JPH0121173B2 - - 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 product, and "dropless agent" refers to an agent that imparts dropless properties to a synthetic resin molded product. . The surface of molded synthetic resins such as polyethylene, polypropylene, polyvinyl chloride, polyester, and polymethyl methacrylate is hydrophobic and has little affinity for water, so water droplets tend to adhere to it.
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, forming water droplets. As a result, the film or sheet becomes opaque and the transmittance of sunlight decreases.
Crop growth 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.
Alternatively, a method has been adopted in which it is applied to the surface of a synthetic resin molded article. However, the synthetic resin molded products obtained by these methods have the disadvantage that their drip-free properties are short-lived, lasting only a few months, and those with good drip-free properties can be used in greenhouses from evening to night. There were drawbacks such as the generation of haze, which could cause disease outbreaks. In general, the better the drip-free property, the more significant the mist generation, and it is presumed that the cause of the mist generation is as follows. That is, at night, the temperature of the ground is higher than the surrounding air, and water vapor that evaporates from the ground is cooled by the 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 greenhouses due to the non-droplet effect, but the surface of this water film contains dissolved surfactant, which prevents mist droplets from forming. This prevents water from condensing into a film, causing mist droplets to accumulate inside the greenhouse and form a mist. It has also been proposed to use a mixture of an inorganic aqueous sol and a surfactant as a type of non-droplet coating 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), silkasol with a surfactant added (JP-A-55-56177, JP-A-54-
20979) etc. were proposed. Although the surfactant concentration of the products described in these publications is considerably reduced, in many cases the spray-on type non-drop formulation still contains surfactant in an amount of 0.1% or more, usually much larger than this. Then, when they are applied and dried, the surfactant contained therein remains, creating a mist. This means that in order to wet low-energy surfaces such as polyethylene film, it is necessary to lower the surface tension of the coating liquid to about 31 dynes/cm or less, and all of the above publications also discuss the surface tension of the non-droplet agent. The lowering wets the plastic surface, thereby allowing the dropless agent to be applied to the plastic surface. Thus, this type of spray-on type non-droplet agent generally requires the presence of a surfactant in an amount of 0.1% by weight or more, but usually in a much larger amount, especially for industrially advantageous applications such as roll coating methods. It has been considered desirable to add a surfactant at a significantly high concentration in order to coat plastic films or sheets uniformly and continuously at high speed.
In the examples of the above publication, the concentration of surfactant is
Although some contain less than 0.1% by weight, the coating method in such cases is limited to spray coating, which is industrially disadvantageous. 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, making it wet. Of Colloid and Interface Science Vol42, No.3 589-596
(1973)]. However, according to the same report, in order to make a polyethylene film wet by water by depositing colloid particles on the surface of the film by immersing it in iron hydroxide sol or tin hydroxide sol, it should be immersed for 2.0 minutes or 0.25 minutes. It is said that it is necessary to keep In addition, the present inventors actually produced a polyethylene film on which these colloidal particles were deposited using this method and evaluated its performance by using it in an agricultural greenhouse, and found that it was completely impractical in the following respects. . That is, the film was wetted by liquid water, but became cloudy when used in agricultural greenhouses and came into contact with water vapor. Particularly in winter, when the amount of water vapor transpiration was low, significant cloudiness persisted for a long period of time. It was found that this was caused by the fact that the density of the colloidal particles on the film surface was low, and the polyethylene surface was exposed between the colloidal particles.
In other words, when it comes into contact with liquid water, even if there is a large exposed area of the polyethylene surface, the water spreads out as a liquid film and wets the film, but water vapor condenses on the film surface in the form of small droplets. It is repelled by the exposed areas of the polyethylene surface and remains as droplets, giving it a cloudy appearance. To improve 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. in sol
It was found that this method cannot be implemented industrially, as it requires immersion for 15 minutes, preferably about 30 minutes. The present inventors have produced synthetic resin molded products that use as low a concentration of surfactants as possible to suppress the generation of haze, enable industrially advantageous coatings, and maintain drip-free properties for a long period of time. As a result of various researches aimed at achieving this goal, the present invention has been arrived at. That is, in the method for producing a synthetic resin molded product with excellent drop-free properties according to the present invention, colloidal silica is mixed in an amount of 0.05 to 20
Surface tension 35% by weight, containing 1×10 ^-4 to 0.1% by weight of cationic surfactant and/or amphoteric surfactant
A synthetic resin molded product is immersed in an aqueous solution of ~70 dynes/cm, or the aqueous liquid is sprayed onto the synthetic resin molded product to deposit colloidal silica particles on the surface of the synthetic resin molded product. This is a method to do so. The surface tension of the present invention, which contains 0.05 to 20% by weight of colloidal silica and 1 x 10 ^-4 to 0.1% by weight of cationic surfactant and/or amphoteric surfactant, is 35 to 35% by weight.
The 70 dynes/cm aqueous liquid is sometimes simply referred to as "deposition liquid" below. If the silica concentration in such a deposition solution is less than 0.05% by weight, deposition will be difficult to occur, and if it is greater than 20% by weight, the stability of the solution will deteriorate and the deposition treatment will become difficult. If the surfactant concentration is less than 1 x 10 ^-4 % by weight, silica deposition will be difficult to occur, and if it is more than 0.1% by weight, the deposited solution will aggregate to a large extent, resulting in poor storage stability and making deposition treatment difficult. In addition, if the surface tension is greater than 70 dynes/cm, the compatibility with the synthetic resin will be poor and deposition will be difficult to occur. From the viewpoint of processing synthetic resin moldings, it is preferable that the surface tension be as low as possible, but in order to create a state in which deposition occurs, it is necessary to set the surface tension to 35 dynes/cm or more. When a synthetic resin molded article is immersed in such a deposition solution of the present invention, it is usually almost instantaneous, at least 20 minutes after being immersed.
Silica particles are deposited in a high density (finely) on the surface of the synthetic resin molded article within a period of about seconds. Even when the deposited surface is dried and brought into contact with water vapor, no clouding is observed, showing excellent drip-free properties. Conventionally,
On a hydrophilic and negatively charged surface like glass,
There are reports that positively charged alumina sol is deposited in a short period of time, but silica sol is deposited almost instantaneously on the surface of hydrophobic, electrically neutral or nearly neutral materials such as polyethylene. The thing is,
This is completely unexpected and surprising. At first glance, the deposition liquid used in the present invention appears to be similar to a conventional coating-type non-drop agent made by adding a surfactant to silica sol or alumina sol, but in reality, the two can be clearly distinguished in the following points. be. (i) Conventional spray-on type non-drop agents are applied by adding a relatively large amount of surfactant to lower the surface tension to about 31 dynes/cm or less so that it leaks onto the surface of the synthetic resin. In contrast, the deposition solution of the present invention has a relatively low surfactant concentration and a surface tension of 35 to 70 dynes/cm, preferably 35 to 70 dynes/cm, and has a surface tension of 35 to 70 dynes/cm, preferably 35 to 70 dynes/cm. Even if you try to apply it using a roll coater method or a brush coating method, it will be repelled and cannot be applied, so it can only be deposited and applied by spraying or dipping methods. (ii) When 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 conid particles are washed away and the product returns to its water-repellent state. In contrast, even if a synthetic resin molded article is immersed in the deposition solution of the present invention for a few seconds, then taken out and immediately rinsed with water, the surface of the synthetic resin molded article is still wet with water, and the deposited colloidal silica remains. is not washed away by water. Thus, the deposition solution in the present invention contains 0.05 to 20% by weight of colloidal silica, preferably 0.5 to 20% by weight.
5% by weight, cationic surfactant and/or amphoteric surfactant from 1×10 ⁻⁴ to 0.1% by weight, preferably
It contains 0.05 to 0.1% by weight, and is usually easily prepared by mixing a dilute aqueous solution of the above surfactant with silica sol diluted with water. Generally, when a cationic surfactant or an amphoteric surfactant is added to silica sol, the charge on the silica is neutralized, causing precipitation or gelation, but when the surfactant is added at a relatively low concentration, The deposition solution of the present invention is in a state where almost no sedimentation occurs or it is only slightly cloudy. In addition, even if some precipitation occurs, it does not have much of an adverse effect on the deposition properties or drip-free properties. However, in that case, the transparency of the film etc. after the treatment is somewhat reduced, but this can be easily solved by rinsing the film etc. with water after the immersion treatment. As the surfactant in the deposition solution of the present invention,
Cationic surfactants, amphoteric surfactants, and mixtures of both are used. The surfactant may be of any type as long as it is a cationic surfactant and/or an amphoteric surfactant. Examples of the cationic surfactant include alkylamine salts, alkylammonium salts, alkylpyridinium salts, and the like. Examples of amphoteric surfactants include betaine type surfactants, glycine type surfactants, sulfuric acid ester salt types, sulfonic acid type surfactants, and phosphoric acid ester type surfactants.
Two or more of these surfactants may be used in combination. The alkyl group constituting the lipophilic part of the surfactant should have 8 carbon atoms from the viewpoint of surfactant action.
Generally, the number of carbon atoms is 18 to 18, but in the present invention, there is no need to lower the surface tension with a surfactant, so the number of carbon atoms is outside the range of 8 to 18, and therefore the surface active effect is poor. It can also be used as a compound. That is, the surfactant in the present invention includes:
It is also intended to include homologs of cationic surfactants that have poor surfactant action. A particularly preferred surfactant in the deposition solution of the present invention belongs to the cationic surfactants, and has the general formula
It is an alkyltrimethylammonium salt represented by RN ⁺ (CH ₃ ) ₃ ·X ⁻ (wherein R is an alkyl group having 8 to 18 carbon atoms, and X is Cl or Br). This alkyltrimethylammonium salt has a wide concentration range in which it does not cause turbidity in the silica sol, has an extremely high deposition rate, and can instantaneously deposit silica and provide extremely excellent dropless properties. As a method for implementing the present invention industrially and with high efficiency, there is a method in which a synthetic resin molded article (for example, a film or sheet) is continuously immersed in the deposition solution in a liquid tank containing the deposition solution. can give. The residence time (immersion time) of the synthetic resin molding in the depositing solution differs depending on the composition of the depositing solution and the type of resin, but it usually takes a few seconds to 10 seconds to achieve sufficiently uniform deposition. can be done. The deposition liquid of the present invention has a low surfactant concentration and a high surface tension, so even if an attempt is made to apply it by a roll coater method or a brush coating method, the liquid will be repelled and cannot be applied. The immersion method is used. When using the immersion method, the synthetic resin molded product is immersed in an aqueous liquid and the non-droplet component is deposited on its surface before it is pulled up, so there is little residual liquid component of the non-droplet agent and, therefore, the amount of surfactant is reduced. The amount remaining will be reduced. When using the spray method, use a squeeze roll to remove residual liquid components, or hold the treated film vertically to remove residual liquid components. The synthetic resin molded article that has been immersed in the deposition solution according to the present invention is then normally dried using hot air or the like to form a product, which is desirable in terms of product handling and performance. In fact, it can be put to practical use even if it is left undried. Further, depending on the concentration of the depositing liquid, excessive depositing liquid may adhere to the synthetic resin molded article after being immersed in the depositing liquid in the present invention, and the surface of the molded article after drying may become rough. To prevent this, the synthetic resin molded article after the immersion treatment may be subsequently passed through a water tank, rinsed with water to wash off excess deposited liquid, and then dried. Rinsing with water does not change the drip-free property; in fact, excess surfactant is washed away, which reduces the occurrence of mist inside the greenhouse when used in agricultural greenhouses, etc. is possible and preferable. As the gelling agent used in such gelling agent treatment, any substance can be used as long as it has the effect of coagulating colloidal particles of silica sol. In general, colloidal silica particles in silica sol have a negative charge on their surface, and the electrical repulsion between the charges prevents the particles from agglomerating, maintaining a stable sol state. However, when a substance that neutralizes the charge is added to this, the particles coagulate and gel. Such gelling agents include acids, alkalis, salts, cationic surfactants, amphoteric surfactants, alumina sol, and organic substances such as methanol and acetone. The concentration of the gelling agent in the gelling agent aqueous solution used for this purpose varies depending on the type of gelling agent, but is usually 0.1 to 10% by weight, preferably 1% by weight.
~5% by weight. When the synthetic resin molded products obtained by the production method of the present invention, such as synthetic resin films and sheets, are used in agricultural greenhouses, etc., they do not fog up even in winter and exhibit extremely excellent drip-free properties. And the drip-free property lasts for a long period of 6 months or more. In addition, despite the excellent drip-free properties, there is hardly any mist generated inside the greenhouse at night. Furthermore, the film has good transparency, does not have a sticky surface, and the strength of the silica coating is high both when dry and wet, and the coating film cannot be rubbed by fingers or other objects. Silica particles do not fall 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 noted. Examples 1 to 7 Various treatment solutions (deposition solutions) shown in Table 1 were prepared by mixing various commercially available diluted aqueous solutions of silica sol and various commercially available aqueous cationic or amphoteric surfactant solutions. The silica sol used was Snowtex 40 (trade name, manufactured by Nissan Chemical Co., Ltd.) in Examples 1 and 2, Snowtex O (trade name) from Nissan Chemical Co., Ltd. in Examples 3 and 4, Snowtex C (trade name) (trade name) from DuPont Co., Ltd. in Examples 6 and 7, and Ludotux HS- (trade name) from Dupont Co., Ltd. in Examples 6 and 7. It was 40. Agricultural low-density polyethylene films were immersed in each of the resulting deposition solutions for various times shown in Table 1, taken out, rinsed in water for 5 seconds, and then air-dried. We examined the wet state of the film surface when it was removed from the water after rinsing, and the state of the film surface when the air-dried film was held over the steam for 5 seconds over a water tank filled with 50℃ water. The evaluation results were as shown in Table 1. Comparative Examples 1 to 9 Colloidal iron hydroxide (Comparative example 1), colloidal tin hydroxide (Comparative example 2), colloidal silica (Comparative example 3), colloidal alumina (Comparative example 4), cationic surfactant (Comparative Example 5), an aqueous liquid in which a relatively large amount of nonionic or anionic surfactant was added to colloidal silica or colloidal alumina (Comparative Examples 6 to 8), a relatively large amount of cationic surfactant in silica sol, The same polyethylene film was immersed in the same manner as in Examples 1 to 7 using each of the aqueous liquids (Comparative Example 9) added in large amounts to the above, rinsed with water in the same manner, and then air-dried in the same manner. The preparation of colloidal iron hydroxide in Comparative Example 1 and colloidal tin hydroxide in Comparative Example 2 was carried out using FeCl ₃ 6H ₂ O and
This was carried out by dissolving mixtures of SnCl ₄ .5H ₂ O and SnCl ₂ .2H ₂ O in water, adjusting the pH and aging. In addition, all colloidal silica in the comparative examples was manufactured by Nissan Chemical Co., Ltd. under the trade name Snotex.
40 was used, and the colloidal alumina was Alumina Sol 200 (trade name, manufactured by Nissan Chemical Co., Ltd.).

【table】

【table】

[Table] As shown in Table 1, the films of Examples 1 to 7 were uniformly wet with water when they were rinsed with water and pulled up, indicating that colloidal silica was deposited. . Furthermore, the film did not become cloudy and remained transparent even when it was held up to steam after being air-dried.
In order to obtain such a deposited film, only 20 seconds of immersion in the deposition solution was required, and in some cases even several seconds were sufficient. It should be noted that in the films of Examples 1 to 7, silica was deposited even after rinsing, and the surfactant content of the deposited layer after rinsing was extremely low, as determined by X-ray photoelectron spectroscopy (ESCA) and electron spectroscopy. Confirmed by microscopic analysis. On the other hand, the films obtained in Comparative Examples 1 and 2 remained wet even after rinsing with water, so
Although deposition of colloidal particles was observed, the immersion time required for the air-dried film to remain cloudy even when exposed to steam was at least 15 minutes in Comparative Example 1, and at least 5 minutes in Comparative Example 2.
Furthermore, as in Comparative Example 3, colloidal silica alone does not actually cause silica deposition, and as in Comparative Example 4, although colloidal alumina alone causes deposition, the deposition rate is extremely slow. Comparative examples 5 to 8
Products that use relatively large amounts of various surfactants to lower the surface tension to below 19 to 30 dynes/cm, such as those used in this article, have a high resistance to water after immersion, regardless of whether colloidal particles are used in combination or not. However, when rinsed with water, both the surfactant and the colloidal particles were completely washed away, and the product began to repel water, showing virtually no dripping properties. Further, in the treatment liquid in which a relatively large amount of cationic surfactant was added together with colloidal silica as in Comparative Example 9, agglomeration was severe and stable coating treatment could not be performed. Examples 8 to 13 Comparative Examples 10 to 15 As shown in Table 2, various synthetic resin films or sheets were treated in the same manner using the same treatment liquid (deposition liquid, etc.) used in the above Examples and Comparative Examples. A film or sheet obtained by immersion treatment, rinsing in the same manner, and air drying in the same manner was evaluated in the same manner. The results were as shown in Table 2. That is, the films or sheets obtained in Examples 8 to 13 exhibited excellent drip-free properties that did not cloud due to steam even when immersed for 20 seconds or less. On the other hand, the films obtained in Comparative Examples 10 to 15 required immersion for 5 minutes or more to become unclouded by steam, and were not practical.

[Table] Examples 14 to 17 Comparative Examples 16 to 18 As shown in Table 3, Examples 14 to 17
An agricultural low-density polyethylene film was continuously passed through a first tank containing the same deposition solution as in , and subjected to immersion treatment. The immersion time was about 20 seconds in each case. The film after immersion is as shown in Example
14, it was dried continuously with warm air at 80°C.
In Example 15, the material was rinsed by continuously passing through a second tank containing water, and then continuously dried with warm air at 80°C. Furthermore, in Example 16, the water was continuously passed through a second tank containing a diluted aqueous solution of alumina sol, and in Example 17, it was passed continuously through a second tank containing water containing a cationic surfactant. Continuously dried with hot air. In Comparative Examples 16 or 17, the agricultural low-density polyethylene film was continuously passed through a first tank containing the same treatment solution as used in Comparative Examples 6 or 8, and then subjected to immersion treatment. Continuously dried with warm air at 80℃. The immersion time was about 20 seconds in each case. In the case of Comparative Examples 16 and 17, the coating film was uneven when immersed and dried only once, so the immersion and drying were repeated twice. In Comparative Example 18, low-density polyethylene pellets mixed with 0.3% sorbitan monooleate as a dropless agent were formed into a film by an inflation method. Using each of the films obtained in Examples 14 to 17 and Comparative Examples 16 to 18 above, agricultural greenhouses were assembled in the winter (February), and the drip-free properties, the sustainability of the drip-free properties, and the time of house assembly were evaluated. The evaluation was conducted by examining the occurrence of scratches and the occurrence of haze inside the greenhouse at night. The results were as shown in Table 3.

[Table] In each of the films obtained in Examples 14 to 17, silica was uniformly deposited on the film surface and exhibited excellent drop-free properties, even though the immersion time in the deposition solution was extremely short. On the other hand, the films obtained in Comparative Examples 16 and 17 were repeatedly immersed and dried twice, but their drop-free properties and other properties were significantly inferior to those of Examples 14 to 17. That is, the films obtained in Examples 14 to 17 did not develop fog and were transparent immediately after being assembled in the house. Also, there was less haze. On the other hand, the films obtained in Comparative Examples 16 to 18 developed cloudiness due to adhesion of water droplets for the first week or so, and the water droplets gradually became larger during use, causing the water droplets to contact each other. It became transparent only after a continuous water film was formed. The occurrence of haze was also more significant than in Examples 14-17. and,
The persistence of drip-free property was the best in Examples 14 to 17, followed by Comparative Examples 17 and 16, and Comparative Example
18 was the most inadequate. Also, when assembling the house, the film etc. is rubbed or bent, so part of the coating peels off and becomes scratched, resulting in partial cloudiness. Although it was observed to some extent in Examples 14 to 15 and Comparative Examples 16 and 17, it became almost unnoticeable during use of the greenhouse. In contrast, in Examples 16 and 18, virtually no such scratches were observed. From this, it has been found that the strength of the colloidal silica deposited film can be significantly improved by post-treating the silica sol with a gelling agent such as an alumina sol or a cationic surfactant-containing liquid.

Claims (1)

[Claims] 1 0.05-20% by weight of colloidal silica, 1× cationic surfactant and/or amphoteric surfactant
Surface tension including 10 ^-4 ~0.1% by weight 35~70 dynes/cm
A dropless method characterized by depositing colloidal silica particles on the surface of the synthetic resin molded article by immersing the synthetic resin molded article in an aqueous liquid or spraying the aqueous liquid onto the synthetic resin molded article. A method for producing excellent synthetic resin molded products.