MOULDING METHOD FOR ARTICLES OF FOAMED PLASTIC MATERIAL

Abstract: A method and an installation for producing moulded articles of foamed plastic material having stiffening portions or stiffeners preformed by spraying onto the internal surfaces of the mould which are subsequently embedded into the body of the moulded article. According to the invention, the stiffeners (15, 17) are preformed in the same mould (1) for the article to be moulded, by spraying a quick-reacting mixture of a first plastic material having definite physical and/or mechanical properties, which adheres in pre-established positions to the internal surface of the mould (1). Then a foamable mixture (16) of a second plastic material having physical and/or mechanical properties different to those of the first material, is fed into the cavity of the mould (1), embedding the preformed stiffeners (15, 17).

Description: MOULDING METHOD FOR ARTICLES OF FOAMED PLASTIC MATERIAL BACKGROUND OF THE INVENTION This invention refers to a method and an installa¬ tion for producing articles made of foamed plastic material, for example polyurethane or polystyrene, having outer and/or inner stiffening portions or stiffeners obtained by spraying a quick-reacting mixture of a plastic material having different physi¬ cal and/or mechanical properties from those of the foamed body of the moulded article; the invention also refers to the articles moulded by the ' method claimed herein. In the manufacture of polyurethane or polystyrene foamed plastic articles, it is often necessary to provide stiffeners or additional stiffening portions or elements having physical and/or mechanical proper- ties such as hardness, density, elasticity or other, different to those of the foamed body of the moulded article. For example, in the manufacture of chairs, armchairs and the like, in the furnishing, automobile and transport industry, use is made of soft polyure- thane padding which must adapt to the shape and di¬ mensions of the seat and/or backrest or, more gener¬ ally, to the shape of the armchair or article to be manufactured. In the past use was made of padding obtained from a layer of soft polyurethane material which was cut to the desired shape. However, in the automobile or transport sector in particular, the padding is required to have a sufficient degree of softness, to make the armchair more comfortable, and at the same time provide sufficient support for the person sitting in it. Therefore it has been suggested to mould the paddings comprising stiffen¬ ers or elements of differentiated elasticity, mould¬ ed separately or cut from blocks of polyurethane material and subsequently positioned in moulds spe¬ cially designed for the padding to be produced. Due to the constant evolution in the manufacture of arm¬ chairs, chairs and moulded articles, it became ne¬ cessary to provide the inner padding of armchairs and the like, with less deformable stiffening por¬ tions, which would withstand the tension exerted by the fabric upholstery on the padding, especially in correspondence with the corners and/or edges of the padding, in order to preserve the correct shape of the chair or seat, and ensure the desired amount of lateral support. The insertion of separately made stiffening por¬ tions in the moulds proves to be somewhat complex and difficult to carry out on automatic machines for large-scale production of foamed polyurethane paddings, whilst it is problematic to provide inner or superficial stiffening portions of harder poly¬ urethane, using the conventional moulding techniques. In fact, the raising time of the polyurethane foam, in conventional formulas for padding and the like, is in the region of ten to twelve seconds; conse¬ quently, there would be an insufficient amount of time to allow for over-moulding of stiffening por¬ tions, once the main polyurethane mixture has been poured or introduced into the mould. Moreover, in order to have the necessary requisites in terms of softness and elasticity, the polyurethane mixture used is in the form of a liquid mixture which would therefore tend to blend with any other mixture sub- sequently introduced in the required positions. In other words, according to conventional mould¬ ing techniques, it is not possible to obtain foamed plastic articles, with inserts and/or stiffening portions having different physical and/or mechanical properties, in the desired positions of the articles, in a controllable and automatic way. Consequently, a scope of this invention is to provide a method and an installation for producing foamed plastic articles, having inserts and/or stif- fening portions preformed into the same mould, in an automatic and controllable way, by using a plastic material having physical and/or mechanical proper¬ ties different to those of the plastic material used for producing the moulded articles. A further scope of this invention is to provide a method and an installation for producing padding and the like, for the aforesaid uses, by means of which it is possible to mould padding provided with superficial stiffening portions in