NO843876L - PRODUCT BASED ON FOAM POLYVINYL CHLORIDE AND PROCEDURE FOR OR PREPARATION OF SAME - Google Patents

Description

The present invention relates to a product for producing a foamed polyvinyl chloride and the method for producing the same.

Foamed polyvinyl chloride, also called foamed PVC, can be produced using a number of methods. For example, nitrogen can be mixed into the polymer melt under high pressure (approx. 200 bar) according to the so-called Airex method.

Another method is the Trovipor method, where paste PVC is used and where e.g. carbon dioxide C02 is mixed into the PVC mixture under high pressure. With both methods, a pre-gelatinized, gas-propelling polymer mass is obtained which, after pressure relief, is brought to foaming. Instead of using gases, such as nitrogen or carbon dioxide, solid or liquid blowing agents can also be added to the polymer. In the present case, blowing agents are understood as substances which split into gaseous species when heated at the decomposition temperature for the substance.

According to a known procedure, a solution or dispersion of the blowing agent will thus be formed in the molten polymer when the blowing agent and polymer are mixed in e.g. an extruder.

When the polymer melt is then pushed out through an extruder nozzle and onto e.g. a moving belt, the decomposed blowing agent in the polymer melt will expand and cause the polymer to rise (rise). During this, the foamed product is also cooled to a temperature lower than the polymer's glass transition temperature, Tg, which causes the foam to become self-supporting.

However, it has been a problem in the production of foamed polyvinyl chloride to obtain this in the form of an intermediate product, in which the blowing agent is decomposed and the polyvinyl chloride is in an unexpanded but gelatinized state.

Such an intermediate product will be particularly suitable when you want the foaming to take place at a later time and when the conditions on site indicate that an intermediate product that has already been prepared for foaming is advantageously used. One could e.g. imagine this intermediate product used to fill defined cavities in buoyancy elements by filling the pre-fabricated intermediate product in a measured amount into the cavity and then exposing it to heat so that it expands and fills the cavity.

For such purposes of use and where it would otherwise be desirable to carry out the actual expansion of the polyvinyl chloride at the point of use, a method has been developed in which polyvinyl chloride resin, blowing agent, stabilizers and any other process regulating agents are carefully mixed with each other in ordinary mixing devices under such a low temperature that the blowing agent is not subjected to splitting, after which the well-mixed product is divided into small pieces or granules which are then transferred to a high-pressure press with a mold in which the granules are placed and in which they are subjected to a pressure of 150-200 bar exerted by a piston against the granules in the mold, while the granulate is heated in the mold to a temperature of approx. 150°C. The blowing agent is thereby split, but due to the back pressure the polymer mass will not expand. After the blowing agent has been decomposed, the polymer mass is cooled to below the polymer mixture's glass transition temperature, Tg, after which the pressure is released. This intermediate product in the form of pressed briquettes can then be expanded at the user site itself by filling a measured amount of briquettes, depending on the space to be filled, into a cavity, after which the cavity is closed and the briquettes in the cavity are heated to the temperature at which the gas pressure inside the briquettes overcomes the briquette material's resistance to deformation and thereby causes the briquettes to expand into foamed polyvinyl chloride.

This known method is very cumbersome. The presses used also have a limited production capacity and are expensive to acquire.

The aim of the present invention is therefore to provide an intermediate product and to produce this in such a way that the resulting foam product is produced by a far simpler and less expensive process than the pressing process mentioned above.

The present invention relates to an intermediate product based on a foam-PVC mixture and the method for its production

this, where the polyvinyl chloride resin is mixed with blowing agent, stabilizer and any other process-regulating additives to obtain a carefully processed, so-called gelatinized mixture which, in the form of a shaped solid material, is transferred to a high-pressure heating device in order to decompose the blowing agent in the mixture without the mixture expanding, after which the mixture with the split blowing agent is cooled under pressure. After the pressure is released, the intermediate product obtained can later be expanded into foamed polyvinyl chloride. The method is characterized by the fact that the mixture of polyvinyl chloride, stabilizer, blowing agent and any other process-regulating additives is transferred to an extruder or other suitable plastic processing machine, in which the mixture is kneaded without splitting the blowing agent and, if the plastic processing machine is an extruder, is extruded with any shape, length and width depending on the design of the extruder nozzle, and is brought to solidify, after which the extruded

that solidified mixture is transferred to an autoclave in which a pressure-transmitting and barrier-forming agent circulates at a pressure of 20-300 bar and a temperature of 50-270°C, and pressure- and temperature-treated in the autoclave for a time of 5-80 minutes to cleaving the blowing agent in the extruded and solidified product, after which the circulating hot agent is displaced by colder agent of the same type to lower the temperature in the autoclave to below the glass transition temperature of the pressure and heat treated product, Tg, after which the pressure is released, and the pressure and heat treated intermediate product removed from the autoclave in order to then be subjected to expansion in a closed room in another location, possibly after being divided into smaller pieces, by heating the product in a manner known per se until the gas pressure in the product overcomes the product's resistance to deformation and the product is thereby brought to expand.

