FI68436B - FOERFARANDE FOER FRAMSTAELLNING AV POROEST PAPPER - Google Patents

Description

68436

Method for making porous paper

The invention relates to a process for the production of porous paper for further processing into filters for internal combustion engines and the like, which paper was impregnated with electron beam curable resins and cured with electronic beams.

For various technical purposes, filters are required which, on the one hand, must have a high retention capacity and, on the other hand, must withstand the medium to be filtered. Today, it is used to purify the combustion air of engines without filters made of, for example, star-corrugated special impregnated papers. The structure of these filter papers is such that, on the one hand, their air resistance is low due to the innumerable pores and, on the other hand, due to their low porosity, they allow only the smallest, i.e. harmless, dust particles to pass through. Filters of similar construction are also used as oil filters for internal combustion engines.

20 Filters are made of porous paper webs impregnated with uncrosslinked phenolic resins. After impregnation, the crosslinking or curing of the phenolic resins takes place at an elevated temperature. This method of preparation is very laborious as a whole, because the curing of the resins takes place at a temperature of about 160-180 ° C and the residence times in the curing installations of 30-50 m are long. In addition, the phenolic resin vapors generated during curing constitute a significant environmental nuisance. This is mainly due to the fact that alcohol-soluble phenolic resins or phenolic resin vapors can enter the exhaust air or wastewater.

A further disadvantage of the method is that the curing process cannot be performed in a single step, but must be interrupted during filter manufacture. The curing or condensation process must be interrupted during the creasing or folding of the paper. Only after corrugation, 68436 where the edge of the corrugated paper may tear in places, can the condensation be completed. This final condensation is necessary to ensure that no volatile constituents remain in the paper which may enter the medium to be filtered.

5 The precondensation is carried out to such an extent that the paper or the resin it contains no longer adheres, allowing further processing.

A further problem with sudatin fabrication is that the contacting edges of the phenol-impregnated and cured filters 10 do not readily adhere.

In order to avoid the disadvantages described above, DE patent application No. P 29 33 998.8, (Wikolin Polymer Chemie GmbH and Otto Diirr Anlagenbau GmbH) has already proposed a process in which the impregnating agent is a resin based on acrylic acid and / or methacrylic acid esters and polyols with polyols. solution or dispersion. In addition, it is proposed that the curing be performed by electron irradiation. Thus, in this method, the phenolic resins are replaced by other resins, and the curing of the impregnated paper web takes place by electron irradiation and not, as was customary in the past, by thermosetting in a drying channel.

In addition to the fact that impregnated paper is required in the manufacture of filters for internal combustion engines, there is a general need in various fields of technology and in other fields to use impregnated, high porosity paper.

Accordingly, it has been an object of the invention to provide a process for the production of impregnated papers which are particularly suitable for the production of filters for internal combustion engines and enable the very economical production of high-porosity filters. Such a method must be economical, must not pollute the environment and must be kept to a minimum.

The set object is achieved in that the paper web is impregnated in a paper machine with an aqueous emulsion containing at least one high-energy radiation-curable resin and / or monaner, and that the impregnated paper web is then cured by electron irradiation.

In order to implement the method according to the invention, only the paper machine necessary for the production of the paper web and the means for performing the electron irradiation curing are required, the paper machine being provided with a paper web impregnation device at suitable points. Impregnation can be carried out with a coating device, e.g. a gluing press. It is also possible to apply the impregnating agent to the paper web by spraying. An aqueous emulsion of a resin curable by electron irradiation is preferably used as the impregnating agent.

However, DE-A-25 51 479 20 already discloses a method for producing impregnated and surface-treated films for coating chipboards and the like, which is impregnated in a paper machine in connection with papermaking. The aim of this known method is to produce paper which is as small as possible in the form of a finished impregnated web. This results in a dense paper which, due to the good appearance required, is well suited for coating chipboard. The urea and / or melamine resins used are heat-curing and, after drying, make the paper very hard and dense. Such paper is therefore not suitable as filter paper. In general, it is airtight and waterproof and resembles more and more plastic as the amount of resin increases.

The resin used in the process of the invention is added to a paper web in a paper machine in the form of an aqueous emulsion or solution. Resins and / or monomers based on acrylic acid and / or methacrylic acid esters formed with polyols are used. The proportion of resin in the emulsion itself is 15-70% by weight. The advantage of using an emulsion is that the resin particles are very well able to penetrate the paper.

If impregnated paper is to be used, 10-30 and preferably 20% by weight of resin is deposited on the paper for filter production. The resin must be evenly distributed for the filter as a whole to be filter-10 capable.

The recommended resin content of the filter paper is 20% by weight. For economic reasons, the resin content must be as low as possible. Depending on the intended use of the filter material and the required values such as burst pressure, filter stiffness, etc., the resin content may vary. When the strength must be high, enon resin up to 30% can be used. With lower strength requirements, a resin content of up to 10% is sufficient. This consideration also applies to papers in other applications. For safety reasons, it is also not necessary to use solvents due to the risk of explosion.

In a curing apparatus where curing takes place by electron irradiation, the resin particles are completely crosslinked. This is very important because, as already mentioned above, uncrosslinked ingredients may end up in the medium to be filtered. The proportion of soluble constituents in the finished filter must be as small as possible.

For certain types of filters, the preparation according to the invention has the advantage that the resins used are insoluble in alcohol. For example, internal combustion engines running on new ones, e.g. with fuels containing alcohols, the alcohols in the filters may dissolve conventional resins. Alcohol-containing fuels can also dissolve, for example, incompletely condensed phenolic resin from the filters.

In order to achieve good porosity and, above all, high strength of the paper web, the paper web is mainly made of long-fiber pulp. Preferably, the proportion of long fiber pulp is more than 90%. It is also an advantage to use cotton pulp.

The degree of grinding of the pulp used is small, i.e. 10 13-15 ° Schopper-Piegler. The pulp used, which, as mentioned above, is preferably cotton pulp, i.e. the so-called cotton linters, thanks to the low grind level, the paper web and later also the filter becomes very strong. In order to improve the strength of the paper web, conventional so-called wet strength resins.

The resin uptake of the paper web is controlled by the initial moisture of the paper web when the web enters the gluing press. The higher this initial humidity, the lower the resin uptake. In addition, the resin uptake 20 can be adjusted at the speed of the paper web. As the rate increases, resin uptake decreases.

After irradiation curing, the paper web is cut into separate sheets corresponding to the filter size. These sheets are corrugated, one edge is provided with an adhesive-25 strip, and the sheets are glued together.

It is worth mentioning that the porosity of the filter papers prepared in this way is remarkably high. The less resin used, the better the filtration efficiency. But the burst pressure also decreases at the same time.

Thus, depending on the intended use of the filter, more or less resin can be added to the paper web, i. the strength of the paper web can be more or less increased.

It turned out that the paper webs prepared according to the invention could be corrugated without damaging the corrugated edges of the paper web. Thus, the paper web can very well be made of corrugated air filters required for internal combustion engines.

68436 The filters thus prepared have a number of additional advantages, e.g. filters withstand high pressure. For example, the burst pressure required for filters in combustion plants is 2.2-2.5 bar. The lower limit is generally considered to be 1.8 bar.

5 Filters made with the new method have a significantly higher burst pressure.

While filters previously made of phenol were brown in color, the method of the invention does not stain the filters, i. the filters are white.

This is particularly advantageous, for example, in cases where the inactivity of the filter alone must be inferred from the color.

The invention uses as an impregnating agent an aqueous emulsion of monomers or resins which can be cured by electron irradiation or other high-energy irradiation. Particularly suitable monomers are polyacrylated and / or polymethacrylated polyols, with polyacrylated polyols being preferred due to their higher reaction rate. Suitable for the preparation of emulsions are e.g.

20 resins and / or monomers proposed in the DE application publication p 29 33 998.8 mentioned at the beginning.

The polyols on which the monomers used according to the invention are based may be straight-chain or branched and may have one or more heteroatoms in the chain, e.g. in the form of oxygen bridges.

They preferably have from 2 to about 10, in particular from 5 to 9 and in particular from 5 or 6 carbon atoms. They preferably have 2 to about 5 and especially 2, 3 or 4 hydroxyl function. Preferred examples of such polyols are trimethylolpropane, pentaerythritol or pentaerythritol, hexanediol, especially hexane-1,6-diol and polyethylene glycols or propylene glycols, 7,68436 e.g. triethylene glycol or tripropylene glycol.

