Note: Descriptions are shown in the official language in which they were submitted.
A LAYERED ARTICLE PREPARED BY SPRAYING A
THERMOSET RESIN TO FORM EACH LAYER
Background of the Invention
A layered structure has superior properties because it is prepared by spraying
two part liquid resin polymers that chemically react very quickly to become solid, to
form each layer. A novelty is preparing all layers from a thermoset resin, which is
possible because all layers are added by a spraying means. Structures are formedinto articles such as boat hulls (canoes), truck liners, bathtubs, and automobile parts,
10 using suitable molds. The articles have desirable properties such as durability, and
relatively light weights. Moreover, they are produced more rapidly and inexpensively
than layered articles produced by other methods.
Layered articles have been prepared by a variety of methods using a variety of
materials. The choice of materials and methods is dictated by the specifications of
15 the structure of the specific article to be produced and by the availability of the
compositions and apparatus available at a particular point in time. For a multilayered,
performed, deformable plastics part, a layering method requiring a heated mold for a
first layer, and adding subsequent layers by moving the model through a curtain of
flowing plastic is suggested in GB,A, 1, 374 829.
Layered structures have been produced using thermoplastics, for example,
which do not have as desirable properties as thermoset resins. In EP A, 0 401 150
a layer of thermoplastic is covered with a "sprayed on layer of a preferably glass fiber-
reinforced curable plastic." This is proposed for construction of bath tubs. Thestructures are less resilient, and the method of producing thermoplastic structures is
25 lengthier and more costly than a method for producing layered structures fromthermoset resins. Thermoplastics are polymers which soften under heat and are
therefore amenable to molding by being injected or poured into cavities.
Thermoplastics are not amenable to application by spraying.
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Gel coat layers have been sprayed on inner cores prepared by methods other
than spraying, but this tends to produce relatively heavy structures. A spray gun was
used to create a bath tub with a multicolored design and a polyester gel coat. (JP,
A 59 103 716) Multilayered structures used for insulation have been described, for
5 example, in JP 60,201,934, that have a foam core and thermoplastic resin outersheets, but the design of this type of structure does not have to take into account
damage to structural integrity, an important
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consideration for articles such as boat hulls and automobile parts.
Multilayered sheets have been formed by extruding plastic polypropylene and
polystyrene followed by thermoforming using a vacuum. See W0 8,302,747.
Laminated structures have also been produced by injectional molding (EP 419829)
5 and rotational molding as described in U.S. Pat. No. 5,096,652. In rotational
molding, the laminate is made while the molded structure is being formed. Rotational
molding has been used to produce boat hulls having three layers of polyethylene, with
the middle or intermediate layer containing a foaming agent. U.S. Pat. No.
4,913,944. The layers are formed by particulate plastic being released into the mold
10 cavity while the mold "rocks and rolls" in an oven, or at least goes in an oven at
some point in the process. This process generally takes several hours, and requires
a metal mold.
Fast-curing thermoset resins are relatively new compositions that form
permanent and durable structures after being formed by heat or chemical reaction.
15 Reactive injection molding (RIM) can be used with thermoset resins by injecting the
mold cavity with the resins, but the result is not layered. (See, e.g., "Le RIM par
projection" 818 Plastiques Modernes et Elastomeres 36, 9, Nov. 1984 p. 68).
Layered compositions have advantages of incorporating desirable characteristics of
different materials into one structure, and even creating synergistic improvements
20 over characteristics of the combined individual materials.
Thermoset polyesters, epoxys, polyurethanes, phenolics and other thermoset
resins may be hand-layered, but this is time consuming and difficult due to the hand
labor and the fact that some resins are slow setting. To increase tensile strength and
stiffness, chopped glass fibres and foam may be added to layers. DE 3206468.
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A method of applying a composition to a structure is spraying. Generally
spraying will result in one layer of
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a composition. However, spraying has been used to apply multilayers of polymers
to wire strands, where the wire strands are layered within the layers of polymer. U.S.
4,891,086. A news report alludes to a resin spray gun for spraying "Rimspray" a
urethane elastomer ("Reaction molding by spray gun," European Plastics News 10:45 (May, 1983). Spraying has not been applied to produce layers of two part thermoset
resins .
There are problems in production of multilayered structures and in the nature
of the articles produced by the methods in the art. Problems include costs due to
expense of preparation of molds suitable for the methods and compositions in the art,
10 the length of time needed to prepare the structure, which increases cost and limits
output, and difficulties in adapting to robotic manufacturing methods.
