DE2944359A1 - COMPOSITE BODY - Google Patents

Description

29U359

October 30, 1979 D-Hg / K

Composite Technology Corporation Troy, Michigan, USA

"Composite body"

The invention relates to a construction and a manufacturing method layered composite body of the type in which several materials are bonded together to form a one-piece Creating bodies that have the combined physical and chemical properties of the materials used owns. More precisely, the invention relates to laminates which are assembled predominantly from non-metallic materials are, such as high strength fiberglass, open cell resin foam, thermosetting resin binder, and rigid syntactic

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Foam core elements consisting of small hollow spheres embedded in a resin matrix.

In the past, closed-cell ones were used in the manufacture of such composite bodies and where relatively thick cross-sections are required Foams are used as core elements and on these rigid elements were resin-impregnated open-celled and resilient foam layers pressed and cured.

The use of a rigid, closed-cell foam element consisting of a single resin phase in such a composite body presents numerous problems with regard to the confinement of gases, which on the one hand (1) the Ability to completely encapsulate the core element in a reinforced resin skin or outer casing and on the other hand (2) the resin curing temperature and thus the amount in which such composite bodies can be produced, limits.

The complete encapsulation of a closed-cell core element in a hard and impermeable housing is important to the To protect the core element from being mechanically damaged during use or from harmful liquids or gases can penetrate into it. For a time, such intrusion can either reduce the value of the core element reduce, or cause a lifting of the outer housing from the core element.

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The impermeable outer housing of such a composite body comprises one which is flexible in the initial state and is open-celled Foam impregnated with a thermosetting resin and generally covered with a glass fiber reinforcement layer is. When producing the composite body, the impregnated foam layer and the reinforcement layer are against the hard The core element is pressed and the resin is cured by applying heat, while the resilient foam layer is under pressure is held until the resin has hardened. The duration of the cycle to cure the resin is a combination of Time and temperature. In general, the higher the curing temperature, the shorter the curing time of the resin required. At the same time, fast curing cycles are highly desirable for the use of the molds to increase and thus to reduce manufacturing costs. When using a rigid, closed-cell core element, which has a single resin phase, however, it is necessary to keep the curing temperature of the resin below a certain level to keep to the outgassing of air or other gases that are commonly found in the closed cell end of the rigid foam core element are caught or contained, prevent or control.

Outgassing trapped air or other gases creates two problems. First: if great care is taken will, including the use of relatively low

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Resin curing temperatures, for example from 66-93 ° C, the outgassing can cause the outer protective layer to lift off rigid open-cell core element cause what in a so-called "pillowing" results. Secondly a complete encapsulation of a core element with a single resin phase cannot be achieved, as there is a way to escape of the trapped gases must be created during the heat treatment of the outer protective layer.

The present invention prevents outgassing and other difficulties previously associated with the use of conventional rigid, closed-cell foam elements adhered) in_dem Rigid core element is used which contains small hollow spheres made of either organic or inorganic Materials are made and embedded in a thermosetting resin. In their smallest dimensions such Balls referred to as micro-balls or micro-balloons.

The US-PS Nm. 3,193,437, 3,193,441 and 3,867,221 show the concept of an open-celled structure that is compliant in the initial state Foam material which is impregnated with a thermoplastic resin and which alone or in conjunction with Reinforcing fibers is used, wherein the foam layer is compressed with relatively low pressure such that the thermosetting resin essentially fills the cells of the foam and is cured, while the resilient foam

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- is held in a compressed state. These known methods are in some cases advantageous in producing a relatively thin-walled, high-strength composite body and density. At the same time it is possible to use these methods to build up laminate parts of considerable thickness. However, since it is necessary in both of these processes to use the initially flexible, open-cell foam material It is to press to about half to a quarter of its original thickness in order to fill the open cells with resin necessary, either a very thick, initially compliant, open-cell foam layer or multiple layers of this material, all with a thermosetting resin are impregnated in order to achieve a relatively thick body. The disadvantage of using these methods to manufacture alone of a body with a large cross-section is that the body in terms of its strength and rigidity becomes relatively heavy, secondly because of the basically solid resin matrix that extends over the entire part, is very expensive and, thirdly, is a bad insulator, which is indicated by a low K-factor will.