The hydroxyl groups of said polyols may be fully or partially esterified with acrylic acid and / or methacrylic acid.

5 in accordance with the invention, the monomers used in the specific examples are trimetylolipropaanitriakry-methacrylate, hexanediol diacrylate, pentaerytritolitet-trans-acrylate, pentaerytritolitriaksylaatti, hexane-1,6-diol diacrylate, dietyyliglykolidiakrylaatti, 10 triethylene, tetraethylene glycol acrylate, tripropylene glycol diacrylate, 2-hydroxy-ethyl acrylate, 2-hydroksipropoyyliakrylaatti, hexanediol monoacrylates and butanediol monoacrylates and the corresponding methacrylates or mixtures of acrylate-15 methacrylates.

The monomers can be used alone or in mixtures, optionally with high or low molecular weight prepolymers.

Particularly suitable monomers are pentaerythritol-20 tolytriaacrylate or pentaerythritol acrylate mixtures with an average degree of esterification of 3-3.3 and a viscosity of 600-1200 mPa.s (measured at 20 ° C with a Brookfield viscometer, type RVT).

Suitable resins are large and small molecular resins or oligomers. Examples of these are polyurethane acrylates formed from the above-mentioned hydroxy-functional acrylate monomers.

Such resins or oligomers preferably have a molecular weight in the range of 800-8000 and a viscosity of 1000-50,000 mPa.s. The number of acrylic and / or methacrylically unsaturated monomer units is e.g.

2-6 per molecule.

68436 8 These resins are prepared in the usual manner, e.g. as described in DE-A-25 30 896 and DE-A-25 42 314. For example, the polyol is reacted with a diisocyanate. The resulting free NCO groups are then saturated with hydroxy-functional acrylate or methacrylate monomers. One skilled in the art will be able to select the amounts and reaction conditions so as to achieve the desired molecular weights and the desired concentration of acrylic and / or methacrylically unsaturated monomer units. The viscosity can be adjusted, for example, by diluting the resins with monomers, respectively.

When used as resins or oligomers e.g.

The following raw materials can be used as starting materials for polyurethane acrylates:

Isocyanates such as a) 4,4-diphenylmethane diisocyanate b) toluene diisocyanate c) hexamethylene diisocyanate 20 d) 4,4-dicyclohexylmethane diisocyanate

Polyols such as a) polypropylene glycols and polyethylene glycols, molecular weights 400, 1000, 2000, 3000, 4000 b) polyesters based on aliphatic and aromatic dicarboxylic acids, preferably adipic acid and sebacic acid and sebacic acid, divalent aliphatic alcohols, aliphatic aliphatic alcohols -diol-1,6 and polyhydric alcohols such as trimethylpropane and pentaery-tritol 68436 9

Hydroxy-functional acrylate monomers reacted with 2-hydroxyethyl acrylic NCO groups 2-Hydroxyethylethacrylate and methacrylate monomers prepared by 2-hydroxypropyl acrylate 5-hydroxypropyl methacrylate 10-acrylate acanate thiolate diol monolacrylate

Resins prepared depending on the required viscosity hexanediol-1,6-di-acrylate are diluted with monomers to butanediol-1,4-di-concentration 40-80% seucacrylate with a scraper diacrylate 20

The acrylic or methacrylic unsaturated monomers and / or oligomers clarified by the above examples are processed into oil-in-water (0 / W) emulsions by means of emulsifiers. These emulsions, which consist mainly of monomers and / or oligomers and an emulsifier, generally have a total solids content of about 15-70% by weight, preferably 20-60% by weight and in particular about 40% by weight, based on the finished emulsion. The particle size of the emulsion formed is less than 1 μm for reasons of stability and preferably 0.4 to 0.6 μm. This particle size is achieved by conventional means such as the selection of suitable emulsifiers and emulsification conditions.

Suitable emulsifiers for the emulsions used according to the invention are in principle non-ionic emulsifiers and anionic and cationic emulsifiers, alone or in mixtures with one another.

However, the use of nonionic emulsifiers surprisingly showed that the results obtained in terms of particle size and stability were surprisingly good. Thus, emulsions with a particle size of less than 1 μm and a heat storage stability of 2-6 months at 30-60 ° C could be prepared.

