SE443590B - CONTINUOUS, MACHINE-MADE, EASY PAPER PRODUCT OF INORGANIC FIBER MATERIAL - Google Patents

Description

The persion medium is usually an acidic aqueous solution and may be slightly thick to help maintain the dispersion and insulation of the individual fibers in the multi-stranded bundles. The fibers in the dispersion medium are processed in a Dutcher to effect separation of the fiber bundles, and then the stock is transferred to storage tanks, containing conventional stirrers, to keep the fibers in the desired suspended state. It will be appreciated that failure to perform sufficient agitation during the initial phase of the dispersion of the fibers gives rise to an incomplete separation of the glass fibers, whereby fiber bundles become visible in the final continuous fibrous material.

In recent years, glass fibers of greater length than that usual for papermaking have, namely fibers with a length of between approx. 0.63 and 2.54 cm and above, used. When these fibers have been dispersed according to prior art methods. it turned out, however, that the individual fibers had a tendency to hook up or become entangled in the Dutch and the storage tanks and could not be easily dispersed again, but lumps and other irregularities were obtained in the manufactured paper product. It also turned out that the long glass fibers tangled into bundles of fibers, which in shape resembled "haystacks" or "spiders".

Although such "haystacks" may be permitted in heavier, coarser goods and for certain purposes, where the aesthetic appearance of the goods does not play a decisive role, they are considered as serious defects in light goods and for such purposes, where the glass paper is intended as a surface or to form a smooth and even surface on an object of reinforced plastic.

Thicker or heavier boards have been used in vinyl floor tiles and the like. to achieve dimensional stability. However, the heavier glass material has poor resin penetration properties and thus poor lamination, leading to a tendency to delamination. Thin, light test sheets with good fiber distribution can be produced one at a time, if you are very careful. However, the homogeneous fiber distribution required to eliminate the visible, total density variation, commonly referred to as the "cloud effect" and associated with a significant limitation of insulated fiber bundles or "haystacks", has not been achieved with continuously operating paper machines for making lighter fiberglass paper and similar materials.

In the continuous manufacture of paper on an industrial scale, long-fiber material is generally made from very highly diluted fiber suspensions using a sloping wire or similar type paper machine. In such a machine, a conventional, open headbox of sufficient volume is used to provide a smooth and relatively calm flowing current up to and into the web forming zone of the wet section. The advantage of such a headbox is that the residence time of the fiber suspension in the headbox is sufficient for air bubbles to have time to release from the fiber suspension before the formation of the fibrous material web. However, the desired even and calm distribution of the suspension on the wire has a certain disadvantage, in the case of suspensions with long glass fibers. Namely, it has been found that the air bubbles, when released in the vicinity of the headbox, have a tendency to allow and even promote the formation of "haystacks" of fibers. The blisters bring these fiber accumulations to the surface of the web material, where they are deposited. on this surface during the web forming process.

This results in a paper web which is unacceptable not only in appearance but also in that the product acquires an uneven or rough surface or "feel", which is easily detected by simply stroking a hand over the surface of the product.

The main object of the invention has thus been to provide a new, improved long-fiber glass paper or the like. with extremely low basis weight and homogeneous fiber structure and which is produced by means of a paper machine of normal, industrial size.

Another object of the invention has been to provide a new, improved glass fiber material in web form of the above type, which has a visible, totally homogeneous fiber distribution and a minimum of defects in the form of insulated fiber bundles. Thereby you can e.g. produce a lightweight glass fiber web of continuous length which is substantially free of visible "cloudiness" type fiber density variations. Yet another object of the invention has been to provide a lightweight fiberglass material which has improved appearance and physical properties and makes the material well suited for use in reinforced plastic sheets, floor tiles and the like.

