JPH04147832A - Method of manufacturing a synthetic resin hollow body with a foam wall - Google Patents

Abstract

PURPOSE: To obtain a hollow part having a foam wall of a rough inner surface by extending a preform in a foaming mold by an externally operating negative pressure, and generating an overpressure existing therein. CONSTITUTION: The synthetic resin hollow unit having a foam wall made of many layers including different void fractions is manufactured by extruding at least one type of foamable thermoplastic resin by a multiple layer extruder, and foaming its preform by a negative pressure operating at an outside of the preform in the mold. An overpressure higher by 0.1 to 0.8 bar than a pressure of an outside of the hollow unit is generated in the preform. To manufacture the foam synthetic resin hollow unit, a thermoplastic resin to be foamed by a foaming agent is suitable. For example, a low density, intermediate density and high density polyethylenes, polypropylenes, polystyrenes, polyvinyl chlorides, polyacetal or the like are used. Preferably, the low density, intermediate density and high density polyethylenes, and polypropylene are used. Among them, the polypropylene is preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a synthetic resin hollow body having a foam wall consisting of multiple layers of different porosity.

It is known to produce hollow bodies whose walls are partially made of foamed synthetic resin by extrusion of at least two or more layers of tubular preforms. At least one of these layers consists of a foamable synthetic resin (European Patent No. 281,971). In the foaming mold, the preform is expanded by internal pressure, the internal pressure being such that the foamed layer is not compressed at all or only slightly. It is difficult to control because the pressure for this must be low.

It has therefore been proposed to mold synthetic resin hollow bodies with foamed walls not by foaming the preform in a foaming mold, but by using negative pressure applied to the preform from the outside. In this case, a hollow body with a smooth inner surface is obtained.

[Problem to be solved by the invention]

However, for many applications it is desirable to have a hollow body with foam walls with a rough inner surface.

[Means to solve the problem]

The inventors of the present invention have found that the above problems can be solved by not only expanding the preform in the foam mold by means of negative pressure applied from the outside, but also by generating an internal overpressure.

The present invention therefore provides a method of extruding at least one foamable thermoplastic resin in a multilayer extrusion device and foaming the preform in a mold by means of negative pressure applied to the outside of the preform. A method for producing a synthetic resin hollow body with a foam wall consisting of a number of layers of different porosity, in which an overpressure of 0.1 to 0.8 bar is applied inside the preform above the pressure on the outside of the hollow body. The present invention relates to a method characterized by generating.

In order to produce a foamed synthetic resin hollow body according to the present invention,
All thermoplastic resins that can be foamed with blowing agents are suitable, such as low-density, medium-density and high-density polyethylene, polypropylene, polystyrene,
These include polyvinyl chloride and polyacetal. Preferably, low, medium and high density polyethylene and polypropylene are used, with preference given to using polypropylene.

Suitable foaming agents for pre-foaming are those which are customary for the above-mentioned synthetic resins, and which decompose at a temperature of, for example, about 120°C to 230°C. Such blowing agents include, for example, penzole sulfohydrazide, toluorubis-sulfohydrazide, xylo-rubis-sulfohydrazide, biphenyl-bis-sulfohydrazide, p.

p゛-oxy-bis-penzole sulfohydrazide,
Aromatic sulfohydrazides such as methanesulfohydrazide, isobutanesulfohydrazide, octane sulfohydrazide, α-dolol sulfohydrazide, xylo-rubis-sulfohydrazide etc., aliphatic sulfohydrazides and aralkyl sulfohydrazides 1 such as penzole sulfo semicarbazide, toluorubis-sulfosemicarbazide, xylo-rubis-sulfosemicarbazide, biphenyl-bis-sulfosemicarbazide, p,
Aromatic sulfosemic carbazides such as p'-oxy-bis-penzole sulfosemic carbazide, methanesulfosemic carbazide, isobutanesulfosemic carbazide, octane sulfosemic carbazide, a-dolol sulfosemic carbazide, xylo-rubis-sulfosemic carbazide, etc., aliphatic sulfosemic carbazides, Semicarbazides and aralkylsulfosemicarbazides, such as N,N'-dimethyl-N,N'-dinitrosoterephthalamide and N,N
Based on N-nitroso compounds such as '-dinitroso-pentam-methylenetetramine, azo compounds such as azodicarbonamide and also citric acid hepta-bicarbonate (various systems are included. As blowing agents) is especially p, p
'-Oxy-bis-penzole sulfohydrazide, azodicarbonamide and mixtures thereof and the citric acid heptabicarbonate system can be used. The amount of blowing agent is
0.1 to 1.0%, especially 0.3 to 0.8%, calculated as active substance.

