JPS6152861B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a thermoplastic resin composition having water-absorbing and swelling properties and comprising a thermoplastic resin such as an olefin resin or a styrene resin and a saponified starch-acrylonitrile copolymer. .

Currently, natural rubber, synthetic rubber, and partly vinyl chloride resin are used as packing materials for the joints of humid pipes used in sewerage systems and the like. However, these packing materials tend to sag easily, and not only can water leak from the joints due to sagging, but groundwater and rainwater can also seep in, increasing the amount of water to be treated at water treatment plants and exceeding their processing capacity. This often happened. In addition, various thermoplastic resins are used as joint materials and fitting members in architectural structures, but if left for a long time, they often shrink and deform over time, and in some cases, There was a disadvantage that it had to be replaced.

The inventors of the present invention have been intensively studying methods that do not have the above-mentioned drawbacks, such as preventing water from leaking from sewerage pipes, and preventing underground water from flowing back into the pipes. It has been found that using a saponified acrylonitrile copolymer film expands upon contact with water and has the effect of making the joint tighter. Water oozes out, and the packing effect is not sufficient.Also, a special method must be used to form the film by dissolving the raw materials in a solvent and then casting them.Furthermore, starch-acrylonitrile copolymer The drawback of using only a compound was that the strength was weak and the durability was poor.

The present inventors further discovered that thermoplastic resin and starch-
It was discovered that when a composition obtained by heating and kneading a saponified acrylonitrile copolymer is molded into various shapes using a normal thermoplastic resin molding method, and the molded product comes into contact with water for a long period of time, it absorbs water and expands. The composition was found to be strong and durable without losing the properties of a thermoplastic resin. Then, when the composition was used as a packing material, it was found that it exhibited an extremely high sealing effect, and there was no leakage of water from the humid pipe, and there was no backflow of underground water, etc., and the present invention was achieved.

Although a composition similar to the composition obtained by the method of the present invention is known from JP-A-51-75747, the present invention is based on an aqueous solution of a saponified starch-acrylonitrile copolymer. It is a homogeneous mixture of an aqueous dispersion of a polymer or copolymer with a secondary transition point of 35°C or lower, and is used by casting, coating or impregnating pulp paper, etc., and then drying it. This is different from the method for producing the composition of the present invention, which involves heating and kneading in a state substantially free of water.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for producing a thermoplastic resin composition having water absorption and expansion properties suitable for use in packing materials, joint materials, fitting members, and the like.

That is, the gist of the present invention is to dry blend 2 to 300 parts by weight of a saponified starch-acrylonitrile copolymer to 100 parts by weight of a thermoplastic resin such as an olefin resin or a styrene resin in a substantially water-free state. , a method for producing a thermoplastic resin composition comprising heating and kneading.

The thermoplastic resins used in the method of the present invention include olefin resins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymers, and styrene resins such as polystyrene, styrene-butadiene copolymers, and ABS resins. Thermoplastic resins are used alone or in mixtures.

The saponified starch-acrylonitrile copolymer used in the method of the present invention is obtained by graft copolymerizing an acrylonitrile compound onto starch such as wheat starch, rice starch, or corn starch, and then subjecting the obtained graft copolymer to starch such as wheat starch, rice starch, corn starch, etc. in the presence of an alkali. It is a saponified product, and its chemical structure consists of a graft copolymer with starch as the backbone and a copolymer of acrylic acid or its alkali salt and acrylamide as branches. Therefore, an acrylonitrile compound refers not only to acrylonitrile, but also to the α-position or β-position of a double bond, such as methacrylonitrile.
It may have a substituent such as an alkyl group or an aryl group at the - position. A typical method for producing a saponified starch-acrylonitrile copolymer is, for example, by heating a 5 to 10% by weight starch aqueous solution to form a paste, cooling it, and then applying the mixture in the presence of a cerium catalyst.
A starch-acrylonitrile copolymer is produced by adding and stirring an acrylonitrile compound in a range of 0.2 to 15 moles, preferably 0.5 to 10 moles per mole of starch constituent units, and adding an alkali metal hydroxide to this. It is heated and saponified, then purified, separated, and dried. The saponified starch-acrylonitrile copolymer preferably has a molar ratio of acrylic acid or its alkali metal salt to acrylamide in the range of 1:0.1 to 10, preferably 1:0.5 to 2. used for. Of course, the saponified starch-acrylonitrile copolymer is a graft copolymer whose branches are a copolymer of a polymerizable monomer having a carboxyl group or an alkali metal salt thereof and a polymerizable monomer having an acid amide group. If so, the manufacturing method is not particularly limited.

