Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
  • B01J13/02—Making microcapsules or microballoons
  • B01J13/06—Making microcapsules or microballoons by phase separation
  • B01J13/14—Polymerisation; cross-linking
  • B01J13/18—In situ polymerisation with all reactants being present in the same phase

Definitions

• This invention relates to methods for encapsulating phase transitional paraffin compounds, and the resulting microcapsules.
• phase change materials available are well known for their thermal characteristics in that during their phase change stage they can absorb or release the latent heat while the temperature of the material is kept constant. Textiles and other products incorporated with the phase change materials, especially in the microencapsulated forms, may establish a microclimate surrounding the modified goods in the temperature ranges of the melting points of the employed phase change materials (PCMs) and so may meet the requirement for comfort.
• PCMs phase change materials
• the use of microencapsulated PCMs may be found in U.S. Pat Nos. 4,756,958 and 5,290,904.
• U.S. Pat. Nos. 5,456,852 and 5,916,478 both describes processes of microcapsule manufacturing employing in situ polymerization, in which formaldehyde used may impose an environmental danger.
• Examples of useful inherently flame retardant phase change materials may include halogenated paraffins having 10 to 22 carbon atoms and, more specifically, mono or poly-chlorinated and brominated paraffins such as bromooctadecane, bromopentadecane, bromononodecane, bromoeicosane, bromodocosane, and so on.
• halogenated paraffins having 10 to 22 carbon atoms and, more specifically, mono or poly-chlorinated and brominated paraffins such as bromooctadecane, bromopentadecane, bromononodecane, bromoeicosane, bromodocosane, and so on.
• the first layer is a layer in high density comprising a substrate coated with a polymer binder in which a plurality of microspheres containing a phase change material are dispersed.
• the second layer is a low density fibrous mesh in which individual fibers contain a plurality of microspheres containing a phase change material dispersed therein.
• a third layer is a flexible substrate. The fibrous mesh is sandwiched between the coated layer and the third layer.
• the shell of the microcapsules as prepared in the above processes may be somewhat permeable especially when heated at high temperatures (for example at 130 °C and above) in a dry state, which may be necessary for fabrics coating in the curing stages. Further, residual formaldehyde in the emulsion ' may not be controlled effectively.
• this invention provides a method for encapsulating a core component comprising paraffin compounds that can undergo phase transition, including the steps of:
• said first monomers are a polypropylene glycol with an average molecular weight higher than about 400 and a polyisocyanate soluble in said core component.
• the second solution includes at least one protective colloid being a polymer having at least one anionic functional group.
• the anionic functional group is selected from the group consisting of carboxylic group, sulfonic group, phosplionic group, or their mixture. Further, said anionic functional group is preferred to be carboxylic group.
• said polyisocyanate are selected from the group consisting of tolylenediisocyanate, 1,6-hexamethylenediisocyanate, or their mixture.
• Said polyisocyanate can be in an amount of about 0.2 to 3%, more preferably about 0.3 to 1%, weight with respect to the weight of the core component.
• said polyisocyanate is dissolved in the core component at a temperate of about 5°C higher than the melting point of the core component.
• the first solution is dispersed into the second solution at a temperate of about 5°C higher than the melting point of the core component.
• the method of this invention may also have the following options: second solution has a pH of about 4 to 7, preferably about 4.7 to 6, and more preferably about 5.5 to 5.7.
• the protective colloid is in an amount of about 1 to 3%, more preferably 1.5 to 2.5%, weight with respect to the weight of the second solution
• the first solution is dispersed into the second solution at a stirring rate of about 2000 revolutions per minute for about 10 to 15 minutes
• the melamine and formaldehyde is in a molar ratio of about 1:3, preferably 1:2, and more preferably 1:1.3 to 1:1.8 (melamine:formaldehyde) the melamine and the formaldehyde are mixed at about 70°C and for about 1 to 1.5 hours to form the precondensate.
• the emulsion is added to the third solution at a stirring rate of about 400 to 600 revolutions per minute.
