Rigid polymer foam

Abstract

A rigid polymer foam having specific characteristics in terms of resin absorption, and a structural element made from such rigid polymer foam and adapted to be used as a core layer in a multilayer structural element.

Claims

1. A polymer foam comprising: an unsealed surface, wherein the unsealed surface comprises a plurality of openings having depths with an average dimension not larger than an average cell size of the polymer foam, expressed as an average cell diameter of the polymer foam determined according to ISO28962001EANNEXA, and wherein the unsealed surface has a resin absorption from 450 to 600 g/m.sup.2.

2. The polymer foam according to claim 1, wherein the average dimension of the depths of the openings present on the unsealed surface of the polymer foam is lower than the average cell size of the polymer foam, expressed as the average cell diameter.

3. The polymer foam according to claim 1, wherein the polymer foam is an expanded polymeric material based on polyethylene terephthalate (PET).

4. The polymer foam according to claim 1, wherein the unsealed surface of the polymer foam has a contact angle that is less than 105° determined according to ASTM D7334-08 (2013).

5. The polymer foam according to claim 1, wherein the average cell size of the polymer foam, expressed as the average cell diameter, ranges from 0.05 to 2 mm.

6. The polymer foam according to claim 1, wherein a density of the polymer foam ranges from 30 to 400 kg/m.sup.3.

7. A structural element, adapted to be used as a core layer in a multilayer structural element, comprising: a polymer foam having an unsealed surface, wherein the unsealed surface of the polymer foam is charged with a resin and with reinforcing fibers and has an average dimension of a depth of openings present on the surface of the polymer foam not larger than an average cell size of the polymer foam, expressed as an average cell diameter of the polymer foam determined according to ISO28962001EANNEXA, and wherein the unsealed surface has a resin absorption from 450 to 600 g/m.sup.2.

8. The structural element according to claim 7, wherein the unsealed surface of the polymer foam is charged by infusion.

9. The structural element according to claim 8, wherein a penetration depth of the resin infused in the unsealed surface of the polymer foam is not higher than the average cell size.

10. The structural element according to claim 7, wherein the resin is a polyester resin, a vinyl ester resin, an epoxy resins, or a phenolic resin.

11. The structural element according to claim 7, wherein the unsealed surface of the polymer foam has been subjected to a final processing treatment or surface finishing, carried out by processing the unsealed surface of the polymer foam with a high precision cutting, without tearing and keeping the openings on the surface intact before charging with the resin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other objectives, advantages and characteristics appear from the following non-limiting examples, and from the figures of the attached drawings, in which:

(2) FIG. 1 illustrates the different resin absorption by a foam according to the state of the art (PY105 ref1), a foam according to the present invention (PY105 NF1) and an alternative product having a low average cell size without precision surface processing (HP80);

(3) FIG. 2 shows the different wettability of a foam according to the state of the art (PY105 ref1, above) and a foam according to the present invention (PY105-NF1, below), with the measurement of the contact angle;

(4) FIG. 3 shows how the infused foam has a greater penetration of the resin in the case of a foam according to the state of the art (PY105 ref1, below) and less in a foam according to the present invention (PY105-NF, above);

(5) FIG. 4 shows the surface of a foam according to the present invention (PY105-NF, on the left in FIG. 4) and of a foam according to the state of the art (PY105 ref1, on the right in FIG. 4), before resin infusion.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(6) In the examples provided below, the various chemical-physical characteristics have been measured using the methods previously indicated.

(7) Furthermore, the contact angle was measured with a 10× optical microscope, with a camera, according to the standard ASTM D7334-08 (2013).

(8) The quantity of infused resin was measured using the same internal method.

(9) Before Infusion

(10) The dimensions and weight of the sheet or structural element of rigid polymer foam were accurately measured before infusion with the resin; the area of the sheet was recorded as Al (m.sup.2) and the weight as m1 expressed in grams.

(11) Infusion According to the Internal Procedure

(12) A sealing tape was applied on the perimeter of the sheet and the sheet was infused with a layer of removable non-stick film (peel-ply) and biaxial fiber fabric (plies biax), on each side of the core layer and with a drainage mesh (flow net) on the top of the core layer.

