Cross-linked polyvinyl chloride resin foam and method of manufac

Details Cross-linked polyvinyl chloride resin foam and method of manufac Cross-linked polyvinyl chloride resin foam and method of manufac

1982-01-25

1984-02-28

Foelak, Morton

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

2041592, 20415917, 20415924, 264 25, 264 54, 264DIG5, 264DIG18, 521 73, 521 85, 521 91, 521 93, 521140, 521145, 521915, C08J 910, B01J 110, B29D 2700

Patent

active

044342519

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a cross-linked polyvinyl chloride resin foam having uniformly fine cellular structure with low density, which has high thermoformability and heat resistance, and, even after long storage, is neither deformed nor deteriorated, and also to a method of manufacturing said cross-linked polyvinyl chloride resin foam.


BACKGROUND ART

A polyvinyl chloride resin foam has the advantages that it excels in fire retardance, chemical resistance, weatherbility and waterproofness and can be applied at a relatively low temperature, but is handicapped by the drawback that it has low heat resistance. It is known that this difficulty can be resolved by developing a cross-linked polyvinyl chloride resin foam. To date, however, such cross-linked polyvinyl chloride resin foam is actually produced only by the so-called pressurized foaming process such as a high pressure foaming process using a pressure-resistant sealed metal mold or high pressure inert gas process, (set forth, for example, in the Japanese patent publication No. 22,370/64 and Japanese patent publication No. 12,632/66). These proposed processes are inevitably carried out by the batch system, failing to produce the intended foam continuously. To obtain a sheet of cross-linked polyvinyl chloride resin foam, therefore, it has been necessary to slice a batch-produced foam block into a thin sheet.
Consequently, the conventional method of manufacturing cross-linked polyvinyl chloride resin foam which is based on the pressurized foaming process has been accompanied with the drawbacks that said conventional method involves costly manufacturing equipment; is handicapped by low productivity; moreover has to take many steps including, for example, the slicing step; the product becomes unavoidably expensive; and its market still fails to be expanded due to competition by less expensive foamed products such as foamed polyurethane, foamed polystyrene and foamed polyethylene.
For a long time, therefore, studies have been conducted on the method of continuously manufacturing a cross-linked polyvinyl chloride resin foam. To date, however, no process has been proposed which proves fully successful from the practical point of view.
Though not clearly understood, the failure to develop the method of continuously manufacturing cross-linked polyvinyl chloride resin foam at a low cost is inferred from the experiments carried out by the present inventors which complete this invention to have resulted in determining the undermentioned facts. Polyvinyl chloride resin tends to be thermally decomposed by the heat during kneading or molding and give forth hydrogen chloride gas. To avoid this objectionable event, it is always necessary to blend a stabilizer with the polyvinyl chloride resin. Normally, the stabilizer is applied in an amount of about 2 to 5 PHR. Where it is attempted to mix a thermally decomposable blowing agent such as azodicarbonamide with polyvinyl chloride resin, plasticizer and stabilizer by a mixing roller or Banbury mixer, then said blowing agent vigorously decomposes itself even at a lower temperature than the normal decomposition temperature of said blowing agent and evolves gases, making it impossible to obtain a unfoamed polyvinyl chloride resin molding.
Namely, it is impossible to provide a polyvinyl chloride resin composition, whether cross-linked or not, in which a thermally decomposable blowing agent, stabilizer and plasticizer are uniformly blended and is once gelled, that is, a foamable polyvinyl chloride resin composition.
On the other hand, a soft polyvinyl chloride resin foam has been continuously produced by applying a thermally decomposable blowing agent as set forth, for example, in the Japanese patent publications Nos. 18,828/67 and 13,874/68. These proposed processes indeed make it possible to blend a thermally decomposable blowing agent with the polyvinyl chloride resin without giving rise to the premature decomposition of said blowing agent. However, these published processes are necessary to use extremely fi

REFERENCES:
patent: 3562367 (1971-02-01), Shinohara et al.
patent: 4203815 (1980-05-01), Noda et al.

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