From the viewpoint of further decreasing the difference in the SP value, when polypropylene is used as the polymer, a preferable solvent is, for example, xylene, decalin, and butyl acetate. When polyethylene is used as the polymer, a preferable solvent is, for example, decalin. When PVDF is used as the polymer, a preferable solvent is, for example, DMSO.

The temperature of the solvent when the solvent and the member are contacted with each other is Tc of the polymer±50° C. and equal to or lower than the boiling point of the solvent. In particular, with a resin having a proportion of a polymer made of only carbon and hydrogen (or only carbon, hydrogen, and oxygen) in the polymer component in the resin of 80% or more, it is preferable that the temperature of the solvent be higher than Tc of the polymer and be equal to or lower than the boiling point of the solvent. A phase of the solvent when the solvent and the member are contacted with each other may be either of a liquid phase or a gas phase. It is preferable that the temperature of the solvent when the solvent is contacted with the member be 90 to 160° C., and it is more preferable that it be 110 to 150° C. from the viewpoints of removability of the skin layer and formation of a highly hydrophobic and highly water-repellent surface.

[Step (a)]

In the step (a), a time of contacting the member and the solvent with each other in the solvent-contacting region is not particularly limited, and it is preferable that it be at least 30 seconds from the viewpoints of obtaining a highly hydrophobic and good water-repellent surface and forming a continuous and removable skin layer. The contacting time of the member and the solvent, which depends on a type of the used polymer, a type of the used solvent, and the temperature when the member and the solvent are contacted with each other, is typically approximately 30 seconds to 10 minutes with considering efficiency of the process and the layer having high hydrophobicity and good water repellency.

From the viewpoint of the efficiency of the process, it is preferable that the member be preheated prior to the step (a). A temperature of the preheating is not particularly limited, and it is preferable that it be equal to or lower than the temperature when the member and the solvent are contacted with each other.

[Step (b)]

Subsequently to the step (a), the member after the treatment is taken out of the solvent-contacting region where the member and the solvent are contacted with each other, and is dried. A temperature of drying the member after the treatment is lower than Tc of the polymer forming the member by at least 20° C., and preferably lower than Tc of the polymer forming the member by at least 30° C. The drying of the member may also be performed at ambient temperature or room temperature. From the viewpoint of controlling the formation of the skin layer, it is preferable that the drying in the step (b) be divided into a plurality of steps, performed by using the same or different drying means at the same or different temperatures. The number of the steps, drying means to be used, and the drying temperature are not particularly limited, and it is preferable that the temperature of one or more of the drying steps prior to the final drying step be a temperature not higher than the temperature of the final drying step.

In FIG. 1, illustrated is a series of aspects in which: a sheet-shaped or web-shaped member 1 is contacted with a solvent 3 in a solvent vessel 2 (solvent-contacting region); the member 1 is taken out of the solvent vessel 2 and then subjected to a drying means 4; and then a skin layer 5 formed on a surface of the member 1 is removed to obtain a processed body 6 provided with a superhydrophobic and water-repellent surface.

In FIG. 1, further illustrated corresponding to the above steps with each schematic view are: a cross section 1-1 of the member 1 before contacted with the solvent; a cross section 1-2 of the member 1 in which a swelled gel layer 7 is formed on the surface by contacting with solvent 3 in the solvent vessel 2 (solvent-contacting region); cross sections 1-3 and 1-4 of the member 1 taken out of the solvent vessel 2 and having the skin layer 5 formed thereon; and a cross section 1-5 when the skin layer 5 after drying is removed to obtain the processed body 6.

The method according to the present disclosure can also be performed in a batchwise embodiment instead of the continuous embodiment as illustrated in FIG. 1. Any method may be employed, and it depends on, for example, a manufacturing facility, a shape of the member, and the like. Any shape of the member may also be employed, and it is not particularly limited as long as it can be treated with the method according to the present disclosure.

Although an embodiment of the planar member is illustrated in FIG. 1, the shape of the member may be, other than a planar sheet, film, web, board (also referred to as a plank or a plate having a thickness of approximately 1 mm or more) and the like, a three-dimensional shape (a bottle of shampoo and the like are expected, for example). The member may be of a flexible material that can be wound. According to JIS (Japanese Industrial Standards), a film is referred to a membrane-shaped plastic having a thickness of less than 250 μm, and a sheet is referred to a plate-shaped plastic having a thickness of 250 μm or more.

[Processed Body and Skin Layer Having Water-Repellent Surface]

With the method according to the present disclosure, a polymer processed body having a highly hydrophobic and water-repellent surface can be manufactured simply in a short time. It is not necessary to add a water-repellent material different from the substrate or a material for forming a water-repellent structure such as, fo example, nanoparticles of titanium oxide as in the method of the conventional art. The polymer processed body having a highly hydrophobic and water-repellent surface can be manufactured by drying the member in the step (b), and on the member surface that has been contacted with the solvent in the step (a), a layer (skin layer) removable from the member is formed. On a boundary between the skin layer and the processed body, both surfaces of the processed body surface contacted with the skin layer and the skin layer surface contacted with the processed body surface are surfaces having high hydrophobicity and water repellency. The “skin layer” in the present disclosure is referred to a membrane-shaped processed body having a two-dimensional or three-dimensional shape of film, sheet, or web.

