NL9401055A - Method for fabricating a plastic lamina, and lamina obtained by said method - Google Patents

Abstract

A method for fabricating a plastic lamina having a sandwich-like structure comprises the steps of: 1) providing an injection-moulding apparatus with a mould which comprises two mould sections which can be moved relative to one another, in a closed first extreme position delimit a mould cavity contiguous to an injection unit, and in an open second extreme position release a moulded lamina for the removal thereof; 2) providing foaming means to cause plastic injected into the mould cavity to foam in the mould cavity; 3) providing blocking means for temporarily deactivating the foaming means; 4) actuating the blocking means; 5) actuating the injection unit in the first extreme position of the mould; 6) deactuating the blocking means; 7) deactuating the injection unit; and 8) moving the mould sections relative to one another according to the adjacent graph: <IMAGE>

Description

METHOD FOR MANUFACTURING A PLASTIC SHEET, AND SHEET OBTAINED WITH THAT METHOD

The invention relates to a method for manufacturing a monolithic plastic sheet with a thickness of at least 6 mm, preferably (20 ± 10) mm, which sheet is constructed as structural foam and a sandwich-like structure with a foam core and closed skin barrier.

Such a method and the leaf obtained therewith is known, for example, from US-A-4 096 218.

This US patent discloses a method according to which the mold cavity is enlarged in a predetermined time after a few seconds after the injection of the plastic has been completed. The use of a foaming agent and the use of gas backpressure can thus ensure that the foam structure is of good quality, while the skin of the obtained plate has a closed and smooth structure.

According to the said US patent, the mold is kept in its closed starting position for a predetermined time, after which the mold undergoes a certain expansion in a following specified period. After reaching the maximum expansion, cooling takes place for some time, after which the formed plate can be taken out.

Attention is also drawn to US-A-4 133 858, which deals with a related technique and which also mentions a number of possible plastics to be used in the context of this technique and substances to be added thereto, such as foaming agents .

Since it has been found that sheets of a sufficiently high quality cannot be obtained with the known method, it is an object of the invention to provide a method with which a sheet of improved quality can be manufactured.

A further object of the invention is to carry out the known method in such a way that it lends itself to pre-introducing a decorative film into the mold, such that this film is positioned on an outer surface of the obtained plate. ?

Yet a further object of the invention is to carry out the method in such a way that the resulting sheet has an optimum flatness within very narrow tolerances, or, more generally, has a shape which is very narrow within tolerances to the desired nominal shape.

A still further object of the invention is to carry out the method in such a way that also cheaper plastic materials, for example plastics of recycled quality, can be used to obtain a sheet with the desired superior properties.

In order to achieve the above objects, the invention provides a method for manufacturing a monolithic plastic sheet, with a thickness of at least 6 mm, preferably (20 ± 10) mm, which sheet has a sandwich-like structure with a foam core and closed skin plates, the method comprising the following steps to be performed in an appropriate order: (1) providing an injection molding device with a plastic plasticizing and injecting device and a mold, which are at least two relative to mold parts displaceable by displacing means, which mold parts define in a closed first extreme position a mold cavity adjoining the plasticizing and injection unit, and in an open second extreme position release a shaped plate for removal, which displacement means are adapted for moving the mold parts at a selectable speed; (2) providing foaming means for foaming plastic injected into the mold cavity in the mold cavity; (3) providing blocking means for temporarily disabling the foaming means, for example gas supply means for supplying pressurized gas to the mold cavity; (4) energizing the blocking means; (5) energizing the plasticizing and injection unit in the first extreme position of the mold for injecting into the molded cavity of heated plastic? (6) de-energizing the blocking means; (7) de-energize the plasticizing and injection unit? (8) energizing the displacement means such that the mold parts move relative to each other according to the graph below, wherein with the shaded area the limits of the course of the ratio between the displacement (d) and the initial thickness ( a) the time (t) shows:

in which the slope h is not limited in principle; and (9) cooling the molded sheet to a selected temperature, opening the mold cavity completely and removing the cooled sheet.

Attention is drawn to the fact that the invention, unlike the prior art mentioned, is not limited to the use of the so-called gas counterpressure, with which the foaming of the injected plastic in the mold cavity can be temporarily prevented.

The appended claims 2-9 relate to specific embodiments of the method according to the invention. It is noted that the materials and materials mentioned are only listed by way of example, without any limiting significance.