Although it is theoretically possible to make composite bodies of relatively unlimited thickness using the molding process, that described in U.S. Patents 3,193,37 and 3,867,221 is, in practice, lose body with a strength about

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7 to 8 mm have many of their significant advantages including a significant reduction in their strength-to-weight ratio, when the strength increases.

The production of a composite body that contains a stiffened, having an open cell core member with a reinforced resin outer surface or housing is disclosed in U.S. Patent No. 4,042,746. In practice it has been found in the production of a composite body of the type described in this patent specification, that the curing temperature of the resin with which the flexible open-cell outer layer is impregnated in the The order of magnitude of 66 to 93 ° C must be maintained in order to control the outgassing of the air or gases contained in the closed cell Element are included. Likewise, one or more of the side walls of the rigid core element left uncovered to provide an outlet path for some gases that are released or generated during the molding process will.

Although satisfactory composites can be made according to the teachings of U.S. Patent 4,042,746, the amount is in the amount of such bodies that can be produced is limited by the relatively low resin curing temperatures that are used Need to become.

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The use of small glass beads or spheres as an additive to a thermosetting resin used in a composite body is described in U.S. Patent 4,034,137. Then glass beads and glass fibers are added to a liquid resin, with the multiple layers of open-cell, resilient Foam for the purpose of lowering the resin density and increasing the bonding strength between adjacent ones Foam layers are impregnated. The 4,034,137 patent is concerned with increasing the laminar bond strength in relatively thin-walled laminates and does not apply to a closed-cell and relatively thick, rigid core element that consists of small, hollow spheres embedded in organic resin, which in turn is completely enclosed or encapsulated is in an outer reinforced resin layer.

According to the invention it is possible to produce a relatively light, very strong composite body of considerable thickness, the possibility of layer lifting by eliminating and significantly reducing outgassing as much as possible is reduced and wherein much higher resin curing temperatures can be used, reducing the amount in the composite can be produced is increased.

The improved composite body according to the invention takes advantage of the use of a rigid core element, the small one

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Embedded are hollow spheres made of yin in an organic resin binder Connection with an open-cell, flexible one in the initial state Foam layer which is impregnated with a liquid thermosetting resin and which is against the rigid core member is pressed, wherein the liquid resin is cured, while the resin-impregnated foam layer in the compressed state is held.

The rigid core element according to the invention contains organic (e.g. consisting of polystyrene or hienol) or inorganic (e.g. consisting of clay, quartz or glass) hollow spheres, which have a diameter of, for example, on the order of 10 to 200 microns and a wall thickness of 0 , 2 to 0.5 microns, with the spheres embedded in an organic resin matrix. The balls contained in the rigid core member are, for example, about 20 to 50 parts by weight for every 100 resin parts. The resin may be any suitable organic f like; epoxy; Polyester or vinyl ester. The core element described is in fact a foam that has two rigid phases and is sometimes referred to as a syntactic foam.

The rigid core element is brought into the desired strength and shape by a molding or casting process. The core element however, it can also be shaped into a block and afterwards

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cut out or brought into the desired shape. It is starting with the rigid core element in the shape or shape desired for the final composite body then required to encapsulate the core in an appropriate external protective and reinforcement housing.

A layer of compliant and open-celled in the initial state Foam is impregnated with a liquid thermosetting resin such as epoxy, polyester, vinyl ester or the like. The uncured resin impregnated foam layer is placed on top of the rigid core element and is in turn preferred covered with a layer of reinforcement material such as fiberglass in woven or matted form. the Reinforcement layer and the resin impregnated, resilient foam is then against the atarre, syntactic foam core element pressed with some reduction in the strength of the resilient foam layer, creating the open and interconnected connected cells are filled with the liquid resin and the reinforcing fibers are encapsulated by the resin. During this If the composite is held under pressure, heat is applied to cure the resin. The result is a composite that has a thick cross-section in which the rigid core element is completely enclosed in a high-strength and tight protective housing or a skin is encapsulated.