The skin layer may be left not to be removed until just before use of the processed body to, for example, protect the highly hydrophobic and water-repellent surface produced on the processed body surface. Having the highly hydrophobic and water-repellent surface similar to the processed body, the skin layer removed from the processed body may be used as a highly hydrophobic and water-repellent sheet and the like. A thickness of the skin layer, which depends on types of the polymer and solvent to be used, the temperature and time when the polymer member is contacted with the solvent, the time of drying the polymer member, and the like, is typically approximately 10 to 200 μm, and it is more preferable that it be approximately 10 to 100 μm for improvement in light transparency to be used as a translucent member.

The processed body manufactured by the method according to the present disclosure comprises the crystalline or semicrystalline polymer substrate and the crystallite structure layer, and the crystallite structure layer comprises spherulites having an average particle diameter of 300 nm to 70 μm, preferably 20 μm to 70 μm, and nanostructures having an average particle diameter of 60 nm to 1500 nm, preferably 150 nm to 1400 nm, that are present on a surface of the polymer substrate. In this case, the average particle diameter of the nanostructures is not larger than the average particle diameter of the spherulites. That is, the average particle diameter of the nanostructures is smaller than the average particle diameter of the spherulites. Preferably, the nanostructures are present on the surface of the spherulites, and the average particle diameter of the nanostructures present on the surface of the spherulites is smaller than the average particle diameter of the spherulites.

Therefore, according to the present disclosure, the composition of the polymer substrate of the processed body and the composition of the crystallite structure layer are the same.

FIG. 2 shows electron-microscopic photographs of the hierarchal structure of the processed body surface (a photograph a showing the micro-structure and a photograph b showing the nanostructure) and the skin layer surface (photographs c and d showing the micro-structure) that are obtained by the method according to the present disclosure. From these photographs, it is obvious that the hierarchal crystallite structure composed of the spherulitic structure as the secondary structure (a, c, and d) and the nano-crystallite structure as the primary structure (b) are formed on the surfaces of the processed body and skin layer. The particle diameters of these spherulites and crystals are values obtained by: using an SEM to focus on the outermost surface of these structure; specifying at least 20 structures on the outermost surface that have measurable diameters; and measuring the diameters of these structures with ImageJ (image processing software). The above average particle diameter is an averaged value of values of the diameters of the at least 20 structures obtained with ImageJ. The average particle diameters of the spherulites and nanostructures obtained by this method and shown in the photographs a to d are as follows:

- a: 21.1 μm
- b: 48.9 μm
- c: 25.6 μm
- d: 213 nm

Hereinafter, the manufacture of the processed body provided with the highly hydrophobic and water-repellent surface according to the present disclosure will be described based on Examples, but the present disclosure is not limited to the aspects of these Examples.

Example 1

A sheet composed of a polypropylene homopolymer (TIPPLEN H681F, crystallization temperature Tc: 109° C., melting temperature Tm: 167° C., SP value: 16.2 MPa^1/2) was contacted with decalin (boiling point: 187° C., SP value: 18.00 MPa^1/2) at 150° C. over a predetermined time in a solvent-contacting region (step (a)). Then, the polypropylene sheet was taken out of the solvent-contacting region, and was dried at room temperature (step (b)).

Examples 2 to 9

The same procedure was performed as in Example 1 using polymers and solvents shown in Table 1 at a treatment temperature and drying temperature as shown in Table 1.

Comparative Example 1

A polypropylene homopolymer was used as the polymer, and dimethyl sulfoxide (DMSO) was used as the solvent. A difference between SP values of the polymer and the solvent was more than 8 MPa^1/2.

Comparative Example 2

A polypropylene homopolymer was used as the polymer, and acetone was used as the solvent. The temperature of the solvent in the step (a) was 56° C., which was lower than the crystallization temperature of polypropylene of 109° C.

Comparative Example 3

A polypropylene homopolymer was used as the polymer, and decalin was used as the solvent. The temperature of the solvent in the step (a) was 130° C., and the drying temperature in the step (b) was 100° C.

[Results]

Summarized in the following Table 1 are: the polymer used in these Examples and Comparative Examples; the crystallization temperature Tc, melting temperature Tm, and SP value (Hildebrand's solubility parameter) of the polymer; the type, boiling point, and SP value of the solvent; the process condition; and the constitution of the crystallite structure layer and results of hydrophobicity and water repellency of the substrate surface after the treatment or the obtained processed body. The SP values of the solvents and polymers shown in Table 1 are literature values, and each of the crystallization temperature Tc and the melting temperature Tm is a value specified by differential scanning calorimetry (DSC).

TABLE 1

Solvent
Polymer

Hildebrand's

Hildebrand's

Boiling
solubility

solubility
Difference in

point
[MPa{circumflex over ( )}½]

Tc
Tm
[MPa{circumflex over ( )}½]
SP value

Example 1
Decalin
187
18.00
PP
109
167
16.2
<5

homopolymer

H681F

Example 2
Decalin
187
18.00
PP
111
163
16.2
<5

copolymer

K793

Example 3
xylene
137-143
18.00
PP
111
163
16.2
<5

copolymer

K793

Example 4
xylene
137-143
18.00
PP
111
163
16.2
<5

copolymer

K793

Example 5
n-butyl
126
17.31
PP
109
167
16.2