CN1248928A - Encapsulation - Google Patents

Abstract

A colloidal aggregate suitable for use in the curing of resins comprises a continuous phase of a water based encapsulent material and a dispersed phase comprising one or more strong acids. The continuous phase advantageously comprises a mixture of gelatin and xanthan gum. The aggregate is sonicated to encapsulate the acid in the encapsulent material. The encapsulated acid is mixed with a curable resin. The acid capsules may be ruptured by any suitable means, but particularly ultrasound, to release the acid to initiate curing of the resin.

Description

Lagging

The present invention relates to acid microcapsules and equipment for use as well as methods for their production. The invention relates in particular, but not exclusively, to microcapsules of catalysts and/or initiators for the curing of synthetic resins.

In most applications, the processing and curing of the resin takes place under controlled conditions. However, the following situation occurs when the curing of the resin must be controlled/prevented until the appropriate time in order to achieve optimum utilization of the resin.

Most applications of thermosetting resins use heat to cure the resin. The application of heat causes catalysts and/or accelerators in the resin to accelerate the cross-linking of the resin molecules. However, even without the use of heat, the resin cures over a period of several days, thus limiting the time that the uncured resin can be stored. So from the above it can be seen that - when the resin is mixed with the catalyst and used for a particular application, time is bought for the resin/catalyst system to get into place.

The industry is aware of this problem and has made some efforts to solve it by developing special resins curable with light radiation.

Ultrafine microcapsules with a diameter of less than 100 [mu] have been produced, and when the microcapsules are dispersed throughout the resin, they are of suitable size for use in the field of thermosetting resins. When the microcapsules are so small, they are uniformly dispersed and do not settle in the resin.

A particular class of resins are phenolic resins, which are the reaction products between phenols (usually phenol) and aldehydes (usually formaldehyde). A major advantage of the use of phenolic resin systems in the thermosetting resin industry is that the resin initially contains a low molecular weight fusible solid resin which can be easily processed and thereafter when cured the resin is formed into a high molecular weight, strong, heat resistant material.

Phenolic resins are usually initiated/catalyzed by adding strong acids, such as sulfuric acid, hydrochloric acid, phosphoric acid, toluenesulfonic acid, etc., which are highly corrosive and difficult to handle. The corrosiveness of acids is the main reason why it is extremely difficult to encapsulate acids One of the factors, without some type of encapsulation or controlled release, it's not possible to get acid controlled release into the resin. Another resin, urine formaldehyde resin, is also of interest.

An object of the present invention is to provide a strong acid capsule which can be easily dispersed in a resin material without leakage of acid.

Furthermore, the present invention also seeks to provide curable resin systems for rigid article production, wherein the resins can be cured easily and quickly, but retain a long shelf life making them particularly suitable for use in the thermosetting resin industry.

According to one aspect of the present invention, there is provided a colloidal aggregate suitable for curing resins, comprising a continuous phase of a water-based encapsulation material and a dispersed phase comprising one or more strong acids, wherein the continuous phase can be supplied by an external energy source are destroyed to release acid.

Preferred encapsulating materials include acid resistant water-based gelatin.

Strong acids may include sulfuric acid, hydrochloric acid, phosphoric acid, and toluenesulfonic acid or mixtures thereof.

According to another aspect of the present invention, there is provided a resin system for the production of rigid articles, wherein said resin system comprises a resin and a dispersed catalyst/initiator, said catalyst/initiator comprising a water-based encapsulation A colloidal aggregate of a continuous phase of material and a dispersed phase containing one or more strong acids, where the continuous phase can be disrupted by an external source of energy to release the acid into the resin, thereby initiating/catalyzing the curing of the resin.

One advantage of this type of encapsulation over the prior art is that previously encapsulated reactants were produced as dry capsules which tended to disperse poorly when mixed with the resin, whereas the colloidal aggregates of the present invention are easily absorbed. Dispersion ensures complete dispersion in the resin and significantly reduces the possibility of large agglomerates of capsules.

The invention has general application in that a resin impregnated with absorbent material having colloidal capsules dispersed therein can be formed into a final shape and the colloidal capsules are disrupted by, for example, heat or electromagnetic energy to release the catalyst or accelerators, causing the resin and absorbent material to cure in said final shape.

In another embodiment of the invention, the encapsulated catalyst is mixed with a curable resinous material which is then used to impregnate the fibrous carrier layer.

The fibrous layer can be formed into any desired shape while the resin is uncured, such as a boat or a molded part for a vehicle, and then the resin is cured by heat or electromagnetic energy to break the colloidal capsules.

The resinous/colloidal capsule carrier material preferably has a fibrous sheet structure comprising mats, rolls or randomly oriented fibers which may be glass fibers and/or fibers of natural and synthetic origin.

According to another aspect of the present invention, there is also provided a method for microencapsulation of one or more strong acids suitable for use as a catalyst, accelerator or initiator in a resin curing reaction, comprising the steps of: mixing an acid, a water-based lagging material, and water; sonicating the resulting mixture to encapsulate the acid in the lagging material, and substantially removing the remaining water from the mixture to form the acid in the lagging material colloidal aggregates.

As a specific example, when acid-resistant gelatin is used, the application of ultrasonic energy or the gelatin in the sonication step causes free radical-induced cross-linking of protein molecules. Highly reactive radicals, especially H· and OH· are generated from water by ultrasound and react with molecular oxygen present in solution/air to form the peroxide HO ₂ ·. The reaction of peroxides with protein molecules usually forms disulfide bonds between cysteine residues. Ultrasound is capable of producing high concentrations of proteinaceous colloidal capsules with a narrow size distribution, typically in the range of 1-20[mu].

Typical ultrasonic response equipment used in the preparation of this invention includes collimated 20 Khz radiation from a lead zirconate titanate transducer. The reaction can be carried out in a glass sonication bath under an inert atmosphere, preferably under an argon atmosphere. An amplification horn, preferably made of titanium, can be fixed adjacent to the transducer for amplifying its signal. Since the temperature increases as the reaction proceeds, the sonication tank is preferably placed in a water bath. Audible sounds may also be used.

Preferably in the water removal step, the aqueous capsule mixture formed in the sonication step is heated for about 24 hours at a temperature below the destruction temperature of about 80°C, preferably between 60°C and 70°C heating.

The invention will be better understood by the following examples which describe the encapsulation of strong acids in water-based encapsulation materials as polymerization catalysts/initiators.

Example 1

The cure of phenolic resins is usually initiated and catalyzed by the addition of strong acids. The reaction is carried out at normal temperature.

The curing agent that was encapsulated in this example was an appropriate mixture of phosphoric acid and toluene sulfonic acid.

1 part by weight of the acid mixture was mixed with 3 parts by weight food grade gelatin (200 Bloom) dispersed in 3 parts water.

The above mixture was sonicated for 3 minutes (100W power) using a 20Khz probe. This high-intensity ultrasound produces intermediate proteinaceous capsules in a substantially aqueous medium, advantageously of a size less than 100μ, wherein the capsules 2 are dispersed in water and comprise an outer gelatin layer 4 encapsulating a strong acid core 6 .

However, it has been found that since the acid mixture contains strong acid, the gel/water interface expands around the acid catalyst, causing the acid to diffuse through the shell. This appears to be due to the water present in each capsule and surrounding the shell of each capsule acting as a carrier for the acid.

It has since been found that an improved encapsulated product is produced by eliminating water from the aqueous mixture to prevent acid from traversing the capsule wall. Therefore, the sonicated mixture was heated in a 70°C oven until 3 parts of water were removed, forming colloidal aggregates of the final product.

Example 2

In another experiment, mixing a 10% acid mixture by weight with 10% acid-resistant gelatin (Gelatex, Chem. Colloids Ltd) and 10% water and sonicating the mixture using a 20KHz probe (70W) for 3 minutes produced 100μ particle size, advantageously between 1 and 20μ proteinaceous colloidal capsules.

The gelatin/water/acid colloid was heated in an oven at 60°C for 24 hours to remove water from the gelatin/water interface, leaving a gelatin capsule.

It has been found that gelatin capsules of the acid mixture of the present invention have a shelf life of at least 3 months, and curing is achieved within 5 minutes when samples thereof are heated to 90°C in the presence of phenolic resin.

Lagging materials can take many different forms.

