Modifier for methacrylic resin

Details Modifier for methacrylic resin Modifier for methacrylic resin

2000-09-12

2003-02-25

Mullis, Jeffrey (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S078000, C525S080000, C525S083000, C525S085000, C525S228000

Reexamination Certificate

active

06525135

ABSTRACT:

TECHNICAL FIELD
This invention relates to a modifier for high transparency, which can stably provide high transparency under wide ranges of processing conditions in injection molding, particularly when it is used by blending in methacrylic resins.
BACKGROUND ART
Because of their high transparency and excellent weather resistance, methacrylic resins are frequently used in various fields such as lightening apparatuses and outdoor products.
However, it is well known that the transparency of thermoplastic resins which are characterized by their transparency, particularly methacrylic resins, changes within considerable ranges depending on their processing conditions such as injection molding conditions. In addition, in view of the insufficient strength, addition of various impact resistance modifiers has been attempted for the purpose of improving their strength. For example, techniques that relate to the modification of their impact resistance are disclosed in JP-B-55-27576 (the term “JP-B” as used herein means an “examined Japanese patent publication”) and JP-A-62-230841 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). In that case, transparency of methacrylic resins is an essential condition to be maintained but is not sufficient condition from the practical point of view. It is therefore desirable to obtain moldings which can show high transparency and high quality stably under wide ranges of processing conditions.
However, when such resins are processed using the techniques so far disclosed, the just described requirement for obtaining moldings which can show high transparency and high quality stably under wide ranges of processing conditions cannot fully be satisfied. That is, moldings having high transparency can be obtained only within the range of narrow processing conditions, and the appearance of moldings becomes poor at the time of processing due to, for example, the aggregation of impact resistance modifiers. For example, when the molding temperature is increased with the aim of obtaining high transparency, thermal deterioration is apt to occur and burned marks are formed by only slight changes in the processing steps of the resin. On the other hand, when the injection molding temperature is set to a low level, the transparency is greatly spoiled. In other words, not only to simply ensure qualities of high transparency and high strength but also to obtain high transparency, high quality moldings stably within wide ranges of molding (processing conditions) are required as important factors in carrying out injection molding of methacrylic resins.
Though not related to the transparency as intended by the present invention, some attempts have been made to ensure moldings having stable high quality physical properties. For example, JP-B-1-29218 discloses a method in which the balance of strength and fluidity is improved by increasing fluidity using a methacrylic resin having a broad molecular weight distribution, and JP-B-2-2358 discloses a technique which uses a condition that an impact resistance modifier and a dispersing agent are blended in a latex form in order to avoid aggregation of the impact resistance modifier, as a means for reducing so-called fish eye at the time of extrusion molding.
However, these methods are different from the inventive idea of the present invention to narrow fluctuation range of transparency in injection molding under wide ranges of processing conditions.
In view of the above, it is an object of the present invention to provide a modifier which can modify impact resistance and provide high transparency products stably under broad processing conditions in injection molding, when it is used in methacrylic resins of which characteristic is transparency.
DISCLOSURE OF THE INVENTION
With the aim of developing a modifier which can add impact resistance-modifying effect to methacrylic resins without spoiling their transparency and also can keep the transparency of the object resin at a high level under wide ranges of molding conditions, the inventors of the present invention have conducted extensive studies and found that the aforementioned problems can be solved when an impact resistance modifier and a small amount of a polymer processability modifier are used in combination, thus resulting in accomplishment of the present invention.
Accordingly, the present invention relates to
(1) a methacrylic resin modifier, which comprises a blend of an impact resistance modifier and a polymer processability modifier that has a specific viscosity of from 2.5 to 5.0 when measured at a concentration of 0.4% by weight and at a temperature of 30° C. using toluene as the solvent, wherein weight ratio of the impact resistance modifier and polymer processability modifier is from 95/5 to 80/20,
(2) the methacrylic resin modifier according to (1) above, wherein the impact resistance modifier is obtained by polymerizing monomer components comprising from 70 to 100% by weight (to be referred simply to as “%” hereinafter) of a (meth)acrylic ester, from 0 to 30% of an aromatic vinyl monomer and from 0 to 30% of other copolymerizable monomer (100% in total), in the presence of an acrylic rubber and/or a conjugated diene rubber, and
(3) the methacrylic resin modifier according to (1) or (2) above, wherein the polymer processability modifier is a polymer comprising from 50 to 70% of methyl methacrylate, from 1 to 50% of a (meth)acrylic acid alkyl ester, wherein the number of carbon atoms of the alkyl group is from 2 to 8, and from 0 to 30% of other copolymerizable monomer (100% in total).
BEST MODE FOR CARRYING OUT THE INVENTION
The methacrylic resin modifier of the present invention is a modifier which comprises a blend of an impact resistance modifier and a particular polymer processability modifier and can be used in most of the commercially available methacrylic resins without particular limitation.
The aforementioned methacrylic resin is not particularly limited, but it may contain preferably 50% or more, more preferably 70% or more, of a methacrylic ester. Also, as the methacrylic ester, methyl methacrylate is desirable, so that a resin containing preferably 50% or more, more preferably 70% or more, of methyl methacrylate is more desirable.
The ratio of said impact resistance modifier and polymer processability modifier in the aforementioned methacrylic resin modifier, namely (impact resistance modifier)/(polymer processability modifier), is from 95/5 to 80/20, preferably from 95/5 to 90/10, as weight ratio. The ratio of the polymer processability modifier if too small would bear no sufficient effect to improve the aforementioned problems and if too large would produce no greater effect in spite of the high amount of the methacrylic resin modifier but rather reduce the impact resistance-improving effect and cause a tendency to reduce transparency of the methacrylic resin. It is considered that the reduction of transparency occurs due to relatively high molecular weight of the polymer processability modifier, which reduces its compatibility with the corresponding methacrylic resin.
The aforementioned impact resistance modifier is used for improving impact resistance and strength of the base material methacrylic resin, and any modifier conventionally used for methacrylic resins can be used without particular limitation.
A preferred example of the modifier conventionally used for methacrylic resins is an impact resistance modifier (I) which is obtained by polymerizing monomer components (to be referred also to as “monomer (M)” hereinafter) comprising from 70 to 100%, preferably from 80 to 100%, of a (meth)acrylic ester, from 0 to 30%, preferably from 0 to 20%, of an aromatic vinyl monomer and from 0 to 30%, preferably from 0 to 15%, of other copolymerizable monomer (100% by weight in total), in the presence of an acrylic rubber and/or a conjugated diene rubber (to be referred also to as “rubber component (R)” hereinafter).
The term “a (meth)acrylic ester” means an acrylic ester, a methacrylic ester, or a mixture thereof.
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