JPH0448914A - Dehumidifying sheet and its preparation - Google Patents

Abstract

PURPOSE:To obtain a membrane-like dehumidifying sheet holding with hygroscopic capacity equal to that of a particulate moisture absorbing agent, excellent in flexibility and usable at high and low temps. by providing a composite composition wherein fibrillated fluoroplastic is dispersed and interposed in the structure of a hygroscopic filler. CONSTITUTION:1 - 10pts.wt. of fluoroplastic having fibrillating properties is compounded with 100pts.wt. of a hygroscopic filler powder having a particle size of 50mum or less and the obtained compound is kneaded along with a liquid kneading aid until the fluoroplastic is fibrillated to be molded into sheet. By this method, a dehumidifying sheet having high hygroscopic capacity same to that of a particulate moisture absorbing agent, usable under high and low temp. conditions and good anti-staining properties and flexibility is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a thin film-shaped dehumidifying sheet that maintains high moisture absorbing performance on the moisture absorbing side of the granular moisture absorbing sheet, and a method for manufacturing the same.

[Conventional technology]

Calcium chloride, silica gel, activated alumina, zeolite, and the like are useful as moisture absorbing agents for absorbing or adsorbing water. These hygroscopic agents are usually manufactured in the form of powder or sized particles with a large hygroscopic surface area, and are often stored in gas-permeable containers, bags, etc. to prevent scattering and to facilitate handling. available for use. Therefore, if it is possible to integrate it into a sheet shape or the like without impairing its moisture absorption performance as a powder, it will not only ensure non-contamination and facilitate handling, but it can also be expected to significantly expand the range of applications.

Conventionally, as a technique for obtaining a moisture absorbent with an integrated structure, for example, a method of firing a moisture absorbing substance such as magnesium hydroxide (
JP-A-54-24285), a method of impregnating a moisture-absorbing filler substance into a porous material having minute voids, such as a water-resistant nonwoven fabric (JP-A-1-30623), and a method of impregnating a moisture-absorbing filler substance with a thermosetting resin. How to mix and integrate into (
JP-A-1-43346) and the like have been proposed.

[1iff to be solved by the invention] However, with these conventional techniques, it is not possible to produce a flexible thin film sheet, which is the most preferable form for handling, and furthermore,
The methods disclosed in Publication No. 3 and Publication Nos. 1 to 43346 have a problem in that the breakthrough (adsorption equilibrium) life is shortened because the amount of hygroscopic filler packed is limited.

An object of the present invention is to provide a thin film-like dehumidifying sheet that maintains high moisture absorption performance equivalent to that of a powdery moisture absorbent, has excellent flexibility, and can be used at high and low temperatures, and a method for producing the same.

[Means for Solving the Problems] The dehumidifying sheet of the present invention for achieving the above object has a structural feature that it has a composite composition in which fibrillated fluororesin is dispersed in the structure of a hygroscopic filler. It is something to do.

The hygroscopic filler constituting the sheet composition of the present invention is selected from calcium chloride, silica gel, activated alumina or zeolite. What is fibrillated fluororesin?
It refers to a state in which a heat-resistant fluororesin component is converted into a fiber form by cross-wire treatment, and types of fluororesin with this property include polytetrafluoroethylene, polytrifluoroethylene, polyvinylidene fluoride, etc. can.

Therefore, the dehumidifying sheet of the present invention is a composite material in which the fluororesin dispersed in the tissue exhibits the form of fine fibers and becomes entangled, and the fiber network reliably captures and supports the powdery hygroscopic filler. It is formed as a composition.

The manufacturing method according to the present invention for obtaining a dehumidifying sheet having such a composition includes @humidity filler powder 1 with a particle size of 50 μm or less.
00 parts by weight is blended with 1 to 10 parts by weight of a fibrillating fluororesin, kneaded with a liquid kneading aid until the fluororesin becomes fibrillated, and then formed into a sheet.

The hygroscopic filler is selected from calcium chloride, silica gel, activated alumina and zeolite and has a particle size of 50 μm.
Finely pulverized material is used below.

When the particle size exceeds 50 μm, smooth fibrillation of the fluororesin is inhibited, and the resulting sheet becomes brittle.

As the fibrillating fluororesin, fluororesins that can be converted into a fibrous form by kneading treatment are commonly used, such as the aforementioned polytetrafluoroethylene, polytrifluoroethylene, and polyvinylidene fluoride.

Fibrillating fluororesin is hygroscopic filler powder 1
It is blended in a range of 1 to 10 parts by weight per 00 parts by weight. If the amount is less than 1 part by weight, the entanglement of the fiber network will be insufficient, making it impossible to form a strong sheet, and if it exceeds 10 parts by weight, the moisture absorption capacity will decrease and the sheet surface will become 18-aqueous. This causes deterioration of wettability.

A liquid kneading aid such as water, alcohol, glycerin or a mixture thereof is added to these components and kneaded. The amount of kneading aid added is 10% of the hygroscopic filler powder.
It is suitable to set it in the range of 30 to 80 parts by weight per 0 parts by weight.

The hygroscopic filler powder, fluororesin, and kneading aid are kneaded until the fluororesin is fibrillated. Although there are no particular limitations on the equipment used for the mixing process, it is desirable to perform the kneading under shear stress.

