Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
2000-05-22
2001-10-02
Michl, Paul R. (Department: 1714)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C264S328180
Reexamination Certificate
active
06296797
ABSTRACT:
The invention relates to a process for producing polyacetal elastomer composite articles from a combination of the engineering material polyoxymethylene with directly molded-on functional elements made from one or more thermoplastic elastomers, and to the use of these.
The engineering material polyacetal, i.e. polyoxymethylene (POM) has excellent mechanical properties and is furthermore also generally resistant to all of the usual solvents and fuels. Moldings made from polyoxymethylene are therefore used inter alia in automotive construction, and in particular in fuel-conveying systems. Due to good strength and hardness combined with excellent resilience, moldings made from polyacetal are very often used in all areas of daily life for snap connections, in particular clips. Excellent sliding friction properties are the reason for the use of polyoxymethylene for many moving components, e.g. power train components, deflector rolls, gearwheels and adjusting levers. Very good mechanical durability and resistance to chemicals also allow housings and keyboards to be produced from polyoxymethylene.
However, POM has a low mechanical damping factor at room temperature. In some applications, this makes it necessary to use soft damping elements. In addition when moldings made from polyoxymethylene are incorporated a seal is often required at connecting points. The high surface hardness of moldings made from POM and the low sliding friction coefficient of POM can cause items placed thereon to slip and can limit the operating reliability of, for example, switching elements and control elements made from POM.
On the other hand, use is also increasingly often made of combinations of hard and soft materials, so as to combine the particular properties of these materials with one another. The hard material here is intended to give the components their strength, and the soft material, due to its elastic properties, assumes functions of sealing or insulation against vibration and noise or brings about a change in surface feel. In these applications it is important that there is sufficient adhesion between the hard and soft components.
Until now, gaskets and damping elements have sometimes been prepared separately and, usually in an additional operation, mechanically anchored or bonded, causing additional work and in some cases considerable added costs. A newer and more cost-effective method is multicomponent injection molding, in which, for example, a second component is overmolded onto a premolded first component. The adhesion achievable between the two components is very important for this process. Although in multicomponent injection molding this adhesion can often be further improved in physical interlocks by applying undercuts, good basic adhesion through chemical affinity between the selected components is often a necessary condition for their use.
Examples which are well known are multicomponent injection-molded combinations of polypropylene (PP) and polyolefin elastomers or styrene-olefin elastomers, and polybutylene terephthalate (PBT) with polyester elastomers or styrene-olefin elastomers. Polyamides, too, adhere to very many soft components.
There are also known moldings made from polyacetal with directly molded-on functional elements, which were produced using non-crosslinked rubbers (DE-C 44 39 766). However, bond strength in composite articles of this type is not yet satisfactory.
Another publication relates to composite articles of the same type which are composed, inter alia, of a polyacetal, a rubber copolymer, a reinforcing filler, a crosslinking agent and, if desired, other usual additives (DE-A 9611272). Particularly good adhesion of the polymer components is achieved by vulcanization of the rubber portion. However, this additional step is seen as a disadvantage, due to the increased temperatures and times for vulcanization.
It is also possible (DE-C 42 24 145) for the damping element of a locking ram of a motor vehicle door lock to be provided with areas of differing hardness and tensile strength. In such cases, a thermoplastic rubber is used first for the region of lower hardness, and for the region of greater hardness a polyacetal plastic is applied onto this. Although this procedure achieves good adhesion, this process is not very useful due to the low dimensional stability of the thermoplastic rubber.
Thermoplastic elastomers are claimed to be capable of combination with thermoplastics in the overmolding process. In this connection, polyurethane elastomers (TPE-U), for example, adhere to POM (Kunststoffe 84 (1994) p. 709). If, however, the soft component here is molded onto the hard component, as is generally the case, the result is only a few combinations having good ultimate tensile strength. This results from inadequate interdiffusion, since because of the temperature profile in this process diffusion is only very short-lived. The publication does not give any further details concerning the adhesion of the components mentioned. There are also no known relevant applications.
Finally, there is a known process, specifically profile extrusion, and a known apparatus for pre-vulcanization of thermoplastics and elastomers (DE-C 43 14 191). In this process chemical bonding is produced between the components, if desired with the addition of a coupling material. This process differs substantially from the abovementioned multicomponent injection molding, due to the longer times of contact between the components. As is the case for the thermoplastic polymers, a wide variety of substances is also cited for the thermoplastics which can be used. including TPE-U and POM. The publication does not give any specific indication that precisely these substances are to be used together, nor does it indicate the advantages of such a combination.
It was an object of the present invention to provide a composite article made from polyacetal with directly molded-on functional elements made from thermoplastic elastomers by multicomponent injection molding, in which the limitations and disadvantages mentioned are not present.
This polyacetal elastomer composite article is composed of
a) polyacetal and
b) at least one thermoplastically processable elastomer, preferably TPE-U.
The invention provides a process for producing the abovementioned polyacetal elastomer composite article as described in claim
1
in which the material with the greater hardness (component a)) is firstly premolded into the mold. The melt temperature here is in the usual range, i.e. in the range from about 180 to 240° C., preferably from 190 to 230° C., for the polyacetals described below. The mold itself is temperature-controlled in the range from 20 to 140° C. A mold temperature in the upper range of temperatures is advantageous for precise shaping and dimensional stability of the hard component part made from the partly crystalline material.
As soon as the charging of the part has been completed and the holding pressure is no longer acting (gate sealing point), then component a) may be finally cooled and then removed from the mold as the first part of the composite article (premolding). Then in a second and subsequent separate injection-molding step this premolding for example is placed or relocated into another mold with a recessed cavity and the material with the lower hardness (component b)) is injected into the mold and thereby molded onto component a) (insert or transform process). It is particularly advantageous here for the adhesion subsequently achievable if the premolded part made from the hard component a) is preheated in the range from 80° C. to just below the melting point to facilitate fusing-on of the second component b) and its penetration into the boundary layer.
The premolded part made from component a) may also be only partly removed from the mold and, together with a portion of the original mold (e.g. the feed plate, the ejector side or merely an indexing plate), be moved into another larger cavity.
Another way is to inject the second, softer component b) into the same mold without opening up the machine b
Kurz Klaus
Reil Frank
Ziegler Ursula
Connolly Bove & Lodge & Hutz LLP
Michl Paul R.
Ticona GmbH
LandOfFree
Method for producing composite bodies does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing composite bodies, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing composite bodies will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2570504