METHOD OF MAKING POLYMER SEALS
This is a divisional application of application No. 07/148,389 filed on Jan. 25, 1988 now U.S. Pat. No. 4,857,389.
The present invention relates to polymer seals and more particularly to a composition and method of making polymer seals wherein a combination of pre-polymers are cured and bonded together to form a single, multi-layered polymer seal of variable hardness.
BACKGROUND OF THE INVENTION
In various technical fields, seals of elastic variable hardness material are required, which by reason of their configuration or due to the properties of the material must be assembled from two or more components. This requirement arises in the case of sealing rings for pipe couplings and the like, needing a higher elasticity in one cross sectional zone and a higher degree of shape stability in another cross sectional zone.
In processing such materials, it is desirable to produce moldings from components in which in the first working step the components are manufactured partially consolidated and then in a further working step are connected with one another and hardened.
Composite materials of varying hardness such as the present invention are considerably superior to uniform materials as the harder layer resists hard sharp edges while the softer layer is considerably more resilient and yielding. This provides for a considerable reduction of damage due to crushing and fatigue while at the same time reducing the thickness of the material.
In spite of existing composite materials, there is a need in the marketplace for materials having greater impact resistance, longer working lives, lower weight and other positive properties.
tribute wetability, elasticity and rubber characteristics to the seals. The concept of multi-layered plastic bonding structures is known as is the idea of combining prepolymers to form a single bonding structure. See e.g.
5 Martins, U.S. Pat. No. 4,443,518; Willett, U.S. Pat. No. 3,933,675; Fujiwara, U.S. Pat. No. 4,182,898; and Lindenmayer, U.S. Pat. No. 4,410,478. Nowhere in the prior art, however, is disclosed the combination of prepolymers having the characteristics and strengths as
10 found in the present invention. Neither is the method of bonding and forming the polymer seals of the present invention disclosed.
SUMMARY OF THE INVENTION
15 The present invention comprises a polymer seal formed from a combination of pre-polymers, cured and bonded together, forming a single multi-layered polymer seal of varying hardness. The harder outer layer of the seal gives shape stability to the seal and the inner 20 softer layer forms a malleable elastic connection under normal conditions.
In the preferred embodiment of the invention, at least one pre-polymer consists of a polyester-based prepolymer and at least one pre-polymer consists of a 25 polyether-based pre-polymer. When cured, these prepolymers yield an 80 to 90 shore A and 80 to 90 shore D hardness, respectively.
Additionally, the present invention includes a method of making the polymer seals having the above composi30 tion wherein the production process steps are: (1) the combination of pre-polymers is degased; (2) the polyester-based pre-polymer is mixed with a curing agent, heated to a predetermined temperature, and then poured into a preheated mold of a specified shape and 35 design; (3) a predetermined time interval is allowed to elapse; (4) the polyether-based pre-polymer is mixed with a curing agent, heated to a predetermined temperature and poured onto the surface of the polyester-based pre-polymer mixture; and (5) the preheated mold is
The bonding of reinforced plastics as revealed in the 40 placed into a press for a predetermined length of time
prior art is generally accomplished with reactive multicomponent thermal set systems such as peroxide, cured unsaturated polyester, polyol-polyisocyanate systems and epoxy systems. Such systems require precise metering of the components to obtain uniform performance and generally include toxic or sensitive compounds needing special precautions in handling.
Additionally, such systems have a finite open mold time requiring the mating of the bonded parts before the materials cure or advance to a non-bonding stage. Furthermore, such systems require the bonded parts to be held together mechanically for long periods of time until the systems have cured sufficiently to provide a strong bond and consequently require a cleaning or purging of the application equipment to avoid setting of 55 the adhesives and equipment.
Hot melted adhesives such as the present invention overcome such disadvantages since they are single stream systems and are not sensitive to shock. The present invention develops bond strength simply by the 60 passage of short amounts of time and does not require the long curing periods of mechanical fastening. Additionally, they do not present a problem caused by premature cure or set in the application equipment.
The hard crystalline segments in the present invention contribute tensil strength toughness and high temperature performance to the polymer seals. The soft amorphous or low melting segments of the seals con
for providing the final curing of the seal. It should be noted that the longer the cure time is, the longer the demold time will be.
This methodology will yield a polymer seal having one layer with a shore A hardness of 80 to 90 and a second layer with a shore D hardness of 80 to 90. Thus, a multWayered polymer seal of varying hardness is formed which incorporates numerous advantages over the prior art. Other methods and variations of this methodology are discussed in more detail in the following Description of the Invention.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention and the advantage thereof reference may be made to the following description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a prospective view of one example of a polymer seal made from a method described in Example 1;
FIG. 2 is a prospective view of one example of the polymer seal made from a method described in Example 2;
FIG. 3 is a prospective view of one example of the polymer seal made from a method described in Example
FIG. 4 is a cross section view of FIG. 1;
FIG. 5 is a cross section view of FIG. 2; and