                                                much ink. Screen-dotting the image after
For fields of application that require                  Film quality and choice                 exposure eliminates this problem
precision printing and are printed in
                                                     The quality of the finished etched                   Plastic Plates
large series, steel plates are used.
                                                     image is dependent on the type of film
Steel plates can be manufactured
                                                     used during plate exposure. Teca-Print     For small production series, Nylo pla-
using several methods. The first
                                                     uses high-quality film materials for       tes can be used. These plates, if
method for steel plate production is
                                                     exposing plates.                           handled properly, will have a produc-
light exposure. This method involves
several steps.                                                                                  tion life of several thousand prints.
                                                         Screening Steel Plates                 Alcohol wash plates are metal-based
                                                                              (Fig. 7)          plates that are coated with a light-sen-
                              exposure
                                                                                                sitive material that becomes hard
                                                     Screen dotting is used because it eli-     when exposed to light.
                                                     minates the problem of having the
                                                     doctor blade sag into the etched           When a film is placed on the plate and
                              film
                              photosensitive layer
                                                     image, which causes an uneven distri-      exposed to light, the image zones that
                              steel plate
                                                     bution of ink. When screen dotting is      were covered by the film remain soft.
                                                     used, small cones remain in the ima-       The plate is again exposed, but this
                                                     ge's area, which result in the following   time with a screen-dotted film. The
                              area revealed in
                              developer              advantages:                                "dots" on the plate remain hard, and,
                              hardened layer         – The doctor blade is supported by         after washing the plate with the appro-
                                                       the small crests, which prevents the     priate developing agent, small flat
                                                       doctor blade from sagging.               cones remains on the plate.
                              etched area
                              of image               – The screen dots retain the ink's even
                                                       distribution of the entire image area.   The screen-dotted process for plate
                                                     – The pad is supported by the crests       development must always be used to
Fig. 6:
Steel plate production.
                                                       which enables ink pickup to remain       when working with Nylo plates.
                                                       uniform.
The surface of the steel plate is initially                                                     Water Wash Polymer Plates
coated with a light-sensitive material.
                                                             plate
Before exposing the plate to light, a                                                           Another more recent development in
film containing the desired image                                                               plate technology is the use of water
                                                                              pad
design is placed face down on the                                                               wash polymer plates. Instead of a che-
plate. The film and plate are then                                                              mical, lukewarm water is used as a
exposed to light. The light hardens the                                                         developer. The exposure process for
area of the plate not covered by the                                                            these plates is the same as for alcohol
film. The areas that were covered by                                                            wash plates. By air-drying the plates,
                                                              ø 0.02 – 0.03
the film remain soft. The soft area of                                                          and then exposing them to UV light,
the plate is then removed from the                                                              the plastic plate's production life is
plate by soaking the plate in a devel-                                                          increased significantly.
oper bath. The area containing the
image leaves an impression that will be
etched in a bath consisting of nitric
acid, chlorine (III), iron, or other similar
chemicals.                                                     0.125
                                                                                         45°

The actual etch depths for a steel plate
vary depending on its intended use. In
                                                                    The pad printing process

