JPS63110226A - Production of water-absorptive resin material - Google Patents

Abstract

PURPOSE:To obtain the titled resin material outstanding in water absorption rate, water absorptivity and resin retentivity after water absorption, by melting and kneading a carboxylate-contg. water absorptive resin and glycidyl group- contg. polyolefin followed by extrusion forming and expansion. CONSTITUTION:First, a composite composition is prepared by melting and kneading (A) 5-95wt% of a carboxylate-contg. water absorptive resin (pref. a crosslinked sodium polyacrylate) and (B) 95-5wt% of a glycidyl group-contg. polyolefin at temperatures higher than the melting point of the component B, pref. at 130-250 deg.C. Thence, this composition is subjected to extrusion forming and expansion, thus obtaining the objective resin material.

Description

DETAILED DESCRIPTION OF THE INVENTION 0) Industrial Application Field The present invention relates to a method for producing a water-absorbing resin material, and more specifically, it relates to a method for producing a water-absorbing resin material, and more specifically, it relates to a method for producing a water-absorbing resin material, and more specifically, a water-absorbing resin material having a high water absorption rate and excellent retention of the water-absorbing resin after water absorption. Water-absorbing film, sheet,
The present invention relates to a method for producing water-absorbing resin materials such as UL and male-shaped water-absorbing resin materials.

←) Conventional technology Currently, water-absorbing resins are used as absorbents for sanitary materials such as disposable diapers and sanitary products, water retention agents for LK gardening, and other industrial materials. A starch crosslinked product, a vinyl alcohol/acrylic acid alkali metal salt copolymer crosslinked product, a vinyl alcohol/maleic anhydride copolymer crosslinked product, etc. are used. All of these resins are crosslinked in order to maintain their shape after water absorption, and are in powder form.

Furthermore, in recent years, the applications of water-absorbing resins have been expanding steadily, and the forms of use are not only powder, but also films,
There is a strong demand for water absorbent resins in the form of sheets, fibers, etc.

However, since current water-absorbing resins are crosslinked, they lack thermoplasticity, making it extremely difficult to process them into films, sheets, fibers, and the like.

On the other hand, when mixing polyolefins such as polyethylene and polypropylene with water-absorbing resins in order to impart moldability to films, fibers, etc. to current water-absorbing resins, it is difficult to obtain a homogeneous mixture due to poor compatibility between the two. In addition, there are problems in that the water absorption rate and water absorbency are significantly reduced, and the water-absorbing resin is significantly desorbed after water absorption. Although the problem of non-uniform mixing is solved when a polar group-containing polyolefin and a water-absorbing resin are mixed together, other problems remain.

On the other hand, it was reported in Japanese Patent Publication No. 61-37095 that the water absorption rate could be improved instantly by foaming the mixture.
Although an excerpt is known from the publication No. 1, it has not been able to solve the remaining problems mentioned above.

(-) Problems to be Solved by the Invention The present inventors have discovered that a composite composition obtained by melt-kneading a carboxylate-containing water-absorbing resin and a glycidyl group-containing polyolefin at a temperature higher than the melting point of the latter can be molded and processed. The present invention has been developed based on the discovery that it is useful as a material that not only has high water absorption properties but also has excellent retention properties without desorption of water-absorbing resin after water absorption. An object of the present invention is to provide a method for producing water-absorbing resin materials in the form of films, sheets, fibers, etc., which have a high water absorption rate, excellent retention of water-absorbing resin after water absorption, and high water absorption properties. shall be.

B) Means for Solving the Problems The method for producing a water-absorbing resin material of the present invention involves mixing 5 to 95% by weight of a carboxylate-containing water-absorbing resin and 95 to 5% by weight of a glycidyl group-containing polyolefin at a temperature higher than the melting point of the latter. It is characterized in that it is melt-kneaded at a temperature of 100 to form a composite composition, and the composite composition is extruded and foamed.

The carboxylate-containing water absorbent resin in the present invention is
It is defined as follows.

First, "carboxylate" is a neutralized salt of a carboxyl group, and is represented by the general formula -〇〇〇M. This M is -
valent alkali metals (Na, etc.) or ammonium (
NH4). The reaction rate between the carboxyl group of the water-absorbing resin and the alkali metal can be changed depending on the water-absorbing ability, and is generally 40 to 100%.

