WO1999001270A1

WO1999001270A1 - Method of casting and producing ath filled acrylic or polymethacrylate based molded articles by using protecting polyethylene foil in the mold

Info

Publication number: WO1999001270A1
Application number: PCT/TR1998/000012
Authority: WO
Inventors: F. Mehmet Yaman; Turhan Karaoda; Derya TÜRKES
Original assignee: Polifen Kimya Sanayi Ve Ticaret A.S.
Priority date: 1997-07-03
Filing date: 1998-07-03
Publication date: 1999-01-14
Also published as: TR199700579A2; AU7952798A; TR200000083T2

Abstract

The invention is about casting forms by 'polymerization in the mould' from acrylic or polymethacrylate based, ATH (aluminiumtrihydroxide) filled mixtures by using protective polyethylene foil in mould. During the moulding where silicon mould (5) is used, in order to avoid the ATH (aluminiumtrihydroxide) filled, acrylic or polymethacrylate based mixture (8) to stick chemically to the male mould part (2) where the usage surface of the product (9) is formed; a protecting polyethylene foil (3) has been used which is replaced over the male mould part (2), and by this way the filled mixture is poured to the mould (8) will not be able to give damage to silicon mould (5) during polymerization. The used foil (3) is carried over a thin, acrylic sheet (4). After the polyethylene foil (3) is covered over acrylic sheet (4) in order to get in contact with the material poured, these two elements, by using heat and vacuum (thermoform process), will put over the male mould (2) like a hat or cover and is to be shaped in the same form of the male mould (2).

Description

METHOD OF CASTING AND PRODUCING ATH FELLED ACRYLIC OR

POLYMETACRYLATE BASED MOLDED ARTICLES BY USING

PROTECTING POLYETHYLENE FOIL IN THE MOLD

This invention is about obtaining cast forms by "polymerisation in mould" from mixture ATH (aluminiumtrihydroxide) padded, acrylic or polymethacrylate based, by using protecting polyethylene fail in mould.

The manufacture of filled cast acrylic products by "polymerisation in the mould" method, is a process that has been known since long time but a process is applied in a certain limit and not getting commonly used in the industry because of its high investment cost.

LN polymerisation in the mould method, generally, moulds made up of two parts where casting can be done to the empty space between them are used. These are stated as male and female as well. In these moulds made up of two parts of one up and one down generally the male part is placed at the down in casting, so that it forms the usage surface of the product.

The up and down mould parts, before the casting process, are closed over one another tightly by leaving a space between them for the material to be poured or in other words, by leaving an interim as much as the wall thickness of the completed (finished) product.

Micron scale grinded various inorganic powders are used as filling material. ATH (aluminiumtrihydroxide), quartz sand, calcite types, crystobalite, etc.. can be given as an example.

Acrylic and methacrylate polymers, copolymers and their derivations, polyester or acrylic modified polyester resines, polyurethane resines, epoxy resiness, etc.. materials are used as binders with the filling material.

The products manufactured are used in various fields of industry. As an example to these products, all kinds of sanitary ware materials obtained by casting (e.g. washbasins, basins, shower basins, bath basins, kitchen bench; etc.), product used in electric industry (isolators, adapters, bridge, connections, etc..) and various products used in construction industry (interior and exterior face covering elements, decorative goods, columns, etc..) can be given.

LN applications performed by using polymerisation in the mould method, some difficulties have to be faced, especially in obtaining cast forms from ATH (aluminiumtrihydroxide) filled acrylic or polymethacrylate based mixtures.

In order to obtain a product by polymerisation in moulding method from acrylic or polymethacrylate based, ATH (alurniniumtrihydroxide) filled mixture, first the surface of the mould to be used should be in ideal flat, should be as smooth as a mirror for instance. In any condition where the surface is not smooth, "material's tightening the mould that it has been casted" problem can be observed during the polymerisation period reason of it is the volume getting smaller (shrinkage) in material. This problem leads the product not to be separated from the mould or deformation of surface quality, after the polymerisation has been finished. In order to supply a surface in the desired smoothness, special moulds are used which are produced by "galvano technology" at high costs (e.g. each US $ 30 000 - 50 000). Since much numbers of differently designed washbasins, basins will be present in an industrial establishment's production program, and since more than one mould should be present because of serial production; the usage of this type of moulds will lead to high investment costs.

A 20% of reduction in volume performs while the polymerisation reaction of acrylics are developing. During this reduction, in order to follow the shrinkage in the mould, by the help of a system that can be programmed and such a program can control the heating and cooling cycles for polymerisation, parallel with the movement of this mould, the need of such an apparatus and expensive components belonging to this apparatus; affects the costs besides the expensive moulds in a negative way. As a summary, for the manufacturing of filled acrylic based cast products by polymerisation in mould method in commercial quantities and acceptable commercial quality; there is a need of a very expensive mould, very expensive confusing systems and machines for the mould to work.

In obtaining a cast product, ATH (aluminiumtrihydroxide) filled, acrylic or polymethacrylate based mixture by polymerisation in mould method, in applications where cheaper mould are tried instead of the above mentioned moulds; which are manufactured from various materials; the results gained were not satisfactory. The casting performed using various mould release to polyester, aluminium, epoxy and silicon moulds by hot and cold polymerisation procedures, can never supply a production within above mentioned commercial values. The product as a result of polymerisation following the casting, is being broken by sticking to the mould or deformations appear on its surface which needs strict retouch procedures that take a long period of time or not get out of the mould.

As it has been known, in accordance with the volume reduction of acrylic material during polymerisation, the material starts to tighten the mould. This tightening and hardening avoids the product to be taken out of the mould easily after his negative condition which is due to the characteristic of acrylic material; silicon material usage in moulds started to be preferred. Silicon material, since has a flexible characteristic just like rubber, it can follow the volume reduction during the polymerisation of acrylic material by squeezing. This positive characteristics, decreases the tightening and hardening effect during polymerisation and makes it easy the product to get separated from the male mould part.

Besides this, there are some negative points in using silicon mould material. The first of these is that silicon is able to absorb the liquid within the acrylic mixture poured to the mould and take it within its content because of its sponge like structure. The condition lead to deformations on the usage surface of the product. Accordingly, in applications where silicon mould material is used; it is needed the surface of the product taken out of mould to be gone through procedures like sanding with abrasives and thin abrasives. The absorption of silicon material during polymerisation, of the liquid within the acrylic mixture; give harm to the material itself, rapids the depreciation and corrosion of it, and shortens the usage life of this material. This expensive material, in a condition where it looses its characteristic and becomes unusable, brings unacceptable loads to the costs; since it can not be used as raw material.

The aim of this invention is to present a method which can supply to obtain a cast product having enough surface quality, without using the above mentioned expensive moulds, especially ATH (aluminium trihyrdoxide) filled, acrylic or polymethacrylate based mixture, by polymerisation in the mould process.

By using polyethylene protective foil in the mould which has been performed in order to reach the aim of the invention, and by using ATH (aluminiumtrihydroxide) filled acrylic heat and vacuum (thermoform procedure) for it being shaped in the same form with the male mould (2) and which will get stuck over the male mould (2) like a hat or a cover. The method of cast form production by polymerisation in mould from mixtures process, can be used in all applications where cast is performed by polymerisation in mould procedure. And in addition since they are the materials creating most problem in application, they are explained for acrylic or polymethacrylate based mixtures by referring to the figures attached as follows. From the attached figures;

Figure 1 - Cross section of top and down mould parts.

Figure 2a - and figure 2b - Cross section of shaping carrier acrylic plate and polyethylene foil by using heat and vacuum.

Figure 3 - Cross section of the replacement of the acrylic plate with polyethylene foil, over the mould to be casted.

Figure 4 - Figure showing the cast to the mould which has been replaced polyethylene foiled acrylic plate.

Figure 5 - Figure showing the separation of hot product from the mould, together with polyethylene foiled acrylic plate.

Figure 6 - Figure showing the getting out of polyethylene foiled acrylic plate over the product. Figure 7 - Cross section of the replacement of the completed product over the 3D - template

The Correspondence of the part numbers within the figures are as follows:

1. Up (female) mould part

2. Down (male) mould part

3. Protecting polyethylene foil

4. carrier acrylic plate

5. Silicon mould

6. Vacuum mould

7. Heater

8. (ATH) filled acrylic or polymethacrylate based mixture.

9. Cast product.

10. 3D - template

In the method which is the subject of the invention; silicon mould (5) has been used. Silicon mould (5) gives positive results especially in products which tightening and hardening is much in polymerisation, in accordance with the advantages explained above. Besides, the method which is the subject of the invention; for products which are less affected by the volume reduction which polymerisation leaded (e.g. shower basins) it can be applied to moulds other than silicon.

In the method said, to gain from the flexibility characteristics of silicon, but in order to avoid the chemical sticking of ATH (aluminiumtrihydroxide) filled acrylic mixture (8) to the male mould pant (2) during moulding at the same time; a protective foil (3) which will be replaced over the male mould part (2) usage and by this way, the preventing of the harm given by filled acrylic mixture (8) that has been poured to the mould; to the silicon mould (5) during polymerisation is explained. Although the protecting foil (3) can be replaced over the female mould (1); it has been decided to be applied over the usage surface of the product only, since this will lead a useless expense and trouble. In order to avoid the corrosion of the silicon within the female mould, polyvinyl alcohol based mould separators are being used.

The foil (3) used in the invention, is carried over a thin acrylic plate (4). Polyethylene is used as protecting foil (3) material and acrylic is used as foil carrying plate (4) material. Polyethylene is wholly an inert material. It never sticks over acrylics. Both foil (3) and carrier plate (4) are chose from thermoplastic materials. They have the characteristic of to be shaped is the desired form easily when they are thermoformed together by applying heat and vacuum. Foil (3) and this characteristics of the plate (4); supplies the method, which is the subject of the invention, to reply to a production program having the target of a wide product range with different designs.

The thickness of the foil (3) used is approximately 30-70 microns and the thickness of carrier plate (4) is 1-15 mms. By covering the polyethylene foil (3) over the acrylic plate (4), a structure has been gained that will serve as a "mould separator" between the poured material (8) and male mould (2). There are no limitations about the thickness of the acrylic plate (4); but this thickness should be a practical value which will perform the carrying and easily shaping qualification of the mentioned plate (4).

PMMA (polymethilmethacrylate) and various copolymers and derivatives, PVC (polyvinylcloride) and various copolymers, polystyrene, ABS (acrilomitrile - butadiene - styrene), PTFA (polyethylene ethereftalate), polyethylene, polypropylene etc.. and some other plastical materials also can be used as polyethylene foil carrier plastic material only if they have thermoplastic characteristic.

At the first stage of the subject of the invention method where cool polymerisation process has been applied; the female mould of the cast mode or the usage surface of the model in accordance with the polymerisation in mould method; can be get by known methods (by gyps or other procedures). This mould that has been obtained, is used in giving the shape to acrylic plate (4) is shaped by known methods (Figure 2a and 2b) as being stuck over the male mould (2) like a hat or a cover and within the same form with the male mould (2) by using heat and vacuum (thermoform process). The sides of the form in a shell shape are cleaned as to suit to the cast mould.

The shell shaped form made up of acrylic plate (4) covered with protecting polyethylene foil is stuck strictly over the male part (2) within the mould which casting will be performed (Figure 3). After the losing of the female mould (1), passed to casting process (Figure 4).

After polymerisation cycle has been completed, when the system is still hot (>100°C), firstly the mould will be opened and the upper part (1) of the mould is taken. The hot product (9) in taken out of the male part (2) by slightly pulling from the place of the acrylic plate (4) (figure 5) and the acrylic plate (4) over it, by the help of heat resistant gloves in taken out while the product (9) is still hot (Figure 6). By this way the product (9) can be taken out without sticking to the mould and a very smooth usage surface has been obtained. Later as, it has been passed to the cooling stage of the product (9). The completed product (9), for it not to be deformed during cooling is stuck on a form (10) equivalent to the male part (2) that has been casted, called "3D - template" and left for cooling as said (Figure 5).

The method which is the subject of the invention, has presented advantages both as not serves for an easy and a series production. The products obtained, when they are evaluated as their usage surface quality, it has been observed that satisfactory results have been taken.

Claims

1) In order to obtain cast form shapes from ATH (aluminiumtrihydroxide) filled, acrylic or polymethacrylate based mixtures by applying polymerisation in the mould;

• Creating the female mould of the model to be casted or the usage surface of the model which to be produced with polymerisation in the mould method,

• The covering of a protector polyethylene foil (3) over an acrylic sheet (4), in order to obtain a surface serving as "mould separator" between the material to be casted (8) and male mould (2).

• The use as female mould, the usage surface of the model in thermoforming of acrylic sheet (4).

• The shaping of this acrylic sheet (4) which is covered with protecting polyethylene foil (3), within the said female mould, by using heat and vacuum (thermoform process) as to be put over the male mould (2) like a hat or a cover in the same form with the male mould (2).

• The trimming the shell shape form as to fit to the cast mould.

• Placing tightly of the said shell over the male part (2) within the mould to be casted.

• Starting the casting process after the female mould (1) has been closed.

• The opening of the mould, after the polymerisation cycle has been completed and the hotness of the system is still above 100°C

• The separation of the hot product (9) from the male mould part (2) together with polyethylene foil (3) covered acrylic sheet (4) after the top part of the mould (1) is taken out. • The taking out of the shell consisting of the protecting foil (3) over the hot product and acrylic sheet (4) while the product is still hot.

• For the product (9) not be deformed during cooling, the product (9) to be put over a form (10) equivalent of the male part (2) within the mould casted, and to be left for cooling as said.

Is a method characterised by the above mentioned stages.

2) A method like is claim 1, characterised by the said protective polyethylene foil (3) having the approximate thickness of 30-70 microns.

3. A method like in claim 1 or claim 2, characterised by the said acrylic sheet (4) thickness of approximate 1-1,5 mms. 1-1.5 mms

4. A method like in Claim 1-3, characterised by the usage of a plate produced from any kind of plastics having thermoplastic qualification, instead of an acrylic sheet (4).