EP0024703B2 - Process for producing filter-materials - Google Patents

Abstract

1. A process for manufacturing filter materials for oil and air filters used in motor vehicles by impregnating a paper or non-woven fabric substrate with resin and/or monomer and subsequently curing the substrate, characterized by impregnating the substrate with a solution or dispersion of at least one resin and/or curable by electron radiation and having a concentration of 1 to 50% by weight of resin and/or monomer, based on the weight of the solution or dispersion, thereafter removing the solvent and then effecting curing by electron radiation.

Description

FR-A-2 241 384 describes the production of paper substrates by grafting on polymers with optionally monomers onto lignocellulose paper materials. Such paper materials are said to have a high absorption capacity for water and are not suitable for filter materials for oil and air filters. In US-A-4 091 167 cardboard is impregnated with an impregnating agent consisting of a solution of a prepolymer and a monomer, followed by curing with electron beams. This does not address the manufacture of filter materials.

In Tappi, September 1975, Vol. 78, No. 9, pages 125-128, the production of filters from needle-punched nonwovens made of polyester is described. These needle felt fabrics are treated with oil-based acrylic polymers and cured by radiation. The filter materials obtained are, however, described as unsatisfactory and in need of improvement.

DE-A-2150 374 generally describes the curing of acrylic resins; there is no reference to the manufacture of filter materials. DE-A-1 113677 and DE-B-1 174 740 relate to a process for improving the mechanical properties of textiles made from cellulose-containing fibers, the textiles being intended to be made wrinkle-resistant or dimensionally stable.

So far, filter papers have been impregnated with uncrosslinked phenolic resins for the production of oil and air filters, which were then crosslinked or hardened at elevated temperature. Such a procedure has various disadvantages, which are mainly due to the complex hardening process. Thus, the curing must take place at high temperatures in the order of 160 to 180 ° C, in addition, curing zones of 30 to 50 m in length and residence times of 60 to 80 minutes are required, which leads to a high energy expenditure, a high expenditure on equipment and a severe environmental pollution due to the phenolic resin vapors released during the condensation.

The object of the invention is therefore to provide an economical process for the production of filter materials for motor vehicles which can be carried out with little energy expenditure and little outlay on equipment and leads to end products with superior properties.

It has been shown in the context of the invention that the use of resins curable by electron beams is suitable for achieving this aim.

As is known, various polymers can be crosslinked by high-energy radiation, for example by UV radiation, α, β and y radiation. Such crosslinking reactions have hitherto been used, for example, in the curing of paints (DE-A-2 029 145).

It has now been found within the scope of the invention that electron beam curing can also be applied to the partial coating of cellulose-based paper substrates while maintaining a residual permeability of the treated substrates.

The invention therefore relates to a method for producing filter materials for oil and air filters for motor vehicles by impregnating a paper substrate based on cellulose with resin and monomer and subsequently curing the substrate. The process according to the invention is characterized in that the substrate is impregnated with a solution or dispersion of at least one polyurethane-acrylate resin which is curable by electron beams and isocyanates, polyols and hydroxyl-functional acrylate and methacrylate monomers and monomers which are reactive with NCO groups and which have a concentration contains from 1 to 50% by weight of resin and monomer, based on the weight of the solution or dispersion, then the solvent is removed and the curing is then effected by electron radiation.

In the process according to the invention, the substrate to be treated is first impregnated with a solution or dispersion, preferably a solution, of the resin and monomers in a suitable inert organic liquid.

• Trimethylolpropan, Pentaerythrit bzw. Pentaerythritol, Hexandiol, insbesondere Hexan-1,6-diol und Polyäthylenglykole oder Propylenglykole, wie Triäthylenglykol oder Tripropylenglykol.