The slope h corresponds to the greatest possible speed to be realized by the injection molding device concerned. It is therefore to be understood that the upper limit in question is determined solely by the injection molding device used and is not in principle related to the choices made in the context of the invention.

Finally, the invention also relates to a monolithic plastic sheet, which is manufactured using the method according to any one of claims 1-9.

In particular, such a blade can have a shape such that the blade has a non-round shape and a folded peripheral edge.

The accompanying drawings schematically show two possible embodiments of the invention.

In Figure 1a, the injection pressure with which the plastic is injected into the mold cavity is plotted as a function of time.

Figure 1b shows, with the same reference t = 0, the limits within which, in accordance with the teachings of the invention, the two mold parts, which bound together the mold cavity, can move relative to each other.

It will be clear that figure 1a refers to a completely arbitrary example. Injection begins approximately 8 seconds prior to expanding the mold cavity. After some time, the final injection pressure is reached according to a curve that is not relevant in itself. After completion of the injection, after a slight delay, the beginning of the expansion of the mold cavity according to Figure 1b takes place. The shaded area boundaries are those set forth in claim 1. By way of example, a practical curve 1 is drawn in the hatched area, which corresponds to a practical exemplary embodiment. It can be clearly seen that, according to the teachings of the invention, a very slow expansion is initially used, followed by a rapid expansion, which then decelerates again until the final volume of the mold cavity is reached.

Attention is drawn to the fact that the shape of the injection pressure curve can also be varied according to need and wishes. In addition, the injection need not be stopped before time t * 0.

Figure 2a indicates that shortly before time t = -9 gas, for example nitrogen, is introduced under pressure into the mold cavity. Then, in this case at time t = -8, the injection of plastic begins. Around time t = 0, the gas back pressure is reduced, as shown in Figure 2a, while an afterpressure is also exerted by the injection unit, as shown in Figure 2b. Meanwhile, at a time t = 0, a start has been made on expanding the mold cavity in accordance with Figure 1b.

Attention is again drawn to the fact that figures 1a, 2a and 2b may only be given an indicative meaning. Many variants of the shapes of the curves, the values of the various parameters, and the like can be varied without thereby exceeding the scope of the invention. The final shape of the curve 1 in Figures 1b and 2c can also be chosen as desired within the hatched frame. In general, the parameter combinations will have to be determined in such a way that the best result is achieved with a given plastic, possibly with additives.

A sheet according to the invention comprises two solid plates, which define a foam core. The blade is integral and there is an area between each skin barrier and the foam core with a smooth density change.

The blade has a very favorable ratio between mechanical strength and stiffness on the one hand and weight on the other. [

Very favorable properties with regard to thermal and acoustic insulation can be obtained with a sheet which has an increased thickness, in particular of the foam core. The choices for the optimal combination depend on the requirements placed on the relevant sheet.

A sheet according to the invention can also be characterized by the relative density, i.e. the effective average density of the sheet divided by the density of the plastic itself. According to the invention, values of considerably less than 0.75 can be achieved. A value of 0.25 is currently achievable.

Tables I-V below relate to experiments within the scope of the invention.

No. [] 45 49 56 80 82 83 84 material type [] 40K35mlgd 40K35mlgd 40K35mlgd 2k-mlgd 2k-mlgd 2k-mlgd 2k-mlgd propellant type [] BIH-70 BIH-70 BIH-70 BIH-70 ΒΙΗτ70 BIH-70 BIH -70 dose [wt%] 2 2 22333 ssessasssBsssssssssasss sssscssssserssssaassssssssssss aeBeKevoBBBesftvasvsssrKsssaesssc melting temp [oC] 240 240 240 240 240 240 240 dosing path [mm] 340 340 340 340 30 30 30 30 injection pressure [bar] 8 8 8 8 19 6 8 injection 1 [% J 15 15 15 15 20 60 50 profile 2 [% J · 20 20 20 20 20 60 50 3 [V] 50 50 50 50 20 60 50 4 [%] 50 50 50 50 20 60 50 5 [%] 50 50 50 50 20 60 50 6 [%] 50 50 50 50 20 60 50 7 [%] 50 50 50 50 20 60 50 8 [%] 50 50 40 40 20 60 50 9 [V] 50 50 30 30 20 60 50 10 [%] 20 20 15 15 20 60- - 50 focus [bar] 20 20 20 20 20 20 20 focus point [mm] 40 40 40 40 40 40 40 focus time [eek] 5 15 0 1 0 0 0 GTD working pressure [bar] 9 9 9 9 9 9 9 point GTD-off [mm] 160 160 85 85 85 85 85 r.p. walk in [eek] 15 5 15 10 10 10 0 sssacttSBSsssssaavsB & sss eeassasasaasssaMeassssBBMaasae aasaaissssffeseecssssevBSaarsssss initial wall thickness [mm] n n 11 11 11 11 11 final thickness [mm] 16.5 16.5 19 18.9? 19.5 24.1 sasaaataesassssaaasss ^ ss sssBessssassssssseasssrssssess ssasssaaBasaBaaaasBeiseacssastsssa. weight [kg] 8.31 8.63

