FR2640909A1 - Reinforced thermoformed shell and its method of manufacture - Google Patents

Abstract

This thermoformed shell, made of thermoplastic resin, is provided, on one of its surfaces, with a layer of reinforcement resin, this resin being reinforced with glass fibres. According to the invention, the glass-fibre reinforcement is in the form of at least one continuous sheet made of glass mat 2b which matches the shape of the shell 2a and which is connected to the latter, over its entirety, by the reinforcement resin. For the manufacture, a thermoformed assembly 2 is produced which comprises a sheet of thermoplastic resin and one or more stacked sheets made of glass mat, which are thermoformable, and then the assembly 2 thus obtained is reinforced by injecting, under pressure, on its surface made of glass mat 2b, a reinforcement-resin formulation into a space 4 made in a mould. As examples of shells, mention may be made of thermoformed shells for sanitary ware (bathtubs, shower bowls, wash basins, etc.), for protective helmets for motorcyclists and other users and for motor-vehicle body elements (doors, bonnets, etc.).

Description

REINFORCED THERMAL SHELL AND MANUFACTURING METHOD THEREOF
The present invention relates to a semi-finished shaped product, which is constituted by a thermoformed shell of thermoplastic resin, reinforced, on one of its faces, by a glass / resin compound of the unsaturated polyester or acrylic type; the invention also relates to a process for manufacturing this shaped product.

 Examples of shaped products which can be produced in accordance with the present invention include thermoformed shells for sanitary appliances, such as baths, shower bowls, sinks, etc. Mention may also be made of other applications, such as the manufacture of protective helmets for motorcyclists and the like, of body parts of motor vehicles, such as doors, hoods, etc. In general, the invention applies to all the parts constituted by a thermoformed shell requiring reinforcement or a simple internal or external coating.

 The thermoforming of thermoplastic resin plates, such as poly (methyl methacrylate), necessarily leads to zones of thinner thickness of the thermoformed plates, which requires reinforcing them at least in these locations, on their face opposite to the exposed face. at sight at end use.

 Initially, the reinforcement of thermoformed shells with a glass / resin composite was carried out by "contact", that is to say by application, by hand, of pieces of glass fabric, then by spreading the resin by brush, either by spraying, simultaneously or not, with cut glass fibers and unsaturated polyester resins. These polyester resins are formulated to constitute a sprayable syrup, to which is added, at the time of use, a priming system at ambient temperature (accelerator + peroxide) which makes it possible to trigger, immediately upon mixing, the polymerization leading to the hardened reinforcement layer.

 These known techniques, which are described in particular in French Patent No. 2 325 505, however have the drawback of requiring a lot of manpower and leading to significant losses in resin.

Thus, in the case of the projection of the mixture of the polyester formulation and of the cut glass fibers, it is compulsory, after the projection, to carry out an operation of leveling and debubbling with a notched roller.

Furthermore, in order to obtain the best quality of coating, two successive projections are generally carried out, which consequently increases the time necessary to effect this reinforcement.

 To resolve these difficulties of implementation on an industrial scale, a method has been proposed in particular, in accordance with French Patent No. 2,343,580, consisting in supporting one face of the hull using an elastically deformable cushion which conforms entirely this, To be placed in the vicinity of the other face, a mold element with an elastically deformable or non-deformable working surface and of complementary shape, arranged so as to provide a free space between the element and the shell, to be injected under pressing a reinforcing resin in said free space, and demolding the thus reinforced shell.

 This process is also known as "RTM" Cresction transfer molding). In the aforementioned French patent n 2 343 580, it is indicated that before coming to set up the mold element facing the shell, pieces of glass mats are deposited therein so that they overlap mutually. This operation is time-consuming and labor-intensive on an industrial production line. In addition, it generally does not allow a reinforcement by glass fibers over the entire surface of the shell.

 To overcome this drawback, it is possible to envisage injecting a mixture of a reinforcing resin and cut glass fibers. However, there is a risk of problems with the injection, as there may be a poor distribution of the fibers, by an accumulation of these in certain places and an absence of fibers in others, with, as a result, incorrect reinforcement of the shell; in addition, the space to be filled with reinforcing resin must not be too narrow to allow the introduction of the resin loaded with cut fibers and not to increase the time too much nor too wide to avoid excessive exothermicity. Since this solution could lead to low productivity, the Applicant Company therefore sought another solution to rapidly and homogeneously reinforce, by the RTM technique, thermoformed shells made of thermoplastic resin, according to a satisfactory industrial process.

