MXPA98008620A - Injection-moulded refrigerator liners - Google Patents

Abstract

Injection-moulded refrigerator liners of a thermoplastic polymer characterized by the presence of means for mechanical bonding (1, 2, 3) of the insulating foam.

Description

REFRIGERATOR LININGS MOLDED BY INJECTION DESCRIPTIVE MEMORY The present invention relates to injection molded refrigerator liners characterized by the possibility of a mechanical bonding of the insulating foam. In particular, the invention relates to internal cooler linings having shaped portions and appropriately distributed »obtained by injection molding a thermoplastic polymer» in particular of propylene polymer »in order to make possible the subsequent coupling of the foam insulator to the back surface of the liner without using any particular pre-treatment of said surface. Current technology for the production of internal refrigerator liners is based essentially on the thermal formation of a thermoplastic sheet, mainly of polystyrene. However, the technology has some drawbacks, for example, low productivity in the extrusion process of the ho »difficulties in the dimensional control of the sheets» difficulties or even impossibilities to integrate the creation of complex constructive characteristics »such as the tubing by "air flow in the cooling system" without frost "in the main production process.

Furthermore, thermoforming technology can hardly be used with a proprietary polymer "which should be really preferred only on the basis of the symomechanical properties of the polymer" due to some additional difficulties "such as low melt strength» excessive polymer buckling »narrow scale of working temperature. Even more »a polypropylene liner for reliever» prepared with a thermoforming technology could require some special treatment in order to modify its surface and make possible the necessary link with the polyurethane foam. The inventors have found that all these drawbacks can be overcome by the change of the thermoforming technology to the injection molding technology »introducing some innovative features in the shape of the lining» such characteristics being easily obtainable by means of the technology of molding by injection by using molds configured in a timely manner »in order to make possible a mechanical link between the lining itself and the insulating foam. The invention can be applied to any thermoplastic polymer, but it is particularly suitable for pollen and in particular for propylene polymers. The refrigerator liners of the invention have some means of projection on the back surface of the liner "ie" on the surface that is inside on the left side of the body of the refrigerator "in order to acquire an adequate peel strength» more than 100 KPa »of the joint with an insulating foam. The foam is prepared on the spot by carrying the polymer to be foam in the melted or softened state in a mixture with the expansion gas which causes the polymer to foam directly on the back surface of the liner. Examples of the expansion gas are nitrogen »carbon dioxide» volatile hydrocarbons such as butane »isobutane and pentane. Typical examples of foamable polymers that can foam include poly urethane »polypropylene» polyethylene »polystyrene and polyvinyl chloride. In the case of the polyurethane »the foams can also be prepared by the controlled entrapment of an expansion gas during the polymerization which forms the urethane linkages between polyuntional alcohols and polyisocyanates. In this case »the foams are produced from liquid reagents that are mixed in carefully controlled formulations and discharged in contact with the back surface of the liner from the mixing heads. The geometrical characteristics of the inner liner of the refrigerator according to the present invention they will become apparent from the following detailed description "provided for illustration purposes only" for non-limiting purposes "by means of references to the accompanying drawings. Figure 1 shows an inner liner of the refrigerator with a series of raised vertical lines 1 on the rear surface. Figure 2 shows a horizontal cross-sectional view of the lines and presents in detail the "discharge angle" A of the mold. The angle of discharge refers to the acute angle between the projection average and the normal to the back surface of the lining. This angle determines the possibility of extracting the lining from the mold used for its preparation. The existence of this feature significantly improves the bond strength of the insulating foam to the back surface of the thermoplastic polymer. Preferably "the raised lines have an elevation height of 0.5-2 mm» discharge angle of 5-15 ° and a separation between them of 20 to 50 mm. Preferably, the internal liner of the refrigerator of the invention has means for joining point "as shown in Figure 3. The arrangement of the means is important in order to determine the strength of the joint. Experimentally it has been found that a homogeneous stepped rhomboidal arrangement of the dotted means "as shown in detail in the front view of Fig. 4 and in the sectional view of Fig. 5" is quite effective. The form »the size and quantity of the joining means are also very important. One of the best solutions is given by the fungiform heads 3 shown in section view in Fig. 6 »either solid or with a conical cavity open upwards to facilitate the detachment of the mold liner. The most effective values of the parameters that characterize the fungiform heads are: diameter of 5-7 mm »height of 1-2.2 mm» angle A of discharge from the mold of 5-15 ° and distance in the heads of one another in orthogonal lines from 100 to 300 mm. Various other types of link means can be provided and effectively used and should be considered within the scope of the invention. As stated before »any thermoplastic polymer can be used in the formation of the internal coolant liners of the invention» for example »polymers and copolymers of leno» polymers and copolymers of propylene »polymers and styrene copolymers including ABS »And pol vinlo chloride. The preferred thermoplastic polymers "however" are propylene polymers and copolymers "and in particular propylene polymers having a melt index L (ASTM D 1238) greater than 10 g / lO mes and a flexural modulus at 23 ° C ( ASTM D 790) greater than 200 MPa and copolymers of propylene with ethylene and / or α-olefins of C-C3 having a melt index L greater than 10 g / 10 mes and a flexural modulus greater than 170 MPa. As the foaming foam used with the liner of the invention, any polymer foam can be used. The preferred insulation foams »however» are polyurethane foams. The internal cooler liners of the invention can advantageously include additional features which can be easily obtained by injection molding processes. A typical example is given by the inclusion of conductors in the walls or in the margins of the linings, either as a structural element or »more frequently» for s cold air passages in "frost-free" cooling systems. Typically, such conduits can be obtained with so-called technology (air molding). Another characteristic which can be added to the refrigerator liners of the invention is odularity. In fact »with the injection molding process the modular liner having different characteristics» in particular different capacity »can be easily prepared. Domestic modular refrigerators obtained by the assembly of two or more liners according to the invention "whether the same or more frequently different" are therefore included in the rei indications of the instant invention. Obviously the liners that make up the refrigerator must be joined to each other before preparing the insulating foam. Various different means for joining the liner can be planned and prepared in the injection molding process.