                Inks                             Colour mixing systems                             Viscospatula
                                                                                        To enable our customers to make sure
The selection of the proper ink series       In addition to our standard pad printing   that proper ink viscosity is reached,
and type for a particular application        inks, we are also able to provide          Teca-Print AG has developed the
depends on the demands of the appli-         mixing inks that, when combined, can       Viscospatula (Figure 9).
cation. For example, ink type depends        reproduce all Pantone or RAL colours.
on whether or not a glossy or dull finish    This inexpensive and easily used kit       When mixing the ink the following
is required, whether or not thinners or      comes with the twelve basic colour         steps must be observed to assure
other chemicals will be used in the          tones and is available in one- and         proper viscosity:
production process, and on the type          two-component inks.                        – Ink hardener, when added to two-
of adhesion test the ink must pass.                                                       component inks, must be thorough-
                                                           UV Inks                        ly mixed before ink viscosity testing
         Ink Composition                                                                – Thinners and retarders used to con-
                                             In addition to the standard one-com-         dition ink viscosity must be added
All of the inks that are used in pad prin-   ponent ink, we have UV-curable one-          drop by drop into the ink. The ink
ting have been specifically developed        component inks. These inks are               must also be stirred continuously.
and conditioned for a rapid cycle time.      cureed by ultra-violet radiation, this     – If this is not done correctly, pigment
The transfer substance and binders in        process changes inks’ molecular              shock occurs. This means that the
the inks are resins of either an epoxy or    structure by forming macro-molecules.        ink pigments are separated from the
a polyester base with pigments knea-                                                      resin base substance and the ink
ded into the mixture.                        UV inks have several advantages over         can not be used.
                                             the standard inks such as reduced
     One Component Inks                      cureing time, reduced solvent emis-        Ink viscosity cannot be tested using
                                             sions, and a constant ink viscosity.       the above process if they have
In many applications single-com-                                                        thixotropic properties.
ponent inks can be used. These inks          However, because these inks use UV
have a longer pot life and are easier to     radiation to increase cureing time, spe-
process than two-component inks.             cial precautions must be followed
These inks are very resistant to harm-       when using the inks. For example, the
ful solvents. They may also be cured         radiation source must be enclosed
either by drying by the air or by a heat     and direct contact with the cureing
source.                                      source must be avoided. Also, becau-
                                             se such precautions are necessary,
     Two Component Inks                      and because of environmental con-
                                             cerns (ozone is created during the dry-
Two-component inks are used for              ing process, therefore the dryer must
applications that need to have high          be in a ventilated area), the process is
mechanical resistance. These inks are        expensive.
used for example for radio dials, com-
puter parts and typewriter key pads.            Proper Ink Conditioning
These inks chemically bond with the
material on which they are printed after     Teca-Print pad printing inks are ready     Fig. 8:
the thinner in the ink evaporates. It        to use. However, the ink must be con-      Ink mixing and viscosity testing with the
takes around six days on average for         ditioned to reach proper viscosity         viscospatula
the ink to cure completely.                  levels.
The pad printing process

