JPS5980459A - Water-absorbing powdery resin composition - Google Patents

Abstract

PURPOSE:To prepare a composition resistant to blocking caused by moisture absorption, capable of keeping the powdery form even after being left for a long period, and keeping the water-absorptivity, by adding the powder of a compound selected from hydrated silicon dioxide, hydrated aluminum oxide, hydrated titanium oxide, etc. to a water-absorbing resin powder. CONSTITUTION:Dry powder of a water-absorbing resin is compounded with the powder of a material selected from hydrated silicon dioxide, hydrated aluminum oxide, hydrated titanium oxide, their anhydride, and inorganic substance containing the above materials as main component. The water-absorbing resin is the one capable of absorbing >=about 10 times weight of deionized water based on the own weight of the resin, preferably crosslinked polyacrylic acid salt. The particle size of the inorganic powder is <=10mum, and the amount of the inorganic powder is 0.01-10wt%, preferably 0.1-5wt%, based on the resin powder.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a water-absorbing resin powder composition, and more particularly to a new water-absorbing resin powder composition that has improved hygroscopicity (blocking property) peculiar to water-absorbing resins.

In recent years, water-absorbing resins have been used for a variety of purposes, including sanitary products, sanitary products, water retention agents, dehydration agents, sludge coagulants, thickeners, anti-condensation agents, and release control agents for various chemicals.

Known examples of these water-absorbing resins include hydrolysates of starch-acrylonitrile graft polymers, carboxymethyl cellulose, polyacrylate crosslinked products, and other polyvinyl alcohol-based, polyethylene oxide-based, and polyacrylonitrile-based resins. Among these, crosslinked polyacrylates are considered promising as resins with excellent water absorption ability and quality stability.

The present inventors have repeatedly conducted various studies on the above-mentioned water-absorbing resins, especially cross-linked polyacrylates, and through the process, they have developed a compound containing potassium acrylate and a water-miscible polyvinyl monomer, Production of a dry solid water-absorbing resin by adding a polymerization reaction initiator to a heated aqueous solution having a polymer concentration in the range of 55 to 80% by weight, carrying out a polymerization reaction without external heating, and vaporizing water. Method (Patent Application 1982-1)
71559) and an alkali metal salt of acrylic acid, a water-miscible polyvinyl monomer, an organic solvent with a boiling point of 40 to 1506C, and water, and the concentration of secondary monomers is 55 to 80% by weight.
A method for producing a dry water-absorbent resin in which a polymerization reaction initiator is added to a heated aqueous liquid in the range of ) was established.

According to these methods, the polymerization reaction proceeds sufficiently within an extremely short period of time, and the reaction heat of this polymerization reaction quickly evaporates water from the reaction system, which necessitates the need for any subsequent drying step. The desired dry water-absorbing resin solid with a low water content can be obtained directly without any process, and the obtained solid can be easily pulverized and made into a powder suitable for the desired use.
In addition, there is no unevenness in the degree of crosslinking due to overheating due to external heating and drying processes, and there is no decrease in water absorption capacity due to this, and the product has very good quality.
Moreover, in the latter method, resin solids with improved initial water absorption rates are obtained.

However, as a result of continued intensive research, the inventors of the present invention found that although there are some differences depending on the type and manufacturing method, the various water-absorbing resins generally have hygroscopic properties depending on their original water-absorbing ability. It has been recognized that it has the disadvantage that it absorbs moisture relatively quickly and causes blocking, making it difficult to use in powder form and making it difficult to handle.

The present invention eliminates the hygroscopic property, especially the blocking property due to moisture absorption, which is a drawback peculiar to this water-absorbing resin, and maintains the powder form immediately after production even after being left for a long time, and does not reduce the water-absorbing ability of the water-absorbing resin at all. A new water absorbent resin powder composition is provided.

That is, the present invention mixes a water-absorbing resin dry powder with at least one kind of powder selected from anhydrides such as hydrated silicon dioxide, hydrated aluminum oxide, hydrated titanium oxide, and inorganic substances containing these as main components. The present invention relates to a water-absorbing resin powder composition characterized by the following.

The water-absorbing resin powder composition of the present invention is characterized by the fact that the water-absorbing resin 8 does not reduce its original water-absorbing ability at all, and its hygroscopic property (
blocking performance) has been significantly improved.

