Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF THE INVENTION
MET~OD FOR THE MANUFACTURE OF A DYED, MOLDED,
PLASTIC ELEMENT
BACKGROUND OF THE INVENTION
.. .. . .... . _ _ _
Field of the Invention
The invention relates to a method for the
manufacture of a dyed, molded plastic element by
heating a smooth sheet of plastic, which is coated on
at least one side with a detachably adhering plastic
foil that is stretchable when heated to the molding
temperature of the sheet, molding the sheet while
simultaneously molding the foil adhering thereto, and
cooling the molded plastic element to a temperature
below the molding temperaturer
Descriptlon of _he Related Art
A related moldlng process .is taught in DE 27 18 510.
In this method a cast sheet oE polymethylmethacrylate is
detachably coated with a polyethylene foil, heated to
the molding temperature, molded with the Eoil adhering
thereto and cooled. Thereafter, the foil can be pulled
off or left in place on the molded element to protect
the surface until further processing or until use.
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With this method, even dyed or patterned sheets of
polymethylmethacrylate can be worked. In this case,
the polyethylene foil cannot be applied until after the
sheet has been provided with the desired dyes or
patterns. The transfer printing method according to
DE-OS 32 44 355, for example, can be used for this
purpose. Uncolored or unpatterned sheets of
polymethylmethacrylate are provided ~ith a protective
lamination immediately after manuEacture, which
protective lamination is removed before the sheet is
dyed or patterned dur1ng the transfer printing process
or in another manner.
Removal of the protective coating prior to dyeing
or patterning and re-coating with a protective
lamination after this operational step is not very
economical. Canadian Patent Application No. 520,135
describes transfer printing onto foil-
coated plastic sheets, whereby the dye transfer takes
place from a flat dye vehicle through the foil and onto
the surface of the plastic sheet.
DE-A 33 24 709 discloses a method in which a
thermally heated plastic sheet is simultaneously molded
and dyed by trans~er printing. In this method, the
sheet is molded by means o~ a tool which is overlaid
with a flat dye transeer vehicle. This method does not
permit the manufacture of spherically molded, dyed
~r~6~
elements, or only p-~its it with the limitation that
the flat dye vehicl- ~ust first be brought into the
corresponding spher_:al shape.
In spite o~ th~bove-described known methods,
there remains a nee- Eor new, more economical and
simpler methods for ~roducing dyed, molded plastic
elements.
SU~ Y OF THE INVENTION
Accordingly, i- is an object of the present
invention to provic~ an improved method of
manufacturing dyed, ~olded plastic elements in which a
separate operating -ep of dyeing or patterning is
avoided and the ne~- for energy and related materials
is reduced.
This and othe- ~bjects have been achieved by the
discovery of a man ~cturing method wherein duriny the
molding process a pistic sheet is employed which is
coated with a detac::lbly adhering eoil containing a
transEer dye, and crin~ the heating of the sheet to
the molding temper--lre and/or during the molding, dye
is transeerred fro~ :he foil to the surEace of the
sheet. As a rule, ~c dye transeer will take place
primarily during th ~eating Oe the plastic sheet to
the molding temperz- re, but can also continue during
the molding proceSc ~self. If the foil is applied to
the plastic sheet t-:~ugh the use of heat, a portion of
~ ~J~
the dye can even be transferred then. Since there is
no shifting of the foil relative to the sheet dye to
adherence, the method step at which the primary
quantity of the dye is transferred is not critical to
the success of the process. Even the extensions that
occur during molding do not lead to blurred pattern
transfers, because the adhering foil is extended
together with the sheet.
In accordance with the present invention, there
is thus provided a method for manufacturing a dyed,
molded plastic element, which comprises the steps of:
a) manufacturing a plastic sheet;
b) detachably applying to at least one surface
of the plastic sheet, during or immediately after
its manufacture, a plastic foil which is extensible
when heated and which contains therein a transfer dye;
c) heating the plastic sheet coated with the
plastic foil to the molding temperature of the sheeti
and
d) molding the sheet while simultaneously
molding the fo:il adhering thereto to produce a coated,
dyed, molded plastic element, wherein during the
heating or molding, the dye is transferred from the
foil to the surface of the sheet.
The method of the invention leads from an
undyed, flat plastic material to a dyed, three-
dimensional molded plastlc elemen-t in a single
i,.~.~ ~, .