The amount of emulsifier used depends on the monomers and / or oligomers used and the emulsification conditions. In general, emulsifiers or mixtures thereof are required in an amount of 1 to 7% by weight, preferably 1 to 3% by weight, based on the internal phase or total solids content of the O / W emulsion.

Non-ionic emulsifiers alone or in admixture with anionic emulsifiers are preferred for use. Examples of such non-ionic emulsifiers are alkylaryl polyglycol ethers, e.g. octylphenol polyether alcohols having from 20 to 40 moles of ethylene oxide per molecule (e.g.

16 or 40 moles / molecule), nonylphenol polyether alcohols having 10 to 40 moles of ethylene oxide per molecule (e.g., 35 moles / molecule), and ethoxylated polypropylene glycol block polymers having 25 or more moles per ethylene oxide per molecule. Of these, ethoxylated nonylphenols are particularly suitable.

Also very suitable are mixtures of the above-mentioned nonionic emulsifiers and anionic emulsifiers such as a) alkylphenol ether sulfates b) alkali salts of sulfosuccinic acid.

In addition, such an O / W emulsion may be mixed with an effective preservative such as fungicides, which, however, must not impair the stability of such O / W emulsion. Suitable preservatives are those conventionally used for this purpose, such as 68436 a) o-phenylphenol b) p-chloro-m-cresol c) chloroacetamide d) 1,2-benzisothiazol-3-one 5 f) copper-8-hydroxyquinoline g) thiocarbamate

Application rates of 0.02-0.4% by weight and in particular 0.1-0.3% by weight of the total charge have proved to be good.

It may also be advantageous to incorporate into the emulsions a high-performance antifoam which, in high-speed machines, is capable of preventing the formation of foam. Particularly suitable antifoams are compounds and mixtures used for this purpose, such as a) tributyl phosphate and / or b) organopolysiloxanes c) mixtures of organopolysiloxanes and aliphatic hydrocarbons.

The recommended application rate is 0.05 to 0.5% by weight, and in particular 0.1 to 0.4% by weight, based on the total charge.

The impregnating resin emulsions used in accordance with the invention can be prepared according to any suitable method for preparing oil-in-water emulsions which achieves the desired particle size. For example, a 0 / Vi emulsion can be prepared from the above-mentioned monomers and / or oligomers in the following manner.

1. The monomers and / or oligomers are added to a tank equipped with a stirrer and a high-power homogenizer (e.g. stator rotor principle, manufacturer e.g. AGE).

2. An optimal emulsifier for the system is added to the monomer-oligomer mixture, e.g. non-ionic emulsifiers such as ethoxylated nonylphenols.

68436 3. The monomer and / or oligomer mixture and emulsifier are mixed vigorously.

4. Continue stirring and add deionized water. The emulsion is formed as the phases change positions.

5 This occurs when about 40-70% water has been added.

5. After the phase change, other necessary excipients such as antifoams and fungicides are added.

6. After the addition of all necessary recipe ingredients, the inner phase (monomer / oligomer) is comminuted with a homogenizer.

As mentioned, the aqueous emulsions used according to the invention have a solids content (monomers and / or oligomers plus emulsifiers and other additives or auxiliaries) of about 15 to 70% by weight. The concentration of monomers and / or oligomers or resins ultimately depends on the desired amount of monomer, oligomer or resin coating on the substrate.

As initially mentioned, according to the invention, the impregnated gauze or paper materials are cured by high-energy irradiation. The curing of the unsaturated acrylate resin takes place by radical chain polymerization, whereby the chain length increases and the degree of crosslinking is high. The irradiation time is short and the dose of high-energy rays is small. Preferably electron or β-irradiation is used. Irradiation can be generated by conventional electron sources. Generally, a single- or multi-stage electron accelerator is used, e.g. as described in DE-A-P 29 33 998.8.

In this case, the impregnated paper webs according to the invention are optionally fed under an inert gas, e.g. nitrogen gas shield, past a window from which an electron beam is applied to the web. The accelerating voltage of the single- or multi-phase electron accelerators used is, for example, about 150-500 kV and the radiation dose is, for example, about 0.1 to about 16 Mrad.

