Pessina, Valerio (Via Miola, 56 Saronno, I-21047, IT)
| 1. | 1) A heatsensitive adhesive insert formed of two components A and B, wherein : component A is a polyamide polymer, and component B is a compound capable of increasing the viscosity and controlling the resiliency of component A in the molten state and to impart to the heatsensitive adhesive insert such an elastic memory as to cause it to be shortened longitudinally and expanded radially so as to counteract the dripping thereof in the molten state, the ratio of component A to component B ranging from 5% to 95%, component B being chosen among the high functionality elastomers and/or mineral fillers and/or cross linking agents and/or chain elongating agents and/or viscosity control agents or a combination thereof. |
| 2. | A heatsensitive adhesive insert according to claim 1, characterised in that as component B there are used products or additives having at first a viscosity smaller than that of component A and which then react therewith so as to give a compound having a viscosity greater than the initial viscosity, e. g. silica, fibreglass and the like, so that the resulting mixture A + B will have a viscosity greater than that of component A and the heatsensitive adhesive insert achieves a resilience capable of causing it to be shortened longitudinally and expanded radially in order to counteract the dripping thereof in the molten state. |
| 3. | A heatsensitive adhesive insert according to claim 1, characterised in that as component B there are used acrylic elastomers or a combination of olefin polymers with acrylic elastomers or a suitable combination of polymers and elastomers formed of acrylonitrilebutadyene rubber (NBR) and/or ethylenepropylene polymers in an amount ranging from 5% to 95%, provided that the viscosity thereof is greater than that of component A, so that the resulting mixture A + B will have a viscosity greater than that of component A and the heatsensitive adhesive insert acquires such an elastic memory as to cause a longitudinal shortening and a radial expansion of the heatsensitive adhesive insert to contrast the dripping thereof in the molten state. |
| 4. | A heatsensitive adhesive insert according to claim 1, characterised in that as component B there are used cross linking agents, e. g. peroxides, or chain elongating agents, e. g. urethanes, which increase the viscosity of the heatsensitive adhesive insert in the molten state. |
| 5. | A heatsensitive adhesive insert according to claim 1, characterised in that the attained increase in viscosity ranges from 85 to 99%. |
| 6. | A heatsensitive adhesive insert according to one of the above claims, characterised in that it does not drip when it is melted. |
| 7. | Use of a heatsensitive adhesive insert according to one of the claims 16 in the manufacturing of heatinsulating composite metal sections, particularly intended for forming doorand windowframes and the like. |
BACKGROUND ART It is known that in the manufacture of metal door-and window-frames and the like, particularly in aluminium, aluminium alloy or steel, special composite sections are used which are formed of a pair of spaced-apart metal sections connected to each other by means of a pair of heat-insulating crosspieces extending in the longitudinal direction of the metal sections.
The heat-insulating crosspieces are typically made of high strength synthetic material having good thermal insulating properties, e. g. a polyamide, so as to form a heat-insulating bridge between the coupled metal sections.
In most cases, the longitudinal edges of the heat-insulating crosspieces are shaped as a dovetail and engage in appropriate grooves undercut in the opposite sides of the metal sections longitudinally thereto.
In the manufacture of composite sections, the projections which define each groove undercut in the metal section are pressed by means of a suitable tool against the longitudinal dovetail shaped edges of the heat-insulating crosspieces so as to hold them in a close and tight fit relationship between the projections.
In order to improve the close and tight fit relationship between the metal sections and the heat-insulating crosspieces, and moreover to increase the strength of the composite section, a heat-sensitive adhesive insert is generally arranged between the longitudinal dovetail shaped edges of the heat-insulating crosspieces and the wall of the grooves undercut in the metal sections, which heat-sensitive adhesive insert features physical properties which are changing under thermal action so as to achieve the adhesion of the heat-insulating crosspieces to the metal sections.
The heat-sensitive adhesive insert used in the manufacture of the composite sections is preferably in form of a wire, string or tape. The heat-sensitive adhesive insert is arranged preferably in an appropriate longitudinal cavity formed in the longitudinal dovetail shaped edges of the heat-insulating crosspieces or in the wall of the grooves undercut in the metal sections.
The material of the heat-sensitive adhesive insert is heat sensitive and, upon heating, the heat-sensitive adhesive insert expands in cross-section and shortens in the longitudinal direction, and melts, thereby forming a good adhesion and a tight connection between the longitudinal dovetail shaped edges of the heat-insulating crosspieces and the grooves undercut in the metal sections, so that an improved close and tight fit relationship between these parts of the composite section is achieved.
As suitable materials for the heat-sensitive adhesive insert thermoplastic materials are typically used which are adhesive in the molten state, e. g. polymers of the polyamide family.
The heat required for expanding and melting the heat-sensitive adhesive insert is generally supplied during a manufacturing process step of the composite section, e. g. a galvanisation or a furnace coating, during which high temperatures are reached which are capable of causing the adhesive insert to be melted. Alternatively, the heat is supplied by providing an additional step in the manufacturing process of the composite sections, e. g. a thermal treatment by using ultrasonic or high frequency waves.
A drawback of the heat-sensitive adhesive inserts of the kind known in the art used in the manufacture of composite sections consists in that the material of the heat-sensitive adhesive insert may drip out from the ends of the composite section once it has reached the temperature at which it starts to melt.
In order to obviate this drawback it has been proposed to introduce sealing elements at the ends of the composite section which prevent the molten heat-sensitive adhesive insert to drip out upon the thermal treatment. The sealing elements are f. i. in the form of plugs which are arranged in the longitudinal grooves undercut in the metal sections or in the form of plates which are connected by welding, by means of screws or glued to the ends of the composite section. Another suggestion has been to let the heat-sensitive adhesive insert undergo a streching operation upon its extrusion, and this obviously requires an additional manufacturing step, thereby resulting in additional costs.
