JPH0121172B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing synthetic resin molded articles having excellent drop-free properties, such as synthetic resin films, sheets, and plates. In this specification, "dropless property" refers to the property that water droplets do not adhere to the surface of a synthetic resin molded article. The surfaces of molded synthetic resins such as polyethylene, polypropylene, polyvinyl chloride, polyester, and polymethyl methacrylate are hydrophobic and have little affinity for water, so water droplets tend to adhere to them. For example, when a synthetic resin film or sheet is used for an agricultural greenhouse, water vapor evaporating from soil or crops condenses on the surface of the film or sheet to form water droplets. As a result, the film or sheet becomes cloudy, the transmittance of sunlight decreases, the growth of crops is hindered, or leaf rot occurs due to falling water droplets. Conventionally, in order to prevent water droplets from adhering to such synthetic resin moldings, various surfactants and hydrophilic polymer compounds have been kneaded into the synthetic resin before molding, or they have been applied to the surface of the synthetic resin molding. A coating method is used. These methods generally have short-lasting drip-free properties, lasting only a few months, and those with good drip-free properties tend to cause haze to form inside agricultural greenhouses from dusk to night. It had drawbacks such as causing disease outbreaks. And considering that the better the drip-free property is, the more noticeable the mist is,
The cause of the haze is presumed to be as follows. That is, at night, the temperature of the ground is higher than the surrounding air, and moisture evaporates from the ground, but the water vapor is cooled by the surrounding air and turns into mist droplets. On the other hand,
A water film is formed on the inner surface of the film or sheet used in the house due to the non-droplet effect.
The surface of the water film contains a dissolved surfactant, which prevents the mist droplets from condensing on the water film, causing the mist droplets to accumulate inside the greenhouse and form a mist. It has already been proposed to use a mixture of an inorganic aqueous sol and a surfactant as a type of spray-on type non-droplet agent. For example, a product containing a surfactant as its main ingredient and a small amount of silica sol added to it (Tokuko Kokko 1973-
11348), alumina sol with a surfactant added (Japanese Patent Publication No. 49-32668), alumina sol with a surfactant and a hydrophilic polymer added (Japanese Patent Laid-open No. 51-81877), colloidal A product made by adding a hydrophilic polymer and a surfactant to silica (Japanese Patent Application Laid-Open No.
-3832), silica sol with surfactant added (JP-A-55-56177 and JP-A-54-20979)
Publication No.) etc. In these known documents, although the concentration of surfactant is considerably reduced, in many cases the non-droplet still contains 0.1% by weight or more of surfactant, which may cause haze to occur. has not yet been resolved. In other words, in order to wet low-energy surfaces such as polyethylene, it is necessary to lower the surface tension of the coating liquid to 31 dynes/cm or less, but all of the above-mentioned known documents also discuss lowering the surface tension of the non-droplet agent. This wets the plastic surface, making it easier to apply the dropless agent to the plastic surface. Therefore,
In general, this type of dropless agent requires the presence of a surfactant of 0.1% by weight or more, and can be applied continuously, quickly and uniformly to plastic films, sheets, etc. using industrially advantageous methods such as dipping and roll coating. The presence of a higher concentration of surfactant was considered desirable for coating. Some of the examples in the above-mentioned known documents have a surfactant concentration of 0.1% by weight or less, but in that case, the coating method is limited to spray coating, and industrially advantageous dipping or roll coating methods are used. It has not been done. It has also been reported that when a polyethylene or Teflon film is immersed in an aqueous sol of iron hydroxide or tin hydroxide, colloidal particles are deposited on the film surface and the film becomes wet with water. Journal of Colloid and Interface Science, Volume 42, No. 3, No. 589~
See page 596 (1973)]. However, according to the bulletin,
Polyethylene film is immersed in iron hydroxide sol or tin hydroxide sol to deposit colloidal particles on the film surface until it becomes wet with water.