These and other objects are achieved in accordance with the present invention essentially in that a continuous, machine-made, inorganic fibrous material in web form with homogeneous fibrous structure contains inorganic fibers with diameters of micrometer size and a fiber length of approx. 0.63 cm or more and a small amount of binder for the inorganic fibers. The web material has a basis weight of approx. 7800720-0 4 5-30 g / m2 and has a number of defects in the form of insulated bundles of fibers, which amount to less than 1 defect per square meter. In addition, the product produced (fibrous web) has a visible, totally homogeneous fiber distribution, which is substantially free of fiber density variations of the haze formation type, or "cloudiness effect".

The invention will be described in more detail below in connection with the attached block schematic production of a plant and process for the production of the light, web-shaped fibrous material according to the invention.

As stated above, an important factor in obtaining the desired homogeneous fiber distribution in the finished product consists in that a completely homogeneous suspension of the glass fibers in the dispersion medium can be obtained and that this dispersion can be transferred to the web forming area in the unchanged state. In order to clarify the description and facilitate the understanding, the glass fiber material according to the present invention will therefore be described in connection with the method and the process, respectively, which are preferably applied for its manufacture.

A variety of factors affect the quality of a fiber dispersion in water and the ability to transfer it to a web forming area of a paper machine. These include the type of fiber used, including the surface condition of the fibers and the state in which the multifilament roving is, which is used as a source for the fibers, the design of the cut or cut, the composition and properties of the dispersion medium, the efficiency of the mixing or dispersing apparatus and the fiber stock treatment. after leaving the dispersing apparatus. Although all of these factors are important, in the context of the present invention, a weighty, significant factor is the residence time of the fibers in the system from the time they enter the dispersion unit, to the point at which they are removed from the dispersion within the web forming area of the paper machine. In accordance with the invention, it has therefore been found that the best results are obtained by completely excluding the storage tanks or vessels used hitherto and using a series-connected dispersing apparatus instead of the previously used batch mixers. In connection with the exclusion of the reservoir, a direct transfer of the dispersed fibers to a dilution station takes place and the use of a smooth headbox with small volume, which is characterized by strong turbulence and high stock flow rate. In such a system, the flow of the fiber suspension from the disperser to the web forming area of the paper machine takes only a few seconds, and the residence time in the disperser is an important time determining factor for the passage of the glass fibers through the system. Such a timing is important because it has been found that an optimal dispersion of long glass fibers is achieved relatively quickly, namely within about 1-2 minutes, and that the fibers are maintained in their most homogeneously dispersed state for a period of only 4-5 minutes. Thereafter, the glass fibers have a tendency to accumulate, adhere to each other or form such undesirable "haystacks" or multi-fiber clusters as described above. It will of course be appreciated that the wet papermaking process, as described herein, is a dynamic system which is also dependent on many other conditions or factors within the system itself, e.g. of the viscosity of the dispersion medium, the fiber concentration, the amount of stream with which the fibers are fed into the dispersing apparatus and many other variable process parameters. Accordingly, the exact residence time varies depending on these various conditions or factors. However, the best results have been obtained with regulated residence times in the disperser of less than 10 minutes, and generally from approx. one to seven minutes. An acceptable work area is between approx. 2 and approx. 6 minutes, while the particularly preferred residence time is between about 2.5 and 5 minutes.

The inorganic fibers which can be used in accordance with the invention include all the inorganic materials which are commercially available in fibrous form, e.g. asbestos, mineral wool and the like, but fiberglass is generally preferred over others.

The fibers can vary considerably in thickness, but in the particularly suitable embodiment of the material in question the fiber diameters are within the coarser fiber range, e.g. between a 5 and approx. 15 / um.

It will be appreciated, however, that slightly finer or coarser fibers may be used for special purposes. The glass fibers constitute the predominant part of the fiber content, preferably the largest possible part thereof. Thus, for example, 85-90% or more of the fibers in the finished paper may be inorganic fibers, preferably glass fibers. As will be exemplified below, mixtures of different types and dimensions of glass fibers can be used, or the material can be made of glass fibers of only one type and size.