Polyols, which are based on the resins which can be used according to the invention, can be straight or branched chain and one or more heteroatoms, e.g. B. in the form of oxygen bridges. They preferably have 2 to about 10, in particular 5 to 9 and particularly preferably 5 or 6, carbon atoms. They preferably contain 2 to about 5 and in particular 2, 3 or 4 hydroxyl functions. Preferred examples of such polyols are:

• Trimethylolpropane, pentaerythritol or pentaerythritol, hexanediol, in particular hexane-1,6-diol and polyethylene glycols or propylene glycols, such as triethylene glycol or tripropylene glycol.

The hydroxyl groups of the polyols mentioned can be wholly or partially esterified by acrylic acid and / or methacrylic acid.

Specific examples of usable monomers according to the invention are trimethylolpropane triacrylate, hexanediol diacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, hexane-1,6-diol diacrylate, Diäthylenglykoldiacrylat, Triäthylenglykoldiacrylat, Tetraäthylenglykoldiacrylat, tripropylene glycol diacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and Hexandiolmonoacrylat Butandiolmonoacrylate and the corresponding methacrylates or mixed acrylate Methacrylates.

Particularly suitable monomers are pentaerythritol triacrylate or pentaerythritol acrylate mixtures with an average degree of esterification of 3 to 3.3 and with a viscosity of 600 to 1 200 mPa - s (measured at 20 ° C. with the Brookfield viscometer, type RVT).

As polyurethane resins are high or low molecular weight resins or oligomers in question the inert organic liquids used are soluble. Examples of this are soluble polyurethane acrylates formed from the aforementioned hydroxy-functional acrylate monomers.

The molecular weight of such resins or oligomers is preferably in the range from 800-8,000 and their viscosities go from 1,000-50,000 mPa · s. The content of acrylic and / or methacrylic unsaturated monomer units is, for example, 2-6 per molecule.

Resins of this type were produced by customary procedures, for example as described in DE-A-2 530 896 and DE-A-2 542 314. For example, a polyol is reacted with a diisocyanate. The content of free NCO groups reached is then saturated with hydroxy-functional acrylate or methacrylate monomers. The person skilled in the art can choose amounts and reaction conditions so that the desired molecular weights and the desired content of acrylic and / or methacrylic unsaturated monomer units are achieved. The viscosities can be varied, for example, by appropriate dilution of the resins with monomers.

• Isocyanate wie :
  • a) 4,4-Diphenylmethandiisocyanat
  • b) Toluylendiisocyanat
  • c) Hexamethylmethandiisocyanat
  • d) 4,4-Dicyclohexylmethandiisocyanat
• Polyole wie :
  • a) Polypropylenglykole, Polyäthylenglykole mit den Molekulargewichten 400, 1 000, 2 000, 3 000, 4000
  • b) Polyester auf der Basis aliphatischer und aromatischer Dicarbonsäuren, vorzugsweise Adipinsäure und Sebacinsäure und difunktionellen aliphatischen Alkoholen, wie Äthylenglykol und Neopentylglykol, Diäthylenglykol, Hexandiol-1,6 sowie polyfunktionellen Alkoholen wie Trimethylolpropan und Pentaerythritol.

The following raw materials are used as starting materials for the polyurethane acrylates that can be used as resins or oligomers:

• Isocyanates such as:
  • a) 4,4-diphenylmethane diisocyanate
  • b) tolylene diisocyanate
  • c) hexamethyl methane diisocyanate
  • d) 4,4-dicyclohexylmethane diisocyanate
• Polyols such as:
  • a) Polypropylene glycols, polyethylene glycols with the molecular weights 400, 1,000, 2,000, 3,000, 4,000
  • b) polyester based on aliphatic and aromatic dicarboxylic acids, preferably adipic acid and sebacic acid and difunctional aliphatic alcohols, such as ethylene glycol and neopentyl glycol, diethylene glycol, 1,6-hexanediol and polyfunctional alcohols such as trimethylolpropane and pentaerythritol.