      Ink adhesion                                 Corona treatment                                 Ionization
                                            The pre-treatment process can also         Many plastic components build up an
We have already mentioned several
                                            be accomplished by using electric          electrical charge as the result of static
key issues, including proper pad and
                                            corona equipment.                          electricity while processed. Static
ink choice ad the etch depth of the
                                            In the corona pre-treatment process,       electricity has an adverse effect on the
plate.
                                            the substrate's printing surface is        printing process because the image
However, perhaps the most important
                                            bombarded with ions and electrons          "picks up" the charge during transfer
issue that is related to ink adhesion, is
                                            that cause the static charge of the        and the print becomes distorted.
the composition of the part (or sub-
                                            uppermost layer of molecules to chan-      Using de-ionizing equipment on the
strate) that will be printed. Depending
                                            ge. This also results in increased sur-    components not only eliminates static
on the type of substrate used, additio-
                                            face tension.                              electricity build-up, but it also removes
nal processing of component may be
                                            Corona pre-treatment is based on a         dust particles and dirt that have accu-
needed to guarantee proper adhesion.
                                            high-voltage spark with the voltage        mulated on the components.
                                            ranging form 5 and 15 kV at frequen-
  Pre-Treatment Processes
                                            cies between 15 and 30 kHz.                         Post-treatment
                                            This process is preferred over the
Components made of polyolefine,                                                        The main purpose for treating compo-
                                            flame pre-treatment process because
polyethylene, and polypropylene must                                                   nents after the printing process is to
                                            it is less hazardous, that is, there are
undergo a pre-treatment process to                                                     reduce the curing time needed for the
                                            no concerns regarding an open flame.
ensure proper adhesion because their                                                   components.
surface tension is too low. The surface                                                Post-treatment, or curing, is usually
tension for a component can be tested
                                                    Bonding agents
                                                                                       used in applications where the com-
with a pen, and if it is below 38 dyne /    A third pre-treatment process is the       ponents will undergo additional pro-
cm, the component must be pre-trea-         use of a bonding agent. This is a che-     cessing within a relatively short time.
ted using one of the following proces-      mical process which requires the com-      The methods by which the images are
ses.                                        ponent's surface to be coated with the     cured include flame treatment, hot air
                                            agent. The surface is chemically           treatment, or passing through an infra-
              Flaming                       etched and is ready for processing.        red dryer.
The printing surface requiring treat-       The use of the bonding agent as a          It is important to note that with two-
ment is passed under a pure flame.          pre-treatment process is limited to        component inks, even when they
This causes scarification of the sub-       small series runs. This process also       undergo a post-treatment process, full
strate, and the result is increased sur-    requires accesses to a well-ventilated     curing (that is, molecular bonding)
face tension. Flame intensity is control-   room.                                      does not take place for six days.
led by the operator, and the actual
lenght of time necessary for the fla-
ming process to be complete is sub-
strate-specific.
Flaming does, however, remove the
gloss of the component's surface
area. This must be taken into account
if a glossy effect is desired for the
application.
                                                                      The pad printing process
                                                   Fields of application
  Pad and printing                                                                               CONCLUSION
                                             The pad printing process that has its
        Pad printing errors                  origins in the Swiss watch making             Pad printing is very versatile and flexi-
                                             industry has expanded to many other           ble. Many objects can be printed on
The most common error that occurs in                                                       without much preparation needed.
                                             types of industries including, but not
any printing process is poor image                                                         This requires some basic knowledge,
                                             limited to, the:
transfer. Pad printing is no different,                                                    unskilled workers can be used for ope-
                                             – electronic industry
and in some cases the image that is                                                        rating the printing machines.
                                             – semiconductor industry
transferred onto the component may
                                             – automotive component industry
not be clear and unblemished.                                                              Teca-Print printing machines are very
                                             – sporting goods industry
However, unlike other processes                                                            user-friendly, even untrained personnel
                                             – medical component industry
where the error is usually process-rela-                                                   can operate them after very little pre-
                                             – plastic component industry
ted, the errors that occur most often                                                      paration
                                             – compact disc industry
are the result of not following the pad
printing process guidlines.                                                                Teca-Print will be glad to help you with
                                             These industries represent only a frac-
                                             tion of the industries that use pad prin-     complex and innovative printing pro-
Errors, such as poor image transfer,                                                       jects.
                                             ting as a method of decoration.
can be easily resolved by reviewing
                                             The only limitation to the use of pad
the process used. For example, if dots                                                     We hope this brochure helped to
                                             printing, at this point, is the image size.
appear in the final image after transfer,                                                  extend and deepen your knowledge of
                                             Pad printing can even be used to print
it is almost certain that the problem in                                                   the pad printing process.
                                             images on a cylinder shape up to a cir-
the process occurs during image
                                             cumference of 120°. Pad printing is a
transfer from the plate to the pad.                                                        Further information on our company
                                             very versatile and economical method
                                             for marking components.                       and our range of products – from stan-
The reason the dots appear on the                                                          dard machines to complex printing
finished image is that too much thinner                                                    systems – can be found on our web
                                             Teca-Print AG and its agents located
has been applied to the ink. As a                                                          page:
                                             throughout the world are committed to
result, the pad no longer has direct
                                             providing the market with reliable mar-
contact with the ink on the plate's sur-
                                             king equipment and supplies.
face.
To resolve this problem simply reduce
the amount of thinner added to the ink,
use a harder pad, more angular pad,
and reduce the cycle speed on the
printer, so that the air has more time, to
escape when the pad picks up the
image from the plate.




                                                                                           Teca-Print AG       Tel. +41 (0)52 645 2000
                                                                                                               Tel. +41 (0)52 FON TECA
                                                                                           Postfach            Fax +41 (0)52 645 2102
                                                                                           Bohlstrasse 17          info@teca-print.com
                                                                                           CH-8240 Thayngen              teca-print.com

				
DOCUMENT INFO