Due to the type of glass fibers preferably used, it is generally desirable to use a binder in the inorganic, web-like fibrous material, the paper product. Although a binder may be added as a dilute solution, either after the formation of the fibrous web, or also incorporated into the fiber stock as part of the dispersion medium, it is generally preferred to use binder fibers, which do not exceed about 10-15% of the total fiber content, preferably about to 10% of 'this. Several different types of binder fibers can be used with good results, e.g. Polyvinyl alcohol fibers have been found to give superior results, compared with spraying with adhesive solutions and the like performed after web formation. The binder fibers also have a favorable effect on the handling properties of the fibrous material web during transport through the paper machine. The fibers are activated or at least softened in the drying section of the machine to impart to the paper product its desired structural cohesion.

The binder fibers are preferably added to the fiber suspension during or after the dilution of the fiber concentration and before the suspension flows into the paper machine headbox. The polyvinyl alcohol fibers, which act as a binder component in the fibrous web, can thus be conveniently added by means of a fan pump with adjustable speed on the downstream side of the dilution operation, without disturbing the dispersion of the glass fibers in the homogeneously dispersed fiber stock. If desired, a subsequent treatment in adhesive press or other bonding treatments can be performed, depending on the final purpose for which the web material is intended.

In order hereafter referring to the accompanying drawing, more particularly, in the particularly suitable embodiment of the process in question, it has been found desirable to provide a controlled feed of long glass fibers in order to obtain the best dispersion properties.

The fibers are preferably fed in a selected amount per unit time into a continuous, series-connected dispersing apparatus and are fed from dispersion vessels directly to the dilution and web forming range of the conventional paper machine. This device avoids the need to keep the dispersed fibers in a pulp or other storage container or tank, with a consequent deterioration in the quality of the dispersion. In addition, the invention has the advantage that the continuous dispersing equipment is of relatively simple construction and inexpensive in comparison with previously used conventional stock preparation equipment. If desired, the fibers can be cut in advance and supplied by a dry fiber meter, or they can be fed in the form of continuous strands and cut or chopped off when they are introduced into the series-connected dispersing vessel. In the particularly preferred embodiment, it has been found advantageous to apply a fiber cutter at the inlet to the dispersing vessel in such a way that continuous lengths of glass roving can be fed from coils and cut for immediate feeding into the dispersing vessel. By such supply of the continuous threads, an excellent control is obtained over both the fiber length and the amount per unit time in which the fibers are fed into the dispersing vessel. In addition, it offers flexibility in the execution of the process, by allowing the use of different fiber lengths and the possibility of regulating and adjusting the fiber lengths, respectively.

If pre-cut or otherwise cut fibers are used, it is sufficient to regulate the feed rate of the fibers per unit time in the dispersing vessel by using a weighing belt or the like. between the dry fiber meter and the fiber dispersing vessel, in which case the dry fiber meter acts as a feeder, the heral of which is modulated and regulated by a signal from the weighing belt, so that the desired amount of fiber is achieved.

The liquid used as the dispersing medium is also fed to the inlet of the dispersing vessel to achieve the desired fiber concentration in this vessel. This liquid is an acidic aqueous solution, which may contain a suitable agent for controlling the viscosity of the dispersing medium. Thus, in accordance with a particularly suitable embodiment, an aqueous solution of dilute sulfuric acid having a pH between 2 and 4 and containing a sufficient amount of viscosity determining agent is used. The typical viscosity of the solution can vary between approx. 5 and 20 cP. The viscosifying agent may be a natural or synthetic material or a mixture or other combination of such materials. The agents in question are preferably water-soluble substances, e.g. resins or natural rosin species, which can be used alone, alone or in combination with other substances to give the desired viscosity. Examples of natural kdo fl mium species are carob resin and guar resin derivatives. Of these, the guar resin derivatives are preferred, and excellent results have been obtained with an aqueous solution of a guar resin derivative, which is marketed by the General Mills Company under the trade name "GENDRIV". In addition to the natural viscosifying agents, or thickeners, it is also possible to use synthetic substances, e.g. high molecular weight resins, dispersants, surfactants (surfactants) and the like for regulating the properties of the dispersing medium. These synthetics are preferably water soluble and are stable in the acidic environment used for the glass fibers. Of the synthetic thickeners 7800720-08, the particularly suitable resins are acrylamide plastics which can be used in dilute aqueous solutions in low concentration (eg 0.025 - 0.2%) to enable the desired viscosity control. A typical example of such substances is the polyacrylamide resin marketed by the Dow Chemical Company under the trade name "SEPARAN AP-30" and by the American Cyanamide Company under the trade name "Cytame 5".

