Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Patent
1988-11-15
1990-10-02
Woo, Jay H.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
264292, 264325, 264346, B29C 4304, B29C 4356
Patent
active
049605569
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for the crystallizing of thermoplastic material.
DESCRIPTION OF PRIOR ART
It has been known that the mechanical strength of amorphous material can be enhanced by increasing the crystallization of the material. An increasing of the crystallization is linearly related to the density of the material. The increasing of the crystallization is achieved on the one hand through orientation of the material, on the other hand through thermocrystallization of the material.
In the manufacture of articles from plastic material, especially in the mass production of articles, it is necessary to reduce as much as possible the time consumption for the manufacture of each individual article. An example of such applications is the m anufacture of containers for the storage of food products. It should be possible to use such containers also in connection with the preservation of food products, for the pasteurization of food products filled into the containers or for the hot filling of food products at a temperature around or over 100.degree. C.
It is known that by orientation of the material and subsequent heat treatment the necessary temperature stability and capacity to withstand increased internal pressure, e.g. during preservation or pasteurization, can be achieved. Similarly, it is known that by thermocrystallization of amorphous material the properties of the material can be improved so that the thermocrystallized material meets the demands arising in the application mentioned earlier. The heat stabilization of oriented material can be done relatively rapidly, since the material as a rule is relatively thin and it therefore acquires an increased temperature over its whole cross-section by heating it for a relatively short time.
The thermocrystallization of amorphous material, on the other hand, is time-consuming owing to the thickness of the material combined with the low thermal conductivity of the material. This in turn leads to undesirably long periods of residence in the production equipment.
SUMMARY OF THE INVENTION
As a result of the present invention the time consumption for the necessary increasing of the crystallization of the amorphous material is appreciably reduced. This is achieved in accordance with the invention in that the material in connection with the abovementioned heating to a temperature exceeding the glass transition temperature (TG) which often is defined as the temperature at which the material starts to soften is also subjected to compressive forces. These are directed as a rule mainly at right-angles to the boundary surfaces of the material.
In a preferred embodiment of the invention the material is enclosed during the compression between mechanical elements which apply compressive forces to the material. In certain applications the mechanical elements are adapted only to provide the specified compressive forces whilst in other applications they are adapted to constitute also moulding elements which transform e.g. the bottom part of a preform to an intermediate form or to an end form in connection with the manufacture of a container and which elements during the moulding process and/or subsequently apply the compressive forces required in accordance with the invention.
The invention is particularly suitable to be applied to the crystallization of the material in the bottom part of containers with a large opening.
In certain applications the material is preheated before the compression to the temperature at which the compression is to take place. In such applications the mechanical element or elements are coated with insulating material. e.g. Teflon, so as to prevent a variation in the temperature of the material during the course of the compression owing to heat exchange with the mechanical element or elements. In other applications the mechanical elements are set to a temperature adapted to the temperature the material should be at during with the compression. The parts of the mechanical elements which abut
REFERENCES:
patent: 4150070 (1979-04-01), Chang
patent: 4417320 (1983-12-01), Perkins
patent: 4563325 (1986-01-01), Coffman
patent: 4564495 (1986-01-01), Nilsson
patent: 4803024 (1989-02-01), Nilsson
Oehlenschlaeger Ulla
Pedersen Jan R.
Sorensen Erling
Durkin II Jeremiah F.
PLM AB
Woo Jay H.
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