Experimental work 1) Using a polypropylene inner liner for refrigerator of the type shown in figure 1 »with the possibility of a mechanical bonding of the insulating foam to the thermoplastic surface of the polymer due to the raised lines 1. the resistance to detachment The polyurethane foam of the lining surface is measured experimentally. When the raised lines have a height of relief of 0.5-2 mm »the angle of discharge (A) 5-15 ° and the separation between the lines of 20 to 50 mm» a resistance to detachment is obtained in the scale of 80- 90 KPa. For comparison purposes, the values of the resistance to the release of the polyurethane foam from a smooth metal surface and a smooth polypropylene surface is in the range of 170-220 KPa and in the scale of 20 to 40 KPa respectively. These values for the soft polypropylene surface are insuf fi cient for practical applications. 2) Using a polypropylene inner liner for refrigerator of the type shown in FIG. 1 with a mechanical bonding of the insulating foam to the surface of the polymer oplo due to the raised fungiform heads 3 in an alternating rhomboid arrangement. The resistance of the release of the polyurethane foam from the lining surface is measured experimentally. When the enhanced fungiform heads have a diameter of 5-7 mm »a height of 1-2.2 mm. and a discharge angle of 5-15 ° and separation of the heads in orthogonal lines of 100 to 300 mm. a release resistance is obtained in the 140-160 KPa scale.

Claims (5)

NOVELTY OF THE INVENTION CLAIMS

1. - Thermoplastic polymer injection molded liners. characterized by the presence of means for mechanically joining the insulating foam.

2. The refrigerator liners according to claim 1 further characterized in that the thermoplastic polymer consists essentially of a polyolefin and the mechanical bonding of the insulating foam has a peel strength of at least 100 KPa.

3. The refrigerator liners according to claim 1 »further characterized in that the thermoplastic polymer consists essentially of a polypropylene.

4. The refrigerator liners according to claim 1. further characterized in that the means for joining the insulating foam consists of raised lines (1) on the back surface of the linings.

5. The refrigerator liners according to claim 4 »further characterized in that the raised lines have a height of O.5-2 mm" with a discharge angle (A) 5-15 ° and a separation between lines from 20 to 50 mm. S. The refrigerator liners according to claim 1, further characterized in that the means for joining the insulating foam are punctiform means (2) and are homogeneously distributed on the back surface of the liners with an alternate rhomboid arrangement. 1. The refrigerator liners according to claim ß. further characterized in that the punctiform means for joining the insulating foam consist of fungiform heads (3) having a diameter of 5 to 7 mm. with a height from 1 to 2.2 mm and ur, discharge angle (A) from 5 to 15 °. B. The refrigerator liners according to claim 7, further characterized in that the distance of the fungiform heads in orthogonal lines is between 100 and 300 mm. 9. The refrigerator liners according to claim 7 or 8. further characterized in that the fungiform heads have a conical cavity open upwards. 10. The refrigerator liners according to any of claims 1 to 9 »characterized by the presence of the conduits in the walls or in the flanges of the linings as a structural element or for the passage of air in the systems of Reflection "no frost". 11. The refrigerator liners according to any of claims 1 to 10 »characterized by the presence of appropriate means to connect two or more of two liners of the same or different capacity and type in order to make possible the construction of a modular refrigerator lO domestic of various types. 12. The modular domestic refrigerator comprising an internal liner according to claim 11.