2.0 minutes or 0.25 for polyethylene film
It is said that it is necessary to soak each for a minute. In addition, the present inventors actually produced films in which colloidal particles were deposited on polyethylene films using the above method, and used them in agricultural greenhouses to evaluate their performance. These films were found to be practical in the following respects. It turned out that there was no sex. That is, these films were wetted by liquid water, but became cloudy when used in agricultural greenhouses and came into contact with water vapor. In particular, the cloudiness lasted for an extremely long time during seasons when the amount of water vapor transpiration was low, such as winter. This is because the density of the colloidal particles on the film surface is low and the surface of the polyethylene film is exposed between the colloidal particles.
That is, when such a film comes into contact with liquid water, the water spreads out as a liquid film and wets the film even if there is a large exposed area, but water vapor condenses on the film surface in the form of small droplets. In the exposed area, it is repelled and remains as a droplet, so it appears cloudy. To eliminate this, it is necessary to increase the density of the colloidal particles deposited on the surface of the polyethylene film, and in order to give the polyethylene film a droplet-free property that does not cloud with water vapor, the polyethylene film can be coated with iron hydroxide or tin hydroxide. It is necessary to immerse the material in an aqueous sol for 15 minutes, preferably 30 minutes, and this is by no means practical for industrial use. The present inventors have developed an industrially advantageous synthetic resin molded product that uses little or no surfactant to suppress the generation of mist and has excellent drip-free properties over a long period of time. The present invention was achieved as a result of various researches aimed at manufacturing the same. That is, the method for producing a synthetic resin molded product with excellent drop-free properties according to the present invention involves adding 0.05 to 20% by weight of colloidal silica and a water-soluble aluminum salt per 100ml of liquid.
A method characterized by treating a synthetic resin molded article with an aqueous liquid containing 10 ^-4 to 0.1 mol and having a surface tension of 35 to 75 dynes/cm to deposit colloidal silica particles on the surface of the synthetic resin molded article. It is. Conventionally, on a negatively charged surface such as glass,
There are reports of instantaneous deposition of positively charged alumina sol. And the surface of polyethylene etc.
It is estimated that the polyethylene film is close to neutral or has a weak negative charge, but even if such a polyethylene film is immersed in alumina sol, the deposition rate of the alumina particles is extremely slow, and it is not until immersed for an hour that it becomes insufficient. There was only evidence of deposition. In addition, silica sol does not actually deposit on the surface of a synthetic resin molded product such as polyethylene at all. However, when a small amount of water-soluble aluminum salt is added to silica sol, some of the colloidal silica aggregates and becomes cloudy, but when a synthetic resin molded product such as polyethylene is immersed in it, precipitation occurs almost instantaneously. This was discovered in the present invention. Furthermore, when the addition ratio of aluminum salt was increased, agglomeration did not occur,
In fact, it was found that a more transparent aqueous liquid was obtained than when the addition ratio was small, and that this aqueous liquid also caused instantaneous deposition. When the synthetic resin molded product after such deposition treatment was dried and then exposed to water vapor, it did not become cloudy and exhibited excellent drop-free properties. It is thought that aluminum ions or hydrated aluminum ions are adsorbed on the surface of colloidal silica particles obtained by adding a water-soluble aluminum salt to colloidal silica, but the positively charged alumina sol is It is completely unexpected that the deposition rate of silica particles obtained by adding a water-soluble aluminum salt to such colloidal silica is extremely high, even though the deposition rate on films and the like is extremely low. Furthermore, the aqueous colloidal silica sol to which such aluminum salts are added used in the present invention has excellent storage stability, with almost no progress of aggregation being observed even if it is left at room temperature for about a week. The colloidal silica used in the present invention is 0.05
~20% by weight and 100ml of water-soluble aluminum salt solution
At first glance, the aqueous liquid containing 10 ^-4 to 0.1 mol per mol (hereinafter referred to as "deposition liquid") is similar to the known spray-on type non-droplet agent, which is made by adding a surfactant to silica sol or alumina sol. However, the two can be clearly distinguished in the following points. (i) Conventional spray-on type non-drop agents add a relatively large amount of surfactant to lower the surface tension to 31 dynes/cm or less, and apply the product by wetting the surface of the synthetic resin molding. . In contrast, the deposition solution of the present invention does not contain any or almost no surfactant (in this case, the surfactant content is less than 0.0001% by weight), and its surface tension is 35 to 75 dynes/cm, and if you try to apply it to a synthetic resin molded product such as polyethylene using a brush coating method or a roll coater method, it will be repelled and cannot be applied, so it can only be applied by dipping or spraying methods. can. (ii) If a conventional spray-on type non-drop agent is applied to the surface of a synthetic resin molded product and immediately rinsed with water, the colloid particles will be washed away and the product will return to its water-repellent state. On the other hand, even if a synthetic resin molded article is immersed in the deposition solution of the present invention for several seconds, then taken out and immediately rinsed with water, the surface of the synthetic resin molded article remains wet, and the deposited colloidal silica remains wet. Indicates that it will not be washed away by water. The deposition solution of the present invention contains colloidal silica from 0.05 to
It is an aqueous liquid containing 20% by weight, preferably 0.5 to 5% by weight, and 10 ^-4 to 0.1 mol, preferably 10 ^-3 to 0.05 mol of water-soluble aluminum salt per 100 ml of liquid, and its surface tension is 35 to 75. Such a deposition solution of dynes/cm can be prepared, for example, by adding a solid water-soluble aluminum salt to an aqueous colloidal silica solution (i.e., an aqueous silica sol) at the desired concentration; It can be prepared by adding an aqueous solution of aluminum salt dissolved in water in advance. The water-soluble aluminum salt may be of any type as long as it is water-soluble. For example, aluminum sulfate, aluminum nitrate, aluminum chloride,
Examples include various alums and aluminum acetate. If the silica concentration of the deposition liquid of the present invention is too low, colloidal silica cannot be deposited effectively, and if the silica concentration is too high, the smoothness of the surface of the synthetic resin molded article after treatment will be impaired. In addition, if the water-soluble aluminum salt concentration is too high, the surface of the synthetic resin molded product will become rough after treatment, and if the salt concentration is too low, the deposition rate will be slow, and the persistence of the drop-free property of the resulting molded product will also be reduced. do. Examples of the synthetic resin molded product in the present invention include various synthetic resin molded products such as polyethylene, polypropylene, polyvinyl chloride, polyester, and polymethyl methacrylate, and the shapes of the molded products include films, sheets, plates, etc. can be given. A method for carrying out the present invention industrially includes, for example, a method in which a synthetic resin molded article, such as a film or sheet, is continuously passed through a liquid bath containing a deposition liquid, and the synthetic resin molded article is continuously immersed. is an efficient and preferable method. The immersion treatment time at that time, that is, the residence time in the liquid bath or the contact time with the treatment liquid, varies somewhat depending on the composition of the depositing liquid and the type of resin, but is usually sufficiently uniform within a few seconds to 10 seconds. Deposits of silica particles are obtained. The deposition solution of the present invention contains almost no surfactant (in this case, the surfactant content is less than 0.0001% by weight as described above), or does not contain any surfactant at all, so that the surface tension is 35%. Since it is large at ~75 dynes/cm, even if you try to apply it by brush coating or roll coating, the liquid will be repelled and you will not be able to effectively deposit silica particles. For this purpose, the above-mentioned deposition treatment method is most preferred, but
For small-scale implementation, it is also possible to use, for example, a spray method. In the present invention, it is desirable to dry the synthetic resin molded product treated with the deposition liquid using hot air to make a dry product from the viewpoint of handling and performance, but in some cases it may be left undried. However, it can also be used. Furthermore, in synthetic resin molded articles treated with a deposition liquid, depending on the concentration of the deposited liquid, excessive deposition liquid may adhere to the deposited silica particle layer, and the surface of the molded article may become rough after drying. In order to prevent this, the synthetic resin molded article treated with the depositing liquid may be subsequently rinsed (washed) with water by passing it through a water tank to wash off the excess depositing liquid, and then dried. Such rinsing treatment with water does not have any negative effect on the drop-free property, and on the contrary, if the deposited liquid contains surfactant, most of the surfactant is removed by rinsing treatment. This is preferable because it can prevent the generation of mist when used in agricultural greenhouses and the like. The synthetic resin molded product treated with the deposition liquid of the present invention is
Instead of the water rinsing treatment described above, the silica sol may be passed through an aqueous solution containing a gelling agent and then dried. Such gelling agent treatment significantly improves the coating strength of the silica layer after drying, increases resistance to peeling due to finger friction, etc., and also reduces the concentration and temperature of the deposited liquid during dipping treatment. Even if there are some fluctuations in the drying temperature, etc. during drying, there will be less fluctuation in the drop-free property of the product and the level of persistence of the drop-free property, facilitating stable operation, which is extremely advantageous industrially. The above gelling agent for silica sol refers to a substance that has the effect of coagulating colloidal particles of silica sol. In general, colloidal silica particles in a silica sol have a negative charge on their surface, and the electrical repulsion between the charges prevents the particles from agglomerating and maintains a stable sol state. When a substance that neutralizes the electric charge is added, particles agglomerate and gel. Examples of gelling agents for silica sol include acids, alkalis, salts, cationic surfactants, amphoteric surfactants, alumina sol, and organic substances such as ethanol and acetone. The concentration of the gelling agent in the aqueous liquid containing the gelling agent used in the present invention varies depending on the type of gelling agent, but usually
0.1-30% by weight, preferably 0.5-5% by weight. When the synthetic resin molded products obtained by the production method of the present invention, such as films and sheets, are used in agricultural greenhouses, etc., they do not become cloudy even in winter and exhibit extremely excellent drip-free properties. Moreover, the drip-free property can be maintained for a long period of 6 months or more.
Furthermore, despite its excellent drip-free properties, almost no mist is observed inside the greenhouse at night. Furthermore, the films and sheets have good transparency and are not sticky, and the silica particle-deposited coating has high strength both when dry and wet, and the silica particles remain even when rubbed with fingers, etc. Does not peel off easily. The present invention will be explained in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples in any way. The percentages in these examples are by weight unless otherwise stated. Examples 1 to 8 Various water-soluble aluminum salts were added and dissolved in solid form to diluted aqueous solutions of commercially available silica sol to prepare deposition solutions having the compositions of Examples 1 to 8 shown in Table 1. The silica sol used was Snotex 40 (trade name, manufactured by Nissan Chemical Industries, Ltd.) in Examples 1 to 3, Snotex O (trade name, manufactured by Nissan Chemical Industries, Ltd.) in Examples 4 to 5, Snotex C (trade name, manufactured by Catalysts & Chemicals, Ltd.) in Examples 6 to 7, and Snotex C (trade name, manufactured by Catalysts and Chemicals Industries, Ltd.) in Example 8. It was Cataloid SH-30. Also,
All of the aluminum salts used were special grade reagents manufactured by Wako Pure Chemical Industries, Ltd. Agricultural low-density polyethylene films were immersed in each of these deposition solutions for various times shown in Table 1, taken out, rinsed in water for 5 seconds, and air-dried.
At that time, we examined the wet state of the film surface due to water when it was removed from the water after rinsing, and the cloudy state of the film surface when the air-dried film was held over steam in a water tank filled with warm water at 50℃ for 5 seconds. evaluated. The results were as shown in Table 1. Comparative Examples 1 to 8 As shown in Table 1, colloidal iron hydroxide (Comparative Example 1), colloidal tin hydroxide (Comparative Example 2), silica sol (Comparative Example 3), alumina sol (Comparative Example 4),
By adding a relatively large amount of nonionic surfactant or anionic surfactant to aluminum salt (Comparative Example 5), silica sol, or alumina sol, the surface tension of the liquid can be adjusted.
Aqueous liquid with a concentration of 30 dynes/cm or less (Comparative Examples 6 to 8)
A polyethylene film was immersed in the same manner as in Examples 1 to 8 using each of these as a treatment liquid, and was simultaneously rinsed with water and air-dried. Colloidal iron hydroxide in Comparative Example 1 and colloidal tin hydroxide in Comparative Example 2 were prepared using FeCl ₃ .6H ₂ O or SnCl ₄ .
Each was prepared using 5H ₂ O and SnCl ₂ .2H ₂ O by dissolving them in water and subjecting them to pH adjustment and aging treatment. In addition, the silica sol of Comparative Example 3 was a product name of Nissan Chemical Co., Ltd., Snotex 40, and the alumina sol of Comparative Example 4 was alumina sol, a product name of Nissan Chemical Co., Ltd.
100 was diluted with water and used. Moreover, in Comparative Examples 6 to 8, each surfactant was added to each of the above-mentioned commercially available sols.

【table】

[Table] As is clear from the results shown in Table 1, the films obtained in Examples 1 to 8 were uniformly wet with water when they were rinsed with water and pulled up, and the colloidal silica was uniformly coated. It was shown that it was deposited on
Each film did not become cloudy and remained transparent even when exposed to steam after being air-dried. In order to obtain such a film with no droplet properties, the immersion time in the deposition solution was only 20 seconds, and in some cases, several seconds were sufficient. In addition, colloidal silica is deposited on each film after rinsing, and the surfactant content in the deposited silica layer is extremely small. This was confirmed by analysis using an electron microscope. On the other hand, the films obtained in Comparative Examples 1 and 2 remained wet even after rinsing with water, indicating that colloidal silica was deposited.
It took 15 minutes (Comparative Example 1) or 5 minutes (Comparative Example 2) to prevent the film from becoming foggy by holding it over steam after air drying. Furthermore, with only the colloidal silica of Comparative Example 3, no deposition actually occurred, and with only the colloidal alumina of Comparative Example 4, although deposition occurred, the rate of deposition was extremely slow. Comparative Example 5, in which aluminum chloride salt alone was used, practically caused no deposition at all. Furthermore, the conventional spray-on type non-drop agent prepared by adding a relatively large amount of surfactant to colloidal silica or colloidal alumina of Comparative Examples 6 to 8 has a low liquid surface tension, so it is difficult to immerse the film in it. When pulled up, the surface of the film was wet, but when the film was rinsed with water, the colloidal particles were completely washed away, and it began to repel water, but when held over steam, it showed no dripping properties at all. Examples 9 to 14 Comparative Examples 9 to 14 As shown in Table 2, various treatment liquids (deposition liquids) and various synthetic resin films or sheets listed in Table 1 used in the above Examples and Comparative Examples were used. Films or sheets obtained by immersion treatment in the same manner as in Examples 1 to 8, rinsing treatment with water in the same manner, and air drying were evaluated in the same manner. The results were as shown in Table 2.

[Table] As shown in Table 2, the films or sheets obtained in Examples 9 to 14 exhibited excellent drop-free properties that did not cloud due to steam when immersed within 20 seconds. On the other hand, the films or sheets obtained in Comparative Examples 9 to 14 required long-time immersion treatment to prevent fogging due to steam, and were therefore impractical. Examples 15 to 18 Comparative Examples 15 to 17 As shown in Table 3, in Examples 15 to 18, Example 3
An agricultural low-density polyethylene film was continuously passed through a first tank containing the same deposition solution as used in the immersion treatment. The immersion (contact) time in the deposition solution was approximately 20 seconds in each case. In Example 15, the film after the immersion treatment was continuously dried with warm air at 80°C. Further, in Example 16, the water was continuously passed through a second tank containing water for rinsing, and in Examples 17 or 18, an aqueous solution containing ethanol or dodecyltrimethylammonium chloride as a gelling agent was added. After passing continuously through the second tank, both were continuously dried with warm air at 80°C. The residence (contact) time in the aqueous liquid in the second tank at that time was about 6 seconds. In Comparative Examples 15 or 16, the agricultural low-density polyethylene film was continuously passed through the first tank filled with the same treatment solution used in Comparative Examples 6 or 8, and subjected to immersion treatment for 80 minutes. Dry continuously with warm air at ℃. The residence time in the treatment liquid at that time was about 20 seconds in each case. In the case of Comparative Examples 15 and 16, coating unevenness occurred in the coating film after one immersion and drying, so the immersion and drying treatments were repeated twice. In Comparative Example 17, low-density polyethylene pellets mixed with 0.3% sorbitan monooleate as a dropless agent were formed into a film by an inflation method. Agricultural greenhouses were assembled in the winter (February) using each of the films produced as described above, and the results were as follows:
We also investigated and evaluated the occurrence of mist inside the greenhouse at night. The results were as shown in Table 3.

[Table] As is clear from the results in Table 3, Examples 15 to 18
Despite the extremely short residence time in the deposition solution, the film obtained has colloidal silica deposited uniformly and densely on the film surface, and has extremely good drop-free properties and long-lasting drop-free properties. It was hot. On the other hand, in Comparative Examples 15 and 16, the film performance was significantly inferior to that of Examples 15 to 18, even though dipping and drying were repeated twice each. Also,
The film of Comparative Example 17 was also significantly inferior to those of Examples 15-18. That is, the films obtained in Examples 15 to 18 were transparent with no clouding observed immediately after the house was assembled, and no mist was observed. On the other hand, the films obtained in Comparative Examples 15 to 17 initially exhibited a cloudy phenomenon due to adhesion of water droplets, and during use, the water droplets grew and contacted each other to form a continuous liquid film. For the first time (about 1 week after starting use),
It became transparent. The films obtained in Comparative Examples 15 to 17 were transparent from the beginning when evaluated by the above-mentioned method in which they were held over a water tank containing hot water at 50°C; This is because the amount of water vapor generated is large, and when it is used in a greenhouse in the winter when the amount of water vapor transpiration is low, it becomes cloudy for about the first week as shown in Table 3. The generation of haze was also the least in Examples 15 and 16.
Next, Example 17, Example 18, followed by Comparative Example.
15 to 17 caused the most haze. In addition, when assembling the house, the film is rubbed or bent, so part of the coating peels off and becomes scratched, resulting in partial clouding. The smallest amount was observed in Example 18 and Comparative Example 17, and the largest amount was observed in Example 15, Comparative Examples 15 and 16. This shows that the strength of the colloidal silica deposited film is improved by post-treatment with an aqueous solution containing a gelling agent such as ethanol or dodecyltrimethylammonium chloride. Incidentally, the clouding of the films obtained in Example 15 and Comparative Examples 15 and 16 due to scratches that occurred during the assembly of the house became almost inconspicuous during use of the house. Example 19 Comparative Example 18 A greenhouse was assembled using agricultural soft polyvinyl chloride film, and then a depositing solution consisting of silica sol and water-soluble aluminum salt (composition was the same as that of Example 1) was applied to the inner surface in Example 19 for comparison. In Example 18, a silica sol coating solution (composition was the same as that of Comparative Example 3) was sprayed, and the durability of the droplet-free property was immediately evaluated. In this test, the silica-containing liquid deposited on the film surface is exposed to water vapor without drying. The results showed that in Example 19, colloidal silica was deposited on the film surface, and the transparent, dropless state lasted for about 6 months, but in Comparative Example 18, the coating was easily washed away. Because of this, the transparent state only lasted for about a week, after which it became noticeably cloudy due to adhesion of water droplets.

Claims (1)

[Claims] 1. A synthetic resin molded article is treated with an aqueous liquid having a surface tension of 35 x 75 dynes/cm containing 0.05 to 20% by weight of colloidal silica and 10 ^-4 to 0.1 mol of water-soluble aluminum salt per 100 ml of liquid. A method for producing a synthetic resin molded article with excellent drip-free properties, which comprises depositing colloidal silica particles on the surface of the resin molded article.