In other words, the composition does not block even when left alone, has extremely excellent powder fluidity, and is easy to handle, making it very effective in fields where water-absorbing resins have been used. Available.

In the composition of the present invention, any of the various water-absorbing resins conventionally known can be used as the water-absorbing resin;
Resins that have the ability to absorb 0 times more deionized water are preferred. Typical examples thereof include hydrolysates of starch-acrylonitrile graft polymers, carboxymethyl cellulose, crosslinked polyacrylates, polyvinyl alcohol resins, polyethylene oxide resins, polyacrylonitrile resins, and the like. Among these, crosslinked polyacrylates are preferred, and in particular, crosslinked polyacrylates obtained by the method previously developed and patented by the present inventors are most suitable.

The method for producing this particularly preferred crosslinked polyacrylate product will be described in detail below.

That is, in the first method (Japanese Patent Application No. 56-171559), potassium acrylate and a water-miscible or water-soluble divinyl compound are first contained, and the secondary monomer concentration is 55 to 8.
A warmed aqueous solution of mixed monomers in the range of 0% by weight is prepared. The aqueous solution is usually easily prepared by adding acrylic acid, its neutralizing agent potassium hydroxide, and the divinyl compound in amounts to achieve the monomer concentration described above, into water.
At this time, a slight heating operation may be employed to ensure sufficient dissolution. Potassium hydroxide as the neutralizing agent is preferably used in an amount sufficient to neutralize 100% by mole of acrylic acid, but it is not necessary to use the amount to neutralize 100%, but about 70%. The above amount may be neutralized, and therefore, the prepared mixed monomer aqueous solution may contain free acrylic acid in an amount of up to about 30%. The water-miscible or water-soluble divinyl compound used above needs to have water-miscibility or water-solubility such that it can be uniformly dissolved or dispersed in the mixed monomer aqueous solution prepared by adding it. Examples of such divinyl compounds include N,N-methylenebisacrylamide, N,
Bisacrylamides such as N-methylenebismethacrylamide; diacrylamide represented by the following general formula (I) (
or methacrylic) acid esters; common crosslinking agents such as diacrylamides represented by the following general formula 〇 can be exemplified;
Among these, especially N,N-methylenebisacrylamide, N.

Bisacrylamides such as N-methylenebismethacrylamide are preferred.

o=c-o-x-o-c=.

(In the formula, X represents ethylene, propylene, 2-hydroxypropylene, CH9CH8 group, and n and m represent integers of 5 to 40.) The compound of the general formula (I) is, for example, ethylene glycol, propylene glycol, glycerin , polyethylene glycol, polypropylene glycol, and other polyols and acrylic acid or methacrylic acid.

0=C-NH+CH2CHgNH+1C=0 (in the formula, l represents 2 or 3) The compound of the general formula 〇 is, for example, diethylenetriamine,
It is obtained by the reaction of polyalkylene polyamines such as triethylenetetramine and acrylic acid.

The divinyl compound is preferably about 0.001 to 0.3% by weight of the total weight of potassium acrylate salt or, in some cases, this and free acrylic acid in the commonly prepared mixed monomer aqueous solution. is 0.005
It is advantageously used in a range of 0.1% by weight, thereby making it possible to obtain the desired dry solid crosslinked polyacrylate product having excellent water absorption ability.

Next, in the above method, the aqueous solution of the mixed monomers prepared above is heated in advance, and then a polymerization reaction initiator is added thereto to start the polymerization reaction (and crosslinking reaction). Here, the heating conditions are not particularly limited on the premise that the polymerization reaction is initiated by the addition of a polymerization initiator, but are usually about 50 to 80%
5°C1, preferably about 60 to 75°C. Furthermore, as the polymerization reaction initiator, any of the various types known to be used in the production of polyacrylates can be used. A specific example thereof is a redox consisting of a combination of a reducing agent such as an alkali metal sulfite or bisulfite, ammonium sulfite, or ammonium bisulfite, and an initiator such as an alkali metal persulfate or ammonium persulfate. System initiator, azobisisobutyronitrile, 4-t-
Butylazo-4-cyanovaleric acid, 4,4-azobis(4
-cyanovaleric acid), 2,2-azobis(2-amidinopropane) hydrochloride, etc., or a combination of two or more of them can be appropriately selected and used. The amount of the polymerization initiator to be used is not particularly different from the usual one, and usually the solid weight is 0.1 to 100% of the total weight of the acrylate (or acrylic acid and acrylic acid) as monomers and the polyvinyl monomer. 10% by weight, preferably about 0.5 to 5% by weight
It is better to Further, depending on the type and amount of the polymerization reaction initiator used, a common chain transfer agent such as isopropyl alcohol or alkyl mercaptan may be used together with the polymerization reaction initiator to control the molecular weight of the polyacrylate to be produced.

