Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
  • B29C44/34—Auxiliary operations
  • B29C44/3403—Foaming under special conditions, e.g. in sub-atmospheric pressure, in or on a liquid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2067/00—Use of polyesters or derivatives thereof, as moulding material
  • B29K2067/06—Unsaturated polyesters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
  • B29K2105/04—Condition, form or state of moulded material or of the material to be shaped cellular or porous
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
  • B29K2105/06—Condition, form or state of moulded material or of the material to be shaped containing reinforcements, fillers or inserts
  • B29K2105/12—Condition, form or state of moulded material or of the material to be shaped containing reinforcements, fillers or inserts of short lengths, e.g. chopped filaments, staple fibres or bristles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
  • B29L2009/00—Layered products

Definitions

• the present invention relates to a spacer material made of plastic which is intended to be used, amongst other things, in various sandwich constructions. Then, the plastic consists of thermosetting plastic material having foamed structure. The invention also relates to a method for the manufacture of, amongst other things, the aforementioned spacer material. The manufacturing process is particularly suited to taking place inside a low-pressure chamber so arranged as to be capable of achieving a high degree of low pressure, with a vacuum of 60-95% being envisaged in this case.
• Foaming can also be achieved by the use of physical propellants in the form of a volatile gas such as freon (for example freon 11) which is dissolved in (that is to say forms part of a one-phase system with) the base material.
• freon for example freon 11
• a familiar example of the last-mentioned method is provided by the manufacture of rigid polyurethane foam.
• a wish associated with plastic foamed products falling within this category is for technically simple manufacturing processes to be available which in addition provide conditions for mechanically sound products at comparatively low manufacturing costs. In appropriate cases it may be wished to modify the production process to suit existing or intended low-pressure chamber equipment, the environmental advantages of which may thus be utilized in the production facility in question.
• the present invention proposes a spacer material and a method for its manufacture which will resolve, amongst other things, the problem outlined above on the basis that bubbles of air which are able to enter into a two-phase system with the base material are added to the base material, said bubbles being caused to expand at a pressure which is less than the pressure at which the bubbles were added.
• What may more precisely be regarded as being essentially characteristic of the noval spacer material is, thus, that the foamed structure is attained by means of bubbles which expand under pressure in the form of air which has adopted an undissolved state inside the thermosetting plastics material in order to form a spacer material substantially free from additives in the form of chemical foaming agents and/or physical propellants dissolved in the material.
• thermosetting plastics material shall consist primarily of polyester which has been provided with confined air bubbles.
• the spacer material is also reinforced with carbon fibres or glass fibres.
• the spacer material can be provided in a preferred sandwich construction with a covering layer of identical material, but with a smaller number of bubbles or entirely without bubbles.
• a first space which is at a first pressure preferably being atmospheric pressure
• air bubbles are introduced into a curing agent-compatible plastics material
• the plastics material thus provided with air bubbles is applied on whole or parts of the mould or a base inside the first space or a second space which, in each case, preferably consists of the aforementioned low-pressure chamber, in that the first or the second spaces are or are caused to be at a second pressure considerably below the first pressure so that the air bubbles introduced into the material are caused to expand
• the plastics material is taken rigid state/is polymerized with epanded air bubbles at the aforementioned second pressure inside the space concerned for a comparatively short tack-free time, for example 0.5 - 20 minutes, and preferably 5 - 10 minutes.
• the base material must, for example, be essentially free from wetting agents.
• the admixture of small bubbles is preferable in the interests of reducing the rate of ascent.
• the material selected will preferably be a thixotropic thermosetting plastics material having a viscosity at high shear rates of preferably 140-300 mPa.s.
• the curing agent is added preferably at the end of the air admixture period and/or in conjunction with the. pouring operation onto the mould or the base.
• a low-pressure chamber capable of operating at a vacuum of 60-95% and preferably
• a chamber of this type can include a suitable space for the product and can be equipped with, amongst other things, openable and closable hatches and, if appropriate, material application organs, etc.
• Figure 1 illustrates the principle behind the manufacture of a spacer material in accordance with the first example
• Figure 2 illustrates the principle behind the manufacture of a spacer material in accordance with the second example
• Figure 3 illustrates examples of a sandwich construction.
• unsaturated polyester for example laminating polyester (suitable for spray-up operation) of the type used within the small boat industry.
• the polyester is thixotropic and exhibits a viscosity at high shear rates of, for example, 150 mPa.s.
• the polyester should preferbly be at least essentially free from the wetting agents which are otherwise normally used to facilitate the admixture of the filler.
• the unsaturated polyester should preferably be modified in such a way that rapid Kunststoffing can be achieved after the addition of curing agents, for example peroxides.
• the curing time/tack-free time or the gel time should preferably be selected within the range 30 seconds - 20 minutes, and preferably 5 - 10 minutes. The tack-free time can be adjusted in a previously disclosed fashion by means of accelerators, inhibitors and curing agents.
• a high-speed agitator 2 for example an agitator rotating at a speed of about 2000 r/min, is utilized for stirring the unsaturated polyester in the container 1 in such a way that the admixture of the air takes place via the opening la in the container.