• 2-Hydroxyäthylacrylat
• 2-Hydroxyäthylmethacrylat
• 2-Hydroxypropylacrylat
• 2-Hydroxypropylmethacrylat
• Butandiolmonoacrylat
• Hexandiolmonoacrylat
• Pentaerythritoltriacrylat

Hydroxy-functional acrylate monomers and methacrylate monomers reactive with NCO groups such as:

• 2-hydroxyethyl acrylate
• 2-hydroxyethyl methacrylate
• 2-hydroxypropyl acrylate
• 2-hydroxypropyl methacrylate
• Butanediol monoacrylate
• Hexanediol monoacrylate
• Pentaerythritol triacrylate

• Hexandiol-1,6-diacrylat
• Butandiol-1,4-diacrylat
• Triäthylenglykoldiacrylat
• Tetraäthylenglykoldiacrylat
• Dipropylenglykoldiacrylat
• Tripropylenglykoldiacrylat
• Tetrapropylenglykoldiacrylat

Depending on the required viscosity, the resins produced are diluted with monomers to concentrations of 40 to 80% with:

• Hexanediol 1,6-diacrylate
• Butanediol 1,4-diacrylate
• Triethylene glycol diacrylate
• Tetraethylene glycol diacrylate
• Dipropylene glycol diacrylate
• Tripropylene glycol diacrylate
• Tetrapropylene glycol diacrylate

• 1 Äquivalent Polypropylenglykol MG 400
• 2 Äquivalente Toluylendiisocyanat 80/20
• 1 Äquivalent 2-Hydroxyäthylacrylat

The following is an example of a special recipe:

• 1 equivalent of polypropylene glycol MG 400
• 2 equivalents of tolylene diisocyanate 80/20
• 1 equivalent of 2-hydroxyethyl acrylate

• MG_Harz ⁼ 980
• Viskosität: 600 bis 1 200 mPa . s
• Funktionalität 2

The product obtained from this is dissolved 50% in hexanediol 1,6-diacrylate.

• MG _resin ⁼ 980
• Viscosity: 600 to 1,200 mPa. s
• Functionality 2

Suitable inert organic liquids for dissolving or dispersing the monomers or Resins are customary inert organic solvents, such as aliphatic alcohols with, for example, 1 to 6 carbon atoms, in particular methanol and ethanol, aliphatic ketones with, for example, 3 to 6 carbon atoms, in particular dimethyl ketone and methyl ethyl ketone, and also esters, in particular alkyl acetate with, for example, 1 to 4 carbon atoms in the alkyl part, e.g. B. methyl acetate and ethyl acetate. These solvents can be used either alone or in a mixture.

The monomer and the resin are used in the solvent to impregnate the paper substrates in concentrations of 1.0 to 50% by weight, based on the sum of the weight of the monomers and resin and solvent. The solutions thus contain 1.0 to 50 parts by weight of monomer and resin and 99 to 50 parts by weight of solvent. Preferred ranges are 2.0 to 40 parts by weight of monomer and resin and 98.0 to 60 parts by weight of solvent. For example, 10, 20, 30, 40 or 50 parts by weight of monomer and resin and 90, 80, 70, 60 or 50 parts by weight of solvent can be used. The concentration of the monomer and resin in the solvent ultimately depends on the desired degree of coverage of the substrate with the monomer or resin.

The substrate to be treated can be impregnated in any way with the solution or the dispersion of the monomer and resin in the solvents mentioned. Dipping treatment is preferably carried out. After the immersion treatment, the substrate passes through a drip zone and a drying zone, in which temperatures of approximately 120 to 140 ° C. are maintained, depending on the solvent. The solvent is recovered in the pure state from the drying zone and can be used again for the same purpose or for other purposes.