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opera-tional step. According to the previously used
method, the plastic sheet had to be heated both for
the transfer printing method as well as for the
molding; according to -the invention, it is heated
only once. Furthermore, the dye vehicle in the
-transfer printing step simultaneously takes over the
function of the protective foil, so that auxiliary
material for this purpose is unnecessary. Par-ticularly
advantageous is the fact that the foil containing the
transfer dye is applied elther during the manufacture
of the plastic sheet or immediately thereafter, so
that the protective effect of the foil is maintained
from the time of manufacture of the plastic sheet
until the molded and dyed plastic element
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is put into use, and no further auxiliary materials
with planar surfaces are required~
The method of the invention is suitable for the
manufacture of dyed or patterned, inscribed or
otherwise decorated molded plastic elements which are
manufactured by molding flat sheets. sy this method,
equal-area cylindrical moldings may be performed with
the same ease as spherical moldings with partial
surface extension. For example, illuminatable
advertising signs, traffic signs, directional
indicators, device housings, fashion articles such as
hair clips or clasps, packaging containers or closures,
light globe halves, sportin~ articles such as surf
boards or skateboards, plastic lu~gage, items oE
vehicle equipment, among others can be manufactured.
Undyed plastic sheet5 are those sheets which have not
been subjected to dye transfer by the present method,
even if the plastic sheets already have a different
coloration or patterning. The expression "dyed"
includes any coloration produced through transfer
printing, from uniform or continuous colors to single
or multiple color patterns or inscriptions.
Suitable for the invention are solid plastic
sheets, provided that they can be molded cylindrically
or spherically when heated and that they will
permanently retain the shape produced during heating
~r~
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after cooling to room tempera-ture. It is preferred
that -they retain their shape up to at least 50C and do
not have an E-module of less than 1,500 Nmm 2. Mold-
ability in the thermoelastic or thermoplastic condition
should be possible at temperatures of from 50 to
250C. At the temperatures necessary for the dye
transfer, the plastic generally should not be decom-
posed in any appreciable manner.
As examples of suitable plastics, there may be
mentioned polymethylmethacryla-te,polyvinylchloride,
polystyrene, polycarbonates, polysulphone plastics,
polyester, cellulose ester as well as bonded material
sheets made from different layers of such plastics.
By polyester, polycarbonate and polysulfone are
meant polymeric materials as described in Kirk-Othmer's
Encyclopedia of Chemical Technology (1982), Volume 18,
pages 479-494, 549-594, and pages 832-848, respect-
ively. By cellulose ester is meant organic esters of
cellulose such as those described in Kirk-Othmer's
Encyclopedia of Chemical Technology (1982), Volume 5,
pages 118-143. The particular plastics chosen are oE
secondary importance relative to the method oE manu-
fac-ture disclosed herein. One oE ordinary skill in the
art could, without undue experimentation, determine
~J3~
which plastics could be used to success~ully carry out
the method of this invention.
Preferably the sheets are colored homogeneously
white, because any desired coloration is possible with
such sheets. By way of example, the sheets can be from
1 to 15 mm in thickness and may have any desired
dimensions, from a few square centimeters to several
square meters~
The plastic foil serving as the dye vehicle for
the transfer dye must be capable of being molded
together with the plastic sheet while at the same
temperature as the plastic sheet. It does not create a
problem if the foil is softer than the plastic sheet at
the molding temperature, as long as it does not become
detached from the sheet under the mechanical forces
that occur. Preerably the polyester of thç foil has a
glass temperature which is not higher than the glass
temperature of the polyester sheet. Detachability
ater cooling generally remains assured if the plastic
of the foil has a low afEinity to that of the sheet.
This is usually the case when one of the two plastics
is rich in polar groups and poor in nonpolar groups and
the other plastic is more or less free of polar
groups. PolyoleEins have adequate minimal afinity
relative to the exemplary plastics listed above.
Examples of suitable polyolefins are polyethylene and
6~
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polypropyleneO The polyolefins may be homopolymers or
copolymers, and may include plasticizers such as those
described in Kirk-Othmer's Encyclopedia of Chemical
Technology9 Vol~ 18, pages 111-183. A preferred
polyolefin ~or purposes of the present method is
polyethylene. Furthermore, polyester foils are
often well suited. Polyesters include polyethylene
terephthalate and others well-known to those of
skill in the art. Preferred pairs of plastics for
the plastic sheet and the plastic foil are:
polymethylmethacrylate/polyethylene;
polycarbonate/polyethylene;
polysulfone/polypropylene; and
acrylonitrile butadiene-styrol co~olymer/polyethylene.
The affinity should, if possible, be so low that
after cooling, the foil can be removed with a small
application of force without ripping. On the other
hand, the affinity matf not be so low that inadequate
adhesion is achieved. The adhesion must be great
enough tha~ the foil does not shiet relative to the
sheet durin~ molding. Xf necessar~f the adhesion can be
increased through a corona treatment of the foil
surface to be laid on the sheet. It is preferred that
the foil be coated on this side with transfer printing
dye.
