|Title of Invention||
A METHOD FOR THE MANUFACTURE OF A MOULD FOR MAKING COLD CURE FOAM & INTEGRAL SKIN PRODUCTS WITHOUT THE USE OF A RELEASE AGENT
|Abstract||A method for the manufacture of a mould for making cold cure foam products without the use of release agent, comprising the steps of adding Benzoyl Peroxide as a cross linker to the pulverized polyethylene powder, of particle size passing through 50 to 300 microns and of molecular weight between 200000 and 250000 and thoroughly mixing the said cross linker and powder together to form a homogenous, the said cross linker being present in the polyethylene powder, heating a metal box provided with a punch to glass transition temperatures between 200oC and 270oC, adding small quantity of the said powder into the said box; compressing the mass by gradually lowering the punch having the shape of the mould to be produced; lifting the punch to release any entrapped air; transferring some more quantity of the said mass into the box if necessary and lowering the punch once again avoiding air entrapment, to compress the mass until it reaches Glass Transition Phase and takes the shape of the recess between the punch and the box; allowing the box and the punch to cool to room temperature before ejecting the resulting solidified mould from the box.|
|Full Text|| FORM 2
THE PATENTS ACT, 1970
COMPLETE SPECIFICATION (Section 10)
METHOD OF MANUFACTURE OF A MOULD FOR MAKING COLD CURE FOAM PRODUCTS FACILITATING DEMOULDING WITHOUT USE OF A RELEASE AGENT.
PULIN SHAH, I, Mekhia, Samarth Nagar Society, Off N.S. Mankikar Marg, B/H Canara Bank, Chunabhatti East, Mumbai 400 022, Maharashtra, INDIA, an Indian National.
The following specification particularly describes nature of this invention and the manner in which it is to be performed:
The present invention relates to the method of preparation of a mould for making cold
cure foam products, which will allow release of molded Polyurethane part without the use
of a release agent. Release agents are routinely used to prevent the foam products from
sticking to the mould surface that is to act as a barrier between the foam products and the
Prior Art : Polyurethane are a mix of two components: Isocyanates-comprising of
Toluene di Isocyanate and/or Di-methelene-di-Isocyante having free NCO groups which
reacts with hydroxile groups present in the Polyols. Catalysts and Blowing agents are
present within the polyol along with other additives. When reacted with NCO group they
form a long chain, which is known as Polyurethane.
Blowing agents, generally water is available in small quantities, which on reacting with-
NCO group of ISO liberates Carbon dioxide, the librated CO2 forms micro cell in the
Amine catalysts, tin soaps, organic tin compounds are added to hasten the reactions. The
blowing agents present in form of water or in liquefied gaseous state liberates at its
boiling point due to exothermic reactivity.
R1NCO + R2OH — RlNHCOOR2
The resultant mix while extending its chain incorporates liberated gas from the blowing agent and becomes viscous and micro-cellular and gradually achieves solid state. This mix thus formed starts to form long chain, which is popularly known as Gelling. The cross-linking action forms honeycomb like structure, radiating from the bottom of the mould to its outer walls. Once this solid state is achieved and the resultant mix starts to condense, a sticky skin like outer covering is formed. This sticky outer skin sticks to the surface of the mould. To prevent this sticking of the resultant Polyurethane foam to the mould surface release agents are used. The release agents are generally wax or silicon suspended in aromatic solutions hence on application of the release agent to the mould surface, the medium evaporates on contact leaving behind a very fine Patina of wax or silicon on the mould surface.
This Patina adheres to the poured foam and releases itself from the mould. The release agent wears off from the mould surface and hence the need for re-applying release agent. Existing technology includes the following:
(1) A fine spray of silicon/wax suspended in aromatic compounds like benzene-Toluene etc is applied to the mould surface, the solution on spraying becomes exposed to the atmosphere and the solvent evaporates leaving a fine non-permeable layer of wax or silicon on the mould surface. In this instance the layer gets disrupted as the Polyurethane foam on rising sticks to the thin layer of wax/silicon spray and on remolding releases itself from the mould along with the release agent film. This release agent has to be applied after every shot. Data sheet attached.
(2) Italian furniture manufacturers have made a silicon paste which is brush applied to the mould surface, which does not allow the adhesion of Polyurethane foam to the mould surface. However, this layer of dried silicon, which acts as a barrier perishes due to wear and tear. The paste has to be reapplied once in 20-40 shots, which is both expensive and labour intensive.
In both the cases it is seen that the release agent has to be continuously reapplied which is
a cost, and slows down the productivity. Furthermore, when the solvent evaporates on
spraying of the release agent, the solvent is released into the atmosphere and causes
The aforementioned methods are the traditional methods adopted in the industry wherein the polyurethane product, when formed will stick to the mould surface, and the problem of constantly applying the release medium to the mould surface persists. The need of the hour is to develop a release medium, which instead of sticking to the foam, should adhere to the mould surface and release itself from the foam, then there will be no need to re-apply the release agent. Alternatively, the need is to develop a mould such that the surface of the mould is joint less and glossy to prevent the formation of the micro cells, as the adhesion of the foam to the surface is basically due to the micro-
porosity of the cavity material and the cross linking property of the chemical mix. It is proposed to use such mold to make polyurethane moldings.
Cost efficiency in terms of value of release agent and productivity improves considerably. This invention seeks to do away with the old method of manufacture. Accordingly, this invention relates to a method for manufacture of a mould to produce cold cure foam products, without the use of a release agent.
The primary aim of this invention is to overcome the aforementioned drawbacks found in the current methods of manufacture.
It is also the object of this invention to offer a better method of manufacture which will not pollute the environment, as tons of release agents used in the current methods can be done away with completely and cost of ultimate molded product will come down considerably.
Accordingly, this invention provides for a method of manufacture of a mould for cold cure foam products by using Polyolefm powder as a base material for making release agent free moulds wherein the surface is joint less and glossy which will prevent the formation of micro-cells which encourages sticking. Such surfaces cannot be machined but are manufactured. Polyolefm derivates like Polypropelene (PP), High Density Polyethylene (HDPE), Ultra High Molecular Weight High Density Polyethylene (UHMWHDPE), linear Low Density Polyethylene (LLDPE) etc. has the lowest coefficient of friction after Polytetraflouroethylene (PTFE). These are commercially available and are comparatively easier to handle in terms of their processing ability. Such powders are manufactured by almost all companies in the world and in India Reliance, IPCL also makes them. The physical properties of these commercially available powders are easily alterable to improve gloss and compaction.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the present invention and many of its advantages will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings and detailed specification, all of which forms a part of the disclosure:
Fig.l: shows the hollow metal box C in which the polyolefin powder is filled. This box C has ridges R on the sidewalls Wl and W2. Hinges H are placed at the juncture of the sidewalls Wl and W2 and the bottom of the metal box C.
Fig.2: shows the charging of the powdered polyolefin in the box C.
Fig.3: shows the punch A in the shape of the article to be produced attached to the platen B. The bottom platen P is also marked.
Fig.4: shows full compaction of the punch A over metal box C, packing the powder completely.
Fig. 5: shows withdrawal of the punch A from the box C, opening the sidewalls Wl and W2 of the box C sideways by means of the hinges H.
Fig 6: shows the solidified mould cavity with external rib projections, which is ready for metal braces.
Fig. 7: shows the top plate D backed with metal webbing and braced with angles to allow fixing of hinges and clamps.
Referring to the drawings, A Ultra High Molecular Weight High Density Polyethylene
(UHMWHDPE) or Polypropylene — (PP) or High Density Polyethylene (HDPE) powder
of suitable grade having particle size of 50 to 300 microns and molecular weight between
200000 and 250000 is mixed with a chemical cross linker namely, Benzoyl peroxide
thoroughly by hand or by dry tumbling in such a manner that the resultant mix forms a
homogeneous mass. The said cross linker is present in the said resultant roughly in the
proportion 3 parts of the cross linker to one hundred parts of the powder. A metal box C
is made of mild steel plates is fitted with electrical heater bands to impart equal heating
from all sides. The box C can also be heated by hot oil. The box C has ridges R to
accommodate the molten polyolefin derivative, which enables rib formation on the mould
at various places for giving rigidity to the foam and for better heat dissipation. The box C
is placed on a heated platen P to allow even heating from the bottom also. A punch A
which is in the actual shape of the product (plus shrinkage) to be produced, is made of
Aluminum, Zinc or Steel and is highly polished, is heated by electricity or oil. This
punch A is fixed on to the platen B. The box C along with the punch A are heated to
glass transition temperatures between 200°C and 270°C. The said mass is then
transferred to the metal box C either manually or by a mechanical device and charged, the
charge calculated from volume of the metal box C. The said mass fills the mould cavity
by volume to ensure packing of material and prevent air embolism and spreads and fills
the hollow spaces in the box C. The heated punch A is then slowdy lowered to compress
the charged mass. The mass is now evenly distributed between the punch A and the
restraining box C. The punch A is lifted up once to release any air trapped in the cavity
of the box C, to top up the said mass, if necessary, and is once more brought down to
ensure that no air gap is left. Once the mass is heated, compressed and pressurized,
the said mass reaches the Glass Transition Phase and flows and takes the shape of
the recess available the punch A and the restraining metal box C The punch A and the metal box C are then allowed to cool naturally to room temperature. On cooling the said mass solidifies in the shape of the recess provided between the punch A and the restraining metal box C. The punch A is then lifted and side walls Wl and W2 are then
forced open sideways to eject the whole mould cavity. The solidified body is then bolstered, if necessary, by fixing angles on all sides by screwing them by means of a plate D, which is made of polyolefin, backed with metal webbing and braced with angles. This is done to impart rigidity and strength to the mould. The finished cavity and punch joined by hinges and clamps is then mounted on a frame or a trolley for moulding cold cure foam wherein the use of a release agent is completely redundant,
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Having generally described the present invention, a further understanding can be obtained by reference to the specific preferred embodiments which are provided herein for the purpose of illustration only and not intended to limit the scope of the appended claims.
Trial to make one mould:
Product size: 0.3mt x 0.3mt x 0.3mt square block with 50 mm thickness all around.
Box/Cavity C size: 0.315 x 0.315 x 0.315 (on the inside)
Punch size: 0.278 x 0.278 x 0.278.
Punch Plate: 20 mm thick
Metal Box C: The following are the specifications to which the cavity C is to be built:
(1) Heated side walls with recessions so as to get Rib projection on the eventual mould.
(2) Heated bottom platen and top platen either by hot oil or by electrically inserted bands for proper heat transfer.
(3) The metal punch of pre-determined shape with provision for shrinkage allowance which can be lowered or raised as desired, attached to the platen B.
Weight of the powder Ultra High Molecular Weight High Density Polyethylene.
(Polyethylene derivative) with the following physical properties:
(a) Hardness: d67-d69
(b) Modules of elasticity: 9,000 - 10,000 kg/cm2.
(c) Co-efficient of friction: 0.11 - .07
(d) Molecular weight: between 2,00,000 to 2,50,000
(e) Fineness: >500
(f) Density: 0.95
(g) Chemical cross linker: Benzoyl Peroxide (h) Weight of Charge: 2 Kg.
The UHMWHDPE Powder is mixed with cross-linker Benzoyle Peroxide (2 pbw) by dry tumbling to form a homogenous mass. The metal box C along with punch A is heated to 260o C and total powder i.e transferred into the box C The mess is then charged and the weight of charge is 2kg. The punch A_is lowered gradually into the heated box C at the rate of 10 to 15 mm per 30 seconds to compress the charged mass. The said mass is now compressed within the recess provided between the punch A and the box C. The punch A is then slowly taken upwards to allow the air trapped in box C to escape and then immediately lowered and the said mass is once again compressed fully under 100 kg/cm pressure for about 20-30 minutes, till the said mass reaches Glass Transition Phase and flows. On allowing the metal box C and the punch A to cool down naturally, in about 4 hours the powder solidifies and acquires the shape provided between the punch A and the metal box C.
The box is opened from three sides, that is, the punch A is lifted and the two side walls Wl and W2 are opened sideways by using force and the force applied is 1000kg/sq.cm. The mould is now ready for making cold cure foam products.
|Indian Patent Application Number||491/MUM/2003|
|PG Journal Number||43/2008|
|Date of Filing||19-May-2003|
|Name of Patentee||PULIN SHAH|
|Applicant Address||PULIN MEKHLA, SAMARTH NAGAR SOCIETY, OFF. N. S. MANKIKAR MARG, B/H CANARA BANK, CHUNABHATTI EAST, MUMBAI 400 022.|
|PCT International Classification Number||B22C 3/00|
|PCT International Application Number||N/A|
|PCT International Filing date|