The amount of resin or monomer remaining on the substrate is independent of the immersion time in the solution and depends only on the concentration of the solution used. The concentration of the solution used is therefore within the ranges specified above according to the desired degree of occupancy or the desired properties, such as. B. the degree of permeation of the filter material to be produced. Depending on the intended use of the end product, preferred ranges for the coating are 5 to 45% by weight, in particular 5 to 40% by weight, for example 10 to 25% by weight or 15, 25 or 45% by weight. %, based on the mass of the substrate. Depending on the type of paper or filter paper material used, the following resin / oligomer concentrations generally give the following assignments (measured as an increase in paper mass in%):

Surprisingly, it has been shown that the paper materials pretreated in this way are stable in storage. For example, treated paper webs can be transported and stored in the form of rolls. Even if such rolls are stored in a side-by-side form for long periods before crosslinking, no tendency of the impregnated material to migrate due to gravity is observed, rather the applied uncured monomer or resin remains distributed uniformly over the substrate.

This has the advantage of being able to carry out the impregnation and hardening processes at different times and, if appropriate, at different locations. It also opens up the possibility of subjecting the substrates pretreated in this way to intermediate processing before the actual hardening. For example, the impregnated and dried mother rolls can be processed into finished products as desired using customary cutting and / or folding tools. It is also possible now to form adhesive joints using adhesives that are customary for these purposes. This offers the possibility of using adhesives which are cured simultaneously with the applied impregnating resins or impregnating monomers by the later action of electron beams. Of course, it is also possible to subject the impregnated mother rolls to the hardening process directly, if necessary after storage in the meantime, and to subject the actual packaging to the final desired shape, e.g. B. by cutting, folding and / or gluing, after the hardening process. Surprisingly, it has been shown that the materials cured according to the invention are particularly easy to process. For example, they can be easily processed into folded forms, whereby the tendency to form fractures is reduced in comparison with products conventionally treated and hardened with phenolic resins. In addition to the improved mechanical and chemical resistance, this also prevents the formation of unwanted dusts. In addition to the cleaning problems resulting from this, such dusts also pose a health risk when processing, since phenolic products are to be considered as carcinogenic substances.

The paper materials impregnated according to the invention are finally possible before or after a surface treatment hardened. The unsaturated acrylate resin is cured by radial chain polymerization, which leads to chain growth with a high three-dimensional degree of branching. In order to effect the radical chain polymerization, the substrates subjected to the impregnation, draining and drying treatment are subjected to a short-term irradiation with high-energy jets of a low dose. Electron or β radiation is preferably used for this. The radiation can be generated by conventional electron sources. In general, one or more multi-stage electron accelerators are used. It has proven to be particularly advantageous to carry out the curing process using the device described below.

When using single-stage or multi-stage electron accelerators, acceleration voltages of approximately 150 to 500 kV have proven to be suitable. In general, acceleration voltages of 200 kV or acceleration voltages of 150 to 200 kV can be used successfully.

Within the scope of the invention it has been shown that the penetration depth of the electron radiation depends on the specific weight of the impregnated substrate, that is to say on substrate + impregnated monomers and / or resin. For example, an electron voltage of 150 to 180 kV is sufficient to penetrate a substrate impregnated according to the invention with a specific weight of 1 to a depth of about 120 f.Lm to 16 ßp.m.

The curing speed depends on the radiation dose used. In general, dosages from 0.1 to about 16 Mrad, preferably 0.1 to 10 Mrad, and particularly preferably from 1 to about 10 or from 4 to 8 Mrad have been found to be satisfactory for achieving favorable production speeds.

In practice, the substrate impregnated according to the invention, if appropriate in conditioned form, is generally guided past a window under an inert gas, such as nitrogen, for example, from which the electron beam emerges. The distance of the substrate from the exit window is generally 10 to 50 mm. With this method of operation, depending on the useful width of the electron accelerator used, production speeds are achieved at the dosages indicated above, which in practice are between 30 and 60 m per minute. Due to these short reaction times and high production speeds, the method according to the invention is particularly advantageous.

The process according to the invention can be applied to all customary cellulose-based paper materials. Filter papers based on cellulose, such as are used for the production of oil filters in the motor vehicle industry and of air filters in the motor vehicle industry, are suitable. A lignin content in the cellulose does not interfere. A particular advantage that arises when using materials based on pure cellulose is that the products obtained remain practically white, so that when the finished products are used as filter materials, there is an indicator effect on possible contamination of the filter. Such an indicator effect is not possible with conventional coating with phenolic resins, since white coloring is not retained with phenolic resins, but discoloration to a dark brown color occurs.