The viscous dispersing medium is used because it prevents entanglement of the fibers during the dispersing operation and helps to keep the fibers in a dispersed state during the passage of the suspension through the dispersing vessel. It will be appreciated that the viscosity of the solution affects the required residence time and must be adjusted for the particular fiber and fiber concentration used.

An excessively thick medium and a too short residence time in the dispersion vessel can result in a too weakly dispersed fiber stock, while a too low viscosity and a long residence time could result in a too highly dispersed stock and the formation of "haystacks" and other serious defects. A viscosity in the area approx. 5-10 cP and a residence time of approx. 2.5 - 5.0 minutes have been found to give good dispersion results. It should be understood that other additive materials, e.g. Dispersing aids, such as surfactants, such as sodium hexametaphosphate, marketed under the tradename "CALGON", may be added to the dispersing medium to achieve the desired control over the dispersed fibers and help prevent fibers from tangling again to undesirable "haystack" formations.

As mentioned, it has been found that the fibers disperse fairly quickly in the dispersion medium and reach a percentage dispersion peak within a relatively short time, after which the fibers tend to coil slightly and form the undesirable "haystacks". After optimal dispersion has been achieved, it is therefore desirable to continue stirring for a certain, limited period of time and to regulate the residence time of the fibers in the dispersion vessel so that an excessively long stirring time is avoided. In this context, it has also been found that the stirrers in the dispersion vessel, even after optimal dispersion has been achieved during the desired residence time, cannot be stopped immediately without the quality of the dispersion deteriorating. It is of course understood that a surface treatment of the fibers has a considerable effect on the fibers' ability to withstand an extended residence time. However, for most glass fibers currently commercially available, it has been found that the optimum residence time is between 2.5 and 5 minutes when using a dispersing medium having a viscosity of about 5 to 10 cP and a pH. of approx. 2 - 3 at a solution temperature of approx. 27 - 38 ° C and a fiber concentration of about 0.3 - 170%.

The dispersing apparatus should preferably be of the type having a relatively smooth inner surface and free from any sharp edges or surfaces on which the long glass fibers may hook or wrap. However, the dispersing apparatus may also consist of a plurality of continuous flow mixing or dispersing stations or pockets directly from one station to the next to ensure the desired residence time characteristics.

It will be appreciated that the design of the dispersing apparatus may vary as long as it fulfills its intended function of separating the individual fibers from the bundles of fibers introduced into the apparatus, forming a homogeneous dispersion of the individual fibers as the fiber dispersion passes through it within the required range. residence time.

It will further be appreciated that the fibers are metered into the dispersion medium flowing through the dispersing apparatus, in such an amount that the dispersion obtains the intended fiber concentration. Usually this concentration is 10 -10O times as high as the fiber concentration in the headbox. According to the particularly suitable embodiment, the fiber concentration is less than 2% and is generally in the range between approx. 0.3 and 1.3%, preferably between approx. 0.5 and 0.9%.

As stated above, the fiber dispersion flows rapidly from the disperser to the web forming or wire portion of the paper machine, which it actually arrives at a few seconds after it has left the disperser. During this period, however, the fiber concentration of the dispersion is adjusted so that the fiber stock becomes more thinned. This can be accomplished by feeding the dispersion to a special passage and mixing tank, in which it is mixed with the main stream of backwater from the web forming operation. The fiber concentration is thereby reduced from a value of 0.3 - 1.2% to a value of approx. 0.005 - 0.05%. It will thus be appreciated that the thinner is greater than 10: 1 and is usually between 15 and 25: 1 to form the highly thinned fiber suspension which is fed to the headbox of the paper machine.

As indicated in the drawing, the headbox used in accordance with the present invention is different from the open headbox used in conventional sloping flat wire napping machines, 7800720-0 10 and has a smooth, smooth contour and reduced volume, so that the strongly thinned fiber suspension flows rapidly through the headbox on its way to the path forming or wire section. The reduced volume of the headbox, together with its smooth, smooth contours, not only causes an increase in the flow rate of the fiber suspension through the box, but also an increase in the random turbulence immediately over the inlet zone of the wire section. The increased turbulence level prevents the accumulation of foam and fibrous masses, which would otherwise float to the surface and form "haystacks" or other defects. It will be appreciated that a smoothing control of the diluted fiber dispersion can be accomplished by means of a suitable control mechanism, e.g. in the form of a variable speed vane pump, provided that the flow channel of the pump has smooth, smooth walls and is free from details which could give rise to eddy currents or otherwise cause entanglement of the fibers. The headbox used in accordance with the present invention thus prevents the fiber dispersion from being retained for a long time, thereby preventing the dispersed fibers from tangling and forming defects in the structure of the glass paper web.

The invention will be further elucidated in the following by a number of practical embodiments. Where not otherwise specified, the quantity data refer to parts by weight and percentage by weight, respectively.

EXAMPLE I A lightweight glass fiber web was prepared using a paper machine of normal industrial production size. Glass fibers with a fiber diameter of 9 .mu.m were cut into lengths of 1.27 cm by strands of glass roving, which were unwound from spools. The staple fibers thus obtained were transferred directly to a disperser connected in series in a weight amount of 0.454 kg / min. This apparatus had a capacity of 379 liters and was operated at a flow rate of 114 liters per minute, thus giving a residence time of slightly more than 3 minutes. The dispersion medium used was a dilute sulfuric acid solution, containing a quartz resin derivative ("GENDRIV-492 SR") in sufficient quantity to give the solution a viscosity of approx. 5 cP at a pH of 2.3 and a temperature of 31 ° C. The fiber dispersion was fed at a fiber concentration of 0.4% from the disperser to a mixing vessel, where the fiber concentration was diluted in a ratio of approx. 24: 1. Polyvinyl alcohol fibers were added to the diluted suspension in sufficient amounts to give a polyvinyl alcohol fiber concentration of 8% of the total weight of the glass fibers. The fiber dispersion was then fed to a low volume, high flow rate inlet tray at a concentration of 0.017% and a glass fiber web was formed at a medium production rate.

The finished glass paper product has a basis weight of 13.6 g / m2, a thickness of 84 .mu.m and an air permeability ("porosity") of 8263 liters per minute per 100 cm at a pressure of 12.7 mm water column. A dry tensile strength of 507 p / 25 mm in the machine direction and 333 p / 25 mm in the transverse direction It exhibited a tongue tear of 34 p in the machine direction and 44 p in the transverse direction.

Samples taken from different parts of the product showed larger defects in a number of 0 - 2 and minor defects in a number of 0 - 5 10 m2, corrected to a basis weight of 17 g / m2. A major defect is classified as a fiber bundle, either of undispersed or partially dispersed nature, or of a "haystack" form, while a minor defect may be classified as consisting of two or three fibers which have not been dispersed or joined.

Commercially acceptable goods are those that have a maximum of approx. 10, preferably at most 5 major defects per 10 m2 of the product. The minor defects are considered insignificant. The glass paper material also showed a homogeneous fiber distribution, mainly free from visible density variations on visual inspection.

EXAMPLES II - VI The one in Ex. The procedure described in 1 was repeated with the same paper machine, with the exception of variations in the working parameters of the process, the fiber stock and the basis weight of the glass paper material produced. The results are summarized in the following table: TABLE I Ex. 11 Ex. 111 Ex. Iv Ex. v Ex. v1 Fiber: 9/1111 (s) 70 46 90 70 22 13 / um 1%) 22 46 - 22 70 Binder 8 8 10 8 8 basis weight (g / m2) 19.8 18.3 22.0 22.4 23.1 Thickness VHM 123 115 133 138 115 Air porosity (1 / min) 5648 6552 4742 5512 6149

Claims (10)

7800720-0 12 (continued Table I): Ex.II Ex.III Ex.IV Ex.V Ex.VI Dry tensile strength (g / 25mm) in the machine direction 1109 609 1828 1456 1121 in the transverse direction 915 765 1034 1362 1037 Tear strength (g ) in the machine direction 51 60 40 62 89 in the transverse direction 51 44 60 63 99 Number of surface defects (defects) per 10m2 larger 0-3 0-4 0-3 0-1 smaller 3-4 0-5 7-14 1-4 2- EXAMPLES VII - IX The procedure described in the preceding examples was repeated with a small production machine and using glass fibers of smaller diameters and without binder fibers. In all cases, the glass fibers constituted 100% of the fiber component and had a length of 1.27 cm and 6 .mu.m diameter. The basis weight and the number of defects (surface defects) per 10 m2 are given in the following Table II. The large number of minor errors is due to the very small fiber thickness and the subjective analysis, but the material is considered in all three cases to be fully acceptable from a commercial point of view. TABLE II 2 Number of defects (surface defects) Ex. No. Surface weight (g / m) Larger Minor VII 15.8 1 241 VIII 16.6 0 386 IX 17.6 0 215 Patent claims Continuous, wet-formed ("wet-laid"), machine-made lightweight paper inorganic fibrous material with a homogeneous fiber distribution, characterized in that the product contains inorganic fibers with a fiber length of at least approx. 0.63 cm and about 15% by weight of a binder for the inorganic fibers, and that the product has a basis weight of approx. 5 - 30 g / m2, a number of insulated fiber bundles consisting of defects or surface defects less than 10 defects per 10 m2, and a visually observable, homogeneous fiber distribution, which is substantially free from fiber density variations of the "cloudiness" or "haze" effect 13 78OÛ72Û-0 Paper article according to claim 1, characterized in that the inorganic fibers consist of fine glass fibers with a diameter of the order of micrometers. Product according to claim 1, characterized in that the content of inorganic fibers amounts to approx. 85% by weight or more. Item according to claim 1, characterized in that it has a basis weight of approx. 10-25 g / m2. 5. An article according to claim 1, characterized in that the inorganic fibers consist of glass fibers with a diameter in the range 5-15 μm and a length in the range 0.63-2.54 cm. Item according to claim 1, characterized in that the inorganic fibers consist of a mixture of glass fibers of different diameters of the order of micrometers. 7. A product according to claim 1, characterized in that the inorganic fibers constitute approx. 90% by weight of the product and consists of glass fibers with a fiber diameter in the range 5-15 / um, and that the product has a number of defects (surface defects) of significance not exceeding 10 per 10 m2. Product according to claim 1, characterized in that the product has a number of defects (surface defects) of significance amounting to approx. 5 or less per 10 m2. Product according to claim 1, characterized in that the binder is incorporated in the product from the beginning in fiber form. 10. A product according to claim 1, characterized in that the inorganic fibers are glass fibers with a diameter of less than 15 .mu.m and a length of at most about 2.54 cm, that the amount of glass fibers amounts to at least about 90% of the weight of the product, that the binder consists of a thermoplastic material, which is initially incorporated into the product in fibrous form, that the product has a basis weight of approx. 25 g / m2 or less, and that the product has a number of significant defects (surface defects) amounting to approx. 5 or less per 10 m2.