• the pH of the encapsulation mixture is adjusted to about 4 to 7, preferably about 4.7 to 6, and more preferably about 5.5 to
• the method of this invention may also include the step of raising the temperature of the encapsulation mixture to about 70 to 80°C.
• the method of this invention may also include the step of at least one adding formaldehyde scavenger to the encapsulation mixture, wherein the formaldehyde scavenger is selected from the group consisting of ethylene urea, diethylene glycol, or their mixture.
• the formaldehyde scavenger is preferred to be in an amount of 0.1 to 1%, preferably 0.3 to 0.6%, weight with respect to the weight of the emulsion mixture. Additionally, the formaldehyde scavenger is added at about 0.5 to 1 hour before the end of the step of maintaining the temperature of the encapsulation mixture at about 70 to 80°C. Further, the pH of the encapsulation mixture may be adjusted to about 7.5 after the end of the step of maintaining the temperature of the encapsulation mixture at about 70 to 80°C.
• Figure 1 shows the SEM photo of microencapsulated octadecane prepared according to Example 1.
• Figure 2 shows the SEM photo of the state of the microcapsules prepared according to the method of this invention of damaged fabric.
• Figure 3 shows the SEM photo of the state of the microcapsules prepared according to the method of this invention of fabric surface.
• Figure 4 shows the relationship between microcapsule content and Q ma ⁇ .
• Figure 5 shows relationship between microcapsule content and thermal conductivity.
• paraffin compounds refers to both paraffin compounds and their relative bromo-derivatives.
• Phase transitional paraffin compounds refer to those paraffin compounds that can undergo phase transition.
• paraffin compounds with the straight molecule chain of 10 to 22 carbons and their bromo-derivatives may suit this requirement.
• the shell should possess low permeability at both ordinary and high temperatures.
• a conventional in situ condensation process with melamine and . formaldehyde as the monomers
• the paraffin compounds with different lengths of strait alkyl chains are difficult to be well emulsified due to their low surface tension and therefore proper surface tension modifiers should be added for satisfactory emulsification.
• polyisocyanates capable of being dissolved in the paraffin compounds were employed, because they can react with the free amino groups on melamine, methylolated melamine and the precondensate of melamine-formaldehyde to form the first outer layer of the shell.
• the precondensate of melamine in the continuous phase when it become less soluble along with the condensation, will possess much higher affinity for the first layer aforementioned than for the surface of the oil droplets of the paraffin compounds alone and deposits more easily on the "pre-wrapped" droplets.
• the procedures including both preparing the microcapsule emulsion and coating fabrics are given in the following steps.
• the first preparation step in the manufacturing of the microcapsules is the synthesis of the melamine-formaldehyde precondensate.
• This process comprises mixing the melamine, formaldehyde and water to form a precondensate or third solution.
• the system is heated at 70 °C under . stirring for 1 to 1.5 hours to enhance the forming of the precondensate.
• the precondensate or third solution may then be cooled to ambient temperature and stored for further use. It was found that the molecule ratio of melamine to formaldehyde in the preparation of the precondensate is important to the microencapsulation of this invention.
• the molar ratio of melamine to formaldehyde can be from 1:1 to 1:6.
• the low melamine to formaldehyde ratios may not be suitable to the PCMs of this invention, which are generally paraffin compounds.
• the precondensate formed with low melamine to formaldehyde ratios may be too hydrophilic causing unsatisfactory deposition. It was found in this invention that a relatively high molar ratio of melamine to formaldehyde in the precondensate preparation should be employed for satisfactory deposition of the precondensate onto the droplets of the core materials.
• the satisfactory molar ratio of melamine to formaldehyde may be 1 :3, more preferably 1 :2 and most preferably 1:1.3 to 1:1.8. It is believed that this may provide more free amino groups on the melamine ring in the precondensate and under acidic condition, which may in turn affect the choice of protective colloids in this invention and will be discussed later.