 This objective is achieved in accordance with the present invention by the fact that, firstly, a thermoformed assembly is formed of thermoplastic resin continuous sheet (s) made of glass fiber mat, then, in a second step, a resin is applied. reinforcement, not containing glass fibers, by the RTM process, the resin coming, upon injection, to fill the interstices of the glass mat conforming to the shape of the shell, then inflate this glass mat to constitute, after polymerization a reinforcement layer joining the glass mat to the shell.

 This process, proposed in accordance with the present invention, makes it possible to benefit from a uniform layer of glass mat over the entire surface of the thermoformed shell, thereby improving the mechanical characteristics of the latter, generally for a lower quantity of resin. reinforcement, the invention thus offering the additional advantage of being able to lead to lighter products.

 The present invention therefore firstly relates to a thermoformed shell of thermoplastic resin, provided, on one of its faces, with a reinforcing resin layer reinforced with glass fibers, characterized in that the reinforcement of glass fiber is in the form of at least one continuous sheet of glass mat which follows the shape of the shell and which is bonded to the whole thereof by the reinforcing resin.

The glass mat sheets which can be used to manufacture the reinforced thermoformed shells according to the invention are thermoformable sheets, being, for this purpose, impregnated with a binder which coats the son or glass filaments which constitute them. They are preferably chosen from those having characteristics of very high deformability, homogeneity and easy and rapid impregnation with the syrup of the reinforcing resin formulation, while retaining their good cohesion throughout the application. reinforcing resin and in the product obtained. Thus, it is advantageous to use a felt of uncut (continuous) glass wires or filaments, arranged in one or more layers, preferably at least two regularly nested layers, these wires or filaments being agglomerated by a binder with low solubility in the impregnation syrup. It is useful to choose glass mats of the aforementioned type, having a nominal surface mass 3 of 300 to 500 g / m
According to a preferred embodiment, the thickness of the layer of reinforcing resin does not appreciably exceed that of the sheet (s) of glass mat. The resulting reinforcement laminate can thus have a relatively small thickness, providing a quality of reinforcement that is just as acceptable, or even better, than known reinforcement layers, with a saving in reinforcement resin. Furthermore, a single sheet of glass mat is generally sufficient to obtain the desired effect.

 The thermoplastic resin constituting the shell is in particular a resin constituted by a homopolymer of methyl methacrylate or by a copolymer containing at least approximately 55% by moles of methyl methacrylate units and at most approximately 45% by moles of at least one chosen comonomer , for example, among alkyl acrylates. Homopolymers and copolymers of methyl methacrylate may also contain small amounts of crosslinking agent chosen in particular from polyol di- or tri (meth) acrylates, such as alkylene glycol dimethacrylates, an example of which is dimethacrylate. ethylene glycol, which will be the case in particular for thermoformable shells for sanitary appliances obtained from cast plates. Finally, the thermoplastic resin constituting the shell can be obtained from a thermoplastic composition consisting of a mixture or alloy of a polymer rigid thermoplastic, such as the homopolymers and copolymers of methyl methacrylate defined above, which constitutes a matrix, and of an elastomeric reinforcing material. These alloys are well known to those skilled in the art. By way of examples in the field of thermoformed shells for sanitary appliances, mention may be made of alloys comprising up to approximately 60 by weight of polymer or copolymer of rigid matrix, the complement being constituted by the reinforcing elastomer matrix in the form of nodules. Examples of such alloys have been described in French patent applications No. 2,620,327 and No. 2,610,328.

 The plates of thermoplastic polymer, like the homopolymers and copolymers of methyl methacrylate which can be used to constitute the shells according to the invention, are just as well cast plates, obtained in particular from poly (methyl methacrylate) of relatively high molecular weight, or crosslinked, than extruded sheets, obtained in particular from poly (methyl methacrylate) of relatively low molecular weight, in which case they must be modified to be resistant to cracking (crazing) at least on their face intended to receive the reinforcing resin, in order to prevent them from cracking during the injection of said resin. It is possible to use, in a conventional manner, plates extruded from the abovementioned alloys, the plates therefore being modified to be uniformly crack resistant and therefore also reinforced on their exposed side at sight upon final use. One can also use a plate obtained by coextrusion of an unmodified thermoplastic polymer and an alloy of the indicated type, for example, a coextruded plate having a layer of approximately 4 mm thick of unmodified poly (methyl methacrylate) and a layer of about 1 mm thick of poly (methyl methacrylate) modified to be resistant to cracking. A third possibility lies in the use of a plate of unmodified thermoplastic polymer or copolymer, for example methyl methacrylate , to which a protective film, or skin, of thermoplastic polymer modified to be crack resistant (alloy defined above) has been hot-applied, this film being sufficiently thick to ensure the protection of the base plate against cracking at the time of resin injection.

