EP0223922B2 - Process for producing paper webs impregnated with synthetic resins in a soluble or dispersed form - Google Patents

Abstract

A description is given of the soaking or impregnation of a paper web consisting mostly of cellulose fibres by a combination of dispersions and solutions of synthetic resins in a roll-type application unit installed in the papermaking machine, where the nature, degree of beating and dispersion particle size and the mixing ratio of dispersion and solution are matched to one another, for the manufacture of a fibre-containing sheet, in particular for covering parts of furniture.

Description

The invention relates to a process for the production of paper webs impregnated with course resins in the form of solutions and dispersions.

It is customary and known to completely coat or encase housings for televisions and radios, hi-fi towers and other furniture parts with plastic film. PVC film of various thicknesses is preferably used for this.

These PVC films are e.g. B. glued on chipboard and then are made of this composite material in accordance with furniture principles furniture parts or housing in one operation, d. H. that one cuts into the chipboard V-shaped grooves and then folds or bends the plates in these grooves and so produces housing, furniture part or the like in one operation.

It is important in this process that the film does not tear at the fold line. A disadvantage of this process is that the PVC film must be subjected to a corresponding surface treatment, for example a corona treatment, before it can be used directly and in order to achieve good printability.

In addition, the chipboard must have a very clean and smooth surface so that economically justifiable results can be achieved (application of thin foils).

It is particularly disadvantageous, however, that the PVC film has a very unfavorable dimensional stability (expansion / shrinkage behavior) when there are temperature changes, has low tear resistance, has low light stability and has high electrostatic chargeability and softening at 75 to 85 ° C . When heated to more than 120 ° C, there is also an HCI separation.

From DE-PS 25 50 980 it is known to impregnate raw paper webs with aqueous impregnating resin solutions and / or dispersions by sucking in the impregnating liquid at a suction zone, an amount sufficient at least for complete saturation being applied to the surface of the paper web and then the paper web over leads to a suction zone in which the impregnation liquid is sucked through to the other surface. Impregnating resin solutions, however, are resins based on urea, melamine and phenolic resins and contain formaldehyde and lead to brittle products.

With this method, it is necessary to feed the raw paper web to a second device after it has been produced and to unroll it again, to impregnate it using additional devices such as a suction zone and drying device, and to re-roll it.

In addition, with this method the distribution of the impregnating liquid over the paper cross-section is uneven, so that zones of greater impregnation are formed alongside zones of less impregnation, which can lead to the splitting of the paper core.

"DE-OS 2 034 263 discloses a modified anionic paper sizing agent for surface sizing with good flowability even at concentrations> 20%, which contains a mixture of polymer latices and copolymer salts containing succinimide units. The copolymer latices serve as diluents for those composed of imide groups anionic sizing agent based on solutions.

The subject of this publication is therefore only solutions based on succinimide units. The aim is to produce preparations which, without loss of sizing effect per concentration unit, are as thin as possible at concentrations above 20 percent by weight in aqueous solution that they can be diluted well with further water at room temperature. "

DE-OS 30 24 394 describes a method for producing a plastic tournament in a paper machine, in which the paper web in the dryer section is provided with an impregnation which is carried out in the size press. The impregnation of the paper web with the impregnation liquid, which is not described in more detail, in the However, the press is only complete when the paper web is already pre-impregnated, so that additional facilities are also required here.

From DE-OS 29 49 306 a plastic veneer is known, which is produced by resin impregnation of a paper fiber mass with paper fibers with a freeness of more than 25 ° SR, the fiber mass containing approximately the same proportion by weight of long fibers as of short fibers. A mixture of a urea-formaldehyde resin and a self-crosslinking acrylic resin dispersion is proposed for the impregnation.

The object of the invention is to provide a paper impregnation process with which a sheet-like, synthetic resin-containing sheet-like material is obtained which does not have the disadvantages mentioned above and has good flexibility and layer strength.

In addition, the web-shaped material should have water resistance and resistance to solvents and good dimensional stability under the influence of moisture and temperature changes and should be able to be produced economically from economical raw materials, if possible without additional process steps, with the exception of the production of the smoothed paper web itself.