• the quantity and the size of the air bubbles which are mixed in is determined by the speed of agitation, the design of the agitator, the period of agitation and the chemical structure of the unsaturated polyester.
• Bubbles of sizes within the range 0.1 mm - 0.001 mm or smaller should preferably be aimed at, with the total quantity of air mixed in representing 10-30 per cent by volume, and preferably 15-20 per cent when mixed in at atmospheric pressure.
• Small air bubbles exhibit a low rate of ascent, moreover, with the result that the air bubbles will take longer to rise to the upper surface and to pass into the surrounding atmosphere. This means that, the smaller the air bubbles which are obtained in a given unsaturated polyester, the longer will be the permissible gel time. It is worth mentioning in this respect that longer gel times will result in less critical manufacturing processes and in the possibility of increased quality in the finished product.
• a curing agent 3 is added, for example via a pipe 4, and the polyester thus provided with a curing agent is tapped off into a mould 5 via a pipe 6 equipped with a tapping cock 7. Agitation, the addition of the curing agent and tapping into the moulds should preferably take place in a first space 8 at a first pressure, preferably being atmospheric pressure.
• the mould thus filled with the polyester containing a curing agent is introduced into a second space 9 which can be placed under a second pressure considerably below the first pressure.
• the second space should preferably consist of a chamber, which may be of a previously disclosed type, operating at a very high degree of low pressure.
• the chamber is equipped with an openable and closable unit 9a and with air evacuation equipment (not shown), and can be positioned inside or outside the first space.
• the mould is placed inside the chamber at atmospheric pressure, whereupon the chamber is sealed and the air evacuation equipment is actuated until a partial vacuum of 50-400 mbar has been achieved, and preferably 100-300 mbar.
• the bubbles of air which have been stirred in will expand thanks to the partial vacuum which has been created, and thanks to the aforementioned short curing/take-free time and ascent time the expanded air bubbles will become trapped in the plastics material, producing a polyester foamed material.
• the density of the material is controlled by the quantity of air bubbles which are mixed in and caused to expand, by the degree of partial vacuum, and by the length of the curing time.
• the density of the material is controlled by the quantity of air bubbles which are mixed in and caused to expand, by the degree of partial vacuum, and by the length of the curing time.
• the product is suitable to be included in sandwich constructions in which the covering layer consists of more or less bubble-free material of the same kind.
• a first bubble-free layer can be placed on the mould 5, whereupon the material provided with bubbles followed by more bubble-free material are added in turn. Expansion and curing can take place in accordance with the above. It is also possible for the curing of one or both of the covering layers to take place outside the chamber at the first pressure, that is to say at atmospheric pressure.
• Example 2 Figure 2
• the air bubbles are mixed in as in Example 1 by means of an agitator 2' inside the container 1' with polyester of a similar kind.
• the material is pumped by means of a pump 10 to a material application arrangement 11, for example a spray pistol of a previously disclosed type.
• a similarly previously disclosed cutter 12 for example a glass fibre cutter, may be mounted on the pistol. With the help of the cutter chopped fibres 13 are thrown into the jet of polyester 14 which is directed towards the mould 5'.
• Curing agents, for example peroxides, for the polyester are added from a container 15 and are mixed in the pistol 11 with the polyester in a previously disclosed fashion.
• the curing agent may alternatively be mixed with the jet outside the pistol.
• the cutter is not activated or may be omitted.
• Spraying of the mould can take place at atmospheric pressure or at partial vacuum inside a low-pressure chamber 9 in accordance with Figure 1, in which case, in the event of spraying taking place inside the chamber, the chamber is also provided with material application organs and, if appropriate, with cutter equipment. Curing takes place in accordance with Example 1.
• a sandwich construction may also be produced in this instance, in which case the spacer material is cured under a partial vacuum, and the covering layer is cured preferably at atmospheric pressure.
• Figure 3 shows examples of a sandwich construction in which the spacer material (the core) is identified by the reference designation 16, the covering layer by 17 and 18, and the expanded bubbles in the spacer material by 19.
• the fibre reinforcement is identified by the reference designation 20.
• epoxy or phenol-formaldehyde and their compatible curing agents may be used.
• the invention is not restricted to the embodiments shown above by way of example, but may undergo modifications within the context of the following Patent Claims and the idea of invention.
• the admixture of air bubbles (agitation), the addition of the hardener, the pouring onto the mould or onto the base, and the curing process may thus take place inside one and the same space, in the form of the aforementioned low-pressure chamber, to which the first and the second pressures are applied depending on what pressure is required in order to execute the Idea of invention.
• the application of plastic material and curing agent may, alternatively, take place under a partial vacuum. Either all or parts of the manufacturing process may be automated.

Landscapes

• Laminated Bodies (AREA)
• Moulding By Coating Moulds (AREA)
• Joining Of Glass To Other Materials (AREA)
• Casting Or Compression Moulding Of Plastics Or The Like (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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Cited By (1)

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Citations (3)

• 1983
  • 1983-09-12 SE SE8304871A patent/SE438113B/sv not_active IP Right Cessation
• 1984
  • 1984-08-31 WO PCT/SE1984/000286 patent/WO1985001248A1/en unknown
  • 1984-08-31 EP EP19840903297 patent/EP0155289A1/en not_active Withdrawn

Patent Citations (3)

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