Considering various possible uses, this carboxylate-containing water-absorbing resin preferably has a water absorption rate of about 30 to 2000 times.

Typical methods for producing the carboxylate-containing water-absorbing resin in the present invention include JP-A-58-42602, JP-A-58-71907, JP-A-59-62665, and JP-A-JP-A-Sho 61-61.
It is shown in JP157513 and the like.

Specific examples of carboxylate-containing water absorbent resins suitable for use in the present invention are alkali metal salts of crosslinked polyacrylates, such as, for example, sodium, potassium, and lithium crosslinked polyacrylates. It is desirable that these are crosslinked.

Crosslinked structures can be introduced by copolymerizing divinyl-resacrylic compounds, especially those that are water-soluble, such as N,N'-methylene bis-acrylamide, ethylene glycol bis-acrylate, and others.

The water-absorbing resin suitable for use in the present invention has a particle size of 40 microns or less, particularly preferably 1 to 10 microns. If the particle size is larger than 40 microns, stable productivity will be lacking, especially when extruding the composition into a film.

The glycidyl group-containing polyolefin in the present invention is defined as follows.

First, this may be either a main chain copolymer or a graft copolymer as long as it is a polyolefin truncation containing Grindyl groups.

The main chain copolymer includes a copolymer of an olefin, such as ethylene, and a monomer containing a glycidyl group. Specifically, ethylene-glycidyl acrylate copolymer,
Examples include ethylene-glycidyl methacrylate copolymers and ethylene-glycidyl crotonate copolymers, and generally all copolymers of olefins, such as ethylene, and vinyl group-containing epoxy compounds are included. Further, these ethylene copolymers may be copolymerized with other comonomers in order to impart properties such as flexibility. Here, other comonomers that can be used include all monomers that can be copolymerized with ethylene. For example, vinyl esters such as vinyl acetate and vinyl propionate; acrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and octyl acrylate; methacrylic esters such as methyl methacrylate and ethyl methacrylate; vinyl chloride; Examples include vinyl halides such as vinyl fluoride.

Examples of graft copolymers include grafts of glycidyl group-containing monomers onto polyethylene, polypropylene, polybutene, polymethylpentene, and the like. Specific examples of hexamers used for grafting include glycidyl acrylate, glycidyl acrylate, glycidyl crotonate, and vinylglycidyl.

The glycidyl group-containing stitch of such a glycidyl group-containing polyolefin is suitably 0.1 to 20% by weight. If the glycidyl group content is less than 0.1% by weight, the water-absorbing resin material tends to have insufficient retention of the water-absorbing resin after water absorption.On the other hand, if the glycidyl group content is less than 20% by weight If it exceeds it, it tends to gel and lose moldability.

Preferably 0.5 to 15% by weight, more preferably 1 to 10% by weight
Weight%.

Further, the glycidyl group-containing polyolefin suitable for use in the present invention has a melt flow rate of 0.01 t/
The duration is preferably 10 minutes or more, preferably 0.1 to zoor/lo minutes, and particularly preferably 1 to 502/10 minutes. If the melt flow rate is less than o, oxr/lo, the composition will have poor fluidity and will be difficult to extrude.

Further, the shape of the glycidyl group-containing polyolefin may be either powder or pellet, but powder is preferable from the viewpoint of dispersibility.

In the present invention, the blending ratio of the carboxylate-containing water-absorbing resin and the glycidyl group-containing polyolefin is 5 to 95% by weight, preferably 10 to 70% by weight of the former water-absorbing resin, and 95 to 5% by weight of the latter polyolefin. , preferably 90 to 30% by weight. If the former water-absorbing resin has a type content of less than 5%, the water-absorbing performance will be low, and the advantage of using this composition as a water-absorbing material will be lost.
If it exceeds % by weight, extrusion molding becomes difficult.

The blending ratio of both can be set as appropriate within this range depending on the intended use, but generally, for applications where water absorption performance is important, a large amount of carboxylate-containing water absorbent resin is used, while for applications where moldability is important, a large amount of water absorbent resin is used. It is preferable to increase the proportion of the glycidyl group-containing polyolefin.