This object is achieved by a process for producing paper webs impregnated with synthetic resins from a cellulose fiber mixture of high absorbency and strength from eucalyptus cellulose and pine wood sulphate cellulose in a ratio of 50:50 to 10:90, preferably 30:70 to 15:85, to the a grinding degree of at most 35 ° SR is ground or subjected to a cutting grinding up to a grinding degree of 15 to 25 ° SR, optionally formed in combination with synthetic fiber materials, an impregnating liquid comprising a mixture of aqueous, anionic copolymer dispersions being applied to the paper web obtained the basis of acrylic acid, acrylic acid esters, acrylonitrile, vinyl acetate and / or styrene with an average particle size of less than 0.2 microns of low to medium film hardness and a minimum film formation temperature of below 30 ° C and conventional aqueous, anionic solutions of copolymers based on maleic anhydride or maleic acid with styrene, acrylic acid and / or acrylic acid esters in a ratio of 100 to 10: 1, calculated on the active substance, with a pH between 7.5 and 10 in a size press in the dryer section of the paper machine. The pH is preferably between 8 and 9.

Further chemical auxiliaries such as wet and dry strength agents, precipitants (fixing agents), synthetic resin dispersions, surfactants, dyes and fillers, which vary the properties of the base paper, can be added to the fibrous material of the paper web.

The fillers are to be understood as white pigments, e.g. B. TiO ₂ , chalk, kaolin.

Formaldehyde-free wet strength agent in an amount of 1 to 5% by weight, based on the dry fibrous material, in the form of, for example, polyamideamine-epichlorohydrin resin and the addition of a synthetic resin dispersion, for example based on acrylic acid ester, has proven particularly advantageous in the sense of the invention or styrene-butadiene in an amount of 1 to 20%, based on dry fiber, and a small addition of surfactants for better wettability of the paper in an amount of <0.5% based on dry fiber.

In the context of the present invention, it is also possible to use other plastics, for. B. styrene-butadiene copolymers, polyurethane or polyolefin dispersions and impregnating resin solutions based on urea or melamine-formaldehyde resins in portions of the impregnating substance.

The brittle character of the impregnated paper can be reduced by using the mixture according to the invention with a portion of impregnating resin solution.

Other auxiliaries such as wetting agents, viscosity regulators, non-stick and penetration aids, pigments, dyes and defoamers can also be added to these impregnation substance mixtures.

Substances are used as wetting and penetration agents, which change the interfacial tension between liquid phase and solid phase, e.g. B. surfactants and emulsifiers.

According to the invention, the penetration of the impregnation liquid can be advantageously influenced by a combination of aqueous, anionic solutions of copolymers based on maleic anhydride or maleic acid with styrene, acrylic acid and acrylic acid esters and these substances which change the interfacial tension.

The most complete impregnation and impregnation of the base paper is therefore only possible according to the invention if, in addition to the selection of a suitable application or impregnation device, the properties of the paper, such as, for. B. grinding condition and degree of grinding, absorbency of the fibrous materials, porosity and surface roughness on the properties of the impregnation or. the coating mixture, d. H. whose surface tension, viscosity, charge status and solids content are coordinated.

According to the invention, this impregnating substance is in the form of a mixture of aqueous, anionic copolymer dispersions based on acrylic acid, acrylic acid esters, acrylonitrile, vinyl acetate and / or styrene and aqueous, anionic solutions of copolymers based on maleic anhydride or maleic acid with styrene, acrylic acid and acrylic acid esters with a Solids content of 5 to 60% used, the viscosity between 10 and 60 s (according to DIN cup, 4 mm).

This impregnation and coating mixture is applied to the nonwoven within the paper machine in a roller application device (size press). According to the invention, the nonwoven fabric with a dry matter content of 98 to 92% is fed through a size press and the mutual impregnation is carried out.

According to the invention, a further one-sided or double-sided surface covering, ie. H. Coating, the nonwoven within the paper machine with the same or a similarly constructed copolymer mixture are carried out, with an intermediate drying should take place between the two individual process stages.

A subsequently applied coating on one side of the dried web results in a denser surface which is easier to print or coat or laminate. If only a further one-sided surface coating is carried out, this can be carried out by means of a doctor application device. One-sided rolling of the coated paper web can be avoided by an additional application on the back.

Such an application can be, for example, a strongly aqueous solution of starch or CMC. An additional smoothing of the impregnated and coated on one side z. B. with known machine smoothing equipment or in a separate operation in a calender increases the desired printability and paintability of the coated side.

This fibrous film produced in this way of different thickness and different bulk density, depending on the pressure used in the manufacture of nonwovens and smoothing of the impregnated and coated web, is particularly suitable in a firm bond with a relatively rigid and rigid base, e.g. B. chipboard, as a decorative and protective covering of furniture parts such. B. television and radio housings or hi-fi towers (housing casing). By using this economically Fibrous film which can be produced inexpensively avoids the disadvantages mentioned at the outset when using PVC or other plastic films.

