Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1998-07-10
2002-06-04
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C252S391000, C427S212000, C427S241000, C428S407000
Reexamination Certificate
active
06399201
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Filed of the Invention
The present relates to a blowing agent powder and a process for producing the same.
2. Discussion of the Background
Blowing agents have conventionally been used in the form of a fine powder, and have posed a problem of dusting in the working atmosphere.
As a means for eliminating the above problem, a technique has been proposed in which a blowing agent powder is mixed with a wax under heating using a mixer having shearing blades, mixing blades, or the like, and the resultant mixture is granulated (see Japanese Published Unexamined Patent Application No. 90543/77). However, the granulated blowing agent obtained by the above technique has poor homogeneity and poor dispersibility into resins. It is therefore difficult to use the granulated blowing agent to obtain a finely and evenly foamed object, and therefore, the granulated blowing agent is hence unsatisfactory for practical use.
Furthermore, such conventional blowing agents have a problem that they agglomerate and are solidified with the lapse of time or under load to thereby show impaired flowability in the step of addition to resins to cause hopper clogging, or to thereby have impaired dispersibility into resins. Mitigation of this solidification is desired more and more with the recent trend toward quality improvement in foamed resins and labor saving in the production thereof.
On the other hand, techniques which have been employed for inhibiting the solidification of blowing agents include (1) technique of adding inorganic powder particles, e.g., silica, metal silicate or the like, as a solidification inhibitor to a blowing agent, (2) technique of batchwise drying a blowing agent for a sufficient period to thereby diminish the water contained therein in a slight amount, and the like.
However, use of these techniques has various drawbacks. Namely, technique (1), although effective in solidification prevention in some degree, cannot impart the effect which lasts beyond several months. For application to a blowing agent comprising finer particles, inorganic powder particles should be added in a larger amount. However, the addition of a larger amount of the inorganic powder particles is causative of cell enlargement during foaming, and is hence undesirable in applications where fine cells are required. Technique (2), on the other hand, has significantly reduced productivity because the drying requires much time, resulting in an increased production cost. In addition, technique (2) cannot cope with continuous production.
Japanese Published Unexamined Patent Application No. 320432/92 discloses a method of adding a silane coupling agent dissolved in a solvent to azodicarbonamide to thereby improve flow ability and dispersibility into resins. Furthermore, Japanese Published Unexamined Patent Application No. 295872/96 discloses a method of adding an aluminum coupling agent dissolved in a solvent to a chemically blowing agent to thereby improve flowability and dispersibility into resins. However, these techniques each is in sufficient in the effect of solidification prevention and ineffective in eliminating the problem of dusting.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a modified blowing agent powder which is inhibited from causing dusting in the working atmosphere during each of packaging, transportation, storage, use, and the like, and is inhibited from aggregation and solidification with the lapse of time or under load, is homogeneous, and has satisfactory dispersibility into resins.
Another object of the present invention is to provide a process for producing the blowing agent powder.
These and other objects of the present invention have been attained by a powder comprising a blowing agent powder core which is coated with at least one oil-like substance on its surface.
Furthermore, these and other objects of the present invention have been attained by a process for producing a powder comprising a blowing agent powder core which is coated with at least one oil-like substance on its surface, comprising the following steps (a) and (b):
(a) adding at least one oil-like substance in the form of a mist to a blowing agent powder; and
(b) mixing the oil-like substance with the blowing agent powder under such mixing conditions that the blowing agent powder is less susceptible to pulverization.
DETAILED DESCRIPTION OF THE INVENTION
The present inventors made intensive studies in order to resolve the above problems. As a result, the inventors have found that a blowing agent powder having the desired properties is obtained by adding an oil-like substance in the form of a mist to a blowing agent powder and mixing the oil-like substance with the blowing agent powder under such mixing conditions that the blowing agent powder is less susceptible to pulverization. As a result, dusting in the working atmosphere is inhibited during each of packaging, transportation, storage, use, and the like, and a blowing agent powder which is homogeneous and has satisfactory dispersibility into resins is provided.
Furthermore, the present inventors assumed that the solidification of a blowing agent powder proceeds because a slight amount of water, specifically the water contained in a slight amount in the blowing agent particles and the water absorbed by the blowing agent particles from the atmosphere during production, transportation, and storage, serves to bond the blowing agent particles to one another on their surfaces. Further investigations were made based on this assumption. As a result, the present inventors have found that a blowing agent powder significantly inhibited from solidification and satisfactory in flowability, dispersibility into resins, and the like, even after the lapse of a prolonged period of time is obtained by reacting the water contained in blowing agent particles with a surface-treating agent capable of removing water from the blowing agent, such as a coupling agent, and preferably form a film of the surface-treating agent on the surface of the blowing agent particles. As a result, solidification of the blowing agent powder is markedly inhibited, and a blowing agent powder which is homogeneous and has satisfactory dispersibility into resins is provided.
The blowing agent powder which can be used in the present invention is selected from conventionally known blowing agents. Examples include blowing agents, for example, azodicarbonamide (ADCA), hydrazodicarbonamide (HDCA), p,p′-oxybis(benzenesulfonyl hydrazide) (OBSH), dinitropentamethylenetetramine (DPT), p-toluenesulfonyl hydrazide (TSH), benzenesulfonyl hydrazide (BSH), 5-phenyltetrazole (5-PT), and the like, and salts of these with an alkaline earth metal (e.g., calcium, barium, or strontium) or with aluminum, and the like; and inorganic blowing agents, for example, sodium hydrogen carbonate, anhydrous monosodium citrate, and the like. Among these, preferred are ADCA, OBSH, DPT, TSH, BSH, 5-PT, and the like; and salts of these with calcium, barium, strontium, aluminum, and the like. Especially preferred is ADCA.
In the present, invention, these blowing agent powders are used alone or as a mixture of two or more thereof.
Although the particle diameter of the blowing agent powder is not particularly limited in the present invention, the process of the present invention is generally applicable to blowing agent powders having a particle diameter of about 1 to 100 &mgr;m, which often pose the problem of dusting. The particle diameter of the blowing agent powder is preferably about 2 to 50 &mgr;m, more preferably about 3 to 30 &mgr;m, and most preferably about 3 to 20 &mgr;m. The term “particle diameter” as used herein for a blowing agent powder means the median size thereof determined with a laser diffraction type particle size distribution analyzer.
The blowing agent powder for use in the present invention may contain one or more other ingredients known in this field, such as a stabilizer, a pigment/filler, a blowing inhibitor, and the like. A blowing agent powder containing these ingredien
Maekawa Tsukasa
Shono Sadafumi
Sumitomo Shigeru
Tachi Yoshifumi
Takao Toshinori
Le Hoa T.
Otsuka Chemical Co. Ltd.
Whitham Curtis & Christofferson, PC
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