 The reinforcing resin is, for example, a polyester resin or an acrylic resin. Such resins are well known to those skilled in the art. Unsaturated polyesters are obtained by polycondensation of diols with mixtures of saturated or unsaturated, aliphatic and / or aromatic diacids or anhydrides. The most widely used unsaturated anhydride is malic anhydride; the aromatic units are generally introduced by phthalic anhydride, for example, orthophthalic. Immediately after its synthesis, the unsaturated polyester is stabilized, then mixed with styrene, as a latent crosslinking agent. A peroxide is added at the time of use which, by heating at the time of shaping, triggers the polymerization of the assembly.

The present invention also relates to a process for manufacturing the thermoformed shell, as defined above, characterized in that - in a first step, an assembly is produced
thermoformed with a thermoplastic resin plate and
one or more superimposed sheets of glass mat
thermoformable, and - in a second step, we reinforce the whole
thermoformed thus obtained by injecting under pressure onto
the glass mat face of this set, in a space
formed in a mold, a resin formulation of
enhancement.

 In accordance with a first embodiment, in the first step, the assembly of the thermoplastic resin plate and the (or> sheets of thermoformable glass mat) is carried out first, then the assembly thus obtained is heated and it is formed.

 According to a second embodiment, in the first step, a plate of thermoplastic resin and the <or) sheet (s) of thermoformable glass mat (s>) are heated separately, then each of them is formed. , before making their assembly in a mold.

 For thermoforming (heating then forming), the thermoplastic resin-glass mat composite sheets in the aforementioned first embodiment, and the thermoplastic resin sheets in the aforementioned second embodiment, once softened, can be deformed to constitute the product shaped according to the various conventional methods, for example, by the maintenance of a depression or a pressure deforming the sheet without contact with the molding surfaces, or else by the exercise of a pressure or a vacuum to blow or apply the sheet on a molding surface, or even by stamping. As for the thermoforming of the glass mat sheets in the second embodiment, it is carried out by stamping, the glass mat sheets not being perfectly airtight.

To better illustrate the object of the present invention, two embodiments will be described in more detail below, with reference to the appended drawing in which
- Figure 1 is a longitudinal axial section view
of the apparatus used to reinforce a
thermoformed bathtub shell whose manufacture is described & Example 1
- Figure 2 is a perspective view of a cover
automotive; and
FIG. 3 is a view similar to FIG. 1,
illustrating the manufacture of the cover of FIG. 2.

EXAMPLE i
This example relates to the production of a bathtub in poly (methyl methacrylate) (PMMA), reinforced on its external wall in accordance with the invention.

 A sanitary quality PMMA plate is used (according to standard NF EN 263 (February 1988V, compliant with European standard EN 263 of 1987), obtained by polymerization by casting, having a viscosity index <according to ISO 1233 standard> greater than 400 ml / g, and a thickness of 5 mm.

A glass mat with continuous wires, sold under the name UNIFILO U812 <Saint 2, is used.
Gobain), having a nominal basis weight of 450 g / m
In a first step, the PMMA plate and the glass mat are applied to each other, and they are assembled by clamping on a rigid frame. Then, the mat-plate composite thus obtained is subjected to heating, in an air oven heated to a temperature between 140 and 190-C, for example 180 ° C for about 20 minutes.

 The plate / mat composite thus heated is then transported in a vacuum molding chamber, where it is adapted to the contour of a bathtub shell mold, so that the suction face of said composite is that comprising the glass mat. A vacuum is created so that this face comes into contact with the surface of the mold. After cooling, the thermoforse plate / mat composite is removed.

 Next, a polyester reinforcing resin is applied, intended to be combined with the glass mat, using the apparatus of FIG. 1.

