JPH0530618B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a highly hydrated material made of a composite of a polyvinyl acetalized porous material and a nonwoven fabric, and a method for producing the same, and more specifically to cleaning tools such as towels and wipers, various water-retaining materials, Polyvinyl acetal (hereinafter referred to as polyvinyl acetal) with fine pores useful for water-absorbing materials, etc.
This invention relates to a composite of a porous material (PVAF) and a nonwoven fabric. [Prior art] Aldehydes and pore generation aids are mixed in advance with an aqueous solution of polyvinyl alcohol, and the aqueous solution is heated to acetalize the polyvinyl alcohol, which is then washed to form uniform micropores.
Methods for producing PVAF sponges are already well known (Japanese Patent Application Laid-Open Nos. 1983-57088, 1982-20019, 1972-10147, and 1972-99167).
Publications, etc.). In addition, manufacturing methods for basic fiber structures (knitted fabrics, woven fabrics, or non-woven fabrics) or composites of porous elastic bodies and PVAF porous bodies have already been proposed (Japanese Patent Publication No. 51-7954, Japanese Patent Application Laid-open No. 58-141132). Publication, JP-A-59-76247, JP-A-51-38351
No. 63-46240, etc.). These known methods generally have a saponification degree of 80 to 100.
%, polyvinyl alcohol with a degree of polymerization of about 500 to 3000 is dissolved in water to make an aqueous solution of about 4 to 18%, to which a pore aid is added depending on the application, and aldehydes and mineral acids are added as a catalyst. , further add coloring agents, preservatives, fragrances, etc. as necessary, and add these alone or after applying them to the fibrous structure substrate, at room temperature or higher, generally 40 to 90 ° C., preferably 50 to 70 ° C. to increase the reaction rate. The acetalization reaction is gradually carried out by heating at ℃ for 4 to 40 hours, usually 6 to 24 hours, and then unreacted substances, impurities, etc. are removed, and a PVAF-based porous material is obtained by washing with water. be. [Problem to be solved by the invention] In general, the state of pores in a porous body has a great influence on the properties of the porous body, and the pore size and uniformity of the porous body are important issues depending on the application of the product. Become. Therefore, in addition to the above-mentioned production method, a method of controlling the reaction temperature in a specific pattern (Japanese Unexamined Patent Application Publication No. 49-1998)
63755) or a method using classified starch (Japanese Unexamined Patent Publication No. 1983-6663), which require very strict control and, as mentioned above, require a long period of acetalization. As a result, productivity is extremely low. The present invention eliminates these troublesome controls and provides a method for producing a porous material composite with excellent water-holding properties in a short acetalization time. [Means for Solving the Problems] That is, the present invention consists of a nonwoven fabric and a porous body of polyvinyl alcohol with a degree of acetalization of 35 to 70 mol% imparted to the inside and surface of the nonwoven fabric, and the surface thereof has open pores. More than 80% of them have an open pore diameter of 20 to 200μ, and a water retention rate of
It is a highly hydrophobic composite characterized by having a porosity of 700% or more, and a polyvinyl alcohol aqueous solution foamed to a volume of 50 to 50% of the weight of the nonwoven fabric is added to a nonwoven fabric with a porosity of 80% or more.
