Plant husbandry – Mulching
Reexamination Certificate
2000-08-01
2002-07-16
Hoke, Veronica P. (Department: 1714)
Plant husbandry
Mulching
C423S306000, C423S327100, C423S328100, C423S328200, C252S587000, C523S135000, C524S405000, C524S417000, C524S423000, C524S424000, C524S435000, C524S436000, C524S450000
Reexamination Certificate
active
06418661
ABSTRACT:
TECHNICAL FIELD
This invention relates to hydrotalcite compound which has excellent infrared absorption ability and a characteristic property of exhibiting excellent light-transmission when it is contained in agricultural film; a process for producing the same; infrared absorbing agent containing said hydrotalcite compound as the active ingredient; and agricultural film which contains said infrared absorbing agent.
BACKGROUND ART
Agricultural films have been widely used for greenhouse cultivation or tunnel cultivation of agricultural products. Those agricultural films are required to concurrently exhibit good light transmission and heat insulating property. That is, temperatures within a greenhouse or tunnel which are raised by the daytime sunbeams of 0.29-4.3 &mgr;m in wavelength rapidly drop in night, in particular, clear weather night, due to radiational cooling. Such rapid temperature drop inside a greenhouse or tunnel incurs adverse effect on growth of crops. While various causes are considered to induce the rapid temperature drop, there is an opinion that heat radiation from surface of the earth or cultivated plants to the outside atmosphere (radiation as long wavelength infrared rays) in nights is the reason for the temperature drop. According to that view, the heat radiation is calculated, using Planck's formula, i.e., the following formula (3), as black body radiation energy:
E&lgr;·d&lgr;(erg. sec
−1
.cm
−2
) E&lgr;·d&lgr;=
2
&pgr;hC{circumflex over ( )}
2
/[&lgr;{circumflex over ( )}5{e{circumflex over ( )}(hC/&lgr;kT)−1}]·d&lgr; (3)
in which
&lgr;: wavelength
h: Planck's constant
C: velocity of light in vacuum
k: Boltzmann's constant
T: absolute temperature.
From the calculation, it is explained that the rays of wavelengths within the infrared region, in particular, infrared rays (black body radiation energy) of 400-2000 cm
−1
, the maximum being at 1000 cm
−1
, are said to be emitted within the temperature range of from 30 to −10° C. to induce the temperature drop.
For preventing such rapid temperature drop inside a greenhouse or tunnel, heat insulating film having infrared-absorbing ability is used. Such heat insulating film is provided by either using, as thermoplastic resin which is the base material, the one having infrared absorbing ability itself or the one to which a substance having ability to absorb infrared rays (in particular, rays of wave-lengths ranging 400-2000 cm
−1
), i.e., an infrared absorbing agent, is blended so as to impart to the film infrared absorbability. As infrared absorbers, for example, silica; silicate; hydroxide, oxide, aluminate, borate or sulfate of lithium, calcium, magnesium or aluminium; or hydrotalcite compounds are used.
Of those, hydrotalcite compounds excel in infrared absorbing ability and light transmission when blended in resin, over those of silica; silicate; or hydroxide, oxide, aluminate, borate or sulfate of lithium, calcium, magnesium or aluminium and, therefore, are particularly useful as infrared absorbing agents, and many patent applications have been filed on inventions relating thereto. (Hydrotalcites are complex hydroxide having lamellar structures formed of complex hydroxide layers (base layers) of Mg and Al, separated by interlayer wherein holding anions (e.g., carbonate ions) and water. Those which are represented by the formulae (1) or (4) in the present specification are complex hydroxides having base layers formed of Mg and Al; or Mg, other divalent metal(s) and Al, holding anions and water in the interlayer. Whereas, those represented by the formulae (2) or (5) also are complex hydroxides differing in composition of the base layers, having base layers formed of Li and Al; or Li, other divalent metal(s) and Al, holding anions and water in the interlayer. All of those have structures similar or analogous to those of hydrotalcite, and hence they are collectively referred to as “hydrotalcite compounds” in the present specification. Those which are expressed by the formula (1) or (4) are referred to as Mg—Al hydrotalcite compounds, and those of formula (2) or (5), as Li—Al hydrotalcite compounds).
Among patent applications filed in the past on inventions relating to Mg—Al hydrotalcite compounds, there are, for examples, Sho 62 (1987)-31744B-JP (corres. to U.S. Pat. No. 4,686,791 and EP 142,773), Sho 62-53543B-JP, Sho 62-41247B-JP, Sho 63 (1988)-175072B-JP, Sho 63-115743B-JP, Sho 63-149147B-JP, Sho 63-149148B-JP, Sho 64 (1989)-6041B-JP, Hei 4 (1992)-11107B-JP, Hei 6 (1994)-6363B-JP, Hei 6-6364B-JP and Hei 9 (1997)-176390A-JP. Examples of those relating to Li—Al hydrotalcite compounds include: Hei 7 (1995)-300313A-JP (corres. to EP 672,619), Hei 9 (1997)-142835A-JP (corres. to EP 790,214), Hei 9-279124A-JP, Hei 9-800828A (second)-JP (corres. to U.S. Pat. No. 5,767,179 and EP 778,241) [This is the domestic republication of PCT international publication for the patent application. Similar case shall be hereafter marked as “A (second)”], Hei 9 (1997)-235420A-JP (corres. to EP 781,800), Hei 10 (1998)-52895A-JP, Hei 10-235776A-JP and Hei 10-226739A-JP.
While the hydrotalcite compounds are expressed by various structural formula in these patent applications, they can be generally represented by the following formula (4) or (5).
(General formula of Mg—Al hydrotalcite compounds):
[
{
Mg
y1
M
y2
2
+
}
1
-
X
Al
X
(
OH
)
2
]
(
base
layer
)
X
+
[
A
X
/
n
n
-
·
b
H
2
O
]
(
interlayer
)
X
-
(
4
)
in the above formula,
M
2+
stands for at least one kind of divalent metal ion of Zn, Ca and Ni,
A
n−
stand for a n-valent anion of, e.g., inorganic or organic acid such Cl
−
, Br
−
, I
−
, NO
3
−
, CIO
4
−
, H
2
PO
4
−
, HBO
3
2−
, SO
4
2−
, CO
3
2−
, SiO
3
2−
, HPO
4
2−
, PO
4
3−
, Fe(CN)
6
3−
and Fe(CN)
4
4−
,
and x, y
1
, y
2
and b are positive numbers each satisfying the following conditions, respectively,
0<x≦0.5, y
1
+y
2
=1, y
1
≦1, y
2
<1, 0≦b<2.
(General formula of Li—Al hydrotalcite compounds)
[
(
Li
1
-
X
G
X
2
+
)
Al
2
(
OH
)
6
]
(
1
+
X
)
+
(
base
layer
)
[
(
A
n
-
)
(
1
+
X
)
/
n
·
b
H
2
O
]
(
interlayer
)
(
1
+
X
)
-
(
5
)
in which
G
2+
stands for at least one kind of divalent metal ion of Mg, Zn, Ca and Ni,
A
n−
stands for a n-valent anion,
and x and b are positive numbers each satisfying the following conditions, respectively,
0≦x<1, 0≦b<5.
Of these, in most cases hydrotalcite compounds having carbonate ions in the interlayer (which are hereafter referred to as carbonate ion-type hydrotalcite compounds) are used.
Taking examples of carbonate ion-type Mg—Al hydrotalcite compounds, however, while they exhibit favorable absorption of infrared rays around 400-800 cm
−1
and 1400 cm
−1
, the absorbing ability of the infrared rays of 900 to around 1300 cm
−1
is poor. When they are contained in agricultural film whose base material is polyethylene exhibiting infrared absorption at around 700 and 1300-1500 cm
−1
only, the agricultural film exhibits combined infrared absorption of that of the polyethylene and that of the infrared absorbing agent and hence shows poor infrared absorption in the vicinity of 900-1300 cm
−1
, i.e., poor heat-insulation property. Also carbonate ion-type Li—Al hydrotalcite compounds show infrared absorbing ability at around 1000 cm
−1
which however is not strong, and their over-all infrared absorbing ability is about the same as that of carbonate ion type Mg—Al hydrotalcite compounds. Agricultural films containing those compounds, furthermore, are considered to exhibit better light transmission compared to that of the films containing other infrared absorbing agents, but still the light transmission is not fully satisfactory.
As a means to enhance the infrared absorbi
Okada Akira
Takahashi Hideo
Hoke Veronica P.
Kyowa Chemical Industry Co Ltd
Sherman & Shalloway
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