It is also possible to produce specific colors for the filter papers that are adapted to the intended use and which can act as an indicator for larger stocks (example: air filter blue, oil filter green).

By the procedure according to the invention, depending on the amount of the substrates used with resins, products can be produced which, depending on the starting substrate used and the amount of partial coverage, have a controllable residual permeability and can therefore be used as filter materials for oil or air filters in the motor vehicle industry . The substrates according to the invention proved to be resistant to mechanical, chemical and temperature influences. The polymerized impregnating resins are present as rasites, i.e. H. they are insoluble in organic solvents and can no longer be melted, which is advantageous, for example, for use in motor vehicles at high engine temperatures.

Compared to conventional coating with phenolic resins, the process according to the invention is characterized above all by the lower energy expenditure, ie. H. due to the elimination of high hardening temperatures and the reduction of the expenditure on equipment (no long furnace channels are required) and the increased throughput speed. In addition, there is no danger to the environment and workplaces from the development of harmful vapors, since no low-molecular cleavage or reaction products are released during the polymerization of the impregnating resins used according to the invention. Further advantages are that the soaked intermediate products obtained are stable in storage and are not subject to mass migration. In contrast to the previous coating with phenolic resins, the solvents used can be easily recovered and can be used for a wide variety of purposes. The products obtained are particularly stable and are not subject to discoloration. In addition, the thermal stress on the substrates is eliminated in the method according to the invention. It is therefore possible to use more sensitive substrates than before. Changes in the paper materials used due to the ionizing effect of the electron beams were not found.

The shortest treatment time with low space requirements of the system required for the method according to the invention results if at least the removal of the solvent and Electron irradiation of the substrate - optionally also impregnation or coating with the solvent or with a solution of impregnation and solvent - is carried out in successive operations with the substrate strip preferably running continuously.

The method according to the invention can be carried out favorably with a device such as that shown in the figure, the device being included. (C) for removing the solvent and the device (D) for irradiating the substrate strip freed from solvent are combined to form a common structural unit.

In a - in practice multi-part - housing assembly A is a supply or storage chamber or station for a material strip or substrate to be treated f, z. B. a roll of paper filter material wound onto a supply roll 10, B an immersion bath for impregnating the substrate with an impregnating agent dissolved in a solvent or, if the material tape f is already coated with impregnating agent, with the solvent, C a chamber to remove the solvent again using one or more nozzles 11, D an irradiation housing part containing the irradiation device 12 with electron accelerator 13, scanner 14 and irradiation channel 15 and E an outlet chamber or station for the treated material or substrate band f.

The material strip f running off the supply roll 10 at a certain speed is continuously passed through the housing parts or chambers or stations A to E. In the immersion bath B, the substrate is first exposed to the radiation-crosslinkable impregnating agent, e.g. B. an acrylic resin, soaked. The solvent has the task of allowing the impregnating agent to penetrate into the substrate and thus fulfilling a transport function for the impregnating agent. Subsequently, the further impregnated substrate in the chamber C - optionally after passing through a drip zone - by blowing using the nozzles 11, z. B. hot air nozzles, which can be supplied by a fan arranged in or on the housing assembly, again freed from a solvent. It can therefore immediately afterwards by using an inert gas, e.g. B. nitrogen, filled radiation channel 15 of the radiation housing part D, in which the impregnating agent is crosslinked by electron radiation and the substrate is thereby hardened and stiffened.

Electron irradiation with an acceleration voltage of 150 to 200 kV has proven to be particularly economical for the aforementioned purpose. In order to accelerate the polymerization and the hardening process caused thereby, large-area irradiation with a beam region widened in the running direction and fanned out in the scanner 14 is provided. With an irradiation time of about 0.05 to 0.5 sec, a running speed of the material band f of z. B. 30 to 60 m / sec can be achieved. This radiation is generally sufficient to penetrate with a cross-linking of z. B. to achieve 120 to 160 g / m ² in the impregnated layer.

