Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2000-05-11
2001-03-13
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C524S801000, C524S802000, C428S402210, C428S402220
Reexamination Certificate
active
06200681
ABSTRACT:
The present invention relates to the use as latent heat storage media of microcapsules I comprising as core materials one or more lipophilic substances whose solid/liquid phase transition is within the range from −20 to 120° C. and as shell a polymer obtainable by free-radical polymerization of a monomer mixture comprising
from 30 to 100% by weight, based on the overall weight of the monomers, of one or more C
1
-C
24
-alkyl esters of acrylic and/or methacrylic acid (monomer I),
from 0 to 80% by weight, based on the overall weight of the monomers, of a bi- or polyfunctional monomer (monomer II) which is insoluble or of low solubility in water, and
from 0 to 40% by weight, based on the overall weight of the monomers, of other monomers (monomers III).
The invention additionally relates to novel microcapsules Ia, to spray-dried microcapsules Ia′ and to processes for producing them. Further subjects of the invention are shaped articles and coating compositions comprising these microcapsules.
An important research goal for reducing energy consumption and utilizing existing heat energy is constituted by latent heat storage media. These find multifarious application; for example, as heat transfer media in heating and cooling systems or as heat storage media in insulating materials or building materials. The way in which they operate is based on the enthalpy of transformation accompanying transition from the solid to the liquid phase or vice versa, which results in energy being absorbed from or released to their surroundings. They can therefore be used firstly for maintaining a constant temperature within a defined range and secondly, in a suitable arrangement, for improving heat insulation. Since one form of the storage medium is liquid, microcapsules, inter alia, have been used for ease of handling.
Microcapsules with a shell formed from polymers and copolymers of methyl methacrylate are known from EP-A-457 154 for reactive copy paper. It is therefore very important that these capsules have a flawless shell of uniform thickness so as to allow well-defined text.
In addition, US-A-3 615 972 describes a process for producing foamable microcapsules from methyl methacrylate with neopentane as the core of the capsule and colloidal silica as protective colloid.
DE-A 19 654 035 describes microcapsules for use as a heat transfer medium, the storage medium being surrounded by a shell of melamine/formaldehyde resin.
Melamine/formaldehyde resin microcapsules are again disclosed, but this time with a specific storage medium as their core, in US-A-5 456 852. The stability of such capsules to hydrolysis in the transport medium, however, which is generally aqueous, is not satisfactory in the longer term.
US-A-4 747 240 teaches the use of macroencapsulated storage substances with a particle size of more than 1000 &mgr;m, whose shell is a high-melting resin, in plaster. Capsules of this size, however, require very thick walls in order not to be destroyed when mixed with the building materials.
It is an object of the present invention to use microcapsules of improved stability to hydrolysis as laten:. heat storage media. They should in particular be suitable for use with building materials.
We have found that this object is achieved by the use of the microcapsules I defined at the outset and by novel microcapsules Ia and Ia′, and have found processes for their production, shaped articles, and coating compositions.
The lipophilic substances which form what is later the core have their solid/liquid phase transition within the temperature range from −20 to 120° C. Examples of suitable substances are
aliphatic hydrocarbon compounds, such as saturated or unsaturated C
10
-C
40
hydrocarbons, which are branched or preferably linear, such as n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane, n-eicosane, n-heneicosane, n-docosane, n-tricosane, n-tetracosane, n-pentacosane, n-hexacosane, n-heptacosane, n-octacosane, and also cyclic hydrocarbons, such as cyclohexane, cyclooctane, cyclodecane, for example;
aromatic hydrocarbon compounds, such as benzene, naphthalene, biphenyl, o- or m-terphenyl, C
1
-C
40
-alkyl-substituted aromatic hydrocarbons, such as dodecylbenzene, tetradecylbenzene, hexadecylbenzene, hexylnaphthalene or decylnaphthalene;
saturated or unsaturated C
6
-C
30
fatty acids, such as lauric, stearic, oleic or behenic acid, preferably eutectic mixtures of decanoic acid with, for example, myristic, palmitic or lauric acid;
fatty alcohols, such as lauryl, stearyl, oleyl, myristyl and cetyl alcohol, mixtures such as coconut fatty alcohol, and also the oxo alcohols obtained by hydroformulating (&agr;-olefins and other reactions;
C
6
-C
30
fatty amines, such as decylamine, dodecylamine, tetradecylamine or hexadecylamine;
esters, such as C
1
-C
10
-alkyl esters of fatty acids, examples being propyl palmitate, methyl stearate or methyl palmitate and, preferably, their eutectic mixtures, or methyl cinnamate;
natural and synthetic waxes, such as montanic acid waxes, montan ester waxes, carnauba wax, polyethylene wax, oxidized waxes, polyvinyl ether wax, ethylene-vinyl acetate wax, or hard waxes from the Fischer-Tropsch process;
halogenated hydrocarbons, such as chlorinated paraffin, bromooctadecane, bromopentadecane, bromononadecane, bromoeicosane and bromodocosane.
Mixtures of these substances are also quite suitable provided the melting point is not lowered to a point where it is outside the desired range.
The abovementioned halogenated hydrocarbons, for example, can be admixed as flameproofing agents. It is also possible to add flameproofing agents such as decachlorodiphenyl oxide, octabromodiphenyl oxide, antimony oxide or the flameproofing additives described in US-A 4 797 160.
It is advantageous, furthermore, to add to the capsule core-forming substances compounds that are soluble therein, so as to prevent the reduction in freezing point which occurs in some cases with the non-polar substances. It is advantageous to use, as described in US-A 5 456 852, compounds having a melting point which is higher by from 20 to 120° C. than that of the core substance itself. Suitable compounds are the fatty amides, fatty alcohols and fatty acids mentioned above as lipophilic substances.
The choice of lipophilic substances depends on the temperature range within which the heat storage media are required to operate. For example, substances used for heat storage media in building materials in Europe are preferably lipophilic substances whose solid/liquid phase transition is within the temperature range from 0 to 60° C. Hence the individual substances or mixtures are chosen usually with transition temperatures of 0 to 25° C. for exterior applications and of 15 to 30° C. for interior uses. In the case of solar applications in conjunction with building materials as storage medium, or for preventing the overheating of transparent thermal insulation, as described in EP-A 333 145, transition temperatures of 30 to 60° C. are particularly suitable. It is advantageous, for example, to use alkyl mixtures in the form in which they are obtained as an industrial distillate and in which they are available commercially.
The microcapsules used are composed of from 30 to 100% by ewight, preferably from 30 to 95% by weight, of one or more C
1
-C
24
-alkyl esters of acrylic and/or methacrylic acid, as monomers I. The microcapsules may also be composed of up to 80% by weight, preferably from 5 to 60% by weight and, In particular, from 10 to 50% by weight, of a bi- or polyfunctional monomer, monomer II, which is insoluble or of sparing solubility in water, and of up to 40% by weight, preferably up to 30% by weight, of other monomers III.
Suitable monomers I are C
1
-C
24
-alkyl esters of acrylic and/or methacrylic acid. Particularly preferred monomers I are methyl, ethyl, n-propyl and n-butyl acrylate and/or the corresponding methacrylates. Preference is given to isopropyl, isobutyl, sec-butyl and tert-butyl acrylate and the corresponding methacrylates. Methacrylonitrile shoul
Jahns Ekkehard
Reck Bernd
Acquah Samuel A.
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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