(13) Vacuum containers and feeding tubes were used for feeding the resin.

(14) In the examples, an epoxy bis-phenol A diglycidyl ether (CAS: 1675-54-3, trade-name Hexion RIMR 035c) was used, together with an amine catalyst (trade-name RIMH 037), which is a formulate based on 3-aminomethyl-3,5,5 trimethyl-cyclohexamine (CAS: 2855-13-2) and polyoxypropylene diamine (CAS: 9046-10-0).

(15) The infusion was carried out at a controlled temperature of 35° C. and under vacuum at 0.6-0.9 bars, for 15-30 minutes. The subsequent cross-linking was carried out at 60° C. for at least 10 hours. After the infusion, the non-stick film and the drainage mesh (peel-ply and flow net) were removed together with the excess parts of the resin on the infused sheet.

(16) At the same time, the single biaxial fiber fabric (plies biax) was infused to determine its contribution to the total weight, and thus allow the calculation of the quantity of resin alone absorbed by the exposed surface cellularity.

(17) After Infusion

(18) The exact weight of the infused sheet m2, expressed in grams, was determined.

(19) The contribution was calculated of the infused biaxial fiber fabric (biax plies) to the total weight as mbiax, expressed in grams.

(20) The quantity of resin absorbed (RU) was then calculated as follows:
R=(m2−m1−mbiax)/A1

(21) The quantity of absorbed resin R is expressed in (g/m.sup.2).

Example 1 (Infusion and Resin Absorption)

(22) The product HP 80 is a PVC polymer foam having an average cell size of 0.3 mm but which does not have a high surface quality, as it has been subjected to a sanding process with sandpaper.

(23) The product PY105ref1 is a PET polymer foam having an average cell size of 0.6 mm, but which does not have a high surface quality, as it has been treated with sandpaper, so that the average depth of the exposed cellularity, i.e. the openings present on the surface of the polymer foam, is much greater than the average cell diameter.

(24) The product PY105 NF1 is a PET polymer foam having an average cell size of 0.6 mm and which has the correct surface quality, as it has been treated with high-precision knife blade cutting, so that the average dimension of the depth of the exposed cellularity is lower than the average cell diameter.

(25) The three rigid polymer foams indicated above were subjected to vacuum infusion, according to the internal lamination procedure, with the epoxy resin Hexion RIMR 035c, amine catalyst RIMH 037 and reinforcing fibers; the quantity of absorbed resin was measured according to the internal method indicated above, obtaining the results shown in table 1.

(26) TABLE-US-00001 TABLE 1 Core layer material Absorbed resin (g/m.sup.2) HP80 487 PY105 ref1 749 PY105 NF1 493

(27) The data indicated in Table 1 are also shown in FIG. 1 and clearly illustrate the different resin absorption by foams according to the state of the art and a foam according to the present invention.

(28) In particular, it has been demonstrated that the presence of the correct average dimension of the depth of the exposed cellularity is necessary, preferably achieved by means of high-precision finishing, in order to obtain a correct and non-excessive resin absorption, for PET foams having an average cell size of 0.6 mm.

(29) Furthermore, the average dimension of the depth of the exposed cellularity for PET foams, such as those of PY105 NF1, i.e. a foam according to the invention, allows an absorption of a non-excessive quantity of resin to be obtained, also in the case of a foam with a high cellularity (0.6 mm), i.e. a foam with a double exposed cellularity with respect to HP80 (0.3 mm): as shown by the data of Table 1, the resin absorption is completely analogous for HP80 (coarse processing) and PY105 NF1 (high-precision processing).

(30) The same polymer foam, with the same average cell size, PY105 ref1, which does not have an average depth dimension of the exposed cellularity according to the invention (as demonstrated in the following example 3) and not subjected to high-quality and high-precision final processing, showed an absorption of an excessive quantity of resin.

Example 2 (Wettability and Contact Angle)

(31) The rigid polymer foams PY105 NF1 and PY105 ref1, prepared as indicated in Example 1, i.e. with a high-precision final processing for PY105 NF1 (with knife blade cutting) and with a coarse-quality final processing (sanding with sandpaper) for PY105 ref1, and infused according to the internal lamination method, were evaluated in terms of wettability, as shown in FIG. 2.