The obtained kneaded paste can be formed into a sheet by, for example, using two constant-velocity rolls and passing between the rolls multiple times. At this time, the conditions for smooth molding without cutting the fibrillated fibers are that the roll rotation speed is 7.5 mm at room temperature. It is preferable to set it to about Orp-.

The formed sheet is dried and then subjected to heat and pressure treatment to harden the fluororesin.

The dehumidifying sheet thus obtained has a thickness of 4001 mm.
Although it has a thin film shape of around 1a, it has a tough texture.

[For production]

The dehumidifying sheet of the present invention has a diameter of 3-20 μm and a length of 100-20 μm.
It has an integrally strong composite form in which the hygroscopic filler is captured and carried within the mesh structure in which the fluororesin, which has been converted into fine fibers of about 200 μm, is intertwined.

This unique composite composition form is formed based on the manufacturing process of the present invention, particularly the fiberization and entanglement effect of the fluororesin in the kneading process, and the firming effect of capture and support in the sheet forming process, and this form is formed into a powder-like form. It functions to provide non-contamination and flexibility for easy handling without impairing the high moisture absorbing performance of wet cutting.

Further, due to the excellent high temperature resistance and chemical resistance of the fluororesin that constitutes the fine fibers, it is possible to use the product without being affected by conditions such as high temperature and low temperature.

〔Example〕

Examples of the present invention will be described below in comparison with comparative examples.

Examples 1-2, Comparative Examples 1-2 Silica gel powder (hygroscopic filler) with different particle sizes 100
Fibrillating polytetrafluoroethylene (P-Pε) powder (manufactured by Mitsui DuPont Fluorochemical Koji Koji, 6C-J) was blended in different composition ratios based on the weight parts. To this was added 65 parts by weight of alcohol per 100 parts by weight of silica gel powder as a kneading aid, and the mixture was charged into a kneader-type mixer and sufficiently stirred and mixed until the fluororesin was fibrillated.

Next, the mixed wire paste was mixed using a constant speed two roll forming machine.
Temperature 40℃, rotation speed 7. The sheet was formed by passing between rolls repeatedly for 10 times under the conditions of ORPM.

Dry the formed sheet at a temperature of 150℃, and then dry it at a temperature of 3℃.
The fluororesin component was completely cured by heat pressure treatment using a hot press at ℃.

The obtained dehumidifying sheet was in the form of a thin film with a thickness of about 400 μm.

Various physical properties and moisture adsorption capacity were measured for each produced dehumidifying sheet, and the results are shown in Table 1 in comparison with the application conditions.

The moisture adsorption capacity was measured by placing glycerin aqueous solutions of different concentrations in a desiccator (20°C, normal pressure), adjusting the relative humidity to 10%, 50%, and 90%, and suspending each specimen in the desiccator. In this state, the change in weight f# is measured at 5 minute intervals to detect the overlap at the time of equilibrium moisture adsorption, and this weight and 15
It was determined from the difference in weight of identical specimens dried at 0'C for 5 hours.

Table 1 The dehumidifying sheet of Example 1.2 has good non-contamination properties that do not cause powder to scatter when handled, has flexibility to easily deform, and has relatively good physical properties and efficient moisture absorption. It had both performance.

On the other hand, in Comparative Example 1 in which the amount of the fibrillating fluororesin was less than 1 part by weight, the strength properties of the sheet became low and the structure was broken in a size of 5.
It was observed that the sheet of Comparative Example 2, in which the fibrillating fluororesin amount exceeded 10 parts by weight, had a deteriorated moisture absorption performance.

Examples 3 to 5 Calcium chloride, activated alumina, and zeolite powders each having a particle size of 50 ttm or less were used as hygroscopic fillers, and the same fibrillating polytetrafluoroethylene (PTPE) as in Example 1 was added to 100 parts by weight of this powder. ) powder was blended in an amount of 5 parts by weight.

The mixture was kneaded, molded, and heat-pressed under the same conditions as in Example 1 to produce a dehumidifying sheet with a thickness of about 400 μm.

Each of the obtained dehumidifying sheets was a flexible and strong sheet, and its hygroscopic performance was determined by the hygroscopic filler used as the raw material powder, as can be seen from the measured moisture adsorption capacity in Table 2 (at relative humidity of 50χ). It showed the same moisture absorption performance.

Table 2 [Effects of the Invention] As described above, according to the present invention, it has high @humidity performance equivalent to that of granular water-absorbing soybeans, can be used under high and low temperature conditions, and has good non-contamination properties. It becomes possible to use a flexible dehumidifying sheet.

Therefore, the sheet can be directly laid or attached to the dehumidifying area, and can also wrap around the object to be dehumidified, resulting in the effect of greatly expanding the range of applications to which it can be applied.

Applicant: Tokai Carbon Co., Ltd. Agent: Patent Attorney Masaya Takahata

Claims (1)

[Scope of Claims] 1. A dehumidifying sheet having a composite composition in which fibrillated fluororesin is dispersed in the structure of a hygroscopic filler. 2. The hygroscopic filler is calcium chloride, silica gel,
The dehumidifying sheet according to claim 1, which is made of activated alumina or zeolite. 3. Blend 1 to 10 parts by weight of a fibrillating fluororesin with 100 parts by weight of hygroscopic filler powder with a particle size of 50 μm or less, knead with a liquid kneading aid until the fluororesin fibrillates, and then form a sheet. A method for producing a dehumidifying sheet characterized by: