A controlled release product is provided having a suppressed initial release period and a predetermined longevity. The product includes a particulate water soluble core material and a semi-permeable coating layer applied on the core material for controlling the release rate of the core material. The semi-permeable coating layer is formulated in accordance with the following equation to provide a release rate wherein initial release of core material from the product is suppressed so that less than about 15 weight percent of core material is released from the product within a 24 hour period after application of the product and wherein longevity of release, at ambient temperature, between the time of application and the time at which at least about 75 weight percent of the core material is released from the product is 60 days or less:
1
WVTR
=
φ
·
δ
π
⁢
⁢
d
2
wherein:
(i) WVTR is the water vapor transmission rate of the semi-permeable coating expressed in grams·&mgr;m/meters
2
·day;
(ii) &phgr; is the water diffusion rate (water flux) through the semi-permeable coating expressed in grams/day;
(iii) &dgr; is the thickness of the coating layer expressed in &mgr;m; and
(iv) d is the average diameter of the particulate core material expressed in meters.
一种控释产品具有被抑制的初始释放期和预定的持久性。该产品包括颗粒状
水溶性芯材和涂在芯材上用于控制芯材释放率的半透涂层。半透性涂层层按下式配制,以提供一种释放率,其中芯材从产品中的初始释放被抑制,从而在施用产品后的 24 小时内从产品中释放的芯材少于约 15 重量百分比,并且在环境温度下,从施用时间到至少约 75 重量百分比的芯材从产品中释放的时间之间的释放寿命为 60 天或更短:
1
WVTR
=
φ
·
δ
π
⁢
⁢
d
2
其中
(i) WVTR 是半透涂料的
水蒸气透过率,以克-&mgr;米/米表示
2
-天;
(ii) &phgr;是通过半透涂层的
水扩散率(
水通量),单位为克/天;
(iii) &dgr;是涂层的厚度,单位为米
(iv) d 是颗粒核心材料的平均直径,以米为单位。