 This apparatus is essentially constituted by a lower male part 1, on which there is the thermoformed composite 2 (thermoplastic shell proper 2a - glass mat sheet 2b), and an upper female part 3 which covers the male part 1, the parts male and female having complementary shapes to the internal and external shapes of the thermoformed composite, respectively, so that the male part 1 closely matches the internal PMMA surface thereof, while the female part 3 provides a space 4 between it- same and the external glass mat surface of said composite, this space 4 being partially occupied by the glass mat 2b.

 The male part 1 (or counter-mold) is constituted by a rigid element 5, for example, made of epoxy resin, supporting a flexible and elastically deformable element 6.

for example, made of silicone elastomer. Element 6 could be made of another elastomer, provided that it is firm enough to effectively support the thermoformed composite, while being sufficiently elastically deformable to closely match the shape of the latter.

 The female part 3 is made of epoxy resin and it has a central cavity 7> occupied by an insulating mass of expanded polyester-glass. It is crossed by several injection channels 8 which open into the space 4, at the periphery, in line with the end part of the horizontal rim of the bathtub, as well as by several vent channels 9 which are arranged in line from the bottom of the tub. The interior wall zone of epoxy resin of the female part 3 is crossed by regulation channels 10.

 At the time of the injection of the syrup of the polyester resin reinforcement formulation, the two male and female parts are connected to each other by means of conventional connecting members, not shown in the drawing.

The syrup used has the following composition in parts by weight - Orthophthalic resin with low acidity
residual, marketed by NORSOLOR under the name "NORSODYNE I423" *. 95 - Styrene, 5 - Calcium carbonate .......................... 30 - Cobalt octoate (accelerator) ....... ........ 0.25 - Dimethylaniline <accelerator> .................. 0.25 - Polymerization inhibitor, O, 10 - Acetylacetone peroxide
With the help of an injection machine, this syrup is introduced via the channels 8, at a pressure of between 1 and 10 bars, for example 3 bars, and care is taken to carry out this operation as slowly as possible, so as to allow correct boiling of the glass mat and to avoid the formation of air pockets, the injection continuing until the syrup overflows through the vent channels 9.

 The polymerization is completed after 10 minutes, the temperature of the female part 3 being regulated at a value of 50 C by circulation of fluid in the channels 10. Once the polymerization is complete, it is allowed to cool, then it is removed from the mold.

 A bath shell was then obtained having a total thickness of between 5 and 9 mm, the thickness of the 18 layer of PMMA varying between 0.8 and 5 mm. As a result of thermoforming, and the glass mat sheet being embedded in the hardened polyester resin layer. We can, in the same way, with a PMMA plate having, at the start, a thickness of 3 mm, to obtain a reinforced thermoformed shell having a total thickness of 4 to 7 mm for a thickness of layer of PMMA varying between 0.8 and 3 mm.

 These shells have substantially the same mechanical strength, rigidity and ball drop (according to standard NF EN 19ES, February 1988, corresponding to European standard EN 198, 1987), as thermoformed shells reinforced in a known manner according to the RTM technique involving an injection of polyester mixed with cut glass fibers, with a reduction in the thickness of the thermoformed shells according to the invention compared to these known reinforced shells, of the order of 1 to 3 mm depending on the case.

The polyester savings that can be achieved in this way are significant on an industrial scale.

EXAMPLE 2
An automobile hood is produced as shown in FIG. 2, from an extruded PMMA plate to be crack resistant with a thickness of 1.5 mm and of the same glass mat as that used. Example 1
The thermoforming of the PMMA plate and that of the glass mat sheet are carried out separately.

Thus, on the one hand, the PMMA plate and the glass mat are first of all heated separately between two radiant panels, the first, at a temperature between 120 and 160 ° C., for example, at 140- C for 1.5 minutes, and the second, at a temperature between 100 and 180 ° C, for example at 150 ° C, for 5 minutes. Then, still separately, they are subjected to thermoforming, by suction as described in Example 1 for the FME ~ IA plate, and by stamping for the glass mat sheet.

 The two thermoformed elements are assembled by interlocking, the thermoformed glass mat 2b being placed against the concave surface of the thermoformed PMMA part 2a. Then the composite thus obtained is reinforced in the apparatus of FIG. 3 which is of the same type as that of FIG. 1 - the same reference numbers designating the same elements -, except that part 3 is the lower male part receiving the thermoformed glass mat, and that part 1 is the upper part female against which the thermoformed PMMA part 2a is supported. The syrup of the reinforcement polyester resin formulation is injected under the same conditions as in Example 1, through the central injection channel 8, from bottom to top, the syrup overflow 5a flowing laterally via the vent channels 9. The temperature of the mold 3, in its part comprising the regulation channels 10, is 50 C. The polymerization lasts approximately 10 minutes.

