阅读说明：本技术 一种高分子防水材料及其制备方法 (High-molecular waterproof material and preparation method thereof ) 是由 何志强 于 2020-12-22 设计创作，主要内容包括：本发明公开了一种高分子防水材料,由如下重量份的组分制成：氯丁橡胶40-50份,末端胺基化SBS 30-40份,松香基超支化环氧树脂5-7份、2,4,6-三(4-羧基苯基)-1,3,5-三嗪4-8份、2,4-二氨基苯磺酸3-5份、五氧化二磷1-3份、2-羟基-4-(3-三乙氧基硅烷基丙氧基)二苯甲酮改性莫来石纳米纤维3-5份、抗氧化剂1-3份。本发明还公开了所述高分子防水材料的制备方法。本发明公开的高分子防水材料防水效果显著,性能稳定性和综合性能佳,胶粘性能足,施工性能、机械力学性能、耐老化性能和耐久性好,使用寿命长。(The invention discloses a high-molecular waterproof material which is prepared from the following components in parts by weight: 40-50 parts of chloroprene rubber, 30-40 parts of terminal aminated SBS, 5-7 parts of rosin-based hyperbranched epoxy resin, 4-8 parts of 2,4, 6-tri (4-carboxyphenyl) -1,3, 5-triazine, 3-5 parts of 2, 4-diaminobenzene sulfonic acid, 1-3 parts of phosphorus pentoxide, 3-5 parts of 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofiber and 1-3 parts of antioxidant. The invention also discloses a preparation method of the polymer waterproof material. The high-molecular waterproof material disclosed by the invention has the advantages of obvious waterproof effect, good performance stability and comprehensive performance, sufficient adhesive performance, good construction performance, mechanical property, aging resistance and durability and long service life.)

1. The high-molecular waterproof material is characterized by being prepared from the following components in parts by weight: 40-50 parts of chloroprene rubber, 30-40 parts of terminal aminated SBS, 5-7 parts of rosin-based hyperbranched epoxy resin, 4-8 parts of 2,4, 6-tri (4-carboxyphenyl) -1,3, 5-triazine, 3-5 parts of 2, 4-diaminobenzene sulfonic acid, 1-3 parts of phosphorus pentoxide, 3-5 parts of 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofiber and 1-3 parts of antioxidant.

2. The waterproof polymer material according to claim 1, wherein the antioxidant is one or more of di-tert-butyl-p-cresol, butyl hydroxyanisole and dibutyl hydroxytoluene.

3. The polymeric waterproof material of claim 1, wherein the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofibers are prepared by the following steps: dispersing the mullite nano fiber in an organic solvent, adding 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone, stirring and reacting at 50-70 ℃ for 4-6 hours, and removing the solvent by rotary evaporation to obtain the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nano fiber.

4. The polymeric waterproof material according to claim 3, wherein the mass ratio of the mullite nanofibers to the organic solvent to the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone is (3-5) to (10-20) to (0.1-0.3).

5. The polymer waterproof material as claimed in claim 3, wherein the mullite nanofibers have a diameter of 200-500nm and an aspect ratio (12-16): 1.

6. The waterproof polymer material according to claim 3, wherein the organic solvent is one or a mixture of N-methylpyrrolidone, dimethyl sulfoxide and N, N-dimethylformamide.

7. The waterproof polymeric material of claim 1, wherein said neoprene is CR1212 type neoprene.

8. A method for preparing the polymeric waterproof material according to any one of claims 1 to 7, comprising the following steps: the components are uniformly mixed according to the parts by weight to obtain a mixture, and then the mixture is added into a double-screw extruder to be extruded and molded to obtain the high-molecular waterproof material.

Technical Field

The invention relates to the technical field of waterproof materials, in particular to a high-molecular waterproof material and a preparation method thereof.

Background

In recent years, with the development of economy and the acceleration of the pace of modern urban construction, various major construction projects including municipal engineering have come, and the major construction projects are expected to further improve the living environment of people, improve the happiness of people and promote the further development of economy. In building engineering, the problem of leakage is always a difficult and complicated disease which puzzles the engineering world, and is an important subject which scientific researchers are focused on researching and solving. The damage of leakage accelerates the development of concrete aging diseases, and the damage of buildings even fails to be estimated if the damage of leakage is light.

Currently, the most effective way to solve the problem of permeation is to use waterproof materials. The waterproof material is a flexible building material product which can resist external rainwater and underground water leakage in a building, is used as a leakage-free connection between an engineering foundation and the building, is a first barrier for waterproofing of the whole engineering, has the performance directly influencing the waterproof effect and the safety and durability of the building, and plays a vital role in the whole engineering.

The existing common waterproof materials mainly comprise asphalt-based waterproof materials and synthetic polymer waterproof materials. The traditional asphalt-based waterproof material has low peel strength and insufficient waterproof performance, the waterproof performance of the traditional asphalt-based waterproof material is weakened along with the prolonging of the service time, and the use of the asphalt causes threats to the environment and the physical health of construction personnel due to the carcinogenic effect of the asphalt. The synthetic polymer waterproof material is used as a product of high and new technology, has more and more prominent importance in buildings in recent years, has excellent water resistance and high and low temperature resistance, and also has good elasticity, tensile strength, weather resistance, corrosion resistance and aging resistance, and is one of important materials of modern buildings. However, the existing synthetic polymer waterproof material is hard in texture and poor in construction smoothness, and due to the fact that equipment is complex, the trafficability characteristic in the welding process is poor, the construction difficulty of waterproof nodes is high, and potential safety hazards exist. In addition, the synthetic polymer waterproof materials on the market also have the defects of high manufacturing cost, easy damage, poor waterproof effect, aging resistance, flame retardance, puncture resistance, corrosion resistance and the like, and insufficient adhesive property.

For example, chinese patent application No. 201510338044.X discloses an anti-aging polyester non-woven fabric PE waterproofing membrane, from top to bottom is equipped with polyvinyl chloride film isolation layer, anti-aging layer, PE layer, polyester non-woven fabric protective layer in proper order, bond through the hot pressing respectively between polyvinyl chloride film isolation layer, anti-aging layer and the PE layer and become an organic whole, pass through PE gasket welded connection between PE layer and the polyester non-woven fabric protective layer. The waterproof coiled material has the advantages of firm material, high flexibility, strong bonding force, durability, weather resistance, leakage resistance, good waterproof performance and the like, but the waterproof coiled material is easy to delaminate, so that the waterproof engineering quality is seriously influenced; the performance stability and durability are to be further improved.

Therefore, the development of the high polymer waterproof material with obvious waterproof effect, good performance stability and comprehensive performance, sufficient adhesive performance, good construction performance, mechanical property, aging resistance and durability and long service life meets the market demand and has very important significance.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides the high polymer waterproof material which has the advantages of obvious waterproof effect, good performance stability and comprehensive performance, sufficient adhesive performance, good construction performance, mechanical property, aging resistance and durability and long service life. Meanwhile, the invention also discloses a preparation method of the high polymer waterproof material, which is simple and easy to implement, convenient to operate and control, small in equipment dependence, low in energy consumption, high in production efficiency and finished product qualification rate, suitable for industrial production, and high in economic value and social value.

In order to achieve the purpose, the invention adopts the technical scheme that the macromolecular waterproof material is prepared from the following components in parts by weight: 40-50 parts of chloroprene rubber, 30-40 parts of terminal aminated SBS, 5-7 parts of rosin-based hyperbranched epoxy resin, 4-8 parts of 2,4, 6-tri (4-carboxyphenyl) -1,3, 5-triazine, 3-5 parts of 2, 4-diaminobenzene sulfonic acid, 1-3 parts of phosphorus pentoxide, 3-5 parts of 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofiber and 1-3 parts of antioxidant.

In one embodiment of the invention, the antioxidant is one or more of di-tert-butyl-p-cresol, butyl hydroxy anisole and dibutyl hydroxy toluene.

In one embodiment of the invention, the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofiber is prepared by the following steps: dispersing the mullite nano fiber in an organic solvent, adding 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone, stirring and reacting at 50-70 ℃ for 4-6 hours, and removing the solvent by rotary evaporation to obtain the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nano fiber.

In one embodiment of the invention, the mass ratio of the mullite nano-fiber to the organic solvent to the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone is (3-5) to (10-20) to (0.1-0.3).

Preferably, the diameter of the mullite nano fiber is 200-500nm, and the length-diameter ratio (12-16) is 1.

In one embodiment of the present invention, the organic solvent is one or a mixture of N-methylpyrrolidone, dimethyl sulfoxide and N, N-dimethylformamide.

In an embodiment of the present invention, the rosin-based hyperbranched epoxy resin is prepared according to the method for preparing the rosin-based hyperbranched epoxy resin in chinese patent application No. 201610861045.7, embodiment 4.

In one embodiment of the present invention, the terminally aminated SBS is terminally aminated SBS prepared according to the method for preparing terminally aminated SBS described in chinese patent application No. 200710011136.2, example 2.

In one embodiment of the invention, the neoprene rubber is CR1212 type neoprene rubber.

Another object of the present invention is to provide a method for preparing the polymer waterproof material, which comprises the following steps: the components are uniformly mixed according to the parts by weight to obtain a mixture, and then the mixture is added into a double-screw extruder to be extruded and molded to obtain the high-molecular waterproof material.

Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:

1) the preparation method of the high-molecular waterproof material provided by the invention is simple and easy to implement, convenient to operate and control, small in equipment dependence, low in energy consumption, high in production efficiency and finished product qualification rate, suitable for industrial production, and high in economic value and social value.

2) The high-molecular waterproof material provided by the invention overcomes the defects that the existing synthetic high-molecular waterproof material is hard in texture and poor in construction smoothness, and has the potential safety hazard due to the complex equipment, poor trafficability in the welding process, high construction difficulty of waterproof nodes and the like; the synthetic polymer waterproof material on the market also has the defects of high manufacturing cost, easy damage, poor waterproof effect, aging resistance, flame retardance, puncture resistance, corrosion resistance and the like and insufficient adhesive property; through the synergistic effect of the components, the prepared high-molecular waterproof material has the advantages of obvious waterproof effect, good performance stability and comprehensive performance, sufficient adhesive performance, good construction performance, mechanical property, aging resistance and durability and long service life.

3) The polymer waterproof material provided by the invention combines the advantages of materials such as chloroprene rubber, SBS and rosin-based hyperbranched epoxy resin, so that the prepared polymer waterproof material has good comprehensive performance and obvious waterproof effect, and effectively avoids the defects of poor heat resistance and performance stability caused by the compatibility problem of the direct blending of the traditional chloroprene rubber and SBS; under the action of phosphorus pentoxide as a catalyst, a benzene ring on the terminal aminated SBS reacts with a sulfonic group on the 2, 4-diaminobenzene sulfonic acid, an amino group is introduced, and the amino group can also react with an epoxy group on the rosin-based hyperbranched epoxy resin to generate epoxy ring opening reaction; benzene rings on benzophenone on the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofiber can also react with sulfonic acid groups on 2, 4-diaminobenzenesulfonic acid under the catalytic action of phosphorus pentoxide, so that all components of the whole material are connected by chemical bonds to form a three-dimensional network structure, and the comprehensive performance and the performance stability of the material are effectively improved.

4) The high-molecular waterproof material provided by the invention combines excellent bonding properties of chloroprene rubber, SBS and rosin-based hyperbranched epoxy resin, so that the high-molecular waterproof material is convenient to use and good in durability; the phenyl triazine structure is introduced, and the phenyl triazine structure and other components have synergistic effect, so that the comprehensive performance, particularly the weather resistance and the aging resistance, can be effectively improved; the hydrophobic phenyl triazine structure of the material enables the prepared material to have better waterproof performance; SBS and rosin-based hyperbranched epoxy resin are chemically crosslinked by taking 2, 4-diaminobenzene sulfonic acid as a medium, so that the comprehensive performance and the performance stability can be effectively improved, and the flame retardance and the aging resistance of the material can be improved by using the sulfone group introduced by the reaction of the SBS and the benzene ring, so that the mechanical property of the material is more excellent.

5) According to the high-molecular waterproof material provided by the invention, the mullite nanofiber not only can enhance the heat resistance and the waterproofness of the material, but also can improve the mechanical strength of the material through a dispersion strengthening mechanism, and is modified through 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone, so that the compatibility of the mullite nanofiber and other components is improved, and the mullite nanofiber is easier to disperse uniformly; secondly, the benzophenone structure on the material can improve the ultraviolet aging resistance of the material and can provide a crosslinking site; the components of the invention interact, influence and cooperate, so that the material has obvious waterproof effect and good comprehensive performance and performance stability.

Detailed Description

In order to make the technical solutions of the present invention better understood and make the above features, objects, and advantages of the present invention more comprehensible, the present invention is further described with reference to the following examples. The examples are intended to illustrate the invention only and are not intended to limit the scope of the invention.

