JPS6235827A - Manufacture of rubber extruded product - Google Patents

Abstract

PURPOSE:To obtain a high-quality rubber extruded product with no defect such a air bubble at all by vulcanizing under normal pressures by a method wherein rubbers are extruded under a pressure higher than the specified value and, after that, vulcanized under normal pressures. CONSTITUTION:A reinforcing layer 4, which has an overlapped portion 3 continu ously running in the longitudinal direction of a hose,is arranged by coextrusion between an inner layer rubber 1 and an outer layer rubber 2 with two extruders respectively extruding the inner layer rubber 1 and the outer layer rubber 2 and with a cloth head introducing band-shaped fabric in conjunction with the extruders. Rubbers are extruded under a pressure of 150kgf/cm<2> or higher and after that vulcanized under normal pressures. The pressure of 150kgf/cm<2> or higher to be applied to the rubber during extrusion is basically produced by giving resistance to the flow of rubber; or by various methods such as by mak ing the parallel portion of a die (nozzle) longer with the thicker die; by making the rubber channel narrower with a crosshead; by making the cross-sectional area of the rubber channel smaller ahead of the die or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing rubber extrudates. That is, the present invention relates to a novel manufacturing method that allows rubber extrudates such as rubber hoses and weather strips to be vulcanized at normal pressure.

<Prior Art> Conventionally, as a method for producing rubber extrudates such as rubber hoses and weather strips, the extrudate is first extruded using an extruder at a pressure of usually 100 kgf/d or less, and then extruded using a vulcanization pot to which pressure steam is fed. Vulcanization was performed by applying a steam pressure of 5 to 10 kgf/cJ. The main reason for applying steam pressure is to prevent the rubber layer from foaming due to moisture and volatile matter in the rubber compound.

<Problems to be Solved by the Invention> However, with this method of applying steam pressure, the beauty of the rubber surface may be damaged by the pressure steam, and in inner layer reinforced rubber hoses, the reinforcing threads may be severely damaged by the steam entering from the end surface. It has the disadvantage of shrinking and deteriorating. In addition, since a vulcanization pot was used, it was a batch process, which meant that continuous production was not possible, resulting in poor productivity.

In order to avoid such difficulties, a method of vulcanization under normal pressure has been adopted, but in this method, moisture and volatile matter in the rubber compound are removed.

There are two methods: (1) kneading a moisture absorbent such as calcium oxide into the rubber compound, and (2) utilizing vacuum pressure using a vented extruder. However, method (2) cannot achieve sufficient effect unless a large amount of calcium oxide is used, which deteriorates the physical properties of the vulcanized product, and also has disadvantages such as causing scorch in the unvulcanized state. In reality, it is used in a supplementary manner. In method (2), the extruder is expensive and there are problems such as vent-up (rubber clogging the vacuum chamber).

Means for Solving the Problems> The present invention was made for the purpose of solving the above-mentioned difficulties in the conventional method for producing rubber extrudates. After extruding by applying a pressure of 150 kgf/d or more, vulcanization is performed at normal pressure.

The method of applying pressure of 150 kgf/ant or more to the rubber during extrusion is basically to create resistance to the flow of the rubber.
There are several ways to do this, such as thickening the ferrule and making the parallel part longer, ■ narrowing the rubber flow path using a crosshead, and ■ reducing the cross-sectional area of the rubber flow path in front of the die.

Effects> According to the method of the present invention, an extrudate having no bubbles in the rubber layer can be obtained by normal pressure vulcanization, and a product of satisfactory quality can be obtained.

<Example> The present invention will be described in detail below with reference to Examples.

FIG. 1 is a sectional view of an inner layer reinforced hose used for performance evaluation of the method of the present invention.

The construction of such a hose starts with two extruders that extrude the inner rubber layer (1) and the outer rubber layer (2), and a crosshead that connects these extruders and introduces a band-shaped knitted fabric. , continuous overlap part in the longitudinal direction of the hose (
A reinforcing layer (4) having 3) is provided between the inner rubber layer (1) and the outer rubber layer (2) by coextrusion.

The rubber used in this example was an EPDM compound with a hardness of 70 in a waterless hardness, and the reinforcing knitted fabric was used by knitting polyester fibers, then coating them with a resin and drying them. The head pressure at this time was set to 220 kgf/cd on both the inner layer rubber (1) side and the outer layer rubber (2) side by narrowing the rubber flow path of the crosshead. A metal mandrel was inserted into this unvulcanized hose, and the hose was vulcanized for 30 minutes at normal pressure in heated air at 170°C.

The resulting hose has a rubber hardness that passes press vulcanization test 1-
It had the same 70-wallet hardness as the piece, and no bubbles were observed in any cross section.

Furthermore, it was confirmed that there was no shrinkage of the reinforcing threads at the end surface, as seen in pressurized steam vulcanization, and no deterioration of the reinforcing threads was observed in burst tests.

As described above, by applying a pressure of 150 kgf/d or more, preferably 200 kgf/cJ or more during extrusion, the inner layer reinforced hose is vulcanized at normal pressure and has a satisfactory quality without any defects such as bubbles. was obtained.

<Effects of the Invention> As is clear from the above description, the method for producing rubber extrudates of the present invention eliminates the need for blending a moisture absorbent or an expensive vented extruder, and vulcanizes at normal pressure to completely cure the rubber extrudates. It was possible to obtain a high quality rubber extrudate free of defects such as bubbles.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an inner layer reinforced hose obtained by the method of the present invention. (1) Inner layer rubber (2) Outer layer rubber (3) Overlap portion (4) Reinforcement layer]

Claims (1)

[Claims] 1. A method for producing a rubber extrudate, which comprises extruding the rubber by applying a pressure of 150 kgf/cm^2 or more during extrusion, and then vulcanizing it at normal pressure.