For example, materials comprising a blend of gelatin and xanthan gum have been found to have a particularly beneficial combination of long-term acid corrosion resistance and ease of lagging with acid and susceptibility to failure of the lagging when an external energy source such as ultrasound is used.

The preferred preparation of the above components is in the following ranges:

Xanthan gum 0.1-50.1

Gelatin 99.9-49.9

The material is produced by bonding, agglomerating and coating gelatin with xanthan gum. In addition to the above-mentioned component mixtures, the following components may also be used in the following component mixtures:

(a) Gelatin 99.9-49.9

Gel (Cellan Gum) 0.1-50.1

(b) Gum Arabic 99.9-49.9

Xanthan Gum 0.1-50.1

(c) Gum Arabic 99.9-49.9

Gel Gel 0.1-50.1

(d) Gelatin 99.9-49.9

Tragacanth Gum 0.1-50.1

(e) Gum Arabic 99.9-49.9

Tragacanth Gum 0.1-50.1

(f) Gelatin 99.9-49.9

Gum Arabic 0.1-50.1

(g) Gelatin 99.9-49.9

  Polyethylene glycol alginate                                                  

Blends of all of the above mixtures may also be used.

In any mixture including gelatin, any of the following may be used as substitutes.

- Hydrolyzed gelatin

- alginate

- Antler glue (Kappa, lota and Lambda)

- locust bean gum

- gum arabic

- high methoxyl pectin

- Gel

- methylcellulose and methylcarboxypropylcellulose or any mixtures/modifications thereof

- agar

In any mixture that includes xanthan gum, any of the following may be used as a substitute:

——Carboxyethyl cellulose

—— carboxymethyl cellulose

- gum arabic

- Gum tragacanth

- Gel

- Sulfate monoester of tragacanth gum

——Polyethylene glycol alginate

- low methoxyl pectin

In the foregoing, the following terms have the following meanings:

(a) Gelatin and hydrolyzed gelatin

 Protein obtained from the hydrolysis of animal collagen (including fish) or any composition of amino acids

Any short chain mixture.

(b) Deer horn glue and agar

Extracted from red seaweed with a galactose skeleton linked by alternating glycosidic bonds

product.

(c) Guar gum, locust bean gum, tara gum, bean gum, mesquite gum and gourd gum

Bajiao

Galactomannans—a series of D-mannose residues based on β(1-4) linkages

  Linear polysaccharases.

(d) Gum Arabic, Tragacanth and Karaya

exudate glue—obtained from a tree and shrub which is first liquid and exposed to sunlight

and air-dried to form a transparent lump.

(e) Xanthan gum and gum gel

  Biosynthetic polysaccharide enzyme glue - produced by fermentation using special bacteria.

(f) Alginates and alginates

Salts of alginic acid - typically have a degree of polymerization of 100-3000 equivalent to about 20,000

-600,000 molecular weight.

Propylene Glycol Alginate (PGA) is an ester of alginic acid and propylene glycol.

(g) methylcellulose, methylhydroxypropylcellulose, hydroxyethylcellulose and carboxymethylcellulose

Vitamins

Cellulose ethers - produce "alkaline cellulose" through the reaction of cellulose and alkali, and

After being alkylated or alkoxylated in the presence of an inert diluent (or without a diluent)

or by Williamson esterification.

(h) low methoxyl pectin and high methoxyl pectin

Pectin is a partial fragmentation of the complex structure in the plant cell wall (usually the fruit).

They are modified by deesterification reaction to produce high-methoxyl and low-methoxyl pectins.

The acid capsules may be mixed with the resin to be cured by any suitable method. The resin can be phenolic or urea-formaldehyde resin, and the small capsule size facilitates dispersion in the resin. The mixing process is low-energy, low-shear to avoid premature failure of the capsules. A suitable type of mixer may be a paddle mixer. The shelf life of the product, including the resin to be cured and the encapsulating acid, meets consumer needs. A shelf life of at least three months and possibly more than one year can be achieved.

The capsules dispersed in the resin may be broken by any suitable means to release the acid to initiate cure. Suitable methods include heat, sound, ultrasound, radio waves, microwaves or pressure. The use of pressure methods may be particularly advantageous in products which would otherwise involve the production of pressure, such as laminated products.

It should be understood that the foregoing embodiments have been described for illustrative purposes only and that various modifications are possible without departing from the scope of the invention.

Claims (25)

1. A colloidal aggregate suitable for use in resin curing comprising a continuous phase of a water-based encapsulation material and a dispersed phase comprising one or more strong acids, wherein the continuous phase can be disrupted by an external energy source to release the acid . 2. The colloidal aggregate of claim 1, wherein the encapsulating material comprises a water-based, acid-resistant gelatin. 3. A colloidal aggregate as claimed in claim 1 or 2, wherein the encapsulating material comprises a mixture of gelatin and xanthan gum. 4. A colloidal aggregate as claimed in claim 1 or 2, wherein the encapsulating material comprises a mixture of gelatin and pectin. 5. A colloidal aggregate according to claim 1 or 2, wherein the encapsulating material comprises a mixture of gum arabic and xanthan gum. 6. A colloidal aggregate as claimed in claim 1 or 2, wherein the encapsulating material comprises a mixture of gelatin and tragacanth. 7. The colloidal aggregate of claim 1 or 2, wherein the encapsulating material comprises a mixture of gum arabic and gum tragacanth. 8. The colloidal aggregate of claims 1 or 2, wherein the encapsulating material comprises a mixture of gelatin and gum arabic. 9. The colloidal aggregate of claims 1 or 2, wherein the encapsulating material comprises a mixture of gelatin and polyethylene glycol alginate. 10. The colloidal aggregate of claim 1 or 2, wherein the encapsulating material comprises a mixture of gum arabic and gum gel. 11. A colloidal aggregate according to any one of claims 3 to 10, wherein the mutual ratios of the two components are in the ranges of 99.9-49.9 and 0.1-50.1. 12. The colloidal aggregate as claimed in claim 1, wherein the encapsulating material comprises hydrolyzed gelatin, alginate, antler gum (Kappa, lota and Lambda), locust bean gum, gum arabic, high methoxyl pectin, Gel gel, methyl cellulose and methyl hydroxypropyl cellulose or any mixture thereof or agar. 13. The colloidal aggregate as claimed in claim 1, wherein the encapsulating material comprises a sulfate monoester with following hydroxyethyl cellulose, carboxymethyl cellulose, gum arabic, gum tragacanth, gum gelatin, gum tragacanth Xanthan gum mixed with one of , polyethylene glycol alginate, low methoxyl pectin, etc. 14. The colloidal aggregate of claim 1 or 2, wherein the strong acid comprises sulfuric acid, hydrochloric acid, phosphoric acid, toluenesulfonic acid or mixtures thereof. 15. The colloidal aggregate according to example 1 or example 2. 16. A resin system for the production of rigid articles, wherein the resin system comprises a resin and a dispersed catalyst/initiator, the catalyst/initiator being a colloidal aggregate comprising a continuous flow of water-based encapsulation material phase and a dispersed phase comprising one or more strong acids, where the continuous phase can be disrupted by an external energy source to release the acid into the resin, thereby initiating/catalyzing resin cure. 17. A fibrous support layer impregnated with the resin system of claim 16. 18. A fibrous carrier layer as claimed in claim 17 which is formed while uncured. 19. A fibrous carrier layer according to claim 17 or 18, having a fibrous sheet structure comprising mats, rolls or randomly oriented fibres. 20. The fibrous carrier layer of claim 19, wherein the fibers are glass fibers. 21. A process for preparing microencapsulations of one or more strong acids suitable for use as catalysts, accelerators or initiators in resin curing reactions, comprising the steps of: Mixing a glue material and water; sonicating the resulting mixture to encapsulate the acid in the lagging material and substantially removing the remaining water from the mixture to form colloidal aggregates of the acid in the lagging material body. 22. The method of claim 21, wherein the mixture is treated with ultrasound. 23. The method of claim 22, wherein the mixture is treated with audible sonication. 24. A method as claimed in claim 21, 22 or 23, wherein the capsules formed in the sonication step are heated at a temperature below 80°C for about 24 hours. 25. The method of claim 24, wherein the capsules are heated at a temperature between 60°C and 70°C.