The method of the present invention consists in dry blending a saponified starch-acrylonitrile copolymer as described above with a thermoplastic resin in a substantially water-free state, and then heating and kneading the mixture. The blending ratio of the thermoplastic resin and the saponified starch-acrylonitrile copolymer varies depending on the type of thermoplastic resin used or the use of the resulting composition.
Generally, 2 to 300 parts by weight, preferably 10 to 200 parts by weight, of saponified starch-acrylonitrile copolymer are added to each part by weight, and polyethylene,
It is desirable to add a large amount to resins that are particularly incompatible with water, such as polypropylene. If the amount of the saponified starch-acrylonitrile copolymer added is less than 2 parts by weight, the resulting composition will have low water absorption swelling properties, and if it exceeds 300 parts by weight, the properties of a thermoplastic resin will generally be lost. come. In addition to the saponified acrylonitrile copolymer, various additives commonly added to thermoplastic resins and starch-thermoplastic resins can be mixed in the method of the present invention. For example, plasticizers such as phthalate esters, fatty acid esters, and waxes that give flexibility to thermoplastic resins, various metal-containing heat stabilizers, epoxy stabilizers, antioxidants, lubricants, inorganic or organic fillers, dyes and pigments, etc. May be used together.

The thermoplastic resin composition is produced by adding a thermoplastic resin powder, a saponified starch-acrylonitrile copolymer powder, and optionally other additives to a Henschel mixer or a ribbon blender in a substantially water-free state. , a Banbury mixer or the like, and then uniformly kneaded while heating with an extruder or a kneader such as a roll mill. usually,
The kneaded composition is often used for various purposes after being pelletized.

In the thermoplastic resin composition obtained by the method of the present invention, a powder of a saponified starch-acrylonitrile copolymer is uniformly dispersed in a thermoplastic resin and is coated with the resin.

In the method of the present invention, "substantially water-free" means that the thermoplastic resin and saponified starch-acrylonitrile copolymer can be dry blended in granular or powder form without forcing the addition of water. .

The thermoplastic resin composition obtained by the method of the present invention can be used as a raw material for building parts such as joint materials for panel joints, fitting members for ventilation holes, etc., and as a raw material for packing materials for fume pipes, etc. These building parts and packing materials are generally used by molding the composition by a thermoplastic resin molding method, such as injection molding, extrusion molding, press molding, calendering, or the like. The molding temperature is preferably 230°C, particularly 200°C or lower; if it is too high, the saponified starch-acrylonitrile copolymer will decompose. For example, the joint material is formed into a long length by profile extrusion molding and cut to a desired length, and the fitting member is formed by molding the composition into a desired shape by injection molding. In addition, the packing material can be formed into a desired shape directly by injection molding, or by producing a sheet with a desired thickness by extrusion molding, calendar processing, or press molding, and then forming the packing material into the shape of the sheet. punch out or cut out.