Therefore, there is a need to improve methods of preparing layered structures
which could be quickly and inexpensively formed into articles such as boat hulls,
(canoes), automobile and furniture parts, bathtubs, truck liners to protect against
15 abrasion and the weather, and the like. The improvements needed are to more
quickly and efficiently accomplish the production of a more durable layered structure
which is versatile in its applications. A goal of the present invention is to disclose
and claim a method distinct from rotational molding, injection molding, blow molding,
reactive injection molding, resin transfer molding (RTM), and extrusion molding, none
20 of which have achieved the goals stated herein. It is another aspect of the present
invention to teach how to produce a structure resulting from the method that is
distinct from laminated plastic sheets, including those with foam cores, and from
structures that were not bound to each other by chemical reactions between the
layers. The structure of the present invention has layers that do not dissociate. A
25 particular goal not addressed by the art is to produce canoes and liners for truck
receptacles with layered two-part thermoset resin.
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Summarv of the Invention
- A layered structure with superior properties is prepared by spraying a two part
thermoset resin to form layers. The structure is moldable into various articles
(~A21 5531 7
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such as boat hulls, automobile and furniture parts, bathtubs, and truck liners. The
articles formed from the layered structure of the present invention are more durable,
resilient, lightweight, and inexpensive, than are comparable articles produced by other
methods and compositions.
The present invention is directed to a method for making a layered structure,
where there may be from 1 to n layers. A structure that has two or more layers is
called a "multilayered" structure. In particular, the invention relates a method of
making a canoe and a liner for a truck receptacle. Another aspect is the canoe and
the liner made in accordance with the invention.
The method includes the following steps:
a. Selecting a comPosition for a first laver.
The composition of the first layer is selected depending on criteria dictated by the
type of article to be produced. The composition and structure of the first layer of a
structure is determined by the specification for a particular application. In various
15 illustrative embodiments, the first layer may be composed of a resin, for example a
two-part thermoset resin. Thermoset resins that are suitable for use in the present
invention include resins that are characterized by elongation of at least 10%, and that
are suitable for spraying. In a preferred embodiment, the resin is an elastomer, that
is, a composition with a very high elongation, for example, 100%. Thermoset
20 polymers (resins) when molded to a specific shape cannot be subsequently softened.
Compositions that are suitable for the purposes of the present invention includepolyurea and a mixture of polyurethane and polyester.
An advantage of fast-curing thermoset resins for the present invention is that
the two-part resins harden or set very quickly after they are mixed and form very
25 durable structures. By quickly is meant within, for example, seconds or minutes as
compared with hours needed for some compositions in the art used for pour molding,
resin transfer molding, and injection molding to set.
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For example, a thermoset resin formed of polyurea hardens
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or sets to form an article, within about 3-40 seconds, as compared with polyethylene
used in rotational molding, which may require at least one hour to form an article, and
some other compositions that take 8 hours to set, especially if the goal is to produce
a multilayered article.
In a multilayered structure of the present invention, the layers may all be of
different compositions, or may be of the same composition, or any combination
thereof. In an illustrative embodiment, the composition of at least one of the layers
other than the first layer, that is, a layer which forms an inner (intermediate, middle)
layer of a multilayered structure, may be a foam layer. In an illustrative embodiment,
10 the foam layer is made by mixing a blowing agent such as water with the resin layer.
The water reacts with isocyanide to form carbon dioxide which introduces bubblesinto the resin, to form a foam. An advantage of using the same basic compositionin all layers, is to minimize delamination (undesirable separation of the layers) caused
by differential response of layers of different compositions to the environment.There may be any number of layers in the layered article, from 1 to n. The
upper limit is dependent on the applications for which the structures are to be used.
In a preferred embodiment, there are three layers composed of an outer and an inner
resin layer (or substrate), and an intermediate foam layer. This type of structure,
which may be referred to as a "sandwich", is useful for forming into an article such
20 as a canoe. Where there are layers beyond three, generally at least the inner and
outer layers are solid resins, rather than foam. Generally, foam and solid layers will
alternate. However, any combination of semi-solid or solid resins are within thescope of the present invention.
b. Spraving the composition onto a suitable supPort to form a laver.