The polymerization reaction and vaporization of water by addition of the polymerization initiator are more advantageously carried out by adding and mixing a predetermined amount of the polymerization initiator or its aqueous solution to a heated aqueous solution of mixed monomers, and then transferring this mixed solution. It is carried out by flowing down and spreading on a belt. When using the polymerization reaction initiator in the form of an aqueous solution,
The acrylate concentration in the resulting mixed solution is 55~
It must not fall below a range of 80% by weight. Further, when the mixed liquid flows down onto the belt, a polymerization reaction initiator may be further placed in the downstream part of the belt.

According to the addition and mixing of the polymerization reaction initiator to the heated aqueous solution of mixed monomers, the polymerization reaction starts extremely quickly after mixing, and the reaction is completed in a short time, usually about 30 seconds to 1 minute. . Moreover, this reaction is an exothermic reaction, and the reaction system quickly rises to about 100 to 130°C due to the heat of polymerization, and as a result, the moisture in the system is rapidly removed without any external heating. After evaporation, the desired low water content polymer (dry solid) is obtained. The water content of the resulting polymer varies slightly depending on the reaction conditions, etc., but is usually about 15% or less, more preferably about 10% or less, and this can be achieved by simply using a conventional method without any subsequent drying step. Therefore, a desired powder product can be obtained only by pulverization or the like.

Thus, according to the above method, a dry solid crosslinked polyacrylate product having a moisture content of usually 15% or less can be obtained very quickly and easily. The monomer remaining in the polymer is only 2000 ppm or less based on the polymer, and the polymerization rate is also extremely good.

The thus obtained dry polymer solid can be easily powdered using a conventional grinder or the like.

A second preferred method for producing a cross-linked polyacrylate product (Japanese Patent Application No. 128266/1982) further includes a boiling point of 40
The main feature is that an organic solvent of ~150°C is used as an essential component, and other aspects are basically carried out in the same manner as in Habo. Examples of the above-mentioned specific solvent in the method of No. 11-- include methanol, ethanol, n-propanol, acetone, methyl ethyl ketone, cyclohexane, n-h-t-san,
Examples include n-hebutane, benzene, toluene, tetrahydrofuran, etc., and these are □0.
It is used in an amount of 5 to 15% by weight, preferably 1 to 10% by weight.

As long as the water-absorbing resin used in the present invention is in powder form,
There are no particular restrictions on its shape or size, but it is usually about 10~
Preferably, the particle size is 600 mesh.

The inorganic powder which is the other essential component constituting the composition of the present invention is selected from anhydrides such as hydrated silicon dioxide, hydrated aluminum oxide, hydrated titanium oxide, etc., and those containing these as main components.

The crystal systems of the above-mentioned inorganic compounds are not limited; for example, in the case of aluminum oxide, any of the α-type, β-type, and γ-type can be effectively utilized. Furthermore, the titanium oxide may be any of Tie, Ti2OB, and TiO2.

Furthermore, there is no particular limitation on the water content of the water-containing products, such as the following.

For example, for aluminum oxide, A12oB・[20, A/2
For titanium oxide, TiO2.I(20, TiO2.2H20, etc.) can be similarly used.

Examples of substances containing the above-mentioned hydrous or anhydrous inorganic compound as a main component include those containing hydrous silicon dioxide and/or anhydrous silicon dioxide as a main component, such as colloidal silica, white carbon, and ultrafine particulate anhydrous silicon dioxide; Platy hydrated alumina, fibrous hydrated alumina and other fine powder aluminas whose main component is hydrated or anhydrous aluminum oxide, clay, talc, kaolin and other rutile and anatase hydrated aluminas. Examples include those containing anhydrous titanium oxide as a main component. The secondary inorganic powders can be used alone or in combination of two or more. The amount of water-absorbing resin powder is as follows:
Usually, the amount is about 0.01 to 10% by weight, preferably about 0.1 to 5% by weight, based on the weight of the resin powder, and the desired effect of the present invention can be achieved by this amount.