(32) The different wettability of a foam according to the state of the art (PY105 ref1, above) and a foam according to the present invention (PY105 NF1, below) demonstrates how the smoother surface of the foam PY105 NF1 allows a greater wettability, with a further positive effect on the reduction of the resin absorption.

(33) More specifically, the evaluation was carried out by measuring the contact angle (according to the standard ASTM D7334) as an indication of wettability. In a surface with a high wettability for PET polymer foams, the contact angle is less than 105°, whereas in a surface with a low wettability for PET polymer foams, the contact angle is greater than 105°.

(34) TABLE-US-00002 TABLE 2 Hydrophilic Hydrophobic Contact angle Low High Wettability Good Poor

(35) The measurement of the contact angle, effected on the surface before lamination, is equal to 120.81° for the foam according to the state of the art (FIG. 2, PY105 ref1, above) and 92.84° for the foam according to the present invention (FIG. 2, PY105 NF1, below).

(36) FIG. 4 shows how the surface subjected to final processing with sandpaper (PY105 ref1, on the right) is of poor quality, with chipping and entrainments, and the surface subjected to high-precision final processing with knife cutting (PY105 NF1, on the left), is without striations and with a net sectioning of the cells.

Example 3 (Penetration Depth/Thickness of the Resin in the Foam)

(37) FIG. 3 shows how the infused foam undergoes a penetration of the resin inside the cells exposed on the surface, for a greater thickness/depth in the case of a foam according to the state of the art (PY105 ref1, below) with respect to a foam according to the present invention (PY105NF1, above).

(38) More specifically, in FIG. 3, the area of the laminate (resin+fiber) that has been sectioned has a dimension of 5.08 mm.sup.2: the width is equal to 6.79 mm, therefore the average thickness is equal to (5.08/6.79)=0.75 mm (±1 mm), attributed to the laminate (resin+fiber) alone without considering the penetration into the exposed volume of the foam.

(39) The area of the resin penetrated inside the foam PY105 ref1, FIG. 3 below, i.e. the foam according to the state of the art, is equal to 5.18 mm.sup.2: the width is equal to 6.79 mm, therefore the average thickness of the penetrated resin is equal to (5.18/6.79)=0.76 mm (±1 mm).

(40) The area of the resin penetrated inside the foam according to the present invention, (PY105 NF1, FIG. 3 above, is equal to 1.15 mm.sup.2: the width is equal to 6.79 mm, therefore the average thickness of the penetrated resin is equal to (1.15/6.79)=0.17 mm (±1 mm).

(41) The width was evaluated considering the width of the sections (5-6-7-8) in FIG. 3 and, as indicated above, was used for the calculation of the average penetration thickness/height of the laminate (resin+fiber) alone and the average penetration thickness/height of the resin inside the surface volume, which depends on the surface cellularity and imprecision of the final processing.

(42) The above data clearly show that the average thickness of the resin penetrated into the foam according to the present invention (PY105NF1, above) which is equal to 0.17 mm, is lower than the average cell size of 0.6 mm, whereas the average thickness of the resin penetrated into the foam according to the state of the art (PY105 ref1, below) which is equal to 0.76 mm, is greater than the average cell size of 0.6 mm.

(43) In the case of PY105 ref1, the maximum thickness of the infused resin is equal to 1.69 mm. Consequently, as the thickness of the laminate (resin+fiber) alone is equal to 0.75 mm, it can be deduced that, with the surface processing process with sandpaper (PY105 ref1), the finishing surface imperfections always cause a penetration of the resin inside the surface that reaches a value of 0.94 mm, i.e. (1.69 mm-0.75 mm) i.e. much higher values than an average cell size (0.6 mm).

(44) In the case of the foam according to the invention, PY105NF1, on the contrary, the overall thickness (resin+fiber+penetrated resin) ranges from a minimum value of 0 (0.75 mm) to a maximum value of 1.20 mm, showing that the maximum penetration depth of the resin inside the surface, in the exposed cellularity, is equal to 0.45 mm, i.e. (1.20 mm-0.75 mm), which is still lower than the average cell size of 0.6 mm.