13 _. ... . 68436

Example 1 a) The following is a specific recipe for an emulsifiable resin-monomer mixture according to the invention: 1 eq. polypropylene glycol molecular weight 400 5 2 eq. toluene diisocyanate 80/20 1 eq. 2-Hydroxyethyl acrylate From these products, a 50% solution in hexanediol-1,6-diacrylate was prepared.

Molecular weight of the resin: 980, viscosity: 600-1010 mPa.s, functionality: 2.

b) Example of an emulsifiable monomer: pentaerythritol triacylate (average degree of inhibition 3.3, viscosity 600-900 mPas.s).

Example 2 Emulsification and preparation of oligomer suitable for impregnation a) Recipe: 1 eq. polypropylene glycol molecular weight 1000 500 g 20 2 eq. toluene diisocyanate 80/20 174 g 20 ppm nitrobenzene 1_eq. 4-hydroxybutyl acrylate __ (butanediol monoacrylate) _144.2 g 4 eq. 818.2 g 25% solution in hexanediol diacrylate: substance 1,366.66 g polypropylene glycol molecular weight 1000 substance 2,127.60 g toluene diisocyanate 80/20 substance 3 105.74 g 4-hydroxybutyl acrylate 2q substance 4 400.00 g hexane diol diacrylate 1000.00 gb) Preparation instructions

Add substances and 2 to a 2-liter three-necked flask. The flask is equipped with a water-cooled condenser, a stirrer with a special seal that allows the flask 68436 14 to be protected with nitrogen during the process (due to the reaction of NCO and water) and a thermometer to control the temperature. Substances 1 and 2 are heated with stirring for two hours at 75 ° C. The NCO-5 value is then determined to be 6.24 to 0.1%. When the NCO value is reached, 5-20 ppm of nitrobenzene (which is a thermostability regulator for 4-hydroxybutyl acrylate) are added and substance 3 is added. It is then heated at 75 ° C for three hours. After three hours, determine the NCO value, which must be 0.00%. If free NCO is no longer present, add substance 4 and mix thoroughly. After stirring, the contents of the reactor are cooled to about 40 ° C and the resin is removed.

Example 3 Recipe example for an emulsion: 1. 25.00 to 63.00 parts of monomer and / or oligomer 2. 2.00 to 5.00 parts of ethoxylated nonylphenol 3. 40.00 to 48.00 parts of deionized water 4. 0.01 - 0.30 parts of 1,2-benzisothiazol-3-one 20, 0.05 to 0.500 parts of polysiloxane

Parts are parts by weight.

a) Achieved particle size = 1 μm b) pH value: 6-8 c) Appearance: milky white ^ d) Viscosity: 10-250 mPa.s e) Solids content: 30-65%

Example 4

The paper machine made a paper web from pulp in which the proportion of long fibers was 80%. To impregnate the web into the paper machine drawing press, an aqueous emulsion of Example 3 having a monomer content of 30% is added. The paper web was fed through a gluing press and impregnated. An electronic irradiation curing device was installed at the end of the paper machine through which the paper web was fed. Impregnated paper with a resin content of 21% and a porous and very strong paper was formed. The burst pressure was over 3 atmospheres.

5 The resin was fully cured.

Claims (7)

68436 A method for producing porous paper for further processing into filters for internal combustion engines and the like, which paper is impregnated with electron beam curable resins and cured with electronic beams, characterized in that the paper web is impregnated on a paper machine then by electron irradiation, wherein the paper web consists mainly of long-spun fibrous cellulose with a low, 13 .. .15 Schopper-Riegler degree of grinding. Process according to Claim 1, characterized in that the proportion of resin and / or monomer in the emulsion is from 15 to 70% by weight. Process according to Claims 1 and 2, characterized in that aqueous emulsions of resins and / or monomers based on acrylic acid and / or methacrylic acid esters formed with the polyol 20 are used. Process according to one of Claims 1 to 3, characterized in that resin and / or monoraeers are deposited on the paper in an amount of 10 to 30% by weight, preferably 20% by weight. Process according to one of Claims 1 to 4, characterized in that the proportion of long-fiber pulp is greater than 90%. Method according to one of Claims 1 to 5, characterized in that the pulp is cotton-wool pulp. Method according to one of Claims 1 to 6, characterized in that, after irradiation curing, the paper web is cut into separate sheets corresponding to filter size 17 68436 and that the separate sheets are corrugated, one edge is provided with an adhesive strip and the sheets are glued together.