Of course, it is possible to add an amount exceeding the above range, but in this case, the amount of water-absorbing resin powder itself in the product will decrease accordingly.
A disadvantage is that the apparent water absorption capacity of the composition according to the invention is reduced (requiring the use of more composition for the same application). Further, the above-mentioned inorganic powder can be used in the form of a powder that is usually manually prepared, but preferably the powder particle size is about 10 μm.
It is preferable that it is less than m.

The composition of the present invention is prepared simply by uniformly mixing (powder mixing) a predetermined amount of the above-mentioned specific inorganic powder with the above-mentioned water-absorbing resin powder. The mixing method can be any of the various operations commonly used for powder mixing, typically mechanical mixing operations.

The thus obtained composition of the present invention has significantly improved hygroscopicity (blocking property) without changing the water-absorbing ability inherent to the water-absorbing resin at all, and can be used for sanitary products such as sanitary products, disposable diapers, and disposable cloths. It can be very effectively used for various purposes such as water retention agents for agriculture, forestry, and horticulture, dehydration agents for various industries, sludge coagulants, thickeners, anti-condensation agents for building materials, and release control agents for various chemicals.

Hereinafter, in order to explain the present invention in more detail, a method for producing a water-absorbing resin will be given as a reference example, and then examples will be given.

Reference Example 1 Add 72.1y of acrylic acid to 22.2y of deionized water,
Furthermore, potassium hydroxide 4 with a purity of 85% is added as a neutralizing agent.
9.5y and 0.01y of N,N-methylenebisacrylamide as a divinyl compound are sequentially added to prepare a potassium rum acrylate aqueous solution (neutralization degree 75%) with a mixed monomer concentration of 70% by weight. .

The aqueous solution prepared above was kept warm at 70°C.

Add 2.9y of an 18% aqueous solution of ammonium persulfate (total weight of potassium acrylate, free acrylic acid and N, Nl 5-monethylenebisacrylamide, the same below)
0.5% by weight) and hydrogen sulfite) and 1.7y (0.5% by weight) of a 30.6% aqueous solution of IJium,
The mixed solution is spread on an endless moving belt in a layer having a thickness of about 10 mm. After about 30 seconds, the polymerization reaction starts and is completed in about 1 minute.

The maximum temperature during this period is approximately 120°C.

Thus, the water content was 11% and the residual monomer concentration was 1200 ppm.
A strip-shaped dry solid of crosslinked potassium polyacrylate is obtained. This is pulverized by pulverization using a pulverizer. The water absorption capacity of the resulting powder was 450 in deionized water and 60 in 1% saline. Furthermore, this water absorption capacity is
The evaluation is performed by adding the resulting polymer powder 1y (calculated as absolute dry weight) to test water and then determining the weight (9) of the test water absorbed by the powder.

Reference examples 2 to 9 Concentration of mixed monomer prepared in Reference Example 1, 16- The insulation temperature conditions, the divinyl compound (N.

The amount of N-methylenebisacrylamide used, the type and amount of neutralizing agent used (degree of neutralization), and ammonium persulfate (abbreviated as APS) and hydrogen sulfite (abbreviated as SPS) as polymerization reaction initiators. Polymers were obtained in the same manner by changing the amount of at least one of the mixed monomers used as shown in Table 1 below. In Table 1, the results of Reference Example 1 are also listed.Table 1 Mixed monomer amount Gibini Initiator concentration reference example Body concentration N (wt%) (''C) APS
5PS1 70 70 0.01 0.
5 G, 5 0H75260700,010
,50,511II3 70 75 0.0
1 0.5 0.5 n n4
70 7G 0.03 0.5 0.5
s /15 7G 70 0
．． 05 G, 5 0.5 // n
6 70 70 G, 10 G, 5
0.5 tt u7 70 7
0 0.01 0.8 0.8 II
II8 70 70 0.01 1.
The amount of the divinyl compound used in the OLo n table is expressed in weight% of the mixed monomer (potassium acrylate, free acrylic acid, and the divinyl compound), and the initiator concentration is the proportion of the above mixed monomer and the divinyl compound. It is expressed as the weight % of the initiator in the total weight (in terms of solid content) including the initiator.

The moisture content of the dry solid of each obtained polymer (potassium polyacrylate crosslinked product) was determined by adding the powder after powdering to deionized water and 1% saline in the same manner as in Reference Example 1. The water absorption capacity is shown in Table 2 below.

Table 2 Reference Examples 10 to 13 72.1 ft of acrylic acid was added to 18.0 y of deionized water,
Solid potassium hydroxide (water content 4%) 40.9p and 3rd
Various solvents listed in the table 5.2y (equivalent to 5% of monomer)
This monomer aqueous liquid and 4.0 y of a 10% aqueous solution of 2,2-azobis(2-amidinopropane) hydrochloride were mixed and immediately placed on an endless moving belt. Dry and spread the kudzu to a thickness of 5 mm. Approximately 15
A few seconds later, the polymerization reaction started and was completed in about 30 seconds. The maximum temperature during that time was 130-135°C.

A dried strip of crosslinked potassium polyacrylate was thus obtained. This was ground into a powder of 20 to 100 meshes. In all cases, the moisture content was 4 to 6%.

Accurately weigh 0.1y of each of these powders, add deionized water or
% saline solution for 10 seconds, 30 seconds, and 15 minutes. The results are shown in Table 3.

Table 3 Example 1 To 100 parts by weight of the potassium polyacrylate crosslinked powder (particle size of about 50 to 200 mesh) obtained in Reference Example 1, 0.2 to 5 parts of silicon oxide (5i02, particle size of 12 mμ) was added. .0
The composition of the present invention (sample N) was prepared by mixing powders in the range of parts by weight.
o, , 1 to 5) were obtained.

A powder fluidity test was conducted on each of the obtained mixed powder samples as follows. That is, after each sample was left in a zero atmosphere at 25°C and 175% RH for 24 hours, it was made into a glass with an inner diameter of 42 mm, a height of 90 mm, and 2.5% to 18 mmft' (D, range W) with five different pore sizes. Place each funnel in a manufactured test funnel, suspend each funnel vertically with the orifice downward,
The flow state of the sample flowing out from the orifice was visually determined and evaluated based on the following criteria.

<Fluidity evaluation> l... Outflows from a funnel with an orifice hole diameter of 2.5 mm (very good powder fluidity) 2... Outflows from a funnel with an orifice hole diameter of 5 mm (good powder fluidity) 3...・Flows out from a funnel with an orifice hole diameter of 8 mm (good overall powder fluidity) 4... Outflows from a funnel with an orifice hole diameter of 12 mm (sufficient powder fluidity) 5... Orifice hole diameter of 18 mm, m Outflow from the funnel (lack of powder fluidity) 6... Orifice hole diameter 1B? 717Fl did not flow out from the funnel (insufficient powder fluidity) The results are shown in Table 4 below. For comparison, Table 4 also shows the case where no silicon oxide was added.

Examples 2 to 9 Compositions of the present invention were obtained in the same manner as in Example 1 except that in place of silicon oxide, predetermined amounts of each inorganic powder shown in Table 5 below were used. Table 5 also shows the results of a powder fluidity test conducted in the same manner for each sample obtained.

Table 5 Examples 10 to 23 In Example 1, in place of the potassium polyacrylate crosslinked powder obtained in Reference Example 1, potassium polyacrylate crosslinked powder obtained in Reference Examples 2 to 13 (particle size 20 to 100) was used. commercially available water-absorbing resin A (P” Sanwetsu) IM-1000
J, manufactured by Sanyo Chemical Co., Ltd., starch-acrylonitrile water absorbing resin) and commercially available water absorbing resin B (r Aqua Keep 10 SHJ,
Manufactured by Seitetsu Kagaku Co., Ltd., sodium polyacrylate water absorbing resin)
A composition of the present invention was obtained in the same manner using each of the above, and the amount of silicon oxide added was constant at 1.0% by weight.

The same test as in Example 1 was repeated for each composition, and the results are shown in Table 6 below. As a result of a comparative test in which each water-absorbing resin was tested individually, the fluidity of each resin was evaluated as 6.

As is clear from the results shown in Tables 4 to 6 above, the composition of the present invention has extremely improved powder fluidity and has no hygroscopicity (blocking property) as seen in water-absorbing resins alone. It turns out that it is not acceptable.

Claims (1)

[Claims] ■ The water absorbent resin dry powder is mixed with at least one powder selected from anhydrous substances such as hydrated silicon dioxide, hydrated aluminum oxide, hydrated titanium oxide, etc., and inorganic substances containing these as main components. Characteristic water-absorbing resin powder composition.