Simple paths of the substrate strip f through the chambers B, C and E are shown in the schematic drawing. Additional routes can be used to extend these paths as required. The invention is also not necessarily limited to the fact that the material or substrate tape is first soaked or coated with the impregnating agent using a solvent in immersion bath B or in another suitable application device. If the material or substrate tape that is wound onto the supply roll 10 or that is supplied in some other way is already externally coated with an impregnating agent, the immersion bath B may need only contain the required solvent. If the tape is already fed in a state in which it has already been treated with a dissolved impregnating agent, the belly immersion bath can be used entirely. omitted. A and / or B can also form part of the common housing assembly.

example

Preparation of an oligomer suitable for paper impregnation.

• Pos. 1 und Pos. 2 werden in einen 2-I-Dreihalskolben gegeben.

b) Manufacturing instructions:

• Items 1 and 2 are placed in a two-liter, three-necked flask.

The flask is equipped with a condenser (water-cooled), a stirrer with a patent plug, which allows the flask to be covered with nitrogen during the manufacturing process (due to the NCO / water reaction), and a thermometer for temperature control.

Items 1 and 2 are heated to 75 ° C with stirring for 2 hours.

Now the NCO number is determined, NCO target = 6.24% ± 0.1%.

When the NCO value is reached, 5 to 20 ppm nitrobenzene are added (thermal stabilizer for 4-hydroxybutyl acrylate) and item 3 is added.

The temperature is now kept at 75 ° C. for 3 hours.

After 3 hours, the NCO number is determined, NCO target = 0.00%.

If there is no free NCO left, item 4 is added and mixed thoroughly. After mixing, the reactor contents are cooled to approx. 40 ° C and the resin is filled.

Claims (10)

1. A process for manufacturing filter materials for oil and air filters used in motor vehicles by impregnating a paper substrate on the basis of cellulose with resin and monomer and subsequently curing the substrate, characterized by impregnating the substrate with a solution or dispersion of at least one electron beam-curable polyurethane/acrylate resin of isocyanates, polyols, and hydroxyfunctional acrylate and methacrylate monomers reactive with NCO groups, and with monomer, said solution or dispersion having a concentration of 1 to 50 % by weight of resin and monomer, based on the weight of said solution or dispersion, thereafter removing the solvent, and then effecting curing by electron radiation.

2. Process according to claim 1 characterized by the use of a solution or dispersion having a concentration of 10 to 50 % by weight of resin and/or monomer, based on the weight of the solution or dispersion.

3. Process according to one of claims 1 to 2, characterized by irradiating the substrate with accelerated free electrons reaching a radiation penetration depth corresponding at least approximately to the thickness of the substrate web.

4. Process according to one of the preceding claims characterized by operating at an electron radiation dose of 0.1 to 16 Mrad and preferably 1 to 10 Mrad.

5. Process according to one of claims 1 to 4 characterized in that the radiation width is adaptable to the width of the substrate web -especially for efficient utilization of energy - by focussing the electron beam. ⁱ

6. Process according to one of claims 1 to 5 characterized by effecting irradiation - especially for adaption to various chemical reaction mechanisms in the substrate - by widening the beam or the radiation efficiency in the direction of web travel.

7. Process according to any one of the preceding claims characterized by effecting solvent removal and irradiation in immediately successive operations on the web moving through these two operations.

8. Process according to claim 7 characterized by effecting also impregnation or coating of the substrate web with solvent, or with impregnant and solvent, in continuous operation with solvent removal and irradiation on the web moving through all these operations.

9. Process according to any one of the preceding claims characterized by removing the solvent by blowing a stream of air or gas, e. g. hot air, against the substrate.

10. Process according to any one of the preceding claims characterized by re-using the solvent removed from the substrate.

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