The fiber-containing film produced according to the invention of high flexibility, dimensional stability in the event of a change in temperature and with good barrier properties against water and solvent is also excellently suitable for other purposes such as, for. B. as the base material of high quality sanding paper for wet sanding, printing and advertising media, decorative wall material (e.g. flame retardant pigmented or unpigmented dimensionally stable wallpaper), adhesive tapes, backing paper z. B. for floor coverings.

The invention will now be explained in more detail by means of examples.

example 1

• 80 % Kiefernholzsulfat-Zellstoff
• 20 % Eukalyptus-Zellstoff
• Mahlgrad 30° SR (Schopper-Riegler)
• Zusätze, handelsüblich (auf atro Zellstoff berechnet):
• 1 % Talkum
• 3 % formaldehydfreies Naßfestmittel
• 0,3 % Netz- und Dispergiermittel

According to the invention, a base paper of the following composition and quality was produced as two-ply paper on a duplex paper machine:

• 80% pine wood sulfate pulp
• 20% eucalyptus pulp
• Freeness 30 ° SR (Schopper-Riegler)
• Additives, commercially available (calculated on dry cellulose):
• 1% talc
• 3% formaldehyde-free wet strength agent
• 0.3% wetting and dispersing agent

This base paper with a mass per unit area of 90 g / m ² was impregnated on both sides with the synthetic resin mixture of dispersion and solution in a ratio of 20: 1 in a size press. The surprisingly strong impregnation effect with this synthetic resin mixture according to the invention, particularly characterized by the layer strength and rigidity, taking into account the water absorption which arises, is probably due to a synergistic effect of the dispersion and solution used, which, when used alone, are far from the same desired good Let paper properties achieve.

The following examples prove this. T. with water to the optimal viscosity (<60 s according to DIN cup, 4 mm).

Size press recipes:

• formaldehydfreiem Naßfestmittel und
• Entschäumer,

verdünnt mit Wasser auf einen Feststoffgehalt von ca. 25%. Papiereigenschaften Rohpapier Rohpapier mit Leimpressen-Rezeptur (Flottenaufnahme ca. 15 g/m²) 1 2 3 4 5 Schichtfestigkeit längs/quer, g/cm 550/75 660/88 1050/140 525/70 560/75 1125/155 Steifigkeit, längs (Kodak-Pathé), mNxm > 3,50 3,32 2,83 2,56 2,89 2,30 Wasserabsorption g/m² > 200 23 28 27 26 25
1 - synthetic resin dispersion alone (aqueous anionic copolymer dispersion based on acrylic acid ester, acrylonitrile and styrene), solids content 50%, average particle size approx. 0.1 µm, average film hardness, minimum film formation temperature <1 ° C.
2 - plastic dispersion, diluted with water, solids content 25%
3 - plastic solution alone, diluted with water (anionic aqueous solution of a carboxyl group-containing copolymer based on maleic anhydride), solids content approx. 12%
4 - plastic solution with formaldehyde-free wet strength agent, diluted with water, solids content approx. 10%
5 - plastic mixture according to the invention, consisting of dispersion (according to Example 1) and solution (according to Example 3) in a ratio of 20: 1, with additions of

• formaldehyde-free wet strength agent and
• Defoamer,

diluted with water to a solids content of approx. 25%. Paper properties Base paper Base paper with size press recipe (liquor absorption approx. 15 g / m ² ) 1 2nd 3rd 4th 5 Longitudinal / transverse layer strength, g / cm 550/75 660/88 1050/140 525/70 560/75 1125/155 Stiffness, longitudinal (Kodak-Pathé), mNxm > 3.50 3.32 2.83 2.56 2.89 2.30 Water absorption g / m ² > 200 23 28 27 26 25th

A pure synthetic resin dispersion (formulation 1) reduces the water absorption most strongly due to its good film-forming properties, but the penetration into the base paper is insufficient. This is demonstrated by the only slightly improved values with regard to layer strength and rigidity

By diluting this dispersion with water (recipe 2) there is a greater penetration into the base paper with increased water absorption and still insufficient elasticity of the impregnated paper.

The insufficient impregnation was also noticeable in the inadequate rub resistance of the paper surface. The impregnation of the base paper with the water-diluted synthetic resin solution (recipe 3) leads to an improved elasticity, but at the expense of a greatly deteriorated layer strength.