Although obviating the above mentioned problem of the molten material of the heat-sensitive adhesive insert dripping from the ends of the composite sections, these suggestions cause the manufacture of the composite sections to be more difficult and expensive.
DISCLOSURE OF INVENTION The object of the present invention is to obviate this problem in a more simple and economic manner.
The inventive idea on which the present invention is based is therefore to obviate the dripping of the molten heat-sensitive adhesive insert by changing the viscosity and resiliency thereof, and particularly by increasing them in such a degree to counteract the dripping thereof.
According to the present invention, this object is achieved by a heat- sensitive adhesive insert formed of two components A and B, wherein: component A is a polyamide polymer, and component B is a compound capable of increasing the viscosity and controlling the resiliency of component A in the molten state and to impart to the heat-sensitive adhesive insert such an elastic memory as to cause it to shorten longitudinally and to expand radially so as to counteract its dripping-out tendency in the molten state, the ratio of component A to component B ranging from 5% to 95%, component B being chosen among the high functionality elastomers and/or mineral fillers and/or cross linking agents and/or chain elongating agents and/or viscosity control agents or a combination thereof.
Therefore, as a result, the heat-sensitive adhesive insert obtained in accordance with the invention and used in the manufacture of metal composite section features the characteristic of having a smaller tendency to drip because it has a higher degree of viscosity and resiliency in the molten state, and a greater elastic memory which is adapted to cause it to be radially expanded and longitudinally shortened, counteracting the dripping thereof.
In order to achieve the above mentioned characteristic of the heat-sensitive adhesive insert in the molten state, the heat-sensitive adhesive insert is obtained by mixing the component A and component B in a ratio capable of
greatly reducing the tendency of the molten heat-sensitive adhesive insert to drip.
As component B there can be used, e. g., acrylic elastomers or a combination of olefin polymers with acrylic elastomers or a suitable combination of polymers and elastomers preferably formed of acrylonitrile-butadiene rubbers (NBR) and/or ethylene propylene polymers in an amount ranging from 5% to 95%, provided that their viscosity is greater than that of component A, so that the viscosity of the resulting mixture A + B will be greater than that of component A and the heat-sensitive adhesive insert acquires a degree of resilience capable of causing it to be shortened longitudinally and expanded radially in order to counteract its dripping in the molten state.
As component B there can be also used products or additives which at first generally have a viscosity smaller than that of the component A and that upon reaction and/or mixing cause the resulting compound to have a greater viscosity than the reactants, and therefore obtain the same result as with the component B of higher viscosity than component A. For exemplification purposes, there can be mentioned mineral fillers, e. g., silica, fibreglass and the like.
In a further embodiment, component B may also be formed of cross-linking agents, f. i. peroxides, or it may be formed of chain elongating agents, f. i.
urethanes, which increase the viscosity of the heat-sensitive adhesive insert in the molten state.
In order to show that the molten heat-sensitive adhesive insert according to the present invention achieves a greater viscosity and resiliency, Table A and Table B illustrate the values of viscosity and percentage change of length and diameter, respectively, of a wire shaped heat-sensitive adhesive insert formed of a composition (I) of the kind known in the art and a wire shaped heat-sensitive adhesive insert formed of two different compositions (II) and (m) according to the present invention.
The values of viscosity have been measured indirectly as flow rates at the same conditions of temperature, pressure load and outlet cross-section for the different compositions. The equipment used for measuring the viscosity is the Melt Flow Indexer, the characteristics of which reflect the ASTM D 1238 Standard. According to this Standard, the measurements obtained are expressed in g/min, therefore they represent flow rate values corresponding to the viscosity according to a relation whereby the smaller is the flow rate the greater is the viscosity of the material. The measurement of the viscosity has been made with a material at 190°C, a pressure load of 2160 g and with an equipment employing a nozzle having a diameter of 2.095 mm.
TABLE A Heat-sensitive adhesive Insert Flow rate [g/10 min Composition (I) 12 (priorart) Composition (n) L8 Composition (m) 0,049
In the following Table B there are illustrated the percentage values of the relative change of length AUL and diameter #D/D at three different test temperatures (160°C, 180°C, 200°C). These measured values show that the heat-sensitive adhesive insert made of the compositions (II) and according to the present invention has a resilience capable of causing it to be shortened longitudinally and expanded radially in the molten state.
TABLE B Conditions 20 min, at 160°C 20 min. at 180°C 20 min. at 200°C Dimensions #L/L% #D/D% #L/L% #D/D% #L/L% #D/D% Composition (I) Not measurable Not measurable Not measurable (Prior art) because it drips because it drips because it drips Composition (II)-67% + 110% -73% + 120% - 76% + 127% Compositionosition (III) - 82% + 120% - 80% + 150% - 80% + 143% From the foregoing it is understood that the heat-sensitive adhesive insert according to the present invention used in the manufacture of the above
mentioned composite metal sections reaches the aimed object. In particular, this object has been attained by formulating the composition of the heat- sensitive adhesive insert so that it has a high viscosity in the molten state.
Furthermore, the composition of the heat-sensitive adhesive insert is such as to impart a resilience thereto which is capable of causing it to be shortened longitudinally and expanded radially, thereby reducing the tendency thereof to drip in the molten state.
Moreover, the addition of component B to component A does not impair the capability of adhesion of the heat-sensitive adhesive insert.