The rosin-based hyperbranched epoxy resin used in the following embodiments of the present invention is a rosin-based hyperbranched epoxy resin prepared by the method for preparing a rosin-based hyperbranched epoxy resin in chinese patent application No. 201610861045.7, example 4; the terminal aminated SBS is prepared by the preparation method of terminal aminated SBS in the Chinese patent application No. 200710011136.2 in the embodiment 2; the chloroprene rubber is CR1212 type chloroprene rubber; other raw materials were purchased commercially.

Example 1

A high-molecular waterproof material is prepared from the following components in parts by weight: 40 parts of chloroprene rubber, 30 parts of terminal aminated SBS (styrene butadiene styrene), 5 parts of rosin-based hyperbranched epoxy resin, 4 parts of 2,4, 6-tris (4-carboxyphenyl) -1,3, 5-triazine, 3 parts of 2, 4-diaminobenzene sulfonic acid, 1 part of phosphorus pentoxide, 3 parts of 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nano-fiber and 1 part of antioxidant; the antioxidant is ditertiary butyl p-cresol.

The 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofiber is prepared by the following steps: dispersing the mullite nano fiber in an organic solvent, adding 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone, stirring and reacting for 4 hours at 50 ℃, and then removing the solvent by rotary evaporation to obtain the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nano fiber.

The mass ratio of the mullite nanofiber to the organic solvent to the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone is 3:10: 0.1; the diameter of the mullite nanofiber is 200nm, and the length-diameter ratio is 12: 1; the organic solvent is N-methyl pyrrolidone.

The preparation method of the high-molecular waterproof material is characterized by comprising the following steps of: the components are uniformly mixed according to the parts by weight to obtain a mixture, and then the mixture is added into a double-screw extruder to be extruded and molded to obtain the high-molecular waterproof material.

Example 2

A high-molecular waterproof material is prepared from the following components in parts by weight: 43 parts of chloroprene rubber, 32 parts of terminal aminated SBS (styrene butadiene styrene), 5.5 parts of rosin-based hyperbranched epoxy resin, 5 parts of 2,4, 6-tris (4-carboxyphenyl) -1,3, 5-triazine, 3.5 parts of 2, 4-diaminobenzene sulfonic acid, 1.5 parts of phosphorus pentoxide, 3.5 parts of 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofiber and 1.5 parts of antioxidant; the antioxidant is butyl hydroxy anisol.

The 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofiber is prepared by the following steps: dispersing mullite nano fiber in an organic solvent, adding 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone, stirring and reacting at 55 ℃ for 4.5 hours, and then removing the solvent by rotary evaporation to obtain the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nano fiber; the mass ratio of the mullite nanofiber to the organic solvent to the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone is 3.5:13: 0.15; the diameter of the mullite nanofiber is 300nm, and the length-diameter ratio is 13: 1; the organic solvent is dimethyl sulfoxide.

The preparation method of the high-molecular waterproof material is characterized by comprising the following steps of: the components are uniformly mixed according to the parts by weight to obtain a mixture, and then the mixture is added into a double-screw extruder to be extruded and molded to obtain the high-molecular waterproof material.

Example 3

A high-molecular waterproof material is prepared from the following components in parts by weight: 45 parts of chloroprene rubber, 35 parts of terminal aminated SBS (styrene butadiene styrene), 6 parts of rosin-based hyperbranched epoxy resin, 6 parts of 2,4, 6-tris (4-carboxyphenyl) -1,3, 5-triazine, 4 parts of 2, 4-diaminobenzene sulfonic acid, 2 parts of phosphorus pentoxide, 4 parts of 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nano-fiber and 2 parts of antioxidant; the antioxidant is dibutyl hydroxy toluene.

The 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofiber is prepared by the following steps: dispersing mullite nano fiber in an organic solvent, adding 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone, stirring at 60 ℃ for reaction for 5 hours, and then removing the solvent by rotary evaporation to obtain the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nano fiber; the mass ratio of the mullite nanofiber to the organic solvent to the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone is 4:15: 0.2; the diameter of the mullite nanofiber is 350nm, and the length-diameter ratio is 14: 1; the organic solvent is N, N-dimethylformamide.

The preparation method of the high-molecular waterproof material is characterized by comprising the following steps of: the components are uniformly mixed according to the parts by weight to obtain a mixture, and then the mixture is added into a double-screw extruder to be extruded and molded to obtain the high-molecular waterproof material.