• the second preparation step is to dissolve adequate quantities of protective colloids in water to prepare a second solution as the vehicle for emulsification.
• melamine and formaldehyde as the monomers to form the aminoplast as the shell of microcapsules is known in the art.
• the pre-prepared aqueous solution of precondensate of melamine-formaldehyde including dissolved melamine and methylolated melamine is usually added to the already emulsified core materials and the condensation continues under acidic condition. Along with the condensation process the formed aminoplast molecules become large enough and less dissolved in the aqueous continuous phase and so they deposit on the droplets of the core materials and then continue to condensate to form the polymeric shell.
• the protective colloids possessing the groups reactive towards N-methylol groups on melamine ring should not be employed in order to prevent the reaction between the protective colloids and the partially methylolated melamine and the precondensate of melamine-formaldehyde.
• any natural or synthetic anionic polymer e.g., polymers containing anionic functional groups can be used as a protective colloid.
• "Anionic functional group” means a functional group as defined herein which possesses a net negative charge.
• Representative anionic functional groups include carboxylic, sulfonic, phosphonic, their alkylated derivatives, and so on. The choice of anionic functional group is based upon several factors including the reactivity of the resulting polymer to the reactants of the system including melamine, and cost.
• Examples of suitable natural polymers for use as protective colloids are gum arabic and alginic acid.
• Examples of semi-synthetic anionic polymers are carboxymethyl cellulose, phthalated gelatin, sulfated starch, cellulose sulfate, and lignin sulfonic acid.
• Synthetic anionic polymers which can be used in this invention include maleic anhydride based copolymers (including those copolymers hydrolyzed), acrylic acid based homopolymers and copolymers (including methacrylic acid based hornopolymers and copolymers), vinyl-benzenesulfonic acid based homopolymers and copolymers, and carboxy modified polyvinyl alcohols.
• the copolymer of styrene and maleic acid (or anhydride) and polyacrylic acid are employed. It is found that carboxyl groups are very sensitive to bath pH and low bath pH would cause the agglomeration and bigger particles form. The bath pH also significantly affects the emulsification and usually it is adjusted from 4 to 7.
• bath pH for the condensation should be controlled from 4.7 to 6.0 and preferably from 5.5 to 5.7.
• the addition amount of the protective colloids is limited since overdose of them can adversely affect the formation of the microcapsules and also adversely affect the handles of the coated fabrics.
• the copolymer of styrene and maleic acid (or anhydride) and polyacrylic acid the addition should be limited to 1.0% to 3.0% and preferably 1.5% to 2.5% based on the weight of the continuous phase.
• the first manufacturing step is to dissolve polyisocyanates and polypropylene glycols in the PCMs paraffin compounds to form a first solution.
• this step should be carried at the temperature of at least 5 °C higher than the melting points of the paraffin compounds and the system is mixed well.
• Acceptable candidates of both the polyisocyanates and polypropylene glycols should be those which can be dissolved in the paraffin compounds employed.
• Fine microcapsules are hardly prepared if a poor emulsifier is selected. Modification of the surface tension of the core materials is thus essential for satisfactory emulsification.
• Proper surface tension modifiers should be those organic chemicals, which are compatible with the paraffin compounds, polar in their nature and safe for application.
• polypropylene glycols with the average molecule weight higher than 400 were found to be satisfactory candidates for the above purpose. Easier and better emulsification could be obtained when 0.2% to 3.0%, preferably 0.3% to 1.0% of such propylene glycols, based on the weight of the core material, was added to the hydrophobic mixture to be emulsified. It is believed that the droplets of the core materials with modified surface tension became much more stable in the hydrophilic environment. The relative little amount of the glycols to the core phase may not significantly affect the phase transition properties of the paraffin compounds.
• Suitable polyisocyanates will be discussed in later paragraphs.
• the amount of polyisocyanates to be added can range from 0.01% to 5% and preferably from 0.05%> to 0.2% based on the weigh of the core materials. 0.2% to 3.0%, preferably 0.3% to 1.0% of propylene glycols based on the weight of the core material, is preferably used.