Details of the invention are explained in more detail below with reference to the drawings. In these drawings show:

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Fig. 1 is a perspective view of a wing made in accordance with the invention;

Fig. 2 shows a rigid syntactic foam core element, which with a reinforced and with a liquid Resin-impregnated, resilient, open-cell outer layer is covered before being pressed together and curing the outer layers;

FIG. 3 shows a view corresponding to FIG. 2

fully cured wing, which is a syntactic foam core element in an outer protective housing includes, and

4 shows an enlarged part of a section through the syntactic foam core element.

1 and 3 show a composite body made in the shape of a wing 10 made in accordance with the invention. The wing 10 is cut open at one end to make a rigid one Core element 12 to show encapsulated by a protective housing 14 is.

Fig. 2 shows an enlarged section from which the assembled Components can be seen before the housing 14 is attached to the kernel ment 12. It is clear that it is

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there is no particular limit to the shape or strength of the core element 12. As illustrated in Fig. 1, the core element 12 has a convex cross-section, which has its greatest thickness at the root of the wing, which is approximately between 25 to 50 mm. Other components are usually molded with rigid core elements that are 125mm to 250mm thick. Essentially, the strength of the core element is determined by the particular use of the composite body that is to be formed ₃ and by the load to be borne by this. In general, the thickness and shape of the composite body is changed by changing the thickness and shape of the core member rather than changing the thickness of the housing 14, which is normally on the order of 1.5 to 3 mm when cured .

As can be seen from Fig. 2, the housing 14 comprises in the initial state compliant foam layers 16 and 18 which have open and interconnected cells. Regarding the open-cell Properties of each of these resilient foam layers are believed to have about 85% of the foam cells open and are in communication with neighboring cells. It has been found that a flexible or compliant Polyurethane foam is particularly suitable for practicing the invention. However, other open-cell, compliant foams can be used insofar as they are compatible with the thermosetting resin with which such foam is im-

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- is impregnated.

The open-cell foam layers 16 and 18 can be used as containers to take up the liquid, thermosetting resin during the molding process. The strength of the open-cell Layers 16 and 18 is generally determined by the amount of reinforcement layers 20 and 22 exposed by the resin to be impregnated or encapsulated. It is common to have an open cell foam layer of 25 mm or less starting or to use uncompressed starch which has a density of the order of 8.0 kg / m * to 80.0 kg / m ^.

The open-cell layers 16 and 18 are preferably impregnated with a thermosetting resin before they are applied to the core element 12 are applied. The resilient foam layers can be impregnated in this way in any known manner, for example by dipping, by passing through a resin bath and then passing through nip rollers to determine the amount of liquid resin absorbed to control, or by coating with applicator rollers.

Depending on the compatibility with the others to be merged Materials, the available curing time, the physical strength requirements in the outer reinforcement layers and cost, a number of liquid thermosetting resin systems can be used to make the

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to impregnate open-cell foam layers 16 and 18. For example, it is favorable within the scope of the invention ^ vinyl ester, Use polyester or other epoxy resins for impregnation purposes. When the foam layers 16 and 18 with the liquid resin are impregnated, they usually follow the contour of the core element before pressing and curing 12th

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The reinforcement layer / 20 and 22 are intended to be applied to the liquid-resin-impregnated, open-cell foam layers 16 and 18, as shown in FIG. A preferred reinforcing layer comprises glass fibers in matt or woven form. Depending in part on the final exterior finish desired, other reinforcing materials can be used, either in conjunction with or in place of high strength glass fibers. For example, it has been found that a thin, e.g. 0.25 mm thick, layer of metal, e.g. It has also been found that if a thicker, for example 0.8 mm thick, outer steel layer is used, the glass fiber reinforcement layer can be omitted. For other purposes, for example as electrical shielding, aluminum foil about 0.05 mm thick can be applied and with the reinforcement layer during the pressure-forming process

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get connected .

The core element 12 will now be described in more detail with reference to FIG. 4. As mentioned earlier, the core element is i2 rigid »is, however, particularly of the known types of laminates, as described in US Pat. No. 4,042,746, since the core element according to the invention is the what can be referred to as two rigid phases, while the rigid core according to the aforementioned US-PS has only one has only rigid phase. Numerous significant advantages are achieved if such a core element compared to a those with a single resin phase system is used. The advantages are greater structural strength, improved control of outgassing during the molding process and the ability to better control the density of the core element by more precisely controlling the size of the hollow spheres.

Using conventional single phase closed cell foams of the type described in U.S. Patent No. 4,042,746, it is inevitable that air or other gas will be trapped in the closed cells during foam production will. When such closed cell foam is used in making a composite body that has super-ambient curing of the thermosetting resin, as described in U.S. Patent, is required to produce or The release of gases contained in the core cells is a problem if such outgassing is not controlled or controlled

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2944353

is not prevented, between the core element and the outer protective layer or housing a lifting or a "Pillowing" occur. In practice it has been found that when a composite body according to the teachings of the US patent, the temperature for curing the thermosetting resin in the outer housing to 66 to 93 ° C must be maintained in order to limit the outgassing. Although such a resin can be cured at higher temperatures can, increases when this temperature range is above the outgassing from the rigid single-phase core element, the likelihood of detachment is considerable. In this way, the mold cycle time is considerably greater than this in the case where higher resin cure temperatures could be used.

It is a purpose of the invention to use a rigid core element that can withstand higher resin curing temperatures, whereby faster molding cycles can be achieved without the aforementioned problem of outgassing and the possible withdrawal occurs.

The core member 12 comprises a first continuous resin phase 24 or resin base in which hollow spheres 26 are formed embedded or encapsulated to create a second and discontinuous rigid phase.

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The continuous rigid resin phase 24 can be formed by any suitable polymerizable resin, such as epoxy, polyester, vinyl ester or the like. One factor in the choice of the continuous resin phase is its chemical compatibility with the material of the hollow balls.

The hollow balls 26 can be made of either organic or inorganic material. Typical organic Materials are made from phenolic, urea-formaldehyde or polystyrene resins. Inorganic spherical materials, which are generally preferred are based on sodium sulfate or glass. In smaller sizes from 10 to 200 microns or smaller, the hollow spheres or beads are sometimes referred to as micro-spheres or micro-balloons. Such bullets can have a wall thickness of 0.5 to 2.0 microns.

The balls 26 can be viewed as fillers for the continuous resin phase and are primarily used to lower the density and in this way to make the hardened continuous resin phase lighter. the The number of spheres mixed with the uncured resin continuous phase is generally referred to as the loading volume designated. The larger the loading volume or the number of balls, the lower the density of the core element according to the invention. While the density decreases with increasing loading volume, it must be taken into account that the tensile strength

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of the filled resin material or the core element as well decreases as a proportion to the total spherical volume introduced. In the same way, the viscosity of the mixture tends made of uncured or liquid resin and the balls with higher ball loading volumes. This is how the liquid resin becomes and mixtures containing spheres have a low viscosity at low loading volumes and are therefore easy to pour. at at the other extreme, with a large loading volume, the balls can be crushed into the liquid resin.

The size of the balls will in fact be whether they are micro or macro balloons by the final cross-sectional thickness of the core element influenced. For core elements with a thinner cross-section, smaller ball diameters are used, ee eeeee, while increasingly larger spheres can be used when the core elements are in the Increase cross-section. It is also clear that spheres of different sizes are mixed into the liquid resin can to increase the loading volume and thereby lower the density of the core element.

Although the spheres normally contain trapped air or gases, these gases are trapped in the rigid sphere and normally do not present any outgassing problems during the subsequent molding and curing of the protective housing on the core element. However, removing the

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Air or gases trapped in the liquid resin phase may be desirable and, if necessary, by vibrating the liquid resin-ball mixture in a thin film and through Applying a jet of hot air to the surface can be achieved to break the gas-containing resin bubbles.

