Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-07-14
2001-11-06
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06313204
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for recrystallizing a diacetal, in particular, a method for recrystallizing a diacetal such as a sorbitol diacetal in a resin composition.
The present invention further relates to a resin molded product containing a diacetal recrystallized by said method.
PRIOR ART
Diacetals such as sorbitol acetal compounds have been known to act as excellent nucleating agents for polyolefin resins, thereby contributing to the improvement in the rigidity, transparency and gloss of the resulting polyolefin resin molded articles, and to the improvement in the efficiency of the molding process.
However, diacetals usually decompose or disproportionate into monoacetal and triacetal when mixed with molten polyolefin resins having a high temperature, resulting in impaired product quality such as yellowish tint given to the molded articles, and also produce odor or staining, thereby posing problems of deteriorating working environment.
Consequently, attempts have been made to solve these drawbacks. For example, a method is a known (Japanese Unexamined Patent Publication No. 120788/1988) which comprises the steps of dissolving a diacetal compound, such as a condensation product of an aromatic aldehyde and a polyhydric alcohol having five or more hydroxyl groups, in a solvent such as dioxane, benzene, xylene, etc; cooling the solution to form a gel; and freeze-drying the obtained gel to give a freeze-dried diacetal having a particular microstructure.
The above method, however, have the shortcomings, for example, of necessitating the use of expensive solvents, large-scale freezer and a special high-vacuum apparatus for freeze-drying, and being not highly productive because only a batchwise production is usually feasible.
DISCLOSURE OF THE INVENTION
The inventors of the present invention carried out extensive research in an attempt to produce diacetal which is free from the above drawbacks. In the course of the research, the inventors of the present invention took a different approach in carrying out further research on the assumption that recrystallization of the above diacetal directly in a polyolefin resin could solve the above drawbacks of the diacetal as a nucleating agent to thereby improve its nucleating effect.
Specifically, the inventors of the present invention considered that the technique of recrystallizing the diacetal directly in a molten polyolefin resin would be an effective technique, if the technique could make it possible to eliminate the necessity of pretreatment such as purification of diacetal, to establish the optimal conditions under which the diacetal best functions as a nucleating agent, and to find manners of preventing diacetal decomposition and resin discoloration, etc.
The research of the inventors, however, revealed that the method of recrystallizing diacetal in a resin is not practically feasible for the following reasons: the diacetal may decompose and emit an odor; the diacetal may undergo disproportionation into monoacetal and triacetal, which lessens the purity of the diacetal; the resin may become tinted yellow, leading to uneven transparency of the molded resins.
In order to prevent the yellowish discoloration of the resins, it may be possible to add a special phosphoric acid-based cooperative stabilizers or to mask the yellowish discoloration by a light scattering of blue colour induced by adding a small amount of a pigment. This method, however, requires expensive cooperative stabilizers or complicated operation, and therefore remains to be improved as an industrial technique.
Therefore, an object of the present invention is to propose a method for recrystallizing diacetal-based nucleating agent composition in a molten polyolefin, wherein decomposition and disproportionation of diacetal and yellowish discoloration of resins are suppressed as much as possible, and wherein the effect of modifying polyolefin resins is produced in an inexpensive manner and to the greatest degree.
The inventors of the present invention carried out extensive research to achieve the above object, and surprisingly discovered that the desired effects can be achieved by recrystallizing, under specific conditions in a molten polyolefin resin, a diacetal nucleating agent composition which satisfies a plurality of specific requirements. The present invention has been accomplished based on this finding.
The present invention provides a method for recrystallizing diacetal represented by the formula (1)
wherein R
1
and R
2
are the same or different and each represent a hydrogen atom, a C
1
-C
4
alkyl group, a C
1
-C
4
alkoxy group or a halogen atom; a and b each represent an integer of 1 to 5, preferably 1 to 3; c is 0 or 1; when a is 2, the two R
1
groups may optionally be taken together with the benzene ring to which they are attached to form a tetralin ring; and when b is 2, the two R
2
groups may optionally be taken together with the benzene ring to which they are attached to form a tetralin ring in a polyolefin resin without giving a yellowish tint to the polyolefin resin, the method comprising the steps of:
(i) heating and melting a resin composition comprising (a) a polyolefin resin and (b) a nucleating agent composition comprising at least one diacetal of the above formula (1), at a temperature not lower than the sol-gel transition temperature during the heating cycle of the resin composition, to give a molten resin composition wherein said nucleating agent composition is uniformly dissolved in the molten polyolefin resin; and
(ii) cooling the resulting molten resin composition,
wherein the above nucleating agent composition satisfies all of the following four requirements (A)-(D) simultaneously:
(A) the above nucleating agent composition contains 10 to 5000 ppm of at least one alkaline compound selected from the group consisting of alkali metal salts, alkali metal hydroxides, alkaline earth metal salts and alkaline earth metal hydroxides, and/or 1000-80000 ppm of an organic amine;
(B) the total amount of
(B-1) an aromatic aldehyde represented by the formula (2)
wherein R
3
represents a hydrogen atom, a C
1
-C
4
alkyl group, a C
1
-C
4
alkoxy group or a halogen atom; d is an integer of 1 to 5, preferably 1 to 3; when d is 2, the two R
3
groups may optionally be taken together with the benzene ring to which they are attached to form a tetralin ring; and
(B-2) a dialkyl acetal represented by the formula (3)
wherein R
4
represents a hydrogen atom, a C
1
-C
4
alkyl group, a C
1
-C
4
alkoxy group or a halogen atom; R
5
is a C
1
-C
3
alkyl group; e is an integer of 1 to 5, preferably 1 to 3; when e is 2, the two R
4
groups may optionally be taken together with the benzene ring to which they are attached to form a tetralin ring, in the nucleating composition is not higher than 400 ppm;
(C) the water content of said nucleating agent composition is not higher than 1 wt. %; and
(D) said resin composition contains said at least one diacetal represented by the formula (1) at a concentration of 0.01-4 wt. % based on the total amount of said polyolefin resin and said diacetal.
In the present invention, it is further preferred that (E) the proportion of position isomers of the diacetal represented by the formula (1) in the above nucleating agent composition is not higher than 0.7 wt. %
In the present invention, it is also preferred that the step of cooling said molten resin composition in the present invention is carried out by rapidly cooling the molten resin composition having a temperature not lower than the sol-gel transition temperature of the resin composition, to 10-80° C., particularly 20-80° C.
The present invention will be described below in detail.
Polyolefin Resin
Useful polyolefin resins in the present invention are crystalline resins having a crystallinity of 50-100%, preferably 15-95%. Specific examples thereof are polyethylene-based resins, stereoregular polypropylene-based resins, and stereoregular polybutene-based resins.
Examples of the polyethylene-based resins are high-density polyethylene, medi
Larson & Taylor PLC
Michl Paul R.
New Japan Chemical Co. Ltd.
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