The addition of wet strength agent (recipe 4) does not significantly change the properties of the impregnated paper.

It is only through the synthetic resin mixture of dispersion and solution (recipe 5) that the desired high impregnation effect of the glue liquor and thus all the desired paper properties are achieved, characterized by an approximately 10% higher layer strength than in recipe 2, relatively low water absorption and the highest Elasticity (approx. 10% lower stiffness than with recipe 3).

This disproportionately high impregnation effect, which cannot be expected on the basis of the action of the individual components (dispersion, solution, wet strength agent), can be attributed to the synergism of dispersion and solution.

Example 2

In a further series of experiments, the medium-hard synthetic resin dispersion (5) was replaced by a hard dispersion with a particle size of approximately 0.15 μm, minimum film-forming temperature approximately 25 ° C. This dispersion was an aqueous copolymer dispersion based on acrylic acid ester and styrene.

• 6 - Kunstharz-Dispersion, mit Wasser verdünnt, mit Zusatz von formaldehydfreiem Naßfestmittel, Feststoffgehalt ca. 25 %
• 7 - erfindungsgemäße Kunstharzmischung, bestehend aus Dispersion und der Lösung gemäß Beispiel 3 im Verhältnis 20 : 1, mit Zusätzen von
  • formaldehydfreiem Naßfestmittel und
  • Entschäumer,
  verdünnt mit Wasser auf einen Feststoffgehalt von ca. 25%.

The following properties of the base paper impregnated with it were obtained (the results achieved with recipe 5 from the previous first series of tests were listed again for better understanding): Paper properties Base paper Base paper with size press recipe (liquor absorption approx. 15 g / m ² ) 5 6 7 Layer strength, lengthways / crossways, g / cm 550/75 1125/150 860/115 1110/148 Stiffness, longitudinal (Kodak-Pathé), mNxm > 3.50 2.30 3.10 2.76 Water absorption, g / m ² > 200 25th 28 23

• 6 - synthetic resin dispersion, diluted with water, with the addition of formaldehyde-free wet strength agent, solids content approx. 25%
• 7 - synthetic resin mixture according to the invention, consisting of dispersion and the solution according to Example 3 in a ratio of 20: 1, with additions of
  • formaldehyde-free wet strength agent and
  • Defoamer,
  diluted with water to a solids content of approx. 25%.

With pure synthetic resin dispersion according to recipe 6, as already demonstrated for recipes 1 and 2, the desired high impregnation effect cannot be achieved. Only the combination of dispersion and solution according to the invention in turn leads to the desired paper properties, the elasticity of the impregnated paper being poorer than when using recipe 5 due to the high film hardness of the selected dispersion.

Subsequent calendering of these papers impregnated according to the invention lowers the stiffness by approximately 10 to 20% and water absorption by approximately 15 to 20%, while the layer strength remains almost constant.

Example 3

• 8 - Kunstharz-Dispersion allein gemäß Rezeptur 6 in Kombination mit Harnstoff-Fomaldehyd-Harz im Verhältnis 2 :1
• 9 - erfindungsgemäße Kunstharzmischung, bestehend aus Dispersion und Lösung gemäß Rezeptur 7 (im Verhältnis 20 : 1) in Kombination mit Harnstoffharz im Verhältnis 2 : 1
• 10 - Kunstharz-Dispersion allein (wäßrige anionische Copolymerdispersion auf Basis von Acrylaten) Feststoffgehalt 50 %, mittlere Teilchengröße ca. 0,15 µm, mittlere Filmhärte, Mindest-Filmbildungstemperatur 12° C in Kombination mit Harnstoff-Formaldehyd-Harz im Verhältnis 2:1
• 11 - erfindungsgemäße Kunstharzmischung, bestehend aus Dispersion (gemäß Rezeptur 10) und Lösung (gemäß Rezeptur 3) im Verhältnis 20 : 1 in Kombination mit Harnstoffharz im Verhältnis 2:1

In the next series of experiments, the synthetic resin mixture of dispersion and solution in combination with a urea-formaldehyde resin in a ratio of 2: 1 was used to impregnate the base paper according to Example 1.