,
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The first layer is designated as the layer that is emitted from a spraying
apparatus first during the process of making the layered article. Generally, the first
layer will constitute the outer layer (substrate) of the finished article. The first layer
is sprayed onto a solid support. The solid support is generally a mold, but may be
5 any solid support that allows the first layer to harden in a manner suitable for a
particular application. The solid support in the form of a mold, form or other suitable
type, need not be prepared to a specific temperature, as are such supports used for
other methods in the art. A suitable ambient air temperature is in the range of 15.5-
65.5 C (60-150 F.)
If pigments are to be added to a molded product, they are usually added to the
mold prior to the first layer as paint, or are added to the first layer, or both. If the
article is to be exposed to ultraviolet light, the first sprayed layer may contain an
ultraviolet resistant paint, generally in a layer of about .0254 to .1016 mm (1 to 4
mil) thick. This procedure is referred to as (in mold painting.)
The spraying of the resin to form layers is accomplished by any apparatus that
is capable of distributing a thermoset resin, or a comparable composition, into a layer.
Examples of spraying apparatus include manually operated spray guns, a plurality of
spray guns operated sequentially, a spray gun with multiple nozzles, a single spray
gun used repeatedly, or a robotic spraying apparatus. The robotic method is likely to
20 produce more desirable thickness in layers than a manually controlled spraying
apparatus.
c. Repeating steP a and b as manv times as required to form the multilavered
structure .
As mentioned in parts a and b, the first layer is generaily sprayed onto a solid25 support that is provided initially, for example, a mold. An advantage of the present
invention is that the mold does not have to be heavy, resistant to extreme
temperatures, or have complex
094/14587 PCT~S93/12303
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2~5~3~7
and tight closing means. In fact, a mold may be made of
the same resins used for the layers of the structure
produced by methods of the present invention.
Subsequent layers use as their solid support, a
previously sprayed layer. The second layer may be
sprayed after the first layer sets up, although spraying
of subsequent layers could wait for a long time, as long
as no cont~in~nts, such as oil or silicone-laden air,
affect the surface.
The second sprayed layer is sprayed onto the first
layer, wherein the second layer adheres to the first
layer. The third sprayed layer is sprayed onto the
second layer, and so forth. This process is repeated
until all layers required for a particular article are
sprayed. Other materials, such as metal reinforcements
or ribs, may be incorporated into the layers.
An article is defined as any structure which is
formed from a layered structure, wherein the layers have
been formed by the methods of the present invention. The
term "article~' includes both formed and unformed
structures wherein "formed" includes structures shaped
into recognizable shapes and "unformed" includes
structures that are not useful without further
processing.
The methods of the present invention are suitable to
make any multilayered article including a boat hull, such
as a canoe hull, a liner for a truck receptacle,
automobile parts such as fenders, and furniture.
Advantages of the present invention include quick,
therefore, more efficient means of producing multilayered
articles. Cost is reduced because production time is
dramatically reduced, and the only apparatus required is
a spraying apparatus. The mold does not have to be
heated prior to spraying, and may be comparatively
inexpensively and simply constructed.
~n important advantagc for thc cn~ironmcnt rc~ulting
fro... u_ing f~st ~-ctting rc~in~ i~ that 1~E 60nt-~nant~
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An important advantage for the environment resulting from using fast-setting
resins is that less contaminants escape, e.g., isocyanate, due to a reduced timeduring which compositions are volatile.
An aspect of the present invention is the layered structure formed by the
5 method disclosed. The structure is composed of one or a plurality of layers,
depending on the nature of the application o~ the structure. A suitable composition
of the first layer of the structure includes a thermoset resin. A suitable composition
of at least one of the inner layers of the suitable includes a foam, for example, a foam
composed of water and resin. The resin is a thermoset resin. There is no size
10 limitation associated with an article produced by the methods of the present
invention, although it is most suitable for relatively large articles, such are exemplified
herein.
The advantages of the layered structure of the present invention include
flexibility of construction and of composition of the layers. The layers may be thicker
15 or thinner in areas where a thicker or thinner thickness is advantageous, in contrast
to what can be achieved using other methods, for example rotational molding or blow
molding. If robotic spraying is used, layer thickness is controlled. Additives may be
put in the layers such as pigment, and metal reinforcements. Another advantage is
that when used for a molded article, the composition applied by the methods of the
20 present invention, has a "mold memory," rather than a sheet memory as in the
methods of the art which heat sheets and mold them into forms. Thermoplastic type
compositions are characterized by a tendency to revert to their original form from a
subsequently imposed form, such as that imparted by the thermo-formed molding
process. Therefore, articles of the present invention are more responsive to repairs
25 especially after being damaged, for example, by blows to the article.
.
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The layers of the structure may be any thickness, but a preferred range is from
.0508-1.016 mm (2-40 mil). Layers may be the same or different thicknesses when
compared to each other. Layers of the same composition may be accumulated to
increase the thickness of a particular composition layer, e.g., from to 1.016 mm to
5 50.8 mm (40 mil to 2 inches). The number of layers will be a function of the
thickness of an individually sprayed layer, and the number of repetitions.
Detailed DescriPtion of the Preferred Embodiments
Thermoset Resins
Thermoset resins are suitable for the methods of the present invention if they
10 are capable of being applied to a solid support by spraying, and they have anelongation of at least 10 %. The resins are two-part liquid resins of polymers that
chemically react very quickly to become solid. By a two part resin is meant a
composition which is divided into two components which must be mixed in order for
hardening to occur. By very quickly is meant in as little time as seconds. The exact
15 hardening time will vary with the specific composition.
In an illustrative embodiment, the resins comprise polyurea. In another
embodiment, the resins comprise a hybrid polyurethane and polyester. A suitable
composition is the EC Series 23, which is available from EniChem, Polyurethane
Design Division,1448 V.F.W. Drive, Conyers, Georgia 30207. Characteristics of the
20 EC Series 23 are shown in Table 1. EC Resin System Series 23 is a 100% solid
polyurea system. It has been used for reaction injection molding (RIM). For thatpurpose, key processing benefits are the adjustable gel time from 3 to 45 seconds,
which was purported by the manufacturer to eliminate mold flowing problems.
"Fillers" are easy to process for enhanced properties; "optional internal molding
25 release" is available for optimizing cycle times.
The EC23 system enhances the quality of the molded part by minimizing sink
marks and shrink. Also,
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paintability is said to be excellent using standard automotive paint and techniques.
TABLE 1: Characteristics of EC Series 23
PHYSICAL PROPERTIES:
EC EC
23-21 23-25
Specific Gravity 1.12 1.120
Thickness .125 .125
Tensile Strength atm 238.161 265.379
(3.5K) (3.9K)
Elongation % 95 73
Flexural Modulus atm 5449.68 6804.6
(80K) (100K)
Shore D 60D 65D
Notched Izod-lmpact 7 5
Linear Shrinkage 0.75 0.75
HeatSag-1 hr.@ 121.11C (250F)
MOLDING CONDITIONS
ISO Temperature 32.22C 32.22C
(90F) (90F)
Polyol Temperature 32.22C 32.22C
(90F) (90F)
Mixing Pressure 136.092 atm 136.092 atm
(2000 PSI) (2000PSI)
Mix Ratio 1.14/1 PBW A/B 1 /1 PBW AB
Another resin suitable for use in the present invention is the EniChem series EC 242.
Characteristics of that series of resins are presented in Table 2. EC Resin Systems
Series 242 is a high-modulus hybrid polyurea that was designed for high productivity
RIM production. Gel times are adjustable from 5 to 45 seconds implemented by
30 catalyst changes. According to the manufacturer, EC 242 provides excellent green
strength and good release
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characteristics from the mold. EC Series 242 has excellent impact strength with
minimal heat sag up to 135C (275).
TABLE 2: Characteristics of EC Series 242
5PHYSICAL PROPERTIES:
EC EC
242-21 242-25 ASTM Method
Density 68PCF 68PCF D 1622
Hardness, Shore D 72 75 D 2240
Tensile Strength 360.644 atm 401.471 atm D 412
(5300 PSI) (5900 PSI)
Elongation @ Break 180% 140% D 412
Flexural Modulus
@ 22C 10207 atm 15174.258 atm D 790
(150,000 PSI) (223,000 PSI)
Heat Sag . 101.6mm
"4" "overhang
1 hr. @ 121 C 3.3 mm 3.3 mm D 3769
1 hr. @ 121 C (.13 ins.) (.13 ins.) D 3759
Notched Izod Impact 10.36 Kg/M .8295 Kg/M
(75. ft./lbs.) (6 ft./lbs.)
**Post Cured @ 121 C for one hour
Spraying Means
Any means for spraying a two-part thermoset resin on to a solid support so
25 that the resin forms a layer, is suitable for purposes of the present invention. A spray
gun may be ordered from Tel 908 Gusmer, 1 Gusmer Drive, P.O. Box 110,
Lakewood, New Jersey 08701 -0110. Apparatus for spraying include the gun claimedin FR 2520639; and the thermal spray gun of U.S. 4,999,225.