In addition to the blowing agent, the synthetic resin can optionally contain other customary additives, such as light and heat stabilizers, pigments, lubricants, antistatic agents, flame retardants, etc. Furthermore, the synthetic resins used can contain the customary required amounts of fillers, such as calcium carbonate, chalk, talc, glass beads, magnesium and/or aluminum silicates, clay, carbon, sawdust, etc.

The synthetic resin molding composition containing the foam and optionally other additives is placed in an extruder in which the foaming agent it contains decomposes and the gas formed enters the molten resin under high pressure. It is melted in the extruder so that it remains molten, so that the molding material foams only when it emerges from the extruder.

The method according to the invention uses at least two extruders which melt the same synthetic resin foam material or different resin foam materials. These extruders feed their respective melts into a multilayer head where they are combined in a known manner to form a multilayer tube. This tube of material is cut into lengths, and each cut preform is introduced into a respective mold whose internal space corresponds to the shape of the defined hollow body, and the foam mold is molded by means of negative pressure. Let it expand until it sticks to the wall. A vacuum suction in the intermediate space between the preform and the inner wall of the foam mold is caused by the sealing process of the foam mold, which is optionally delayed in time in order to obtain an optimum negative pressure. As soon as the preform reaches the wall of the foam mold, the gas present inside the preform is sucked out through the bolts projecting into the interior space of the foam mold. In this case, a pressure difference of 0.1 to 0.8 bar occurs between the outside and the inside of the formed hollow body. In this case the pressure on the outside is lower than the pressure on the inside. Due to this pressure difference, the temperature is still quite high (
As a result, the less viscous layer is sucked inward into the space of the hollow body, with the gas bubbles in the foam layer expanding considerably. By suitably selecting the internal negative pressure, it is even possible to submerge the internal air bubbles of the foam, thereby creating an internal porosity of the foamed hollow body.

The inner surface of this foam hollow body is rough.

An advantage of the method according to the invention is that the bubble pressure that would otherwise exist during extrusion foaming does not result in compression of the foam, but is further expanded by the pressure difference of the vacuum.

When a hollow body produced according to the invention is used as an air conduit in a motor vehicle, a higher silencing effect is observed with a tube wall consisting of multiple layers with different specific gravities than with a tube wall of the same density. I can do it.

Moreover, air velocities are significantly higher for rough internal surfaces than for smooth internal surfaces for the same energy force (difference between air/air friction and material/air friction).

[Examples] Hereinafter, the present invention will be explained in more detail with reference to some examples.

example".

About 1.5 g/10 min M with about 2% conventional chemical blowing agent in one extruder in multilayer extrusion equipment
Extrude conventional commercial polypropylene with FI23015 and in the second extruder about 30 g/10 min MFI23 containing 2% of another conventional chemical blowing agent.
Polypropylene with 015 was extruded. In each of these extruders, the mixture is melted and homogeneously mixed using short compression screws, the temperature in each cylinder zone from the suction hopper to the nozzle being 220'/2
25°/200'/200"/180°/180°
/180°C. This resulted in a melt temperature of 197°C. The multilayer head of the extruder was fed with its higher molar weight polypropylene constituting the outer layer of the molding.

The extruded microporous preform was introduced section by section into a hollow foam mold and the mold was closed. A few seconds after the start of the mold closing process, the valve separating the mold from the vacuum conduit was opened, which caused the preform to be sucked against the cold inner walls of the foam mold. This first
The second valve was released 3 to 10 seconds after the release of the second valve. This reduced the pressure inside the reserve. This pressure difference was 0.5 bar. The resulting hollow body had a tube wall with a microporous outer layer and a coarsely porous inner layer.

A three-layer preform was made using the same equipment as in Fengyu Example 1,
This was then molded into a hollow body. Its layer structure before foaming was as follows: Outer layer: polypropylene (containing about 2% blowing agent, MFI
23015 approx. 1.5 g/min) Intermediate layer: Polypropylene (no foaming agent, MF I
23015 approx. 0.5 g/min) Inner layer: Polypropylene (contains approx. 2% blowing agent, MFI
23015 approx. 30 g/min) The hollow body obtained had a tube wall of 3Ii layer with the same foam structure as in Example 1, except that the porous layers on both sides were separated from each other by a dense layer. In the finished hollow body, each layer of its tube wall has the following density: Outer layer: O135g/cm ”Middle layer: 0
．． 9 g/cm” Inner layer: 0.30 g/cm”

Claims (1)

[Claims] By extruding at least one foamable thermoplastic resin in a multilayer extrusion device and foaming the preform in a mold by means of negative pressure applied to the outside of the preform, different porosity can be obtained. In a method for manufacturing a synthetic resin hollow body having a foam wall made of multiple layers, the pressure inside the preform is 0.0.
A manufacturing method as described above, characterized in that an overpressure of 1 to 0.8 bar is generated.