Binding agent mixture and the use thereof

Abstract

The invention relates to a binder mixture based on a pulverulent mix with non-thermoreactive phenolic resin and one or more thermoreactive condensation products, from the group consisting of phenolic resins, amino resins and epoxy resins, and a powder coating material or recycled powder coating material. The mixture can be used as a binder for textile nonwovens, moulding compounds, refractory materials, abrasive materials and friction materials, and also in the foundry industry.

Description

[0002] The invention relates to binder mixtures based on a pulverulent mix of a non-thermoreactive phenolic resin and one or more thermoreactive condensation products from the group consisting of phenolic, amino and epoxy resins. Binders of this kind are known from EP-B 0 254 807. They are used primarily for producing textile nonwovens, where they allow the production of high-grade products which do not disseminate any disruptive amine odour even at relatively high temperature and humidity levels.

[0003] One disadvantage of these binder mixtures is that their reactivity is not up to the requirements of a high-speed mass production operation, with the consequence that it is necessary either to use additional accelerators or to prolong the cycle times when producing corresponding mouldings. This is so in particular when the thermoreactive component used comprises the otherwise highly advantageous condensation products of bisphenols and formaldehyde.

[0004] It is therefore an object of the invention to provide binder mixtures which, just like the binder mixtures comprising a non-thermoreactive phenolic resin and one or more thermoreactive condensation products from the group consisting of phenolic, amino and epoxy resins, are suitable for producing high-grade textile nonwovens which do not disseminate any disruptive odour even at relatively high temperature and humidity levels but whose reactivity is much greater than that of the aforementioned binders and which therefore permit short cycle times on curing even without accelerators.

[0005] This object is achieved by binder mixtures according to claims 1 to 7. The binders are preferably used for producing textile nonwovens and also as binders for moulding compounds, refractory materials, abrasives, friction linings, and in the foundry sector, as claimed in claims 8 to 13.

[0006] It has been found that the reactivity of binder mixtures comprising a non-thermoreactive phenolic resin and one or more thermoreactive condensation products from the group consisting of phenolic, amino and epoxy resins is substantially increased if powder coating material is added as a further binder component to the binder mixture.

[0007] For example, the B-stage time (in accordance with DIN 16916-02-C2, measures at 150° C.) of a mixture of equal parts by weight of a phenol novolac and a resol based on bisphenol A (base binder) is 6 minutes.

[0008] If this base binder is blended, for example, with varying amounts of a powder coating material based on 70% of reactive coating powder based on epoxy resins and 30% on reactive coating powder based on polyester resins, the binder mixtures obtained have the following B-stage times:

Base binder: Powder coating mixture ratio B-stage time
90:10                            3 min, 30 s
80:20                            2 min, 05 s
70:30                            2 min, 05 s
60:40                            3 min, 10 s
50:50                            5 min, 30 s

[0009] It has further been found that the strengths of textile nonwovens produced using these mixtures, as compared with those produced using base binder alone, are substantially increased. Moreover, even after storage at relatively high temperature and high humidity, no disruptive production of odours is perceived.

[0010] Non-thermoreactive phenolic resins are phenolic resins condensed in an acidic medium, with the general formula 1

[0011] where R and R′ are identical or different and denote hydrogen or an alkyl chain having from 1 to 9 carbon atoms.

[0012] Starting products are phenol, cresols, xylenols or relatively long-chain alkylphenols, which are condensed in an acidic medium with formaldehyde or a compound which produces formaldehyde under condensation conditions, the phenol-formaldehyde ratio being situated within a range from 1:0.6 to 1:0.9.

[0013] The thermoreactive resins, which may be used individually on in combination, may hail from three different groups: the phenolic resins, the amino resins, and the epoxy resins. The non-thermoreactive phenolic resin is employed together with one or more of these thermoreactive condensation products in a weight ratio of from 30:70 to 90:10.

[0014] Thermoreactive phenolic resins (resols) are reaction products from the alkaline condensation of a phenolic compound with formaldehyde or with a compound which produces formaldehyde under condensation conditions. As phenolic compounds it is possible to use phenols or mixtures of said classes of compound, including both mononuclear and polynuclear phenols.

[0015] Examples of such compounds are phenol itself and also its alkyl-substituted homologues, such as o-, m- or p-cresol, xylenes or more highly polyalkylated phenols, and also halogen-substituted phenols such as chloro phenol or bromophenol and polyhydric phenols such as resorcinol or pyrocatechol, and also polynuclear phenols such as naphthols or bisphenols. The preferred phenolic compounds are bisphenol A and bisphenol F. The phenolic compounds and formaldehyde are preferably reacted in a molar ratio of from 1:1.0 to 1:4.0 with one another.

[0016] The phenolic resins for use in accordance with the invention, the thermoreactive and the non-thermo reactive resins, ought together to have a free phenol content of less than 1%, and must be present in pulverulent form.

[0017] Thermoreactive amino resins which can be used include not only melamine-formaldehyde but also benzoguanamine-formaldehyde or urea-formaldehyde condensation products, and also the corresponding cocondensates. They can be used alone, but are preferably used in a mixture (in any proportion) with the resols, as a thermoreactive binder component.

[0018] As epoxy resins it is possible to use any commercial solid epoxy resins, preferably epoxy resins based on bisphenol A and bisphenol F, and also epoxidized novolacs.

[0019] All of the resins used are employed dry and in powder form with particle sizes in the range between 1 and 300 μm, preferably between 10 and 60 μm.

[0020] The powder coating materials used in the binders of the invention are pulverulent reactive coating materials which comprise as their binders thermosetting resins such as epoxy resins or polyester resins, but also polyurethane resins or acrylic resins as well, which can be used in the form of one single type or as a mixture. They may be colourless or pigmented, with separation according to shade generally being unnecessary. The preferred powder coating materials are recycled powder coating materials. Such materials are obtained as what is known as overspray from paint booths, as off-specification batches in the production of powder coating materials, as filter dusts during the production and processing of powder coating materials, or as residues from the grinding of the powders. The particle sizes of the recycled powder coating materials employed, at from 1 to 300 μm, preferably between 10 and 60 μm, are situated in approximately the same range as those of the resins. Where recycled powder coating materials are used whose particle size is too small for the desired application, larger particle sizes can be obtained through agglomeration of individual particles.

[0021] The recycled powder coating materials used in the binder mixtures of the invention are as yet uncrosslinked. They contain reactive groups such as carboxyl, epoxy, hydroxyl, amino, amide or capped isocyanate groups which on heating are able to react with one another and with the reactive groups of the non-thermoreactive phenolic resins and of the thermoreactive condensation products from the group consisting of phenolic, amino, and epoxy resins.

[0022] The use of these powder coating materials and/or recycled powder coating materials together with phenolic resins as binders for fibre nonwovens and fibre nonwoven mouldings is known from WO 95/30034 and WO 96/16218. Both of these patent applications provide a possibility for utilizing the powder coating residues which are produced as “waste”.

[0023] In accordance with the present invention, powder coating materials and/or recycled powder coating materials serve to improve further the already good profile of properties of high-grade binder mixtures comprising phenolic resin as one binder component. This opens up the possibility of using the binder mixtures of the invention not only as binders in the production of textile nonwovens but instead, quite generally, in all traditional fields of application where solid phenolic resin binders are employed. In particular, therefore, the binder mixtures of the invention find application as binders for moulding compounds, refractory materials, abrasive materials, friction linings, and foundry sands in the foundry industry. It is a further advantage of these binder mixtures that their use in the respective fields of application can be implemented using the techniques which are customary and known for these applications.

[0024] The binder mixtures of the invention are composed of a mix of a non-thermoreactive phenolic resin and one or more thermoreactive condensation products from the group consisting of phenolic resins, amino resins and epoxy resins, and also a powder coating material. The non-thermoreactive phenolic resin is in combination with the thermoreactive condensation product in a weight ratio of from 30:70 to 90:10. This mix is combined with powder coating material in a weight ratio of from 90:10 to 50:50, so that the binder mixture has the following composition:

[0025] from 90 to 50 parts by weight of a mixture of a non-thermoreactive phenolic resin with a thermoreactive condensation product in a weight ratio of from 30:70 to 90:10 and

[0026] from 10 to 50 parts by weight of a powder resin.

[0027] The binder mixture is prepared by mixing the individual pulverulent components with one another. It is unimportant here whether individual components, of whatever type, are premixed with one another beforehand or whether all of the constituents are combined simultaneously and mixed with one another. At room temperature, the storage life of the mixture is practically limitless.

[0028] The binder mixture is generally cured without the addition of a further curing agent or accelerator, by heating at a temperature in the range from 100 to 220° C., preferably from 140 to 180° C.

Claims

1. Binder mixture based on a pulverulent mix of a non-thermoreactive phenolic resin and one or more thermoreactive condensation products from the group consisting of phenolic resins, amino resins and epoxy resins, characterized in that it further comprises powder coating material.

2. Binder mixture according to claim 1, characterized in that the powder coating material is a recycled powder coating material.

3. Binder mixture according to claim 1 or 2, characterized in that the power coating material is a reactive coating powder based on epoxy resins and/or polyester resins.

4. Binder mixture according to claim 3, characterized in that the powder coating material further comprises reactive coating powders based on polyurethane and/or acrylic resins.

5. Binder mixture according to one or more of claims 1 to 4, characterized in that it comprises the non-thermoreactive phenolic resin with the thermoreactive condensation product in a weight ratio of from 30:70 to 90:10.

6. Binder mixture according to one or more of claims 1 to 5, characterized in that it comprises the mix of non-thermoreactive phenolic resin with the thermoreactive condensation product and the powder coating material in a weight ratio of from 90:10 to 50:50.

7. Binder mixture according to one or more of claims 1 to 6, characterized in that it comprises, as thermoreactive phenolic resins, alkalinically condensed reaction products from the condensation of bisphenols with formaldehyde.

8. Use of the binder mixture according to one or more of claims 1 to 7 as a binder in the production of textile nonwovens.

9. Use of the binder mixture according to one or more of claims 1 to 7 as a binder for moulding compounds.

10. Use of the binder mixture according to one or more of claims 1 to 7 as a binder for refractory materials.

11. Use of the binder mixture according to one or more of claims 1 to 7 as a binder for abrasive materials.

12. Use of the binder mixture according to one or more of claims 1 to 7 as a binder for friction linings.

13. Use of the binder mixture according to one or more of claims 1 to 7 as a binder in the foundry industry.