阅读说明：本技术 耐高温丙烯酸酯压敏胶及其制备方法 (High-temperature-resistant acrylate pressure-sensitive adhesive and preparation method thereof ) 是由 张蒙蒙 屈良端 周峰 吴林群 周晓南 于 2021-09-15 设计创作，主要内容包括：本发明公开了一种耐高温丙烯酸酯压敏胶及其制备方法,所述耐高温丙烯酸酯压敏胶括组分A和组分B,所述组分A按质量份数包括以下原料组分：软单体60～90质量份,硬单体2～10质量份,功能单体2～10质量份,引发剂0.5～2质量份,溶剂120～160质量份,其中,所述组分B为固化剂,本发明通过软单体、硬单体、功能单体的复配使用,采用分步聚合的方法,所制得的耐高温丙烯酸酯压敏胶,无论在常温下还是高温下都具备良好的粘结效果,并且不会出现脱胶、残胶的现象。(The invention discloses a high-temperature-resistant acrylate pressure-sensitive adhesive and a preparation method thereof, wherein the high-temperature-resistant acrylate pressure-sensitive adhesive comprises a component A and a component B, and the component A comprises the following raw material components in parts by weight: 60-90 parts by mass of a soft monomer, 2-10 parts by mass of a hard monomer, 2-10 parts by mass of a functional monomer, 0.5-2 parts by mass of an initiator and 120-160 parts by mass of a solvent, wherein the component B is a curing agent.)

1. The high-temperature-resistant acrylate pressure-sensitive adhesive is characterized by comprising a component A and a component B, wherein the component A comprises the following raw material components in parts by mass: 60-90 parts by mass of soft monomer, 2-10 parts by mass of hard monomer, 2-10 parts by mass of functional monomer, 0.5-2 parts by mass of initiator, 120-160 parts by mass of solvent,

wherein the component B is a curing agent.

2. The high temperature resistant acrylate pressure sensitive adhesive of claim 1 wherein the soft monomer is one or more of isooctyl acrylate, ethyl acrylate, butyl acrylate, lauryl acrylate, n-butyl acrylate, and lauryl methacrylate.

3. The high temperature resistant acrylate pressure sensitive adhesive of claim 1 wherein the hard monomer is one or more of methyl acrylate, ethyl methacrylate, methyl methacrylate, n-butyl methacrylate, t-butyl acrylate, isobornyl methacrylate, vinyl acetate, acrylonitrile, and styrene.

4. The high temperature resistant acrylate pressure sensitive adhesive of claim 1 wherein the functional monomer is one or more of acrylic acid, methacrylic acid, hydroxyethyl acrylate, acrylamide, N-vinylcyclohexamide, hydroxypropyl acrylate, glycidyl methacrylate, isobornyl acrylate, methacrylamide, hydroxyethyl methacrylate and hydroxypropyl methacrylate.

5. The high temperature resistant acrylate pressure sensitive adhesive of claim 1 wherein the initiator is azobisisobutyronitrile.

6. The high temperature resistant acrylate pressure sensitive adhesive of claim 1 wherein the solvent is one or both of ethyl acetate and toluene.

7. The high temperature resistant acrylate pressure sensitive adhesive of claim 1 wherein the curing agent is one or more of isocyanate, amine based resin or metal salt.

8. The high temperature resistant acrylate pressure sensitive adhesive according to claim 7, wherein the mass ratio of the component A to the component B is 100: (1-3).

9. The high-temperature-resistant acrylate pressure-sensitive adhesive according to claim 1, wherein the component A comprises the following raw material components in parts by mass: the soft monomer is a mixture of 10-20 parts by mass of isooctyl acrylate, 15-40 parts by mass of butyl acrylate and 1-15 parts by mass of ethyl acrylate; the hard monomer is 2-10 parts by mass of methyl methacrylate; the functional monomer is a mixture of 1-6 parts by mass of acrylic acid, 0.3-3 parts by mass of hydroxypropyl acrylate, 0.5-3 parts by mass of glycidyl methacrylate and 0.2-2 parts by mass of methacrylamide, the initiator is 0.5-2 parts by mass, and the solvent is 120-160 parts by mass.

10. The preparation method of the high-temperature-resistant acrylate pressure-sensitive adhesive is characterized by comprising the following steps of:

s1, weighing the raw materials of the component A: soft monomers, hard monomers, functional monomers, initiators and solvents;

s2, adding part of soft monomers, part of functional monomers, part of initiators and part of solvents into a reaction kettle, heating to 65-72 ℃, reacting for 60-120 min, and preserving heat for 20-40 min after the reaction is finished to obtain an intermediate product A;

s3, heating the intermediate product A in the reaction kettle to 75-80 ℃, then uniformly mixing the remaining soft monomer, functional monomer, partial initiator and partial solvent, and then dropwise adding into the reaction kettle to obtain an intermediate product B after dropwise adding is completed;

s4, adding all hard monomers and part of initiator into the intermediate product B, and reacting for 60-90 min at the temperature of 80-85 ℃ to obtain an intermediate product C;

s5, adding the residual solvent into the intermediate product C, stirring for 55-65 min, and cooling to below 50 ℃ to obtain a component A;

s6, weighing part of the component A and the curing agent, uniformly stirring, coating on release paper, baking in an oven at 90 ℃ for 3min, transferring to 25 mu mPE, and curing at 50 ℃ for 24h to obtain the high-temperature-resistant acrylate pressure-sensitive adhesive.

Technical Field

The invention relates to a high-temperature-resistant pressure-sensitive adhesive, in particular to a high-temperature-resistant acrylate pressure-sensitive adhesive and a preparation method thereof.

Background

The pressure-sensitive adhesive is an adhesive capable of adhering an adherend and a pressure-sensitive adhesive product under the condition of external force, is an adhesive closely related to the daily life of people, is one of the adhesive varieties which are most widely applied and have the largest output at present, can be roughly divided into six categories of hot melt type, solvent type, water solution type, emulsion type, calendering type, reaction type and the like, and the dosage of the solvent type pressure-sensitive adhesive is gradually reduced along with the development of the pressure-sensitive adhesive and the environmental protection requirement, but has irreplaceability in some fields due to the excellent performance. The acrylic pressure-sensitive adhesive has good performance at normal temperature due to the low polymer glass transition temperature, but the performance is reduced at high temperature, and phenomena such as degumming, adhesive residue and the like occur, so that the use scene of the acrylic adhesive is greatly reduced, and the acrylic pressure-sensitive adhesive is limited to be used at normal temperature.

Therefore, it is necessary to provide a high temperature resistant acrylate pressure sensitive adhesive and a preparation method thereof to solve the above problems.

The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

Disclosure of Invention

The invention aims to provide high-temperature-resistant acrylate pressure-sensitive adhesive and a preparation method thereof, which have good bonding effect at normal temperature and high temperature and can not generate phenomena of degumming, adhesive residue and the like.

In order to achieve the purpose, the embodiment of the invention provides a high-temperature-resistant acrylate pressure-sensitive adhesive, which comprises a component A and a component B, wherein the component A comprises the following raw material components in parts by weight: 60-90 parts by mass of soft monomer, 2-10 parts by mass of hard monomer, 2-10 parts by mass of functional monomer, 0.5-2 parts by mass of initiator, 120-160 parts by mass of solvent,

wherein the component B is a curing agent.

In one or more embodiments of the present invention, the soft monomer is one or more of isooctyl acrylate, ethyl acrylate, butyl acrylate, lauryl acrylate, n-butyl acrylate, and lauryl methacrylate.

In one or more embodiments of the present invention, the hard monomer is one or more of methyl acrylate, ethyl methacrylate, methyl methacrylate, n-butyl methacrylate, t-butyl acrylate, isobornyl methacrylate, vinyl acetate, acrylonitrile, and styrene.

In one or more embodiments of the present invention, the functional monomer is one or more of acrylic acid, methacrylic acid, hydroxyethyl acrylate, acrylamide, N-vinylcyclohexamide, hydroxypropyl acrylate, glycidyl methacrylate, isobornyl acrylate, methacrylamide, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.

In one or more embodiments of the present invention, the initiator is azobisisobutyronitrile.

In one or more embodiments of the present invention, the solvent is one or both of ethyl acetate and toluene.

In one or more embodiments of the present invention, the curing agent is one or more of isocyanate, amine-based resin, or metal salt.

In one or more embodiments of the present invention, the mass ratio of component a to component B is 100: (1-3).

In one or more embodiments of the present invention, component a comprises the following raw material components in parts by mass: the soft monomer is a mixture of 10-20 parts by mass of isooctyl acrylate, 15-40 parts by mass of butyl acrylate and 1-15 parts by mass of ethyl acrylate; the hard monomer is 2-10 parts by mass of methyl methacrylate; the functional monomer is a mixture of 1-6 parts by mass of acrylic acid, 0.3-3 parts by mass of hydroxypropyl acrylate, 0.5-3 parts by mass of glycidyl methacrylate and 0.2-2 parts by mass of methacrylamide, the initiator is 0.5-2 parts by mass, and the solvent is 120-160 parts by mass.

The invention also discloses a preparation method of the high-temperature-resistant acrylate pressure-sensitive adhesive, which comprises the following steps:

s1, weighing the raw materials of the component A: soft monomers, hard monomers, functional monomers, initiators and solvents;

s2, adding part of soft monomers, part of functional monomers, part of initiators and part of solvents into a reaction kettle, heating to 65-72 ℃, reacting for 60-120 min, and preserving heat for 20-40 min after the reaction is finished to obtain an intermediate product A;

s3, heating the intermediate product A in the reaction kettle to 75-80 ℃, then uniformly mixing the remaining soft monomer, functional monomer, partial initiator and partial solvent, and then dropwise adding into the reaction kettle to obtain an intermediate product B after dropwise adding is completed;

s4, adding all hard monomers and part of initiator into the intermediate product B, and reacting for 60-90 min at the temperature of 80-85 ℃ to obtain an intermediate product C;

s5, adding the residual solvent into the intermediate product C, stirring for 55-65 min, and cooling to below 50 ℃ to obtain a component A;

s6, weighing part of the component A and the curing agent, uniformly stirring, coating on release paper, performing crosslinking curing for 3min in a 90 ℃ oven, transferring to 25 mu PET, and curing at 50 ℃ for 24h to obtain the high-temperature-resistant acrylate pressure-sensitive adhesive.

Compared with the prior art, according to the high-temperature-resistant acrylate pressure-sensitive adhesive and the preparation method provided by the embodiment of the invention, the soft monomer, the hard monomer and the functional monomer are compounded and used, and a step-by-step polymerization method is adopted, so that the prepared acrylate pressure-sensitive adhesive has a good bonding effect at normal temperature and high temperature after being crosslinked, and phenomena such as degumming, adhesive residue and the like cannot occur.

Detailed Description

The following detailed description of specific embodiments of the invention is provided, but it should be understood that the scope of the invention is not limited to the specific embodiments.

Throughout the specification and claims, unless explicitly stated otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or component but not the exclusion of any other element or component.

The high-temperature-resistant acrylate pressure-sensitive adhesive comprises a component A and a component B, wherein the component A comprises the following raw material components in parts by weight: 60-90 parts by mass of a soft monomer, 2-10 parts by mass of a hard monomer, 2-10 parts by mass of a functional monomer, 0.5-2 parts by mass of an initiator and 120-160 parts by mass of a solvent, wherein the component B is a curing agent.

In one embodiment, the soft monomer is one or more of isooctyl acrylate, ethyl acrylate, butyl acrylate, lauryl acrylate, n-butyl acrylate, and lauryl methacrylate.

In one embodiment, the hard monomer is one or more of methyl acrylate, ethyl methacrylate, methyl methacrylate, n-butyl methacrylate, t-butyl acrylate, isobornyl methacrylate, vinyl acetate, acrylonitrile, and styrene.

In one embodiment, the functional monomer is one or more of acrylic acid, methacrylic acid, hydroxyethyl acrylate, acrylamide, N-vinylcyclohexamide, hydroxypropyl acrylate, glycidyl methacrylate, isobornyl acrylate, methacrylamide, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.

In one embodiment, the initiator is azobisisobutyronitrile.

In a specific embodiment, the solvent is one or both of ethyl acetate and toluene.

In one embodiment, the curing agent is one or more of isocyanate, amino resin or metal salt.

Wherein the metal salt may be: aluminum acetylacetonate, titanium acetylacetonate and zinc acetate.

In a specific embodiment, the mass ratio of component a to component B is 100: (1-3).

In a specific embodiment, the component A comprises the following raw material components in parts by weight: the soft monomer is a mixture of 10-20 parts by mass of isooctyl acrylate, 15-40 parts by mass of butyl acrylate and 1-15 parts by mass of ethyl acrylate; the hard monomer is 2-10 parts by mass of methyl methacrylate; the functional monomer is a mixture of 1-6 parts by mass of acrylic acid, 0.3-3 parts by mass of hydroxypropyl acrylate, 0.5-3 parts by mass of glycidyl methacrylate and 0.2-2 parts by mass of methacrylamide, the initiator is 0.5-2 parts by mass, and the solvent is 120-160 parts by mass.

The high-temperature-resistant acrylate pressure-sensitive adhesive prepared by combining the raw material components in the embodiment has more excellent high-temperature resistance.

It should be noted that the temperature has a large influence on the movement of the acrylate molecular chain, at normal temperature, the movement of the molecular chain is small, and the good performance can be obtained through the crosslinking effect of the curing agent, but at high temperature, the movement of the molecular chain is large, the phenomena of degumming and glue residue can occur when the same curing agent is added, and the original performance can be lost when the curing agent is added too much.

The invention also discloses a preparation method of the high-temperature-resistant acrylate pressure-sensitive adhesive, which comprises the following steps:

s1, weighing the raw materials of the component A: soft monomers, hard monomers, functional monomers, initiators and solvents;

s2, adding part of soft monomers, part of functional monomers, part of initiators and part of solvents into a reaction kettle, heating to 65-72 ℃, reacting for 60-120 min, and preserving heat for 20-40 min after the reaction is finished to obtain an intermediate product A;

s3, heating the intermediate product A in the reaction kettle to 75-80 ℃, then uniformly mixing the remaining soft monomer, functional monomer, partial initiator and partial solvent, and then dropwise adding into the reaction kettle to obtain an intermediate product B after dropwise adding is completed;

s4, adding all hard monomers and part of initiator into the intermediate product B, and reacting for 60-90 min at the temperature of 80-85 ℃ to obtain an intermediate product C;

the amount of the initiator in the S4 is 2-4 times that of the initiator in the S2, so that the effects of eliminating small molecules and unreacted monomers and improving the reaction rate are achieved.

S5, adding part of initiator into the intermediate product C, reacting for 60-90 min at 80-85 ℃, adding the rest solvent, stirring for 55-65 min, and cooling to below 50 ℃ to obtain a component A;

the amount of the initiator in the S5 is 1-2 times that of the initiator in the S2, so that the effects of eliminating small molecules and unreacted monomers and improving the reaction rate are achieved.

S6, weighing part of the component A and the curing agent, uniformly stirring, coating on release paper, performing crosslinking curing for 3min in a 90 ℃ oven, transferring to 25 mu PET, and curing at 50 ℃ for 24h to obtain the high-temperature-resistant acrylate pressure-sensitive adhesive.

The high-temperature-resistant acrylate pressure-sensitive adhesive prepared by compounding the soft monomer, the hard monomer and the functional monomer and adopting the step-by-step polymerization method has more excellent bonding effect at high temperature.

In the case of the example 1, the following examples are given,

firstly weighing the following raw materials of the component A by mass:

10g of isooctyl acrylate, 40g of butyl acrylate, 3g of acrylic acid, 10g of ethyl acrylate, 1g of hydroxypropyl acrylate, 6g of methyl methacrylate, 1g of methacrylamide, 2 parts of glycidyl methacrylate, 1g of azobisisobutyronitrile, 60g of ethyl acetate and 60g of toluene.

1) 4g of isooctyl acrylate, 16g of butyl acrylate, 1g of acrylic acid, 3g of ethyl acrylate, 0.4g of hydroxypropyl acrylate, 2g of glycidyl methacrylate, 0.2g of azobisisobutyronitrile, 20g of ethyl acetate and 20g of toluene were mixed homogeneously and charged into a four-neck reaction flask equipped with a thermometer, a condenser and mechanical stirring. Then the temperature is increased to 65 ℃, the reaction is determined to start when the temperature in the reaction kettle rises to be more than 0.1 ℃/S and bubbles are generated in the reaction kettle, and the reaction is timed for 60 min. After the dropwise addition, the temperature is kept for 20min to obtain an intermediate product A.

2) 6g of isooctyl acrylate, 24g of butyl acrylate, 2g of acrylic acid, 7g of ethyl acrylate, 0.6g of hydroxypropyl acrylate, 1g of methacrylamide, 0.2g of azobisisobutyronitrile, 25g of ethyl acetate and 25g of toluene are mixed uniformly in advance; when the temperature of the intermediate product A is raised to 75 ℃, the solution is dripped into the reaction kettle through a constant pressure dropping funnel, the dripping time is 90min, and the temperature is 75 ℃. After the dropwise addition, the reaction is carried out for 60min under the condition of heat preservation, and an intermediate product B is obtained.

3) Firstly, 6g of methyl methacrylate is added into the intermediate product B, then 0.4g of azobisisobutyronitrile is completely dissolved in 5g of ethyl acetate and then added into a reaction kettle, and the reaction is carried out for 60min at the temperature of 80 ℃ to obtain an intermediate product C.

4) And (2) completely dissolving 0.2g of azobisisobutyronitrile in 5g of ethyl acetate, adding into the intermediate product C, reacting at 80 ℃ for 60min, adding the rest of ethyl acetate and toluene, stirring for 60min, and cooling to below 50 ℃ to obtain the component A.

5) And (3) adding 2g of isocyanate into 100g of the prepared component A, uniformly stirring, coating the obtained glue on release paper by using a glue coating rod, drying and curing at 90 ℃ for 3min, controlling the thickness of the dry glue to be 25 +/-2 mu m, and transferring to 25 mu mPE to obtain the high-temperature-resistant acrylate pressure-sensitive glue.

In the case of the example 2, the following examples are given,

firstly weighing the following raw materials of the component A by mass:

18g of isooctyl acrylate, 30g of butyl acrylate, 3g of acrylic acid, 12g of ethyl acrylate, 1.5g of hydroxypropyl acrylate, 5g of methyl methacrylate, 1.5g of acrylamide, 1g of glycidyl methacrylate, 1.5g of azobisisobutyronitrile, 100g of ethyl acetate and 60g of toluene.

1) 6g of isooctyl acrylate, 12g of butyl acrylate, 1g of acrylic acid, 5g of ethyl acrylate, 0.5g of hydroxypropyl acrylate, 1g of glycidyl methacrylate, 0.3g of azobisisobutyronitrile, 20g of ethyl acetate and 20g of toluene were mixed homogeneously and charged into a four-neck reaction flask equipped with a thermometer, a condenser and mechanical stirring. And then heating up to 72 ℃, determining to start reaction when the temperature in the reaction kettle rises to be more than 0.1 ℃/S and bubbles are generated in the reaction kettle, timing the reaction for 120min, and preserving the temperature for 40min after finishing the dropwise addition to obtain an intermediate product A.

2) 12g of isooctyl acrylate, 18g of butyl acrylate, 2g of acrylic acid, 7g of ethyl acrylate, 1g of hydroxypropyl acrylate, 1.5g of acrylamide, 0.3g of azobisisobutyronitrile, 30g of ethyl acetate and 20g of toluene were mixed uniformly in advance, and the above solution was added dropwise to a reaction vessel through a constant pressure dropping funnel at a temperature of 80 ℃ for 90min at a temperature of 80 ℃. After the dropwise addition, the reaction is carried out for 90min under the condition of heat preservation, and an intermediate product B is obtained.

3) Firstly, 5g of methyl methacrylate is added into the intermediate product B, then 0.6g of azobisisobutyronitrile is completely dissolved in 5g of ethyl acetate and then added into a reaction kettle, and the reaction is carried out for 90min at the temperature of 85 ℃ to obtain an intermediate product C.

4) 0.3g of azobisisobutyronitrile was dissolved in 5g of ethyl acetate and added to intermediate C, and the mixture was reacted at 85 ℃ for 90 min. Adding the rest ethyl acetate and toluene, stirring for 60min, discharging, and cooling to below 50 ℃ to obtain the component A.