In general, it is desirable to maximize the ball loading volume in order to reduce the density of the core element. One limitation of such ball loading volume is the need to ensure wetting of the balls by the liquid resin phase is. In other words, it is undesirable to have a significant amount of unwetted spheres in the core element to have.

In making composite bodies in accordance with the invention, it is desirable to provide a rigid core member in which the Hollow spheres form 20 to 50 parts by weight per 100 parts by weight of the continuous resin phase.

Although numerous compatible combinations enlim within the framework of the Invention are possible, listed below is an example of materials that can be combined to form a To create high-strength, lightweight laminate that can be used as a structural component.

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1. Core element -

a. Epoxy resin 100 parts by weight

b. Curing agent

c. Wetting agents

d. hollow glass spheres with a diameter of

10 to 200 microns which is about 20 to 50 parts by weight form.

The core element is molded with a thickness of 25 to 50 mm and has a density of 480 kg / m.

2. Container foam layer -

open-cell, flexible polyurethane foam with a thickness of 13 mm and a density of 192 kg / m

3. Reinforcement layer fiberglass mat with staggered ** or continuous Fibers that weigh about 320 grams per square meter.

4.Thermosetting Resin

Epoxy resin system based on 828 (Shell) resin, with incorporated diethylenetriamine plus fillers and if desired, extenders.

A sandwich construction is made by resin impregnated foam layers applied to the rigid core member and these S _c haumschichten with the reinforcing layer are covered. The sandwich construction is then turned into a

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Form introduced, heated to a temperature of about 145 ° C and the mold closed to compress the foam layers to about 25% of their original thickness. While the sandwich construction is held under pressure, the resin is cured in about 2 minutes.

Although the hollow balls 26 are randomly distributed in the resin matrix 2h , the volume of the balls is substantially equal over the entire core member 12. In other words, the ball concentration or distribution over the core member has to be volumetrically the same as in FIG Practice is common. In this way, the density of the core element is as constant as possible over its cross section.

Further modifications are possible without going beyond the scope of the invention step out.

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Claims (7)

Oct. 30, 1979 D-Hg / K Composite Technology Corporation Troy, Michigan, USA claims 1. A composite body which comprises a core element which is an initially compliant, open-cell foam material wears, which is covered with a layer of high-strength reinforcement material and the open-cell Foam material is impregnated with a thermosetting resin material that has been cured while the composite body was kept under a sufficiently high pressure to cover the thickness of the open-cell material to reduce considerably and thereby fill the open cells and remove the excess resin material of the compressed layer to encapsulate the reinforcement material and this and the to connect resin-filled layer to the core element, characterized in that the Core element (12) has two rigid phases, the first phase being a plurality of hollow spheres (26) and the second Phase comprises a resin (24) encapsulating the hollow spheres (26). 'ι π 111 j / _t / υ SM ORIGINAL INSPECTED 2. Composite body according to claim 1, characterized in that the hollow balls (26) in the Core member form about 20 to 50 parts by weight out of 100 parts by weight of the encapsulating resin (24). 3. Composite body according to claim 1, characterized in that the hollow balls (26) are approximately are volumetrically distributed equally over the rigid phase of the core element. 4. Composite body according to one of the preceding claims, characterized in that the first phase hollow spheres (26) have a size of 10 to 200 microns and a wall thickness of 0.5 to 2.5 microns. 5. Composite body according to one of the preceding claims, characterized in that the rigid, hollow balls (26) cover the entire resin base (24) of the second phase are granted and embedded in this. 6. Composite body according to claim 1 to 5, characterized in that the core element (12), comprising a number of rigid hollow spheres (26) dispersed and embedded in a resin matrix (24) have approximately the same density over its cross-section. Π It) 'I j LI o / h _ ₃ _ 29U359 7. Composite body according to one of the preceding claims, characterized in that the first phase of the core element, which consists of two rigid phases, a plurality of inorganic hollow spheres (26) and that the second phase contains an organic resin matrix (24) which the hollow balls (26) embeds. 0 3 0 Π 3 U / 0 B 7 U