After applying or impregnating 600% by weight and solidifying the polyvinyl alcohol, the polyvinyl alcohol is acetalized to a degree of acetalization of 35 to 70 mol% by treatment with an aqueous solution containing formaldehyde and mineral acid, and then washed with water. A method for producing a highly water-retaining composite, which is characterized in that the highly water-retaining composite is particularly preferably cured by treating the highly water-retaining composite obtained by the above method with an aqueous colloidal silica dispersion adjusted to a pH of 6 or higher. The present invention is a method for producing a complex, and a method for producing a highly water-hydrating complex in which the highly water-hydrating complex is treated with an aqueous solution containing glutaraldehyde and a mineral acid. To explain in detail the method for producing the highly hydrophobic composite of the present invention, first, the aqueous solution of polyvinyl alcohol (hereinafter abbreviated as PVA) to be coated or impregnated on a nonwoven fabric (hereinafter sometimes referred to as a substrate) is 5 to 15%, especially 7 to 15%. A 9% PVA concentration aqueous solution is preferred. In the present invention, such a PVA aqueous solution is mixed with a gas, preferably air, to form a foam, and the apparent volume is adjusted to more than twice, preferably 3 to 6 times. The size of the bubbles changes depending on the viscosity of the PVA aqueous solution and the foam mixing conditions. In the conventionally known method, in which aldehyde and acid are blended in advance into a PVA aqueous solution, the diameter of the bubbles changes as acetalization progresses, so obtaining a uniform foam requires varying temperature and substrate conditions. Good control over the time to application and impregnation was required. However, in the method of the present invention, since aldehydes and mineral acids that significantly change the foam state are not substantially added, the same foam state can be maintained for a considerable period of time at around room temperature. Furthermore, it is convenient to incorporate a surfactant in order to keep the foamed state stable. The types include polyoxyethylene, alkyl ethers, fatty acid amides, alkyl phosphate salts, alkyl amines, sulfate ester salt type amphoteric surfactants, alkyl sulfate ester salts, propylene glycol, etc., and they may be used alone or in combination. It is used by mixing. The amount of surfactant added is as follows:
It may be 10% by weight or less based on PVA. Also, regarding the amount of PVA foam applied to the base,
A suitable amount of PVA is 50 to 600% by weight, particularly 80 to 400% by weight. If the applied amount is too small, the shape of the substrate surface will show up on the composite surface and the surface will not be uniform, and the fluff of the substrate fibers will also come out on the surface, so when used as a wiper, there is a drawback that fluff remains after wiping. be. In addition, when the amount of PVA foam applied is increased, the amount of water held as a composite increases, but the amount of water retained as a composite increases.
The strength of the PVA foam part is reduced. In addition, as the required acetalization time becomes longer, the degree of acetalization is uneven in the depth direction, and if the surface is suppressed to a moderate degree of acetalization, the acetalization inside becomes insufficient, resulting in the formation of a composite material during drying. In addition to impairing the softness, a portion of unreacted PVA oozes out onto the surface, causing the surfaces to adhere to each other when the composites are stacked together. After applying 50 to 600% by weight of PVA to the substrate, the substrate is immersed in a coagulation bath to coagulate the PVA. At that time, a bath consisting of an aqueous solution of neutral or acidic salts such as Glauber's salt and ammonium sulfate is used as a coagulation bath.
Solidify PVA. In order to maintain a uniform pore condition on the surface of the composite, after impregnating and applying PVA to the surface of the substrate, immediately introduce it into the coagulation bath as it is.
Preferably, it is coagulated. The complex removed from the coagulation bath is acetalized by conventional methods. That is, the composite taken out from the coagulation bath is acetalized by immersing it in an aqueous solution containing formaldehyde and mineral acid. The formaldehyde concentration in the aqueous solution at that time is 15 to 60
g/, the mineral acid concentration is generally 150 to 300 g/, and sulfuric acid, nitric acid, hydrochloric acid, etc. are generally used as the mineral acid. The temperature of the aqueous solution is 40-60℃
is preferable, and the treatment time is preferably 30 to 60 minutes. Furthermore, an inorganic salt may be added to the aqueous solution for the purpose of preventing the PVA foam from peeling off from the substrate, and the amount added is 60 to 250 g/,
Specific compounds include mirabilite, ammonium sulfate,
Examples include zinc sulfate. The degree of acetalization of the PVA foam part is 35-70
Mol% is appropriate. When the degree of acetalization increases, it becomes paper-like in feel, and its water holding rate decreases, and its water absorption also decreases, resulting in an insufficient function as a cleaning tool. On the other hand, when the degree of acetalization is low, it is soft, has a high water holding rate, and has good water absorption, but when it dries, the degree of hardening is severe and when it is rolled in a wet state or dried after being folded, the surfaces may adhere to each other. is possible. Therefore, it is preferable to control the degree of acetalization of the foam portion to 35 to 70 mol%, preferably 45 to 60 mol%. However, the present inventors focused on the extremely excellent water-holding power, tactile sensation, and elasticity of PVA foam at a low degree of acetalization. As a result of repeated research on means for preventing this, it was found that it is preferable to stop the degree of acetalization at 35 to 50 mol%, and then perform additional acetalization with glutaraldehyde. For example, glutaraldehyde 2~
20-40 containing 6g/ and sulfuric acid 40-140g/
By immersing it in an aqueous solution at ℃ for 15 to 30 minutes, it is possible to prevent surfaces from adhering to each other during drying. Note that hydrochloric acid, nitric acid, etc. can also be used instead of sulfuric acid. The degree of acetalization by glutaraldehyde is preferably 2 to 6 mol%. Also, instead of glutaraldehyde treatment, PVA
The foam contains 7 to 13% colloidal silica,
After immersing in a solution adjusted to pH 7 or higher, heat treatment can prevent surfaces from adhering to each other during drying. When this method is used, it is preferred that the resulting composite has colloidal silica attached thereto in an amount of 2 to 10% by weight based on the weight of the composite. In addition, by acetalizing foamed PVA after applying it, the PVA shrinks, and as a result, the bubbles on the surface become open pores, which also causes improved water wettability after the composite dries. Compared to conventional methods, this method has the dual advantages of improved productivity and improved performance. The diameter of the open pores varies depending on the viscosity of the PVA applied. In other words, as the concentration increases, the viscosity increases and the pore diameter decreases, but
From the viewpoint of water-holding property and texture, it is preferable that 80% or more of the pore diameter is within the range of 20 to 200 μm. Furthermore, the complex obtained by the above-mentioned conventional method is
PVA open pore diameter is smaller than 20μ. Examples of fiber substrates that can be used in the composite of the present invention include cotton, viscose fiber, polyvinylidene chloride fiber, polyvinyl alcohol fiber, polyethylene fiber, polypropylene fiber, polyacrylonitrile fiber, polyurethane fiber, polyamide fiber, polyester fiber, etc. A nonwoven fabric made of fibers alone or in combination is used. In the case of woven or knitted fabrics, they are unsatisfactory in terms of feel, high water retention, and elasticity. In the present invention, a nonwoven fabric containing hot-water shrinkable polyvinyl alcohol fibers and subjected to shrinkage treatment to shrink to 80% or less in terms of area ratio is particularly preferred in terms of softness and integrity with the PVA foam.
In the present invention, most of the hydrated water enters the voids of the nonwoven fabric, and there is a positive correlation between the porosity and the hydrated rate of the nonwoven fabric. For the above-mentioned applications, a water retention rate of 700% or more is required, and in order to achieve this water retention rate, it is necessary to use a nonwoven fabric as a base material with a porosity of 80% or more, preferably 85% or more. be. Moreover, the basis weight of the nonwoven fabric is preferably 50 to 400 g/m ² . The water retention rate referred to here is calculated by immersing the sample in room temperature water for 30 minutes, placing it on a horizontal wire mesh, measuring the weight (W ₁ ) when water drops stop falling, and using the following formula. Water retention rate = W ₁ / sample bone dry weight x 100 (%) The porosity of the nonwoven fabric was determined by the following method. Porosity = ρ - ρ _A / ρ × 100, where ρ: Specific gravity of fiber ρ _A : Apparent specific gravity = Weight (g/m ² ) / 1000 × Thickness (mm
Note that the thickness here means the value obtained by placing the nonwoven fabric on a horizontal surface, looking at the thickness side of the nonwoven fabric with a magnifying glass without pressing it from above, and measuring its substantial thickness. The present invention will be explained below with reference to Examples, in which the concentration percentages in the Examples are based on weight unless otherwise specified. Example 1 Water-soluble vinylon (manufactured by Kuraray Co., Ltd. VPB174×44T-
A nonwoven fabric of 100 g/m ² consisting of 13) is immersed in 60°C hot water to shrink to 65% in terms of area ratio, resulting in a substrate with a porosity of 94%. In addition, fully saponified PVA (manufactured by Kuraray)
POE3 mol lauryl ether sulfate triethanolamine and 60% triethanolamine in a 9% solution of PVA-HC saponification degree: 99.9%, polymerization degree: 1720)
After mixing 0.8% of the 40% compounded product, Suga Machinery Co., Ltd.
The volume was increased by 3.5 times by foaming using a continuous foaming machine manufactured by the company. This foamed PVA solution is uniformly impregnated on the front and back surfaces of the substrate made of the nonwoven fabric in an amount twice the weight of the PVA relative to the weight of the substrate. After that, it was immersed in 400g/g of Glauber's salt solution for 1 minute to solidify, and then the acetalization solution was HCHO: 30g/, H ₂ SO ₄ ; 300
The temperature of an aqueous solution of 120 g/g/Na ₂ SO ₄ was adjusted to 45° C., and the PVA-applied base fabric was immersed in this solution for 40 minutes to fix the PVA in a foamed state to the nonwoven fabric. The obtained complex was mixed with NaOH; 0.2 g/
The mixture was neutralized with a solution for 5 minutes, and then formalin, caustic soda, Glauber's salt, etc. remaining in the composite were washed away with water to produce a highly hydrated composite. The degree of acetalization of the resulting highly hydrated composite PVA foam is 52.