According to the method of the present invention, a saponified starch-acrylonitrile copolymer can be kneaded into a large amount of a thermoplastic resin like a general filler, and the resulting composition is a saponified starch-acrylonitrile copolymer. powder is uniformly dispersed in the thermoplastic resin. Even though the composition is mostly coated with thermoplastic resin, if it is immersed in water or left in the air for a long period of time, it absorbs water or moisture in the air and becomes large. It expands and the properties of the thermoplastic resin used are not significantly impaired. Moreover, a composition that expands by absorbing water over time does not undergo volumetric contraction even if left for a long period of time. Usually methylcellulose, gelatin, polyvinyl alcohol,
When a water-absorbing substance such as casein is mixed with a thermoplastic resin and immersed in water, the body expands slightly at the initial stage, but when immersed for a long period of time, the volume shrinks. Therefore, the thermoplastic resin composition produced by the method of the present invention can be used as a packing material,
It has extremely high utility value as a joint material, etc.

Next, the composition obtained by the method of the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples unless it departs from the gist thereof.

Example 1 150 parts by weight of a saponified starch-acrylonitrile copolymer (monomer: acrylonitrile) was added to 100 parts by weight of low-density polyethylene having a melt index of 0.25 and a density of 0.919, and the mixture was uniformly blended using a Henschel mixer. Roll surface temperature
The composition was heated and kneaded for 7 minutes using a mixing roll at 130° C., and this was made into a 0.7 mm thick sheet and taken out. The sheets were laminated and pressed using a press molding machine at a temperature of 150° C. and a press pressure of 50 kg/cm ² for 5 minutes to produce a sheet with a thickness of 2 mm, which was used as a test piece.

When the test piece was immersed in water (tap water) at 20°C for a predetermined number of days, it expanded three-dimensionally. This water absorption swelling property is expressed as a linear expansion coefficient and is shown in FIG.

FIG. 1 is a graph showing swelling properties that change over time, with the horizontal axis showing the number of days of immersion and the vertical axis showing the linear expansion rate (%).

As is clear from Curve 1, the composition obtained by the method of the present invention exhibits a linear expansion rate of 25% after a immersion period of 2 days, and a linear expansion rate of as much as 40% after about 16 days. No subsequent volumetric contraction is observed.

Example 2, Comparative Examples 1 to 4 100 parts by weight of styrene-butadiene copolymer, 200 parts by weight of starch-acrylonitrile copolymer (monomer: acrylonitrile), carbon black
After adding 40 parts by weight, 5 parts by weight of zinc white, 1 part by weight of stearic acid, 1 part by weight of anti-aging agent, 1.5 parts by weight of sulfur and 1.8 parts by weight of vulcanization accelerator, the mixture was uniformly dry blended, and then mixed into two rolls. The mixture was heated and kneaded to obtain a composition. This composition was press molded under pressure and heat to produce a test piece with a wall thickness of 2 mm.

The water absorption expansion property of this test piece was measured in the same manner as in Example 1, and the relationship between the number of days of immersion in water and the coefficient of linear expansion is shown as curve 2 in FIG.

For comparison, in Example 2, starch-
The test was conducted in the same manner as in Example 2, except that the acrylonitrile copolymer was replaced with methylcellulose (Comparative Example 1), gelatin (Comparative Example 2), polyvinyl alcohol (Comparative Example 3), and casein (Comparative Example 4). A piece was manufactured, and the relationship between the number of immersion days and the coefficient of linear expansion was calculated as curves 3, 4, 5, and 6, respectively.
Also shown in the figure.

As is clear from FIG. 2, the composition obtained by the method of the present invention becomes twice as thick in 15 days.
Thereafter, no volumetric shrinkage was observed, but although the comparative examples exhibited some water absorption swelling properties, volumetric shrinkage occurred when immersed in water for a long period of time.

[Brief explanation of the drawing]

FIGS. 1 and 2 are graphs showing changes over time in the water absorption expansion coefficient of the thermoplastic resin composition obtained by the method of the present invention, where the horizontal axis represents the number of days immersed in water;
The vertical axis shows the linear expansion rate.

Claims (1)

[Claims] 1 Olefin resin or styrene resin 100
1. A method for producing a thermoplastic resin composition, which comprises dry blending 2 to 300 parts by weight of a saponified starch-acrylonitrile copolymer in a substantially water-free state, followed by heating and kneading.