~ 36~
The particular dyes which could be used in the
method of the present invention are not limited, and
may be selected from any of the dyes which are known to
those of ordinary skill in the art of plastic dyeing.
The following non-limiting examples may be mentioned:
Blue Dyestuffs:
NH2 OH
- OX X = rl ' ~r C~i3
CH T 2
O NTI
(~ so20~
O NH2
O NH-CH3
,:~
O N~T-~-OCT13
Yellow Dye.stufs~
NC ~ -N-N-C
--1 0 -
~15~:2~ ~ N--
)~C
C-CH-13- ~C2H40~
Co~C~f ~ N
N ,c--clI-cl~=c~ ~
~3 3CO -C--~--C-OC2~4--1~ _~ CH C~ CN
Orange Dyestuff:
-I~=N--~ -N-N-~ -OI~
Red Dyestuff:
O ~H
[~ ~3 \ CEI;~--( C~I2 ~
O OH
Violet Dyestuff:
~2
~$~ C2H4--~C~3'?
1~}~2
The amount of the transfer printing dye which may
be applied to the carrier foil is preferably from about
1 to about 50 g/m2, relative to the dye-carrying areas.
The dye layer is applied according to known
methods of foil printing, for example throucgh offset,
screen printing or by roller application. The dye,
particularly the binding agent contained therein, can
change the adhesive properties of the oil,
particularly when the foil is entirely or largely
printed upon. It is advantageous if the binding agent
has a polarity as low as the foil itself. If the
printing dye should result in an undesirably high
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adhesion, the unprinted side of the foil can be placed
on the plastic sheet, since the dyes are capable of
di~fusing throu~h the foil. Any of the dyes well known
to those of skill in the art of plastic dyeing and
molding may be used in the method of this invention.
The foil, which is usually 40 to 150 ~m thick, is
best applied by the application of heat, for example by
means of light pressure from a roller heated to between
60 and 100C. The foil can also be adhesively applied
to the sheet if the sheet has an increased surface
temperature of from 60 to 80C. In any case, care
should be taken that as the foil is applied no bubbles
are formed therein.
A foil coated with pressure sensitive glue can
also be used, which can be applied to the sheet without
the application o~ heat. The glue layer does not
hinder dye transfer.
Although it is possible to efEect dye transfer
onto the sheet immediately aEter the placement o~ the
foil by additional application of heat at a temperature
that is adequate for the dye transfer, for economic
reasons it is preferred that no additional application
of heat be employed with the goal of dye transfer after
the placement of the foil but rather that the coated
sheet be allowed to cool, so that only that amount of
dye is transferred that results automatically frorn the
conditions of the foil coating process.
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For thermal molding, the coated sheet is heated
again. For spherical moldings, the molding temperature
must be reached through the entire thickness of the
sheet at least in the area to be molded, while for
cylindrical moldings it is sometimes sufficient if the
molding temperature is reached at least to the center
of the sheet thickness. The heating effectively takes
place through heat radiation or hot air. It is
generally in this stage of the method that the primary
quantity of dye is transferred from the foil to the
sheet. Therefore, at least the foil must attain a
temperature sufficient for dye transfer, and this
temperature must be maintained for the duration of the
transfer process.
Many plastic sheets suited for the method of the
invention are capable of being molded well in the
temperature range of from 120 to 250C. The
temperature range in which the plastic primarily has
thermoelastic characteristics is preferred. For cast
polymethylmethacrylate this temperature lies
approximately between 130 and 200C., for extruded
polyrnethylmethacrylate it lies ~rom 120 to 180C. In
order to achieve these temperatures quickly, the
surface of the sheet is generally heated to
temperatures above 200C., thereby ~acilitating dye
transfer very well. The largest portion of the usable
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transer dye material can best be transferred in the
temperature range from 150 to 250C. The usual heating
periods of from 1 to 15 minutes, depending on the
thickness of the sheet to be printed upon, are usually
sufficiently for the dye transfer.
The molding of the heated sheet while
simultaneously molding the foil therewith takes place
in a known manner by means of molding tools acting on
one or both sides, by one-sided excess or negative
pressure, by foldable clamping frames and the like.
After molding, the molded element is allowed to cool to
a temperature below the softening temperature. After
the molded element is unclamped, the foil is left on
its surface and is not removed until the molded element
is processed further or placed into use.
The invention now being fully described, it will
be apparent to one of ordinary skill in the art that
many changes and modifications can be made thereto
without departing from the spirit or scope of the
invention as set forth herein.
