1. Field of the Invention
This invention relates to a novel polymer composition.
More particularly, it relates to a polymer composition comprising a block copolymer containing a polyvinyl alcohol polymer unit as one constituent and a polymer unit having an ionic group as another constituent, and protein.
It is, among others, concerned with a polymer composition comprising a block copolymer containing a polyvinyl alcohol polymer unit as one constituent and a polymer unit having an ionic group as another constituent, and gelatin as protein, and which improves the drawbacks of a gelatin film, such as brittleness and stickiness resulting from the absorption of moisture.
2. Description of the Prior Art
A polyvinyl alcohol (PVA) is a water-soluble polymer which is particularly excellent as protective colloid and particularly excellent in film strength and used widely in a variety of fields of application. It is used not only alone, but also together with another water-soluble or -dispersible polymer, for example, starches, cellulose derivatives such as hydroxyethyl cellulose, proteins such as gelatin and casein, or latexes such as SBR. Therefore, the compatibility of PVA with any such water-soluble or -dispersible polymer is one of the very important factors which enables PVA to exhibit its excellent properties fully when used with such other polymers.
It is, however, usual that there is only a poor degree of compatibility between different kinds of polymers. PVA does not have good compatibility with any such water-soluble or -dispersible polymer, particularly proteins such as gelatin or casein, though a lot of attempts have been made to improve their compatibility. The gelatins are used for a wide variety of industrial applications and applications relating to food and medicines, including the preparation of a photographic emulsion and the manufacture of microcapsules, owing to its excellent reversibility from gel to sol and vice versa, depending on temperature, and its properties as a protective colloid, as is well known. There are a great number of reports on the results of studies concerning the gelatins and the improvement of their quality, particularly those relating to gelatins for photographic application.
The gelatins are, however, electrolytes and a gelatin film has the drawbacks which the films of other electrolytic polymers possess. It is brittle and low in strength. Moreover, it is highly sensitive to moisture and becomes sticky in an environment of high humidity. There has, thus, been a strong desire toward the elimination of these drawbacks.
Various attempts have been made to improve the strength of gelatins by blending water-soluble polymers, but have failed to produce any satisfactory results. The gelatins are generally poorly compatible with those polymers and it is often the case that the mixtures are even inferior in strength to the gelatins per se. PVA is known as a water-soluble polymer which forms a particularly strong film, but it is so poorly compatible with the gelatins that its mixture with the gelatins fails to improve their strength. While the production of a strong film from a mixture of gelatin and a water-soluble polymer essentially calls for their good mutual compatibility, there are still very few water-soluble polymers that are satisfactorily compatible with gelatins.
Japanese Laid-Open Patent Specification No. 133543/1979 discloses a water-soluble polymer composition which comprises PVA containing a phosphoric acid group and a water-soluble protein. This composition appears to have somewhat improved compatibility, but the compatibility of this composition is still unsatisfactory.
Japanese Patent Publication No. 19046/1971 discloses a PVA derivative of the formula; ##STR1## which can be used with gelatin to form a photographic emulsion. This derivative is also unsatisfactory from the standpoint of compatibility.