• the second manufacturing step is to add the organic core composition (the discontinuous phase or the first solution) into the protective colloid vehicle (the continuous phase or the second solution as prepared above) and emulsify them to form an emulsion.
• this emulsifying step is performed by means of stirring at the temperature of at least 5 °C higher than the melting points of the paraffin compounds for 10 to 15 minutes.
• a normal stirrer used in laboratory with the stirring speed of 2,000 rpm may be capable of producing the oil droplets with the average diameters of 4 to 5 micrometers or less.
• the third manufacturing step is to add the pre-prepared precondensate third solution to the emulsion under mild stirring (usually 400 to 600 rpm).
• mild stirring is of great importance since vigorous stirring is found to adversely affect the deposition of the melamine, partially methoxylated melamine and the precondensate onto the oil droplets in the emulsion and also damage the newly formed microcapsules.
• Acidification of the system after adding precondensate solution is preferred and usually the pH of the system is adjusted to 4 to 7, preferably 4.7 to 6, and more preferably 5.5 to 5.7.
• the temperature of the encapsulation mixture may then be raised to a higher temperature for sufficient time.
• the temperature is preferred to be about 70 to 80 °C to imtialize the condensation and continue the reaction for a period of time ranging from about 1 to 5 hours, preferably 2 to 4 hours.
• formaldehyde scavengers such as ethylene urea and diethylene glycol may then be added.
• the addition amount of ethylene urea or diethylene glycol ranges from about 0.1%) to 1% and preferably from 0.3% to 0.6% with respect to the weight of the microcapsule emulsion.
• the pH of the encapsulation mixture is adjusted to about 6.5 to 8.0, preferably 7.0 to 7.8 by adding suitable base like potassium or sodium hydroxide solution, carboxylate salts, or other readily available strong or weak bases to end the condensation and then cool the bath under mild stirring to ambient temperature.
• suitable base like potassium or sodium hydroxide solution, carboxylate salts, or other readily available strong or weak bases to end the condensation and then cool the bath under mild stirring to ambient temperature.
• the base used is of no importance but merely to achieve the pH adjustment.
• the following process was used to test the result of the encapsulation process in this invention and is described here. However, Of course, other suitable testing methods or process may be used instead.
• One drop of the formed microcapsule emulsion is coated onto a glass slide and then the glass slide is dried at 60 °C in a laboratory oven and then cured at 130 °C for 4 minutes. Some emulsion is taken and mixed with the binders, softeners and water available for fabric coating in a proper ratio to form a stable coating emulsion. As discussed earlier, the emulsion pH is adjusted to around 7.5. The formed emulsion is coated onto a fabric sample, which is then dried and cured to fix the microcapsules on the fabric sample. Usually this process is performed in the same way as employed in the conventional coating process. For the end products such as blankets and the like spray coating technique is preferred. Both of the glass slide and the fabric samples were checked with a scanning electronic microscope for observing the state of the microcapsules.
• the PCM microcapsules were coated onto a series of fabric samples. Scientific experiments were carried out to measure the dynamic surface temperature changes during the transients when the fabrics equilibrated to environment of 20 °C were brought to contact with a hot plate of 33 °C in simulating human skin temperature. Comparing with the control fabric samples, significant differences were found in surface temperature changes, which were measured by using infrared thermal image camera. Also, significant difference were observed between control and treated fabrics in the objectively measurement coolness index Q max . These test results show that the PCM microcapsules produced by this invention were able to provide improvement in thermal functional performance comparing with conventional products.
• Deposition of melamine-formaldehyde precondensate in the third solution onto the droplets of the core materials in the emulsion is essential in the in situ condensation microencapsulation. It was found in this invention that in this process, not all the precondensates in the third solution deposit onto the droplets to be encapsulated and some of them will self-condensate to form the polymer existing in the continuous phase or the third solution. This defect may lead to the very thin capsule shell and more seriously result in some unencapsulated core materials. Thus promoting the deposition of melamine-formaldehyde precondensate on the oily droplets is of great importance for complete encapuslation.