In the foregoing, it is mentioned that the polymer mass can be premixed and gelatinized in an extruder. However, this is only one of the types of plastic processing machines that can be used according to the production of the foam-PVC mixture.

Injection molding machines and kneading machines are also suitable for the aforementioned purpose. For kneading machines, Banbury mixers can be mentioned in particular as suitable for mixing and pre-gelatinizing the aforementioned foam PVC, but other types of Sigma mixers are also applicable. The invention therefore places no condition on the type of plastic processing machine used, only that it must be suitable for the purpose, i.e. that it can mix the components of the foam-PVC mixture and pregelatinize it.

It is further stated in the foregoing that solid or liquid blowing agents can be used in the foam-PVC mixture. Examples of these include Azodicarbonamide, Sulfonylhydrazide and N-nitroso compounds of the solid blowing agents and Diisopropylazodicarboxylate and Diphenylene oxide-4,4'-disulfohydrazide among the liquid blowing agents.

The invention also places no limitation on which type of PVC can be used, since both suspension PVC (S-PVC) and emulsion PVC (E-PVC) either in the form of homopolymer alone or mixed with each other, can be used for the purpose. Copolymer S-PVC and copolymer E-PVC can also be used. Of these, special mention should be made of copolymer S-PVC and E-PVC with a content of from 0.1-20% by weight of vinyl acetate or an acrylic compound. Copolymer compounds of the above type can be used either alone or in a mixture with each other or with homopolymer S-PVC and/or E-PVC. Post-chlorinated PVC is also applicable for the purpose. In practical life, the choice of polymer will often appear as a result of which additives are used or that the additives are adapted to the polymeric compounds used.

An important feature of the method is that the splitting of the blowing agent in the extruded product does not, as previously, take place in an expensive high-pressure press with high requirements for sealing to prevent gas escape from the split blowing agent during processing in the high-pressure press, but in an autoclave or a high-pressure chamber in which both the pressure to which the temperature is provided by a circulating medium. This is, when the desired cleavage of the blowing agent in the extruded mixture has been achieved, displaced by the same agent in a colder state. The pressure- and heat-treated extruded mixture is thereby cooled to below the temperature at which gas from the blowing agent would have been able to expand the polyvinyl chloride after depressurizing the autoclave.

In the mixture introduced into the extruder, there must be a relatively large amount of blowing agents from 2-50 parts per 100 parts polyvinyl chloride. The polyvinyl chloride used can be a homopolymer PVC and/or a copolymer and/or a post-chlorinated PVC of the type S-PVC and/or E-PVC.

As a stabilizer in the mixture, a tin stabilizer is preferred, which is usually used for synthetic polymers, but other metal-containing stabilizers can also be used. Furthermore, it is advantageous that the mixture contains a polyacrylate, preferably in an amount of approx. 6-30 parts per 100 parts polyvinyl chloride. As a blowing agent, azodicarbonamide has proven to be well suited, although other gas-evolving blowing agents which decompose in the temperature range of 130-250°C and at a pressure of 50-300 bar can also be used. A little zinc oxide such as "Kicker" and some lubricant in the form of a mixture of polyethylene wax, paraffin wax or calcium stearate are particularly useful. In addition, the mixture may contain a certain amount of plasticizer and also a certain amount of isocyanate to increase the heat resistance of the foam.

A particular prerequisite for the invention is that the splitting of the blowing agent itself is carried out under high pressure and at high temperature with the aid of an agent which must exhibit low solubility for the separated gases from the blowing agent. In other words, it is important that the thermoregulating agent used exhibits a barrier-forming effect in that the gas species formed from the blowing agent are not or are extremely poorly soluble in the agent.

As means in this context is understood the use of e.g. glycerol or brine with a specific salt content. These are particularly well suited when the blowing agent emits nitrogen (N2) and carbon monoxide (CO), which is the case with azodicarbonamide, but other liquids which exhibit the above-mentioned favorable properties are also applicable, e.g. synthetic oils (Shell N-8401).

If azodicarbonamide is used as a blowing agent, it would be advantageous to use glycerol as a pressure and temperature transfer agent in the autoclave, as glycerol has a high boiling point and is particularly resistant to decomposition at high temperatures and also shows little solubility for nitrogen (N2), which is a of the cleavage products in the decomposition of the azodicarbonamide.

The autoclave itself can have any suitable length and cross-section, as any limitations will only be due to construction considerations and space considerations.

The homogeneously mixed, pre-gelatinized product that comes from, for example, the extruder when carrying out the present method, can thus be extruded in the form of a continuous web with a width and thickness suitable for autoclaving in an autoclave. The continuous web can also be cut into pieces before autoclaving.

After the treatment in the autoclave and cooling to the ambient temperature, the pressure- and heat-treated intermediate product can be divided in a manner known per se into any piece size for later expansion wherever this may be desired.

The expansion itself is carried out by exposing the pressure- and temperature-treated pieces, which contain split blowing agent, to an elevated temperature. Thereby, the pressure of the gas in these pieces increases, so that the pieces rise up at the temperature used and thereby achieve a foamed state. A convenient way of carrying out the foaming in a defined cavity is to introduce superheated water steam of approx. 105°C. The intermediate product containing split blowing agent will thereby expand as a result of the internal increased gas pressure and the polyvinyl chloride's reduced dimensional stability, and by suitable control of the expansion process, light foam polyvinyl chloride is obtained with a density varying from e.g. 0.08 to 0.5 kg/l.

Foamed polyvinyl chloride has a structure with relatively small and interconnected pores. It is relatively hard and has considerable dimensional stability after deformation (compression set), e.g. as a result of compression. Above all, due to its special pore structure and the polymer's hydrophobicity, it has a very low water absorption capacity. Its heat-insulating ability is also very good, and due to its low bulk density and low water absorption capacity, it is particularly suitable as a floating or buoyant material for objects to be used in contact with water. Examples of such objects can be mentioned mooring buoys, buoys, net floats and offshore hollow structures, in which buoyancy must be ensured at the same time that any damage to the structure surrounding the foam polyvinyl chloride must lead to as little absorption of water in the buoyancy material as possible . For this reason, the product produced by the present method is particularly suitable for use as insulation and buoyancy material in platform legs for use in offshore constructions.

Those skilled in the art have, of course, been aware of the advantageous properties of foamed polyvinyl chloride for use in them

above-mentioned purpose, but due to the expensive production process of the above-mentioned intermediate product, the price of such polyvinyl chloride intermediate product for subsequent foaming at the actual user site has been almost prohibitive in competition with other foam plastics, such as e.g. polyurethane. Polyurethane, however, has a poorer holding strength, a poorer dimensional stability

and a much higher water absorption capacity than foamed polyvinyl chloride. There has therefore been a very great need for a method for the production of such a polyvinyl chloride intermediate at a competitive price and with a competitive production capacity. This need has been remedied by the present method.

The invention is in accordance with the requirements.

For a better understanding of the invention, reference is made to examples 1-8, where instructions are given in detail for the manufacture of the product according to the invention.

Example 1

In a powder mixer or other suitable mixing device, mix the following components:

After premixing, the powder mixture is added to a single-screw extruder or an injection molding machine where the PVC mass is heated to approx. 160°C. The finished kneaded and pre-gelatinized mass is then extruded into strips which are cooled. The tape can either be wound up on a roll, cut into suitable lengths or granulated and used in that form during the subsequent autoclaving.

A 50 liter autoclave is fed with 25 kg of pregelatinized PVC granules and 20 liters of glycerol or synthetic oil (Shell N-8401), after which the autoclave is closed and the air in it is replaced with nitrogen. The glycerol or oil is then heated to 180°C in a separate heating flask outside the autoclave and circulates via this to and from the autoclave.

The blowing agent in the pregelatinized product will decompose as soon as the decomposition temperature is reached. This will occur in the temperature range of 155-200°C, depending on the amount of "Kicker". Without "Kicker" one should expect splitting only at temperatures higher than 235°C.

During the heating of the foam-PVC mixture, a pressure increase will occur in the autoclave, depending on the amount of free volume in it, the initial pressure and the amount of added blowing agent. After 30 min. the hot glycerol or oil is pressed out of the autoclave and into a tank while simultaneously supplying cold glycerol or oil and maintaining the pressure in the autoclave and the associated communicating equipment. When the split PVC mass has cooled to a temperature well below the glass transition temperature (Tg) of the PVC mass, the autoclave is relieved and the pressure in it is brought down to the normal pressure outside the autoclave.

The glycerol or oil is drained off and the PVC mass is poured into a centrifuge to separate excess glycerol. The PVC mass is then washed with clean water in the same device.

The foam PVC mass is dried and packed in bags for later use in situ.

Example 2

Instead of the mixture from Example 1, the tin stabilizer is replaced with Ba and Pb stabilizer with 2.0 parts of each, and 2.0 parts of toluene diisocyanate are added. The zinc oxide is removed from the formulation. Otherwise, the raw materials are mixed, and the fully split, unexpanded PVC foam is produced as stated in Example 1.

Example 3

The above components are premixed in suitable equipment for later addition to an injection molding machine. After mass-n is homogeneously mixed and heated to approx. 180°C, suitable molded articles are injection-molded which are either autoclaved as they are or granulated.

Otherwise, the split, unexpanded foam PVC mass is produced as described in Example 1.

Example 4

The same formulation as described in Example 1 is added to a Banbury mixer and kneaded and pregelatinized in this. The split, unexpanded foam PVC mass is then produced as in Example 1.

Example 5

The same formulation as described in Example 1 is mixed, pregelatinized, granulated and autoclaved, but where glycerol is not used in the autoclave as a heat-transferring and barrier-forming medium, but saturated brine (approx. 30 g common salt per 100 g water).

Example 6

The above components are mixed, and the split, unexpanded foam PVC mass is prepared as described in Example 1.

Example 7

A copolymer emulsion polyvinyl chloride is used with

97% by weight polyvinyl chloride and 3% by weight vinyl acetate instead of homopolymer polyvinyl chloride.

Otherwise, proceed as described in Example 1.

Example 8

It is used

Otherwise as in Example 1.

When the polyvinyl chloride intermediate product, which appears according to Example 1-8, is used in a measured quantity for expansion at the user site, this will, as a result of the temperature increase during the foaming, soften to such an extent that each of the foamed PVC-Lite sinters together and thereby forms a whole in the cavity to be filled with PVC foam.

One can of course choose a formulation which means that the PVC foam does not soften sufficiently for sintering. In such cases, the intermediate product can be surface-treated in advance with a sintering aid, e.g. hot-melt glue or an ordinary glue (for example, water-based emulsion glue).

Claims (6)

1. A product that contains a polyvinyl chloride, stabiliser, decomposed or otherwise gassed blowing agent and any other process-regulating additives for the production of a foamed polyvinyl chloride, where the product is present in a form in which the blowing agent has been decomposed or given off gas and where the product is also pre-gelatinised, but still unexpanded, characterized in that the product has been brought into gassed, but unexpanded form using a pressure and temperature regulating, barrier-forming agent in an autoclave and volume stabilized in gassed form at a temperature level lower than the product's glass transition temperature, Tg. 2. Method for manufacturing the product according to claim 1, characterized in that the mixture of polyvinyl chloride, stabilizer, blowing agent and any other process-regulating additives is transferred to a plastic processing machine in which the mixture is kneaded under the influence of pressure and heat without the blowing agent splitting, and from this emerges with any shape, length and width, depending on which way the pregelatinized, homogeneously mixed polyvinyl chloride product leaves the plastic processing machine, after which the solidified mixture is transferred to a pressure chamber in which a temperature and pressure transmitting and barrier forming agent circulates at a pressure of 20-300 bar and a temperature of 50-270 °C, and pressure and temperature treated in the pressure chamber for a period of 5-80 minutes for decomposition or gas removal of the blowing agent in the pregelatinized product, after which the circulating hot agent is displaced with colder agent of the same or similar type to lower the temperature in the pressure chamber under the pressure- and heat-treated product glass temperature (Tg), and that the pressure is then lifted, and the pressure- and heat-treated product is removed from the pressure chamber. 3. Product and method for producing the product according to claims 1 and 2, characterized in that homo- and/or copolymerized suspension polyvinyl chloride (S-PVC) or homo- and/or copolymerized emulsion polyvinyl chloride (E-PVC) is used as polyvinyl chloride or a mixture of both S-PVC and E-PVC in a homo- and/or copolymerized state. 4. Product and method for producing the product according to claims 1 and 2, characterized in that a tin stabilizer is preferably used as a stabilizer for the mixture. 5. Product and method for producing the product according to claims 1 and 2, characterized in that azodicarbonamide is preferably used as blowing agent. 6. Product and method for producing the product according to claims 1 and 2, characterized in that glycerol is preferably used as a pressure and heat transmitting agent among other agents.