The carboxylate-containing water-absorbing resin and the glycidyl group-containing polyolefin are mixed into a composite composition by melt-kneading them at a temperature higher than the melting point of the glycidyl group-containing polyolefin.

The composition of the present invention is not a simple mixture of these two components, but it is presumed that these two components have at least partially reacted due to melt mixing, and in this case, the reaction is as follows:
It is presumed that this occurs between a carboxylate group and a glycidyl group. In the present invention, the composite composition is
This is in the above sense.

The kneading machine used for this melt mixing may be a conventional kneading machine used for kneading thermoplastic resins, and specifically, for example, a two-shaft kneading machine such as a Brabender blastograph, CIM, FCM, etc. There are extruders, etc.

As a specific method for producing the composite composition, the kneading temperature is generally 120 to 280°C, and the maximum temperature varies depending on the type of glycidyl group-containing polyolefin or carboxylate-containing water-absorbing resin used.
A temperature of 30 to 250°C is suitable. If the crosstalk temperature is less than 120° C., the reaction between both components will not proceed well. On the other hand, a part of the resin is accompanied by deterioration. The residence time in the kneader is 2 seconds or more, preferably 3 seconds or more.

If the residence time in the kneader is less than 2 seconds, a satisfactory water absorbent resin composition cannot be obtained.

In addition, in producing the composition, other polyolefin resins such as polyethylene, polypropylene, ethylene-α
- 95% by weight or less of olefin copolymers, ethylene-vinyl acetate copolymers, ethylene-(meth)acrylic acid copolymers and their metal ion crosslinked products, ethylene-(meth)acrylic acid ester copolymers, etc., preferably is 50% by weight
It can also be blended in the following proportions, petroleum resin,
Wax, stabilizer, antistatic agent, ultraviolet absorber, lubricant,
Inorganic fillers and the like can also be blended. These auxiliary materials can be present during the process of melt-kneading the two essential components to form a composite composition, or can be added after the composite composition is formed.

In the present invention, this composite composition is extruded and foamed.

Extrusion molding is carried out by a conventional method for thermoplastic resins, such as T-die molding, inflation molding, calendar molding, filament molding, etc., to form a composition into a membrane-like object such as a film or sheet, or a ribbon. It is considered to be a filamentous substance such as a cylindrical or cylindrical shape.

The above-mentioned composite composition can be manufactured by forming the composite composition into pellets in advance before extrusion molding, or by directly forming the composite composition in the melt mixing section of the molding machine during extrusion molding. Either case may be used, but it is preferable to form a composite composition in advance before extrusion molding.

Further, as the foaming method, a conventional method for thermoplastic resins is used. For example, at the stage of manufacturing the above-mentioned composite composition, chemical blowing agents such as azodicarbonamide, trihydrazinotriazine, p-toluenesulfonyl semicarbazide, dinitrosopentamethylenetetramine, etc. are used. .5 to 30 parts by weight may be added in advance, or the above-mentioned chemical blowing agent may be added at the stage of extrusion molding after the production of the composite composition, or by extrusion of the composition. A method of foaming, a method of foaming after extrusion molding, or a method of injecting a physical foaming agent such as butane, pentane, hexane, heptane, etc. at the same ratio at the extrusion molding stage and extrusion foaming is used. . Among these, the most preferred method is extrusion foaming.

In the present invention, the extrusion-molded and foamed water-absorbing resin material is further stretched in at least one direction (vertical and horizontal) at a magnification of about 2 to 5 times to further improve the water absorption rate and water absorption properties. Can be done.

The water-absorbing resin material produced by the production method of the present invention can be used as a single film or sheet, preferably as a laminated film or sheet with other materials such as polyolefin resin, or as a weave, for food packaging, For pharmaceutical packaging, agriculture and horticulture,
It can be applied to fields such as dew condensation prevention, building materials such as interior decoration, civil engineering applications such as waterproofing, sanitary products, oil/water separation, and antistatic applications.