%, it was a good composite with good elasticity and uniform feel of pores in the wet state, and the water retention rate was 950%. In addition, the diameter of the open pores on the surface is 40 to 200μ.
More than 80% of them were included. Example 2 In the method of Example 1, composites were manufactured by changing the temperature at which a 100 g/m ² nonwoven fabric was shrunk with hot water and changing the porosity of the nonwoven fabric. The results were as shown in Table 1.
The amount of PVA applied and the degree of acetalization are the same as in Example 1.

[Table] Example 3 In the method of Example 1, complexes were prepared by varying the acetalization time. The results are shown in Table 2.

[Table] Water absorption: A 100 x 100 mm sample is immersed in room temperature water for 30 minutes, centrifuged at 3000 RPM for 1 minute, placed parallel to the water surface at room temperature, and expressed as the time until the entire sample completely absorbs water. Example 4 Kuraray vinylon VPB204×51T-13 (30%)
A nonwoven fabric of 120 g/m ² containing polyester 1.5 ^dr × 51 mm (70%) manufactured by Kuraray Co., Ltd. was immersed in warm water at 65°C and shrunk by 50% in area ratio to obtain a nonwoven fabric with a porosity of 91%. Next, PVA manufactured by Kuraray Co., Ltd. (PVA-HC) was dissolved in water to make a 9% aqueous solution, and this was foamed to a volume of 4.0 times using a continuous foaming machine manufactured by Suga Kikai Co., Ltd. to prepare a foamed PVA aqueous solution. This foamed PVA aqueous solution was applied to the nonwoven fabric at a rate of 0.5 times the amount of PVA based on the weight of the nonwoven fabric.
It was impregnated in an amount of 2 times, 3 times, 5 times, and 7 times, solidified in the same manner as in Example 1, acetalized for 40 minutes, and washed to obtain a composite. The results are shown in Table 3 below.

[Table] Example 5 A complex obtained by coagulation in the same manner as in Example 1 was mixed with HCHO; 30 g/, H ₂ SO ₄ ; 300 g/,
The mixture was treated with an acetalization solution containing 120 g of Na ₂ SO ₄ at 50° C. for 25 minutes, and washed with water to prepare a composite. The degree of acetalization of this foamed PVA portion was 37 mol%, and some tackiness was observed on the surface. Next, add NaOH to a 10% aqueous solution of colloidal silica (Snowtex O manufactured by Nissan Chemical) and adjust the pH to 10.
Dip the composite into this solution and adjust the extraction rate.
Squeeze to 150%. After that, it was dried in a hot air drying oven at 130℃ for 40 minutes, and then the NaOH was washed away and the product was made.
This product is an extremely flexible composite with high water retention (850% water retention) and no surface adhesiveness. In this case, 80% of the open pores on the surface have a diameter of 20 to 150μ.
It accounted for more than that. Example 6 The complex obtained in Example 5 with a degree of acetalization of 37 mol% was mixed with glutaraldehyde; 4 g/
It was immersed in a 40° C. aqueous solution containing 100 g of H ₂ SO ₄ for 30 minutes, and then the aldehyde and acid were washed with water to obtain a composite. The degree of acetalization of the applied PVA by glutaraldehyde was 3.9%. This composite has high water-holding properties (water-holding rate of 1000
%), resulting in an extremely soft and highly tactile water-retaining composite. In this case, the diameter of the open pores on the surface is 35~
200μ accounted for more than 80%.

Claims (1)

[Scope of Claims] 1 Consists of a nonwoven fabric and a porous body of polyvinyl alcohol with a degree of acetalization of 35 to 70 mol% imparted to the inside and surface of the fabric, and has open pores on its surface. More than 80% have open pore diameter of 20~
A highly water-retaining composite characterized by a water-retaining ratio of 700% or more and in the range of 200μ. 2 Add polyvinyl alcohol aqueous solution foamed twice or more to a nonwoven fabric with a porosity of 80% or more in an amount of 50 to 600% by weight of polyvinyl alcohol based on the weight of the nonwoven fabric.
After coating or impregnating and coagulating the polyvinyl alcohol, the polyvinyl alcohol is acetalized to a degree of acetalization of 35 to 70 mol% by treatment with an aqueous solution containing formaldehyde and mineral acid, and then washed with water. A method for producing a highly hydrated complex.