• 8 - synthetic resin dispersion alone according to recipe 6 in combination with urea-fomaldehyde resin in a ratio of 2: 1
• 9 - synthetic resin mixture according to the invention, consisting of dispersion and solution according to recipe 7 (in a ratio of 20: 1) in combination with urea resin in a ratio of 2: 1
• 10 - synthetic resin dispersion alone (aqueous anionic copolymer dispersion based on acrylates) solids content 50%, average particle size approx. 0.15 µm, average film hardness, minimum film formation temperature 12 ° C in combination with urea-formaldehyde resin in a ratio of 2: 1
• 11 - synthetic resin mixture according to the invention, consisting of dispersion (according to recipe 10) and solution (according to recipe 3) in a ratio of 20: 1 in combination with urea resin in a ratio of 2: 1

The properties of the impregnated paper obtained are summarized in the following table: Paper properties Base paper Base paper with size press recipe (solids content 34%) 8th 9 10th 11 Fleet absorption g / m ² - 17th 18th 26 28 Porosity, cm ³ / min 160 114 76 140 94 Water absorption g / m ² > 200 26 20th 87 27 Layer strength, across, g / cm 64 126 146 133 144

Combinations of synthetic resin dispersions and impregnating resins, such as. B. urea-formaldehyde resin, as are common for the impregnation of decorative base papers in separate impregnation plants, lead to the improvement of the properties of the base paper. The type of synthetic resin dispersion used essentially determines the liquor absorption, porosity, water absorption and layer strength of the paper (see recipes 8 and 10).

But it is only through the synthetic resin mixture of dispersion and solution according to the invention that the desired high impregnating effect and thus the desired properties of the impregnated paper are achieved even with these special impregnating resin / synthetic resin combinations (see recipes 9 and 11). This includes the z. B. considerable reduction in porosity and water absorption and the increase in layer strength. However, due to the relatively high proportion of impregnating resin, the level of layer strength is somewhat lower than that of recipes 1 and 2.

Claims (9)

1. Process for the production of paper webs impregnated with synthetic resins formed from a pulp fibre mixture of high absorbency and strength of eucalyptus pulp and pine sulphate pulp in a ratio of from 50:50 to 10:90, preferably from 30:70 to 15:85 which is beaten to a freeness of a maximum of 35° SR or optionally is subjected to cutting beating to a freeness of from 15 to 25° SR, optionally in combination with synthetic fibre materials, wherein on the obtained paper web an impregnating liquid consisting of a mixture of aqueous anionic copolymer dispersions on the basis of acrylic acid, acrylic acid esters, acrylonitrile, vinylacetate and/or styrene having an average particle size of less than 0,2 µm and having low to moderate film hardness and a minimum film formation temperature of less than 30°C and customary aqueous anionic solutions of copolymers based on maleic acid anhydride or maleic acid or maleic acid with styrene, acrylic acid and/or Acryl acid esters in a ratio of from 100 to 10:1 calculated on the active substance having a pH value of between 7.5 and 10 is applied using a size press in the drying end of the paper-making machine.
2. Process according to claim 1, characterized in that the pH value is preferably set to a range between 8 and 9.
3. Process according to claims 1 and 2, characterized in that further chemical auxiliaries, such as pH regulators, wet and dry strength agents, synthetic resin dispersions, precipitating agents (fixing agents), surfactants, dyes, fillers and the like are added to the fibre material of the paper web.
4. Process according to claims 1 to 3, characterized in that the ratio of aqueous anionic copolymer dispersions of low to moderate film hardness and a minimum film formation temperature of less than 30° to anionic solutions of copolymers is set to 25 to 15:1 and further additives, such as hardeness, viscosity regulators, anti-adhesion and penetration auxiliaries and pigments and dyes are used.
5. Process according to claims 1 to 4, characterized in that in addition the mixture of dispersion and solution contains a proportion of a surfactant.
6. Process according to claims 1 to 5, characterized in that the proportion of a surfactant, based on the mixture of dispersion and solution, is from 0.05 to 1.5%.
7. Process according to claims 1 to 6, characterized in that in a first process step the impregnation of the fibre mat of the paper web is effected on both sides by means of roller application inside the paper-making machine and in a second process step coating is effected on one side by means of blade application, which is followd by surface smoothing of the paper web.
8. Process according to claims 1 to 7, characterized in that after drying and surface smoothing are complete, the paper web is subjected to further surface finishing on one side, such as coating, printing and/or varnishing.
9. The use of a dried paper web, produced according to claims 1 to 8, for encasing pieces of furniture (housing covering) by the glueing thereof to a rigid substrate and the further processing of a composite material so obtained by making mitre cuts and folding in the region of the mitre cuts to form three-dimensional pieces of furniture (folded carcass).