Table I

No. [] 91 92 93 94 Material type [] 2k-mlgd 2k-mlgd 2k-mlgd 2k-ralgd propellant type Π BIH-70 BIH-70 BIH-70 BIH-70 dosage [wtl] 2222 essseiesassaasssssQSas β3Β8ΒΜ · Β · Β8 ·· · Ν * ·· Β · ν ··· 8 & βν bbsb melting temp [oC] 260 260 260 260 dosing path [mm] 340 340 340 340

Pressure [bar] 30 30 30 30 injection time [sekj 8888 injection 1 [%] 15 15 15 15 profile 2 [%] 20 20 20 20 3 [V] 50 50 50 50 4 [%] 50 50 50 50 5 (* ] 50 50 50 50 6 [V] 50 50 50 50 7 [V] 50 50 50 50 8 [%] 40 40 40 40 9 [%] 30 30 30 30 10 [V] 15 15 15 15 emphasis [bar] 20 20 20 20 focus point [mm] 40 40 40 40 focus time [eek] 0000 GTD working pressure [bar] 9 9 9 9 point GTD-off [mm] 85 85 85 85 delay opening [sek] 10 10 10 10 aesssBsssssBsssesaesssa ssassBaBssBaiBsssuBiBieBtaBaa ·· ·· initial wall thickness [mm] 11 11 11 11 final thickness [mm] 18.6 19.8 21.1 21.6

aesssasssBBBaBMaaaaaaaB SB8BBa: sssaBaBSSSBBaesaBSSS8 & sSBS

weight [kg] 8.43

Table II

No. Π 100 101 102 103 110 112 material type [] 2kmlgd / hopol 2kmlgd / hopol 2kmlgd / hopol 2kmlgd / hopol 2kmlgd / hopol 2kmlgd / hopol propellant type [] BIH-70 BIH-70 BIH-70 BIH-70 * BIH-70 BIH -70 dosing [wt%] 222222 sBSBaessassaSBSssssssas sssa «»> KBaBaiBBsa> BBssssssasasa = saaavsBSSSsaBS = BBaBBSBSBSsassssssaasaBBBa> asssBBS = melt temp [oC] 245 245 245 245 245 245 dosing pressure [mm] 340 340 340 30 30 30 30 injection time [sek] 888899 injection 1 [%] 15 15 15 15 15 15 profile 2 [%] 20 20 20 20 20 20 20 3 [%] 50 50 50 50 50 50 4 [%] 50 50 50 50 50 50 5 [%] 50 50 50 50 50 50 6 [V] 50 50 50 50 50 50 7 [-%] 50 50 50 50 50 50 8 [%] 40 40 40 40 40 40 9 (%) 30 30 30 30 30 30 10 [%] 15 15 15 15 15 15 focus (bar] 20 20 20 20 20 20 focus point [mm] 40 40 40 40 40 40 focus time [sek] 0 0 0 0 0 0 GTD operating pressure [ban:] 9 9 9 9 9 9 point GTD-off [mm] 85 85 85 85 85 85 delay opening [sek] 16 10 5 0 15 30 ksi aaaKc = ssss: === ssss = sss = anBS8B «BiieKasssssrsMse« ssassBEassBas * es3BsssecBS = BBK = initial wall thickness [mm] 11 11 11 11 13 13 final thickness [mm] 20.7 21 20.5 20.2 20.6 20.9 weight [kg] 7.46 - - 7.39 - 8.77

