Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1990-10-31
1993-09-14
Kight, III, John
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525263, 525265, 525316, C08F 202, C08F 206
Patent
active
052449777
DESCRIPTION:
BRIEF SUMMARY
FIELD OF TECHNOLOGY
This invention relates to a process for preparing rubber-modified styrene resins with high mechanical strength, in particular, with good impact resistance.
BACKGROUND TECHNOLOGY
The preparation of rubber-modified styrene resins of good impact resistance requires an exercise of proper control over the particle diameter and particle diameter distribution of rubber dispersed in the resins.
The rubber-modified styrene resins tend to improve in appearance but suffer a loss in impact resistance as the rubber particle diameter diminishes and the optimal particle diameter is generally said to be in the range from 1 to 5 .mu.m, preferably 1.5 to 4 .mu.m.
On the other hand, the impact resistance of rubber-modified styrene resins is closely related to the content of styrene polymers occluded in the rubber particles and is said to improve with the increasing content of the occluded styrene polymers.
It is therefore advantageous for the improvement of the impact strength and other mechanical strengths of rubber-modified styrene resins to increase the rubber particle diameter without adversely affecting the appearance of the resins and, at the same time, to increase the content of styrene polymers occluded in the rubber particles.
The present inventors previously disclosed a process for preparing rubber-modified styrene resins which comprises carrying out preliminary polymerization in two complete mixing type reactors, until before the rubber phase inversion in the first reactor and until after the rubber phase inversion in the second reactor, and completing the polymerization of the effluent from the preliminary polymerization in a plug flow type reactor in Japan Tokkyo Kokai Koho No. 63-118,315 (1988) and proposed to bring the rubber particle diameter and the occluded polystyrene content in an optimal range by controlling the solid content in the aforesaid first reactor at a relatively high level, the solid content in the second reactor at a relatively low level, and the difference of the two solid contents in a specified range.
A process for polymerization is also proposed in Japan Tokkyo Kokai Koho No. 63-118,346 (1988) which measures the viscosity of the effluents from the first and second reactors and controls the ratio of the two viscosities within a minimal range, say, 2 to 3.
The polymerization according to these processes is carried out until immediately before the phase inversion in the first reactor, at a conversion kept as low as possible in the second reactor, and until completion in the following reactor and this mode of operation has proved itself capable of yielding products with a high occluded polystyrene content and markedly improved mechanical strength.
The problem confronting the adoption of a process such as above is, as pointed out in the past, that the rubber particles diminish in diameter after the phase inversion. This phenomenon is more pronounced when a peroxide is added as polymerization initiator for the purpose of increasing the amount of polystyrene captured in rubber during the initial phase of the reaction. The likely explanation is that more graft polymers form between rubber particles and styrene polymers on addition of a peroxide to increase the content of styrene polymers occluded in rubber particles, but the graft polymers thus formed act as surfactant between the rubber particles and the styrene polymer continuous phase to produce a finer dispersion of rubber particles and an excessive reduction in particle diameter.
A process developed as a solution to this problem is based either on decreasing the addition of a polymerization initiator at the start of polymerization to such a level as to allow control of the rubber particle diameter in the range from 1.5 to 4 .mu.m or on carrying out the polymerization in the complete absence of an initiator. Such a process surely reduces the formation of graft polymers and helps to increase the rubber particle diameter, but it does not increase the content of styrene polymers occluded in the rubber particles, a property
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patent: 4098847 (1978-07-01), Stevenson et al.
patent: 4221883 (1980-09-01), Mott et al.
patent: 4640959 (1987-02-01), Alle
patent: 4876312 (1989-10-01), Meister et al.
Fujita Masanari
Hayakawa Akifumi
Sakamaki Yoshitaka
Shibata Hiroyuki
Kight III John
Nippon Steel Chemical Co. Ltd.
Sergent Rabon
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