 The reinforced thermoformed cover according to the invention has a total thickness of between 2 and 4 mm, for a thickness of the PMMA layer of between approximately 0.8 and 1.5 mm.

Comparative Example 3 and Example 3
These examples relate to the manufacture of a 2 acrylic bathtub of 1700 x 730 mm, of about 2.34 m of developed surface.

In accordance with a conventional process (Example
Comparative 3>, we thermoform a sheet of
PMMA, pigmented in the mass, with a thickness of 3 mm, then in a second operation, about 18 kg is sprayed on the rear face, in two layers of polyester reinforced with glass fibers, which form 30% by weight of said polyester, then we proceed to a bubble removal. These different operations take about 37 minutes and consume 19 kg of polyester. The normal cycle time, which includes polymerization, is approximately 127 minutes.

By proceeding as in Example 1, we make an identical bathtub, of the same quality as in Example
Comparative 3, that is to say satisfying the NF EN 198 standard of February 1988, only 17 kg of polyester + glass mat is used, as a result of a better distribution of the polyester on injection, optimizing reinforcing properties, and the absence of projection losses.

 As for the total labor time in this example 3, it is 26 minutes, being, compared to the conventional process, increased by the thermoforming operation of the glass mat (+ 6 mm>, but greatly reduced < -17 mm) by replacing the spraying and bubble removal operations with injection. The cycle time is itself reduced, because the reinforcement is carried out in one step with a very rapid polymerization (36 minutes).

 For equal quality, the savings are therefore per piece, 10 on the quantity of polyester + glass shafts, 30% on labor time and 70% on cycle time.

Claims (10)

 1 - Thermoformed shell in thermoplastic resin, provided, on one of its faces, with a layer of reinforcing resin reinforced with glass fibers, characterized in that the reinforcement of glass fibers is in the form of at least one continuous sheet of glass mat (2b) which follows the shape of the shell (2agent which is bonded to the whole thereof by the reinforcing resin.  2 - thermoformed shell according to claim 1, characterized in that the thickness of the reinforcing resin layer does not significantly exceed that of the (or) sheet (s) of glass mat (2b).  3 - Thermoformed shell according to one of claims 1 and 2, characterized in that it comprises a single sheet of glass mat C2b).  4 - thermoformed shell according to one of claims 1 to 3, characterized in that the thermoplastic resin is a resin consisting of a homopolymer of methyl methacrylate or of a copolymer containing at least 55 moles of methyl methacrylate units , or an alloy of such a polymer or copolymer, with an elastomeric reinforcing matrix.  5 - Thermoformed shell according to one of claims 1 to 3, characterized in that it is formed from a thermoplastic plate coextruded of a homopolymer or copolymer of methyl methacrylate, as defined in claim 4, and of an alloy also as defined in claim 4, the alloy layer being arranged opposite the reinforcing layer.  6 - Thermoformed shell according to one of claims 1 to 3, characterized in that it is formed from a composite thermoplastic plate, made of a homopolymer or copolymer plate of methyl methacrylate, as defined in claim 4, on one side of which a film of an alloy also as defined in claim 4 has been hot applied, the alloy layer being arranged opposite the reinforcing layer.  7 - Thermoformed shell according to one of claims 1 and 6, characterized in that the reinforcing resin is an unsaturated polyester resin or an acrylic resin.  8 - Process for manufacturing the thermo-formed shell as defined in one of claims 1 to 7, characterized in that - in a first step, an assembly is produced  thermoformed <2> with a thermoplastic resin plate  and one or more overlapping sheets of  thermoformable glass, and - in a second step, the whole is reinforced  thermoformed (2> thus obtained by injecting under pressure  on the glass mat face (2b> of this set, in  a space (4) in a mold, a formulation of  reinforcing resin.  9 - Method according to claim 8, characterized in that in the first step, the assembly of the thermoplastic resin plate and the (or) sheet (s) in thermoformable glass mat is first carried out, then the assembly thus obtained is heated and formed.  10 - Process according to claim 8, characterized in that in the first step, a plate of therpioplastic resin is heated separately, and the (or) sheets of thermoformable glass mat, then a forming of each is carried out. them, before carrying out their assembly in a mold.