• the molar ratio of melamine to formaldehyde in the preparation of the precondensate is relatively low for reducing the interfacial tension between the precondensate and the oily core materials that is hydrophobic in nature. Further, there may be more intense ionic interaction under acidic condition between the precondensate and the protective colloids with anionic groups attached on the molecule backbone. This is why the second solution and the encapsulation mixture are preferred to be maintained at a low pH. Therefore, some means for promoting the deposition of the relatively less methoxylated precondensate onto the oily droplets may be required.
• the relatively abundant amino groups on the melamine ring can easily react with the polyisocyanates in the core to form a polyurea layer around the hydrophobic droplets, and the affinity between the polyurea layer and the precondensate in the continuous phase may be relatively high.
• the unreacted polyisocyanates inside the polyurea layer may react with the polypropylene glycols to form yet another polyurethane layer and this layer can be comiected with the polyurea layer through isocyanate functionalities. Therefore, the oily core materials can be wrapped with three layers: a polyurethane layer (formed by unreacted polyisocyanates with polypropylene glycols), a polyurea layer (formed by unreacted polyisocyanates with melamine) and an aminoplast (formed by melamine with formaldehyde) layer. A microcapsule with high retainability may then result.
• some polyisocyanates, especially those with more than two isocyanates groups are not compatible with the paraffin compounds employed in the work for the present invention.
• Polyisocyanates soluble in the core materials should be used.
• Preferred polyisocyanates that work efficiently in the preparation of the microcapsules are tolylenediisocyanate and 1,6-hexamethylenediisocyanate.
• cyclic urea such as ethylene urea
• polyglycols such as diethylene glycol were added under acidic condition as the formaldehyde scavengers to reduce the residual formaldehyde content.
• the microencapsulated paraffin compounds emulsion can generally be handled relatively easily and can be applied as the medium for temperature management in ' many fields.
• the microcapsules prepared in the present invention can be used for the treatment of textile fabrics and the end products can be in the state of stable and neutral emulsion.
• Binders, softeners and other additives necessary for fabric coating can thus be mixed with the above emulsion in proper ratios to form stable coating emulsions.
• Binders for fabric coating compatible with the microcapsule emulsion can be added in a wide range of amounts according to the fastness properties and fabric handles.
• Softeners are mainly the emulsions of polysiloxane and their derivatives and the addition amount is mainly determined in terms of the handle requirement.
• Fabric coatings are carried out in all the conventional procedures and the spray coating is preferred for the treatment of blankets and the similar products. Examples
• Binder used in this example is the emulsion of the copolymer of polyacrylic acid and the softener is the emulsion of epoxy-modified polysiloxane.
• Every emulsion is respectively coated onto a fabric sample and then the sample is dried at 110 °C for 8 minutes and cured at 130 °C for 4 minutes on a curing machine used in laboratory. Scaiming electronic microscope is used to observe the state of the microcapsules in the coated fabrics. The typical photos are respectively given in Fig. 2 and Fig. 3.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Dispersion Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Manufacturing Of Micro-Capsules (AREA)
• Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)

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• 2002
  • 2002-12-24 US US10/327,034 patent/US7442410B2/en not_active Expired - Fee Related
• 2003
  • 2003-12-23 CN CNB2003801073832A patent/CN100374193C/zh not_active Expired - Fee Related
  • 2003-12-23 JP JP2004562462A patent/JP2006512191A/ja active Pending
  • 2003-12-23 EP EP03782070A patent/EP1575704A4/en not_active Withdrawn
  • 2003-12-23 WO PCT/CN2003/001106 patent/WO2004058390A1/en not_active Ceased
  • 2003-12-23 AU AU2003289798A patent/AU2003289798B2/en not_active Ceased
  • 2003-12-23 CA CA002511177A patent/CA2511177A1/en not_active Abandoned

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