Example 4

A high-molecular waterproof material is prepared from the following components in parts by weight: 48 parts of chloroprene rubber, 37 parts of terminal aminated SBS (styrene butadiene styrene), 6.5 parts of rosin-based hyperbranched epoxy resin, 7 parts of 2,4, 6-tris (4-carboxyphenyl) -1,3, 5-triazine, 4.5 parts of 2, 4-diaminobenzene sulfonic acid, 2.5 parts of phosphorus pentoxide, 4.5 parts of 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofiber and 2.5 parts of antioxidant; the antioxidant is prepared by mixing ditert-butyl-p-cresol, butyl hydroxy anisole and dibutyl hydroxy toluene according to the mass ratio of 1:3: 2.

The 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofiber is prepared by the following steps: dispersing mullite nano fiber in an organic solvent, adding 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone, stirring and reacting at 65 ℃ for 5.5 hours, and then removing the solvent by rotary evaporation to obtain the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nano fiber; the mass ratio of the mullite nanofiber to the organic solvent to the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone is 4.5:18: 0.25; the diameter of the mullite nanofiber is 450nm, and the length-diameter ratio is 15: 1; the organic solvent is formed by mixing N-methyl pyrrolidone, dimethyl sulfoxide and N, N-dimethylformamide according to the mass ratio of 1:3: 5.

The preparation method of the high-molecular waterproof material is characterized by comprising the following steps of: the components are uniformly mixed according to the parts by weight to obtain a mixture, and then the mixture is added into a double-screw extruder to be extruded and molded to obtain the high-molecular waterproof material.

Example 5

A high-molecular waterproof material is prepared from the following components in parts by weight: 50 parts of chloroprene rubber, 40 parts of terminal aminated SBS (styrene butadiene styrene), 7 parts of rosin-based hyperbranched epoxy resin, 8 parts of 2,4, 6-tris (4-carboxyphenyl) -1,3, 5-triazine, 5 parts of 2, 4-diaminobenzene sulfonic acid, 3 parts of phosphorus pentoxide, 5 parts of 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nano-fiber and 3 parts of antioxidant; the antioxidant is ditertiary butyl p-cresol.

The 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofiber is prepared by the following steps: dispersing mullite nano fiber in an organic solvent, adding 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone, stirring at 70 ℃ for reacting for 6 hours, and then removing the solvent by rotary evaporation to obtain the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nano fiber; the mass ratio of the mullite nanofiber to the organic solvent to the 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone is 5:20: 0.3; the diameter of the mullite nanofiber is 500nm, and the length-diameter ratio is 16: 1; the organic solvent is dimethyl sulfoxide.

The preparation method of the high-molecular waterproof material is characterized by comprising the following steps of: the components are uniformly mixed according to the parts by weight to obtain a mixture, and then the mixture is added into a double-screw extruder to be extruded and molded to obtain the high-molecular waterproof material.

Comparative example 1

The present example provides a polymer waterproof material, the formulation and preparation method of which are substantially the same as those of example 1, except that no rosin-based hyperbranched epoxy resin is added.

Comparative example 2

This example provides a polymer waterproof material, the formulation and preparation method of which are substantially the same as those of example 1, except that 2,4, 6-tris (4-carboxyphenyl) -1,3, 5-triazine is not added.

Comparative example 3

This example provides a polymer waterproof material, which has a formulation and a preparation method substantially the same as those of example 1, except that 2, 4-diaminobenzenesulfonic acid is not added.

Comparative example 4

This example provides a polymer waterproof material, the formulation and preparation method of which are substantially the same as those of example 1, except that 2-hydroxy-4- (3-triethoxysilylpropoxy) benzophenone modified mullite nanofibers are not added.

Comparative example 5

The present example provides a polymer waterproof material, the formulation and preparation method of which are substantially the same as those of example 1, except that SBS is used to replace terminal aminated SBS; the SBS is prepared according to the preparation method of the Chinese patent invention with the application number of 200710011136.2 in the embodiment 1.

In order to further illustrate the beneficial technical effects of the polymer waterproof materials in the embodiments of the present invention, the polymer waterproof materials described in the embodiments 1 to 5 and the comparative examples 1 to 5 are subjected to a performance test, and the test method refers to GB 18173.1-2006, wherein the thermal aging performance is measured by the retention rate of the tensile strength after thermal aging for 168 hours in hot air at 80 ℃, and the larger the value, the better the thermal aging resistance, and the test results are shown in table 1.

As can be seen from table 1, the polymer waterproof material disclosed in the embodiment of the present invention has more excellent waterproof performance, mechanical properties and aging resistance compared with the comparative product, which is the result of the synergistic effect of the components.

TABLE 1 Polymer waterproofing Material Performance parameters

The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.