5) And (3) adding 2g of amino resin into 100g of the prepared component A, uniformly stirring, coating the obtained glue on release paper by using a glue coating rod, drying and curing at 90 ℃ for 3min, controlling the thickness of the dry glue to be 25 +/-2 mu m, and transferring to 25 mu mPE to obtain the high-temperature-resistant acrylate pressure-sensitive glue.

In the case of the example 3, the following examples are given,

firstly weighing the following raw materials of the component A by mass:

30g of lauryl acrylate, 30g of N-butyl acrylate, 30g of lauryl methacrylate, 2g of isobornyl methacrylate, 2g of vinyl acetate, 3g of acrylonitrile, 3g of styrene, 2g of N-vinylcyclohexylamide, 2g of hydroxypropyl acrylate, 3g of glycidyl methacrylate, 3g of isobornyl acrylate, 2g of azobisisobutyronitrile and 160g of ethyl acetate.

0.5g of isocyanate and 0.5g of amine-based resin were weighed out as curing agents.

Preparation method the preparation method of the above example 1 and example 2 is referred to, and the high temperature resistant acrylate pressure sensitive adhesive is obtained.

Example 4

Firstly weighing the following raw materials of the component A by mass:

25g of isooctyl acrylate, 16g of ethyl acrylate, 10g of butyl acrylate, 30g of lauryl acrylate, 1g of methyl acrylate, 1g of ethyl methacrylate, 1g of methyl methacrylate, 1g of n-butyl methacrylate, 1g of t-butyl acrylate, 1g of hydroxyethyl methacrylate, 1g of hydroxypropyl methacrylate, 0.5g of azobisisobutyronitrile and 140g of ethyl acetate.

2g of isocyanate and 1g of zinc acetate were weighed out as curing agents.

Preparation method the preparation method of the above example 1 and example 2 is referred to, and the high temperature resistant acrylate pressure sensitive adhesive is obtained.

In the case of the example 5, the following examples were conducted,

firstly weighing the following raw materials of the component A by mass:

40g of butyl acrylate, 20g of lauryl acrylate, 20g of n-butyl acrylate, 2g of tert-butyl acrylate, 2g of hydroxypropyl acrylate, 1g of acrylamide, 1g of methacrylic acid, 1g of azobisisobutyronitrile, 100g of ethyl acetate and 35g of toluene.

0.5g of isocyanate and 0.5g of aluminum acetylacetonate were weighed out as curing agents.

Preparation method the preparation method of the above example 1 and example 2 is referred to, and the high temperature resistant acrylate pressure sensitive adhesive is obtained.

In the case of the example 6, it is shown,

firstly weighing the following raw materials of the component A by mass:

40g of isooctyl acrylate, 30g of ethyl acrylate, 10g of ethyl methacrylate, 3g of acrylic acid, 3g of methacrylic acid, 3g of hydroxyethyl acrylate, 1g of acrylamide, 1.6g of azobisisobutyronitrile and 150g of toluene.

Then 2g of titanium acetylacetonate was weighed out as curing agent.

Preparation method the preparation method of the above example 1 and example 2 is referred to, and the high temperature resistant acrylate pressure sensitive adhesive is obtained.

In the comparative example 1,

acrylate pressure sensitive adhesives are commonly available on the market.

The following performance tests were performed on the high temperature resistant acrylate pressure sensitive adhesives prepared in examples 1 to 6 and the acrylate pressure sensitive adhesive of comparative example 1:

tack test at elevated temperature: 180 ℃ permanent adhesion (h): GB/T4851-2014.

The test data are as follows in table 1:

TABLE 1

The high-temperature-resistant acrylate pressure-sensitive adhesives prepared in examples 1 and 2 in table 1 have obviously better high-temperature resistance than those prepared in examples 3 to 6, and the high-temperature-resistant acrylate pressure-sensitive adhesives prepared in examples 3 to 6 have better high-temperature-resistant performance than that of the acrylate pressure-sensitive adhesive in comparative example 1.

Therefore, in conclusion, the high-temperature-resistant acrylate pressure-sensitive adhesive has a good bonding effect at normal temperature and high temperature, and phenomena such as degumming, adhesive residue and the like cannot occur.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable one skilled in the art to make and use various exemplary embodiments of the invention and various alternatives and modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents.