WO2021089653A1

WO2021089653A1 - Catalyst manufacturing process

Info

Publication number: WO2021089653A1
Application number: PCT/EP2020/081012
Authority: WO
Inventors: Humberto Alexandre Vieira BEIRÃO; Ivo PAIS; Hugo Stefaan G SOENS; Roberto Fernando Almeida TEIXEIRA
Original assignee: Devan Chemicals Nv; Devan-Micropolis SA
Priority date: 2019-11-05
Filing date: 2020-11-04
Publication date: 2021-05-14
Also published as: BE1027998A1; BE1027998B1

Abstract

The present invention relates to an improved catalyst for aminoplast resins typically relying on an acid catalyst, to initiate the crosslinking reaction. The improved catalyst according to the invention provides better control over the curing, i.e. the cross-linking reaction, improving the quality of the resin obtained after curing. The improved catalyst is based on the encapsulation of said acidic catalysts in microcapsules, with a controllable release of said acidic catalyst under particular environmental reaction conditions. The present invention further provides methods for obtaining such improved catalyst as well as the applications thereof.

Description

CATALYST MANUFACTURING PROCESS

FIELD OF THE INVENTION

BACKGROUND TO THE INVENTION

Aminoplast resins, urea-formaldehyde (UF) resins, melamine-formaldehyde (MF) resins find wide industrial application. Owing to their characteristic tensile strength and water repellency, their use is noted as binders for cellulosic, fibreglass, and polymeric materials as well as composite blends thereof. Aminoplast resins are thermosetting resins made by the reaction of an aminoplast resin precursor (e.g., an amine such as melamine, urea, or an amide) with an aldehyde (e,g., formaldehyde). The resins can be used in a variety of applications, including moulding, protective coatings, ion-exchange resins, and adhesives, to name but a few. Common thermosetting aminoplast resins are trimethylol melamine, methylol urea, dimethylol urea, ethylene diamine, benzoguanamine, fully alkylated melamine, and partially alkylated melamine. Aminoplast resins are also highly useful as cross-linking agents for other polymers, such as acrylic polymers (e.g., amino- or hydroxyl-functional: acrylic polymers, polyesters, epoxides, phenolics, and urethanes). For the crosslinking of aminoplast resins, a curing reaction catalyst is often employed particularly for urea-formaldehyde (UF) resins. Curing reaction catalysts are typically acidic catalysts including phosphoric acid curing catalyst, sulfonic acid compound curing catalysts such as toluenesulfonic acid and dodecylbenzenesulfonic acid. Such acid catalysts are often employed, particularly for urea-formaldehyde (UF) resins. When added to the resin composition in the conventional way, crosslinking would already start during mixing and tend to result in uneven curing of the resin, which could result in a defective end product. In an effort to address this problem of uneven curing, the application of encapsulated acids has previously been proposed, see for example US 6,335,386 to wax encapsulated oxalic acid in the binding of ligno-cellulosic material; and in US 3,666,597 to cellulose encapsulated phosphoric acid as part of an adhesive, but with unsatisfactory results when it comes to controlling the crosslinking and to reduce or prevent certain defects in the appearance of the resin film after curing. It is an objective of the present invention to provide an improved process in the manufacturing of such resins, with improved control over the crosslinking reaction. SUMMARY OF THE INVENTION

In a first embodiment the present invention provides an aminoplast resin catalyst characterized in comprising an encapsulated acidic catalyst; in particular comprising a microencapsulated acidic catalyst.

In an embodiment according to the invention the acidic catalyst within said aminoplast resin catalyst is encapsulated in a polymeric spherical shell. In a particular embodiment the acidic catalyst is encapsulated in an aminoplast polymeric cell; more in particular in a melamine- formaldehyde (MF) shells.

In an embodiment according to the invention the acidic catalyst is encapsulated in polymeric spherical cells with a range of about 5 pm to about 30 pm; in particular with a volume weight average particle size of about 10 pm to about 20 pm.

In an embodiment according to the invention the acidic catalyst used in the aminoplast resin catalyst according to the invention are the water-insoluble acidic catalysts known to the person skilled in the art and used in the manufacturing of aminoplast resins. In a particular embodiment the acidic catalysts are water-insoluble carboxylic acids such as for example selected from the group consisting of Pentanoic acid, Hexanoic acid, Heptanoic acid, Octanoic acid and Linoleic acid; more in particular the acidic catalyst used in the aminoplast resin catalyst according to the invention is Heptanoic acid.

In an embodiment according to the invention, the aminoplast resin catalyst comprising the encapsulated acidic catalyst is a liquid composition, in particular an aqueous composition comprising up to about 50% by weight of the encapsulated acidic catalyst, in particular up to about 40% by weight, more in particular comprising from about 10% to about 30% by weight of the encapsulated acidic catalyst. In one embodiment according to the invention the aminoplast resin catalyst is a liquid composition comprising about 30% by weight of the encapsulated acidic catalyst.

Typically, the encapsulated acidic catalyst used in such aminoplast resin catalyst composition consist of microencapsulated acidic catalyst as defined hereinbefore stably dispersed in said composition. Hence, in a further embodiment the present invention provides an emulsion for use as an aminoplast resin catalyst comprising microencapsulated acidic catalyst as defined hereinbefore.

In an alternative embodiment the aminoplast resin catalyst comprising the encapsulated acidic catalyst is produced as semi-solid, e.g. as a wet cake wherein the aqueous composition comprising the encapsulated acidic catalyst is mixed with a solid, such as for example resin binders used in the manufacture of resin based products such as moisture resistant MDF (medium density fibreboard), or composite pallet blocks. It is accordingly an object of the present invention to provide a semi-solid for use as an aminoplast resin catalyst comprising the aqueous composition comprising the encapsulated acidic catalyst according to the invention, in particular a semi-solid comprising up to 75%, in particular between and about 60-75% of solids.

In a further aspect the present invention provides a method for curing an aminoplast resin, said method comprising using an aminoplast resin catalyst as herein described; in particular comprising the step of mixing the aminoplast resin catalyst with the components typically used in the manufacture of an aminoplast resin well known to a person skilled in the art. In one embodiment said method further comprises the step of applying such mixture to a surface to be coated or laminated with the aminoplast resin and exposing said surface to pressure of at least two bar; or to pressure of at least two bar and an elevated temperature, i.e. at least above the glass transition temperature (Tg) of the shells encapsulating the acidic catalyst. In particular to a pressure of at least 30 bar; more in particular at least 50 bar; even more in particular at least 70 bar. In a preferred embodiment to a pressure of about 75 bar and a temperature of about 200°C. It is also an object of the present invention to provide a method for manufacturing the aminoplast catalyst resin as herein provided, said method comprising an interfacial polymerisation process to encapsulate the acidic catalyst. In one embodiment said method of encapsulating the acidic catalyst, hereinafter also referred to as ‘the first acidic catalyst or the encapsulated acidic catalyst' comprises; - providing an aqueous solution of a pre-condensate of a shell material;

- dispersing discrete droplets of the first acidic catalyst through said aqueous solution by adding discrete droplets to said solution

- adding a second acidic catalyst to the thus obtained solution for catalyzing the polymerization of the dissolved pre-condensate, and - agitating the thus obtained solution during the polymerization reaction to yield the encapsulation of the first acidic catalyst.

In a particular embodiment the manufacturing method is characterized in that the first acidic catalyst is a water-insoluble acidic catalysts known to the person skilled in the art and used in the manufacturing of aminoplast resins. In a particular embodiment said encapsulated acidic catalysts are water-insoluble carboxylic acids such as for example selected from the group consisting of Pentanoic acid, Hexanoic acid, Heptanoic acid, Octanoic acid and Linoleic acid; more in particular the first acidic catalyst used in the method according to the invention is Heptanoic acid. In one embodiment the manufacturing method is characterized in that the aqueous solution of a pre-condensate comprises about and between 3 to 30% by weight of the pre-condensate. In the methods according to the invention the pre-condensate is a urethane prepolymer; in particular having at least two -NCO group at molecular terminals thereof. In a preferred embodiment the pre-condensate is methylol urea.

In one embodiment the manufacturing method is characterized in that the solution is kept between 20 and 90°C, during the polymerization reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 - Size distribution diagram of the hepatanoic acid capsules obtained in the example of the present application. In said example hepatanoic acid is encapsulated in melamine- formaldehyde (MF) shells. Figure 2 - Scanning Electro Microscopy (SEM) images of the hepatanoic acid MF capsules obtained in the example of the present application.

DETAILED DESCRIPTION OF THE INVENTION Microencapsulation:

Microencapsulation is a technique whereby a core material is contained within a (usually) polymeric spherical shell. One of the first applications of microencapsulation was for “carbonless paper” for making copies on paper; ink was encapsulated and the capsules coated on the rear surface of paper. The action of pressure (writing or typing for example) breaks capsules, releasing ink and transferring a copy to the plain paper below.

Now, microencapsulation is widely used to encapsulate fragrances, flavourings and similar materials. The shell materials are typically polymeric and may be synthetic such as aminoplast polymers (urea-formaldehyde, melamine-formaldehyde and similar), polyacrylic, polyurethane, or may be of natural origin, derived from gelatine or alginate, for example. Capsules can be designed to be robust and to completely retain the core material, or they can be designed to release the core slowly (by diffusion, for example) or more rapidly by some external trigger such as pH or temperature. A common trigger is pressure or friction, whereby the capsules are ruptured to release the encapsulated core.

Capsules containing a core which is water-insoluble (oily materials) are easily manufactured by forming an oil-in-water emulsion of the core with a suitable surfactant; a water-soluble polymerforming material (for example a urea-formaldehyde resin) is added and a polymer shell is caused to form on the outer surface of the emulsion droplets, typically by the action of heat.

Aminoplast resins: Aminoplast resins are produced by the reaction of formaldehyde with amino functional molecules, of which the main ones used are urea and melamine. Depending on the desired application, a range of properties can be obtained by varying the amino to formaldehyde ratio. Processing of these materials is also very sensitive to the polymerization environment, such as the temperature and pH. Since, similarly to phenolics, these resins cure by a condensation reaction, they are generally processed under pressure in closed moulds.

Crosslinking aminoplast resins:

For the crosslinking of aminoplast resins, an acid catalyst is often employed, particularly for urea- formaldehyde (UF) resins. Heat is also required.

As an alternative to a conventional acid catalyst, an encapsulated form was sought to better control the crosslinking and to reduce or prevent certain defects in the appearance of the resin film after curing. The shell material surrounding the liquid acid catalyst core to form the microcapsule can be any suitable polymeric material which is impervious to the materials in the liquid core and the materials which may come in contact with the outer surface of the shell. The microcapsule shell wall can be composed of a wide variety of polymeric materials including gelatine, polyurethane, polyolefin, polyamide, polyester, polysaccharide, silicone resins, chitosan and epoxy resins. Many of these types of polymeric microcapsule shell materials are further described and exemplified U.S. Pat. No. 3,870,542.

Highly preferred materials for the microcapsule shell wall are aminoplast polymers comprising the reactive products of, for instance, urea or melamine and aldehyde, e.g. formaldehyde. Such materials are those which are capable of acid condition polymerization from a water-soluble prepolymer or pre-condensate state. Polymers formed from such pre-condensate materials under acid conditions are water-insoluble and can provide the requisite capsule friability characteristics to allow subsequent rupture of the capsule. Microcapsules having the liquid cores and polymer shell walls as described above can be prepared by any conventional process which produces capsules of the requisite size, friability and water-insolubility. Generally, such methods as coacervation and interfacial polymerisation can be employed in known manner to produce microcapsules of the desired characteristics. Such methods are described in US Patent 3,870,542, US Patent 3,415,758 and US Patent 3,041 ,288.

Microcapsules made from aminoplast polymer shell materials can be made by an interfacial polymerisation process as detailed in US Patent 3,516,941. In such interfacial polymerisation reactions the prepolymer or pre-condensate is typically selected from urethane prepolymer having at least two -NCO group at molecular terminals thereof, polyorganosiloxane diol, polysulfide prepolymer, epoxy resin obtained through reaction between bisphenol A and epichlorohydrin, and reactive polyolefin derivative having a reactive group such as an acid dhloride or thionyl chloride group. In a preferred embodiment the wall constituent is formed from urethane prepolymer by interfacial polycondensation of the urethane prepolymer dispersed in water or an aqueous solution containing amine compound at interfaces between the dispersed particles and the dispersing medium. In a more preferred embodiment the prepolymer or precondensate is methylol urea. In a particular embodiment an aqueous solution of a precondensate (e.g. methylol urea) is formed containing from about 3% to 30% by weight of the precondensate. Water-insoluble liquid core material, such as the liquid acid catalyst mentioned below, is dispersed throughout this solution in the form of microscopically-sized discrete droplets. While maintaining solution temperature between 20 and 90°C, acid is then added to catalyse polymerisation of the dissolved pre-condensate. If the solution is rapidly agitated during this polymerisation step, shells of water-insoluble aminoplast polymer form around and encapsulate the dispersed droplets of liquid core material. Capsules suitable for use in the present invention may be produced by a similar method. Preferably, the polymer of the shell is a melamine formaldehyde resin or includes a layer of this polymer.

Typically, the microcapsules vary in size, and may have diameters from 1 to 300 pm, preferably from 2 to 100 pm more preferably from 2 to 50 pm. The proportion by weight of shell with respect to the liquid core will typically be from 1 :500 to 1 :5,000. If the proportion is lower than 1 : 10,000 the resultant shell may be too thin. If the proportion is higher than 1 : 100, the resultant wall may be too strong to rupture easily. The exact details will depend upon the shell used.

The microcapsules of the present invention must be friable in nature. Friability refers to the propensity of the microcapsules to rupture or break open when subjected to direct external pressures or shear forces.

A series of organic acids was evaluated in the aforementioned manufacturing processes; the key performance characteristics were that the acid should be substantially insoluble in water to aid encapsulation by the above technique. A series of simple organic mono-acids were initially evaluated and heptanoic acid was found the have the optimum properties of low solubility in water (0.24g/100ml_) and a sufficiently rapid effect on the crosslinking of UF resin.

Mono-acids smaller than heptanoic acid were too soluble to encapsulate - hexanoic acid has a solubility of 1 .1g/100ml_ in water and pentanoic acid has a solubility of 5g/100ml_; both catalyse the cross linking of UF resin (in non-encapsulated form) faster than heptanoic acid. Octanoic acid is less soluble in water than heptanoic acid (0.07g/100ml) and is more readily encapsulated but the speed of the crosslinking reaction of the UF resin in significantly reduced. Mono-acids higher than Linoleic acid are increasingly insoluble in water and consequently have a negligible effect on catalysing the crosslinking of UF resins.

EXAMPLE

Encapsulation of heptanoic acid: Heptanoic acid has been encapsulated in melamine-formaldehyde (MF) shells to produce an emulsion containing approximately 30% of capsules; the heptanoic acid content of the capsules is +/-70% as measured by thermogravimetric analysis (TGA) and by titration of a diluted solution of the capsules with standard NaOH solution.

The use of a polymeric surfactant enhances encapsulation of the partially soluble heptanoic acid. A number of polymeric surfactants were evaluated before poly(styrene-maleic anhydride) (PSMA) was chosen. PSMA must first be solubilised by neutralisation with sufficient NaOH to ensure complete dissolution.

The first step is to begin formation of a MF pre-polymer, by mixing Cymel 285 (a MF resin) with Floset 150L (a polyacrylamide) with PSMA solution and adjusting to pH 5.3 (with acetic acid) and heating to 25°C for a period.

Hepatanoic acid is then added and the mixture emulsified under high shear to create emulsion droplets of a suitable size (generally <30pm, preferably <15pm); the pH falls to 4.8 - 4.9 as a result of the slight solubility of heptanoic acid but is not adjusted. The whole mixture is heated over a period of 90 minutes to 80°C and allowed to remain at 80°C for a further 60 minutes before being cooled back to ambient temperature.

The capsules so formed are characterised by particle size analysis (Figure 1 ), TGA / titration for heptanoic acid content (Data not shown) and are imaged using a scanning electron microscope (Figure 2) to ensure satisfactory capsule formation. Crosslinkinq of UF resins with hepatanoic acid capsules:

These resins are used to bond / produce a hard, durable surface on many household goods such as furniture or wood-effect panelling. The whole assembly is subjected to heat and pressure to effect a cure of the resin and to produce the final article.

Using a conventional acid catalyst may result in the promotion of premature curing during mixing or uneven crosslinking of the surface under heat / pressure if the mixing is not uniform, leading to a defective final product. By encapsulating the catalyst, it is protected from the resin by virtue of being contained within the polymeric shell and cannot begin the crosslinking. More effective and consistent mixing is possible if there is no likelihood of initiating the crosslinking reaction prematurely. A uniform distribution of the encapsulated catalyst within the resin mixture ensures a more consistent crosslink behaviour through the article, leading to a better quality of product.

Claims

1. An aminoplast resin catalyst characterized in comprising an encapsulated acidic catalyst.

2. The aminoplast resin catalyst according to claim 1 , wherein the acidic catalyst is encapsulated in a polymeric spherical shell; in particular an aminoplast polymeric shell.

3. The aminoplast resin catalyst according to claims 1 or 2, wherein the acidic catalyst is encapsulated in microcapsules; in particular in polymeric spherical cells with a range of about 5 pm to about 30 pm.

4. The aminoplast resin catalyst according to any one of claims 1 to 3, wherein the acidic catalyst are water-insoluble carboxylic acids such as for example selected from the group consisting of Pentanoic acid, Hexanoic acid, Heptanoic acid, Octanoic acid and

Linoleic acid; more in particular the acidic catalyst used in the aminoplast resin catalyst is Heptanoic acid.

5. The aminoplast resin catalyst according to any one of the preceding claims consisting of a liquid composition comprising the encapsulated acidic catalyst.

6. The aminoplast resin catalyst according to claim 5 wherein the liquid composition comprises up to about 50% by weight of the encapsulated acidic catalyst.

7. An emulsion for use as an aminoplast resin catalyst comprising microencapsulated acidic catalyst as defined in any one of the preceding claims.

8. A method for curing an aminoplast resin, said method comprising using an aminoplast resin catalyst as defined in any one of the preceding claims.

9. The method according to claim 8, comprising mixing said aminoplast resin catalyst with the components typically used in the manufacture of an aminoplast resin.

10. The method according to claims 8 or 9, further comprising the step of applying such mixture to a surface to be coated or laminated with the aminoplast resin and exposing said surface to pressure of at least two bar; or to pressure of at least two bar and an elevated temperature.

11. The method according to claim 10, exposing said surface a pressure of about 75 bar and a temperature of about 200°C.

12. A method for manufacturing the aminoplast catalyst resin according to any one of claims 1 to 6, said method comprising an interfacial polymerisation process to encapsulate the acidic catalyst.

13. The method according to claim 12, wherein the method of encapsulating the acidic catalyst comprises;

- providing an aqueous solution of a pre-condensate of a shell material;

- dispersing discrete droplets of a first acidic catalyst through said aqueous solution by adding discrete droplets to said solution

- adding a second acidic catalyst to the thus obtained solution for catalyzing the polymerization of the dissolved pre-condensate, and

- agitating the thus obtained solution during the polymerization reaction to yield the encapsulation of the first acidic catalyst.

14. The method according to claim 13, wherein the first acidic catalyst are water-insoluble carboxylic acids such as for example selected from the group consisting of Pentanoic acid, Hexanoic acid, Heptanoic acid, Octanoic acid and Linoleic acid; more in particular the first acidic catalyst used in the method according to the invention is Heptanoic acid.

15. The method according to claims 13 or 14, wherein the aqueous solution of a precondensate comprises about and between 3 to 30% by weight of the pre-condensate; in particular of a urethane prepolymer; more in particular of methylol urea.

16. The method according to any one of claims 13 to 15, wherein the solution is kept between 20 and 90°C, during the polymerization reaction.