polyurethane ma- terial having a degree of elasticity which differs from the rest of the padding, in a wholly controlled manner, which is not restricted by- the short foam¬ ing time of the polyurethane material used and which permits the use of conventional installations, for example, installations with automatic mould transfer systems, for producing paddings according to the in¬ vention. SUMMARY OF THE INVENTION The aforementioned scopes are attained by means of a method for producing moulded articles of foamed plastic materials having stiffening portions, charac¬ terized by the steps of preforming stiffening por¬ tions into the empty mould by spraying a quick-react¬ ing mixture of a first plastic material making it adhere in pre-established positions to the internal surfaces of the mould; feeding into the mould a foam¬ able mixture of a second plastic material and allow¬ ing said second mixture to foam and fill the cavity of the mould embedding said sprayed stiffening por- tions. The invention will be described hereunder, with reference to the examples of the accompanying draw¬ ings, in which: BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a plan view of a carousel installa¬ tion, suitable for producing padding by means of the method according to this invention; Fig. 2 shows a view according to the line 2-2 of figure 1 ; Fig. 3 shows a cross-sectional view of a pad¬ ding for the seat cushion of a chair for motor ve¬ hicles; Fig. 4 shows a plan view of the mould for pro¬ ducing the padding of figure 3; Fig. 5 shows a cross-sectional view according to the line 5-5 of figure 4; Fig. 6 shows an enlarged detail of the left side of the cross-section of figure 5; Fig. 7 shows a cross-sectional view similar to that of figure 6 for a different embodiment. DESCRIPTION OF THE INVENTION Figure 1 shows an automatic carousel installa¬ tion for producing paddings made of polyurethane material according to the invention; the installa- tion comprises a plurality of moulds 1, mounted for example on trolleys 2 pulled by an endless chain 3 along a closed path 4 comprising, in pre-established positions, several work stations, for example, a first station 5 for opening the moulds and removing the moulded articles, one or more work stations 6 for the usual cleaning and preparing operations for the moulds 1 , an intermediate station 7 for preform¬ ing the stiffening portions or stiffeners into the same mould by spraying a first polyurethane mixture, according to the method described further on, and a last station 8 for feeding a second polyurethane mixture which, foaming in the closed mould along the rest of the path 4, will complete the moulded padding. Provided in correspondence with the station 7 for the polyurethane stiffeners is a first feeding apparatus 9 which feeds a first polyurethane mixture through one or more spray heads 10 provided on a respective robotized arm 11, or controlled by a pro¬ grammable apparatus to move and actuate the spray head 10 along the mould 1 according to any pre-esta- bushed operating sequence. Likewise, station 8 for pouring a second polyurethane mixture into the moulds 1 to form the padding, is provided with a second apparatus 12 for at least one conventional mixing head 13, for producing and feeding the polyurethane mixture into the mould. Figure 3 shows a cross-sectional view of a pad¬ ding for chair cushions and the like, obtained accord¬ ing to this invention. As can be seen in said fi- gure, the padding 14 is provided, on the sides, with outer stiffening or layers 15 on both sides-, which adapt to the sides and the edges of the padding and which adhere to the latter. The stiffening portions 15 and the same padding 14 are moulded from polyure- thane material, and in particular the stiffening side portions 15 are obtained from a first quick-reacting polyurethane mixture capable, that is, of foaming and curing in a few seconds, for example within the space of approximately two to four seconds, and cap- able of forming a first layer of flexible polyure¬ thane material having a relativel high modulus of elasticity, and in any case higher than that of the polyurethane material for the padding 14 so as to constitute a more rigid stiffening portion. Like- wise, the padding 14 is moulded using a second poly¬ urethane mixture having a longer foaming or raising time than the first one and capable of forming a second softer polyurethane material with a modulus of elasticity lower than the first one. This is achieved, for example, by means of a suitable for- mulation of the polyurethane components, which may vary according to the circumstances, by choosing the appropriate components and catalysts in order to accelerate the polymerization of the resin more or less; in order to form the superficial stiffening portions 15 of the padding, it is generally conve¬ nient to use ^ery quick-reacting mixtures suitable for spraying directly onto the internal walls of the mould and which adhere to the walls themselves, even if sloping or vertical, without dripping or spreading over the bottom of the mould. By using quick-reacting polyurethane mixtures capable of adhering to the internal surfaces of the mould during the spraying, it is possible to preform the stiffening portions 15 in the desired positions and thicknesses, before pouring or feeding into the mould the subsequent polyurethane mixture which will complete the entire padding body 14. The padding 14 can therefore be covered with a fabric upholstery 14a, which will adhere perfectly. Figures 4 to 6 illustrate the various stages of the method with reference to the installation of figure 1. The moulds 1 reach the opening station 5 where they are opened and the moulded paddings 14 are re¬ moved one at a time; then each open mould is moved to the subsequent preparatory station 6, where it is cleaned and sprinkled with a releasing agent. When one mould has thus been prepared, it is moved to the next station 7 in which the stiffening por- tions 15 are preformed directly inside the mould 1 and before the moulding of the padding 14. In this station 7 , one or more spray heads 10 are provided which are moved in a programmed mode to spray a first polyurethane mixture onto the inner surface of the mould cavity, forming a layer of the required thick¬ ness which detachably adheres to the internal sur¬ faces of the mould 1, in correspondence with pre- established positions, for example, corresponding to the outer sides and edges of the padding 14. It is obvious that by calculating the spraying times and the number of spray coating operations in each position, it is possible to form a layer 15 of poly¬ urethane material which gradually builds up until it reaches the desired thickness and distribution of the polyurethane material according to the shape of the padding and the specific requirements. Upon completion of the stiffening portions 15 directly into the open mould 1, the latter is made to move on to the next station 8 where a pre-esta¬ blished quantity 16 of a second polyuretnane mixture is poured onto the bottom of the same mould. The mould is then closed, and as it moves along the path 4, the mixture foams and cures to fill the entire cavity of the mould, embedding and adhering at the same time to the stiffening portions 15 preformed in the mould. After having travelled the entire path 4, each mould 1 comes to rest again in the opening station 5, where the padding 14 is removed and the moulding cycle is repeated. In the case of the previous figures, an example was given for moulding a padding made of soft poly¬ urethane material with superficial stiffening por¬ tions, having a shape and thickness suitable for the specific purpose; it is obvious however that the innovatory principle of the method according to this invention may be extended to other purposes for form¬ ing any type of stiffener in a moulded plastic ar¬ ticle, using a quick-reacting foamable mixture, spray- ed directly onto the latter a second mixture which will constitute the body of the moulded article. A further example is shown schematically in figure 7; this case shows the forming of a stiffener 12 designed to extend for a large extent from the outer surface, towards the inside of the moulded article. The stiffener ' 17 is formed step by step by spraying a suitable quantity of quick-reacting mixture onto the bottom of the mould 1, by means of a spray head 10 capable of forming a jet 18 of suitable width and intensity, acting as a "pencil" so that the spraying operation quickly forms a first layer 17a of suit¬ able size and thickness, which adheres to the sur¬ face of the bottom of the mould, then a second over¬ lying layer 17b which adheres to the first one, and so on to obtain the desired height or length of the stiffener 17, whose growth can be correctly and con¬ stantly controlled, not only by choosing the most suitable plastic materials to be used, and the fea¬ tures of the spray head 10, but also the spraying mode. Once the stiffeners or inserts 17 have been formed in the empty mould, it is moved to the next station of the installation shown in figure 1 or, if possible, remains in the spraying station itself, where the second plastic mixture is introduced; the second mixture then expands to fill the mould cavity thus completing the article to be moulded. It is obvious therefore that the use of quick-re¬ acting mixtures and the possibility of spraying such mixtures directly into the empty mould, enables the foam to adhere immediately, even to vertical or slop¬ ing surfaces, without flowing over the bottom of the mould; it is possible therefore to preform super¬ ficial stiffening portions and/or inside protruding stiffeners, with the utmost simplicity and constant control, using polyurethane or polystyrene materials having proper physical and mechanical properties, such as hardness, density and elasticity," differing from those of the rest of the body of the article to be moulded which, in the case of padding, can be ob- tained by using a softer polyurethane material cap¬ able of " providing a seat with the required comfort and at the same time providing supporting zones by means of the aforesaid stiffening portions 15.

Claims: C LA I MS 1. A method for producing moulded articles (14) of foamed plastic materials having stiffening portions (15, 17) characterized by the steps of preforming stiffening portions (15, 17) into the. empty mould (1) by spraying a quick-reacting mixture of a first plastic material making it adhere in pre-established positions to the internal surfaces of the mould; feeding into the mould (1) a foamable mixture of a second plastic material (16) and allowing said se- cond mixture (16) to foam and fill the cavity of the mould (1) embedding said sprayed stiffening portions (15, 17). 2. A method as claimed in claim 1, characterized by the fact of forming a stiffening portion (17) by successive spraying operations, preforming super¬ imposed layers of said quick-reacting mixture of the first plastic material which protrude into the mould. 3. A method as claimed in the previous claim 1, characterized in that said first and respectively said second mixtures are selected from polyurethane and polystyrene materials. 4. A method as claimed in claim 1 , in particular for producing paddings in polyurethane material hav¬ ing stiffening portions (15, 17) in the cavity of a mould (1) comprising bottom and side walls, cha¬ racterized by the steps of preforming said stiffening portions (15, 17) in pre-established positions on the bottom and/or side walls, by spraying a first quick-reacting polyurethane mixture into the open mould, adhering the sprayed mixture to the internal surfaces of the mould cavity; subsequently feeding into the mould (1 ) a quantity of a second foamable polyurethane mixture (16) and allowing said foamable polyurethane mixture to foam in the closed mould condition to form a padding (14), said stiffening portions (15, 17) being made with a polyurethane material having a modulus of elasticity higher than that of the polyurethane material of the padding. 5. A method as claimed in claim 4, characterized by the fact that the polyurethane mixture for the stiffening portions (15, 17) cures within a period of approximately 2 to 4 seconds. 6. A moulded article, particularly a padding for chairs and the like, comprising an elastically yield¬ ing body (14) of a first foamed plastic material and sprayed stiffening portions (15, 17) of a second quick-reacting plastic material embedded in the body (14) of the moulded article and appearing on deli- mited areas of its surface. 7. An installation for producing moulded articles of foamed plastic material, in particular paddings of polyurethane material, the installation compris¬ ing a plurality of moulds (1 ) for the articles to be moulded; supporting means (2) for each mould (1), and power actuated means (3) connected to said mould supporting means (2) to move said moulds towards work stations (5 - 8) along an annular path (4), said work stations comprising a mould opening station (5) for removing the padding from the mould, at least one mould preparatory (6) and a feeding (8) station for feeding a foaming plastic material into the moulds (1), characterized by the fact of comprising an in¬ termediate spray station (7) between said prepara- tory and feeding stations (6, 8), the intermediate station (7) comprising at least one spray head (10) for spraying a quick-reacting mixture of a plastic material, and power actuated means (9 - 11) for mov¬ ing said spray head (10) in pre-established positions of the cavity of a mould (1 ). 8. Installation as claimed in the previous claim 7, characterized by the fact that said power-actuated means (9, 11) for the spray head (10) comprises a programmable robotized head supporting arm (11).

Inventors: FIORENTINI CARLO, MARTIN PETER, FIORENTINI, CARLO, MARTIN, PETER
Applicants: AFROS SPA, AFROS S.P.A.
Application year: 1986
Main classification: B29C67
IPC codes: B29C37, B29C44, B29C70