While the invention is susceptible to various modifications and alternative
30 forms, specific embodiments
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thereof are shown by way of examples. It should be understood, however, that it is
not intended to limit the invention to the particular forms disclosed, but on the
contrary, the intention is to cover all modifications, equivalents, and alternatives
falling within the spirit and scope of the invention as defined by the appended claims.
5 EXAMPLE 1: Preparation of a Three-Layered Structure
The first layer was composed of thermoset resin EC 491. It was sprayed on
to the solid support using a spray gun and allowed to harden for one minute. A solid
support was a fiberglass canoe mold.
The second layer was a foam layer produced by adding water to the non-
10 isocyanate part of the resin system Part B. When the two parts are mixed, the waterreacts with the isocyanate in Part A to form C02. The more water that is added, the
more C02 that is produced, and the more foaming action, or less density, results.
The second layer was sprayed on to the first and allowed to harden for two minutes.
The third layer was composed of the same resin used in the first layer. It was
15 sprayed onto the second layer and allowed to harden for 45 seconds.
The thickness of the first and third layers was about 1.27 mm (50 mil or .050
inches) .
The temperature at which the spraying was done was 22.22C (72).
EXAMPLE 2: Producing a Canoe
The three layered structure of Example 1 is used to form the structure of the
canoe .
The solid support used was a canoe-shaped mold. The moid that was used is
a hand layed-up polyester fiberglass mold, the same type of mold that is used for a
hand layed-up boat, such as a canoe or other fiberglass structure.
A mold is made using the same equipment and the same basic material as
described in Example 1. This means a
W094/14587 215 ~ 3 ~ 7 PCT~S93/1~03
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Thc fir~t laycr w~s composcd of thcr~Ect rc~in Er
491. It was sprayed on to the solid support using a
spray gun and allowed to harden for one minute. A solid
support was a fiberglass canoe mold.
The second layer was a foam layer produced by add~ g
water to the non-isocyanate part of the resin syste ~Part
B. When the two parts are mixed, the water re ~ s with
the isocyanate in Part A to form CO2. The ~ore water
that is added, the more CO2 that is prod~ ed, and the
more foaming action, or less density/ results. The
second layer was sprayed on to the f~ st and allowed to
harden for two minutes.
The third layer was compos ~ of the same resin used
in the first layer. It was s ~ayed onto the second layer
and allowed to harden for ~5 seconds.
The thicknecs of th~first and third layers was about
50 mil or .050 inche~
The temperatu~ at which the spraying was done was
72
EXAMPLE 2: P~ ducing a Canoe
The t~ ee layered structure of Example 1 is used to
form t ~ structure of the canoe.
~ he solid support used was a canoe-shaped mold. The
m~ d that was used is a hand layed-up polyester
/ iberglass mold, the same type of mold that is used for
/ a hand layed-up boat, such as a canoe or other fiberglass
/ structure.
/ A mold is made using the same equipment and the same
ba~ic ~-t~rial aE dcscribcd in ~Y~rlc 1. Thie ~can~ a
part can be duplicated by waxing the part, spraying the
support as described in Example 1 (to create a mold),
pulling the part from the mold, waxing the mold, spraying
the mold again as in Example 1, to duplicate the part.
EXAMPLE 3: Manufacturing a Liner for a Truck Cavity
A liner that fits snugly into the cavity of a truck
is desirable to protect the basic truck finish from
abrasion, for example, due to articles transported in the
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cavity of a pick-up truck, and from the weather. Liners
available in the art generally are composed of
polyethylene, and must be attached to the truck with
bolts and rivets. The attaching process itself, violates
the integrity of the truck finish. Another disadvantage
of the liners currently available, is that they are not
readily removed.
Using the methods and compositions of the present
invention, superior truck liners are produced that are
resistant to weather and abrasion because of the strength
and resistant surface properties that characterize
thermoset polymers. In addition, because the polymer
layers are sprayed directly on the truck cavity, no extra
mold is needed. This reduces cost and improves fit of
the liner to the truck cavity. If the interior of
thetruck is waxed prior to spraying the first polymer
layer, the liner may be readily removed by simply lifting
it out.
Although the number and composition of the layers may
vary depending on the nature of protection desired, the
three layered structure of example 2 is a suitable
structure for this purpose.