Table III

No. [] 120 121 122 special material type [] 50L20T30 / hopol 50L20T30 / hopol 50L20T30 / hopol 50L20T30 / hopol propellant type Π BIH-70 BIH-70 BIH-70 * Bxocerol-70 dosing [wt \] 2221 SSSBSSaBBSBBSBBSBBSBBSSSSBSBSBBSSSS melting temp [oC] 245 245 245 245 dosing path [mm] 390 390 390 390 thrust [bar] 30 30 30 30 injection time [sek] 9999 injection 1 [%] 15 15 15 15 profile 2 [%] 20 20 20 20 3 [ %] 50 50 50 50 4 I%] 50 50 50 50 5 [V] 50 50 50 50 6 [%] 50 50 50 50 7 [%] 50 50 50 50 8 (%] 40 40 40 40 9 [t] 30 30 30 30 10 [%] 15 15 15 15 emphasis [bar] 20 20 20 20 focus point [mm] 4 0 40 40 40 focus time [sek] 0 0 0 0 GTD operating pressure [bar] 9 9 9 9 point GTD-off [mm] 85 85 85 85 Delayed opening [sek] 25 .30 35 20

BaiS88BSasaKSHeBSBSS «SS SSaSS & aSBSSSSBBBBBBVSSBBSSBBBaSSSSBBBSSarSBSSBBBSBBBBaBBBBBBB

initial wall thickness [mm] 13 13 13 13 final thickness [mm] 21.5 - - 30 BBIBIBSaBBSBSSBSBaSBSBB ΒΒ888ΒΒΒΒΒΒΒΒΒΙΙΒΒΒ8ΒΒ88α · ΒΒ8ΒΒΒΒΒΒ · ββ · Β8 ··· ΒΒ · ΒΒ · ΒΒΒ8 · Β «ΒΒΒ · weight [kg] - 9.46

Table IV

No. [] 1 G

material type t) 30H30 HT-40 HK-40 HK-40 BCK-40 float type [) Bxoc.-70 Exoc.-70 Exoc.-70 Exoc.-70 Exoc.-7t0 dosage [wt%] 11111 · ιον · £ · Μ8 ££ «·« · βιι £ Β · ΠΕ * πε: βη = ηπΒΚ · * «π« Baanailc melting temp [oC] 250 240 240 240 250 dosing path [mm] 390 390 390 390 315 thrust [bar] 30 8 8 8 8 injection time [sekj 9 7.S 8 10 8 injection 1 [V] 50 50 15 40 50 profile 2 [VI 50 50 20 40 50 3 [%] 50 50 50 40 50 4 [V] 50 50 50 40 50 5 [F] 50 50 50 40 50 6 [%] 50 50 50 40 50 7 [%] 50 50 50 40 50 8 [V] 50 50 40 40 50 9 {%] 50 50 30 40 50 10 (*] 50 50 15 40 50 focus [bar] 30 35 35 35 70 focus point [mm] 20 35 40 40 50 focus time [sek] 20 1 10 1 1 GTD operating pressure [bar] 9 8 9 9 8 point GTD-off [mm] 85 85 85 85 85 delayed opening [eek] 1 5 1 1 12.5 saaissssaBSSBsssBSBaaBa cc? == s = sa «assBsssssss ssssasssssBasssssa bbssbssbs initial wall thickness [mm] 10 10 10 10 10 final thickness [mm] - - 15.5 23 SCSSas & sessssssssssssssssssssssssssssssssssssssssssssss Asaasaaaa weight [kg] - - - 9.29

Table V

Claims (15)

A method for manufacturing a monolithic plastic sheet, with a thickness of at least 6 mm, preferably (20 ± 10) mm, which sheet comprises a sandwich-like structure with a foam core and closed skin plates, which method comprises the following, steps to be performed in an appropriate order comprise: (1) providing an injection molding device with a plastic plasticizing and injecting device and a mold, comprising at least two mold parts displaceable relative to each other, which mold parts in a closed first extreme position bounding a mold cavity adjoining the plasticizing and injection unit, and in an open second extreme position releasing a molded plate for removal, which displacing means are adapted to move the selected speed mold parts, · (2) providing foaming means for foaming plastic injected into the mold cavity in the mold cavity; (3) providing blocking means for temporarily disabling the foaming means, for example gas supply means for supplying pressurized gas to the mold cavity; (4) energizing the blocking means; (5) energizing the plasticizing and injection unit in the first extreme position of the mold for injecting into the molded cavity of heated plastic; (6) de-energizing the blocking means; (7) de-energizing the plasticizing and injecting unit; (8) energizing the displacement means such that the mold parts move relative to each other according to the graph below, wherein with the shaded area the limits of the course of the ratio between the displacement (d) and the initial thickness ( a) the time (t) shows:

in which the slope h is not limited in principle; and (9) cooling the molded sheet to a selected temperature, opening the mold cavity completely and removing the cooled sheet. A method for manufacturing a monolithic plastic sheet, with a thickness of at least 6 mm, preferably (20 ± 10) mm, which sheet comprises a sandwich-like structure with a foam core and closed skin plates, which method comprises the following, steps to be performed in an appropriate order comprise: (1) providing an injection molding device with a plastic plasticizing and injecting device and a mold, comprising at least two mold parts displaceable relative to each other, which mold parts in a closed first extreme position bounding a mold cavity adjoining the plasticizing and injection unit, and in an open second extreme position releasing a shaped plate for removal, which displacing means are adapted to move the soot at a speed which can be selected mold parts; (2) providing foaming means for foaming plastic injected into the mold cavity in the mold cavity; (3) providing blocking means for temporarily disabling the foaming means, for example gas supply means for supplying pressurized gas to the mold cavity; (4) energizing the blocking means; (5) energizing the plasticizing and injection unit in the first extreme position of the mold for injecting into the molded cavity of heated plastic; (6) de-energizing the blocking means; (7) de-energizing the plasticizing and injecting unit; (8) energizing the displacement means such that the mold parts move relative to each other according to the graph below, wherein with the hatched area the limits of the course of the ratio between the displacement (d) and the initial thickness (a) the time (t) shows:

in which the slope h is not limited in principle; and (9) cooling the molded sheet to a selected temperature, opening the mold cavity completely and removing the cooled sheet. The method of claim 1, wherein the plastic is thermoplastic. The method of claim 1, wherein the plastic is thermoplastic. The method of claim 1, wherein the plastic contains at least one polymer. The method of claim 1, wherein the plastic contains at least one polymer. A method according to claim 1, wherein the plastic contains a polyolefin, for example PS, PE, PP, EVA, ABS, PPO. A method according to claim 1, wherein the plastic contains a polyolefin, for example PS, PE, PP, EVA, ABS, PPO. The method of claim 1, wherein the plastic contains a homopolymer. The method of claim 1, wherein the plastic contains a homopolymer. The method of claim 1, wherein the plastic contains a copolymer. The method of claim 1, wherein the plastic contains a copolymer. The method of claim 1, wherein a filler (such as chalk, talc, glass fibers), an additive (such as TiO 2, BaSO 3, BaSO 4), a stabilizer, or the like is added to the plastic. The method of claim 1, wherein a filler (such as chalk, talc, glass fibers), an additive (such as TiO 2, BaSO 3, BaSO 4), a stabilizer, or the like is added to the plastic. A method according to claim 2, wherein the plastic contains a chemical foaming agent (such as hydrocerol LC, hydrocerol compound, 5-phenyltetrazole, azodicarbonamide, NaHCOj, (NH4) 2COj, (NH4) HC03), and / or a physical foaming agent (such as N2 , H 2 O) is added. A method according to claim 2, wherein the plastic has a chemical foaming agent (such as hydrocerol LC, hydrocerol compound, 5-phenyltetrazole, azodicarbonamide, NaHCO 3 (NH 4) 2 CO 3, (NH 4) HCO 3), and / or a physical foaming agent (such as N 2, H20) is added. ' A method according to claim 1, wherein the mold cavity has a shape such that the blade has a non-round shape. The method of claim 1, wherein the mold cavity has such a shape that the blade has a non-round shape and a flanged circumferential edge. The method of claim 1, wherein the resulting sheet has a peripheral edge zone of preselected shape and dimensions, for example, having a drooping edge. Monolithic plastic sheet obtained by the method according to any one of the preceding claims. NEW CONCLUSIONS A method according to claim 1, wherein prior to injecting plasticized plastic gas, for example nitrogen or optionally conditioned air, into the mold cavity, is introduced under pressure into the mold cavity. A method according to claim 1, wherein the method is carried out in such a way that the sheet obtained meets the requirements regarding thermal insulation, acoustic insulation, mechanical strength and vibration and / or shock absorption properties. A method according to claim 1, wherein during at least the first part of the first phase of displacement of the mold parts, in which the displacement speed is 0 or relatively small, an additional plastic injection takes place with a pressure, for instance 30 bar, which does not exceed 35% of the pressure used in step (5), for example 700 bar. The method of claim 1, wherein the time of the additional injection is greater, the smaller the pressure applied in the additional injection. Monolithic plastic sheet obtained by a method according to any one of the preceding claims.