(B) Function and Effect The method for producing a water-absorbing resin material of the present invention uses a composite composition obtained by dissolving and kneading a carboxylate-containing water-absorbing resin and a glycidyl group-containing polyolefin. To produce water-absorbing resin materials in the form of films, sheets, fibers, etc., which have a high water absorption rate as a whole and have a high water absorption rate because they are foamed instead of being made by foaming, and have high water absorption properties as a whole. It is something that can be done.

(f) Examples In the following Examples and Comparative Examples, the expansion ratio, water absorption rate, and water absorbent resin retention rate were measured by the following measuring method.

Foaming ratio: Water absorption: Approximately 1 liter of water-absorbing resin material in a 1-liter beaker? and about 1 liter of pure water were weighed and added to each, and left to swell for a predetermined period of time.

Next, the resin material is drained using an 8-mesh sieve, and the water adhering to the surface of the resin material is removed using a door paper, and then the resin material is weighed. The water absorption rate is calculated using the following formula.

The resin material used for water absorption measurement is immersed in water for 5 hours to swell. Next, water is drained and vacuum drying is performed at 70° C. for 24 hours to remove water from the resin material. When the difference between the weight of the resin material before immersion in water and the weight of the resin material after vacuum drying treatment is defined as the drying amount of the resin material, the water-absorbing resin retention rate is calculated by the following formula.

After water-absorbing resin retention rate) = Water-absorbing resin content in resin material before immersion in water 1) × 100 Example 1 Carboxylate-containing water-absorbing resin (polyacrylic acid without surface crosslinking treatment) IJ As a glycidyl group-containing polyolefin, ethylene-
Ethyl acrylate-glycidyl methacrylate copolymer (ethyl acrylate containing Wk5 weight, glycidyl methacrylate v-) containing i [o weight %, melt flow rate]
10F/10 minutes, melting point 96℃) SO weight % and 6 parts of azodicarbonamide per 100 parts by weight of this copolymer were melt-kneaded at 160℃ for 6 minutes in a Banbury mixer. The composite composition was made into a pellet.

The obtained pellet and ethylene-vinyl acetate copolymer (
Vinyl acetate content 12w@%, melt flow rate) 9f
/10 minutes) were coextruded at 200°C with a two-layer circular die using separate extruders, and the composite composition was foamed at a blow-up ratio of 3.0 and a take-up ratio of 2.0. A laminated sheet having a thickness of 1.0 fi of the water-absorbing resin material 1 and 0.1 tm of the ethylene-vinyl acetate copolymer 1 was produced by air-cooled inflation molding.

The expansion ratio, water absorption rate, and water absorbent resin retention rate after water absorption of the water absorbent resin material layer of the obtained laminated sheet are shown in the table.

Example 2 Sodium polyacrylate was 20 weight 1%, ethylene-ether acrylate-glycidyl methacrylate copolymer was 40 heavy cylinders, ethylene-vinyl acetate copolymer was 40 heavy cylinders, azodicarbonamide was the total of both copolymers. 11
A laminate sheet was produced in the same manner as in Example 1, except that the composite composition was prepared by adding 6 parts to the weight of Qo.

The properties of the water-absorbing resin material layer of the obtained laminated sheet are shown in the table.

Comparative Example 1 A water-absorbing resin layer of 0.1 w+m, ethylene-vinegar 2
A laminate sheet with a vinyl copolymer layer thickness of 0.1 wtr was produced.

Comparative Example 2 A laminate sheet was produced in the same manner as in Example 1, except that an ethylene-vinyl acetate copolymer was used instead of the ethylene-ethyl acrylate (IJ cidyl methacrylate) copolymer.

Comparative Example 3 A laminated sheet was produced in the same manner as in Example 1, except that an ionomer resin (Mitsui DuPont ■, Imidine 170'7) was used instead of the ethylene-ethyl acrylate-glycidyl methacrylate copolymer. .

(Margin below) Patent applicant: Mitsubishi Yuka Co., Ltd. Agent: Patent Attorney Masahisa Nagatani (1 other person)

Claims (1)

[Claims] 5 to 95% by weight of a carboxylate-containing water absorbent resin and 95 to 5% by weight of a glycidyl group-containing polyolefin are melt-kneaded at a temperature above the melting point of the latter to form a composite composition, and the composite composition is extruded and foamed. A method for producing a water-absorbing resin material.