Gypsum wallboard paper

(42) Date of commencement of the patent: 15.11.1986 (45) Date of issue: 25. 6.1987

<td>(30) Priority:</td><td>(73) Patent owner:</td>

<td>24. 6.1982 US 391627 claimed.</td><td>UNITED STATES GYPSUM COMPANY CHICAGO (US).</td>

<td>(56) Documents:</td><td></td>

<td>U.S. Patent No. 3,379,609 U.S. Patent No. 4,154,224</td><td></td>

(54) POROUS MINERAL FIBER-CONTAINING PAPER

CQ

AT 383 382

BVR 0379313

Nr.383382

The invention relates to a porous mineral fiber-containing paper and a process for its production.

Building boards, which consist of a cast gypsum core and paper decks, are used in many ways in construction. The product may be in the form of lightweight panels, plaster walls od.ähnl. available. To produce such gypsum boards, usually the front paper is pulled over a forming table, a water stucco slurry is spread over the paper web, and the back deck laid over before the gypsum slurry has set. Then the plate is cut to the desired size and dried in the oven. In use, the plate is cored and crushed or sawed to the desired size and secured to the wall with staples, nails, screws or glue.

The strength and other properties of the finished gypsum board depend to a considerable extent on the paper cover sheets used. The webs must allow a dimensionally accurate production of the plates, have a high strength and suitable surface texture, dry quickly and adhere well to the gypsum core.

The addition of a small amount of mineral fibers to the cellulose pulp can improve the paper cover sheets as described in U.S. Patent No. 3,562,097 and U.S. Patent No. 4,020,237. Thereafter, the webs are prepared by separately dispersing cellulose and mineral fibers in water, mixing the two dispersions in the desired ratio, and finally forming the combined dispersions on a round-screen paper machine into a paper felt. The advantages of adding mineral wool fibers are improved dewatering of the pulp, better values ​​for the porosity of the webs and faster drying of paper and board.

However, paper containing mineral fibers was found to be unsuitable for cover sheets of gypsum board for three main reasons. The first and most important problem resulting from the use of mineral fibers is an excessive amount of precipitating shot (particles of molten and then re-hardened slag) that contaminated the facilities and machines of the paper mill. The meal settled in the storage and mixing tanks and formed deposits on the wire screens. Second, there was a reduction in physical strength in nearly direct proportion to the amount of mineral fiber added. Finally, there was also a poor dispersibility of the mineral fibers with excessive shortening and refraction of the fibers during the mixing process.

The object of the invention is to provide a porous and mineral fiber-containing paper and a process for its preparation, wherein the disadvantages described above are avoided.

According to the invention, this object is achieved by a porous mineral fiber-containing paper, which is characterized in that it is based on dry weight about 65 to about 95% cellulose fibers, about 5 to about 40% schrothältige mineral fibers, cellulose gel in an amount of about 1 to about 10% , polymeric latex binder in an amount of about 1 to about 10% and flocculant in an amount of about 0.05 to about 0.5%, and by a method for producing such a paper, which is characterized in that an aqueous slurry containing cellulose fibers, scrub mineral fibers, cellulose gel, polymeric latex binder and flocculant is prepared, and this paper machine is fed with a slurry and a paper made therefrom and this paper is dried.

The following examples are for further information and are not intended to limit the claims of the invention in any way.

Examples 1 to 5:

According to the procedure TAPP! T-205 were hand-made. By this method, 2000 ml of water was mixed with 24 OD (oven-dried) g of cellulose paper fibers. The mixture was milled for 25 minutes in a TAPPI disintegrator. After milling the paper fibers, a refiner-ground newspaper made of 6% stock was added to the paper pulp stock diluted to 0.3% stock. This mixture was mixed for 5 minutes with a Lighthnin 'laboratory mixer at 1000 rpm. Thereafter, the mineral fiber was added to the paper fiber-gel mixture in a dry state and exposed to Lightnin for 5 minutes¹ Mixer mixed at 1000 rpm. After dispersion of mineral fibers in

No. 383382 of the slurry was then added to the latex to the paper fiber-gel-mineral fiber mixture and stirred again for 2 minutes. Finally, the flocculant was added to the mixture and stirred for a further 2 minutes. From this slurry were taken in a TAPPI

Bogenform hand arch produced, the drainage according to the method TAPPI T-221 tested and the paper then dried by the method TAPPI T-205.

The compositions used in Examples 1 to 5 and the properties of the test sheets found are summarized in Table I below. The paper fiber used consisted of a blend of 70% Altwell cardboard and 30% newsprint, refiner ground to a freeness of 350 ml. The mineral wool used was made from blast furnace slag at the Walworth plant of United States Gypsum Company and is referred to as 'white wool' with 28% shot. A typical example of the composition of the mineral wool gives about 36 wt .-% silica, 36 wt .-% calcium oxide, 15 wt .-% alumina and 13 wt .-% magnesium oxide. The dispersing gel was prepared from cellulose fiber furnish of 70% unbleached kraft pulp and 30% newsprint paper (in

Table I with "Kr / Ztg designated). The millbase mixture was gelatinized by multiple refining cycles to achieve the desired drainage time of at least 5 minutes in accordance with TAPPI T-221 and the desired shrinkage of at least 25% as tested in TAPPI UM238. This fiber hydration is far greater than that commonly used in the paper industry, and the production process is described in greater detail in US Pat

Nr.3,379,608.

Table I

<td>Examples</td><td>1</td><td>2</td><td>3</td><td>4</td><td>5</td>

<td>Examination (TAPPI 220)</td><td>100% paper fibers</td><td>75% paper fibers 25% Mineral- fibers</td><td>72.5% paper fibers 25% Mineral- fibers 2.5% Kr / Ztg- -Gel</td><td>70% paper fibers 25% Mineral- fibers 5% Kr / Ztg- -Gel</td><td>67% paper fibers 25% Mineral- fibers 7.5% Kr / Ztg- -Gel</td>

<td>Areal weight (g / m²)</td><td>74.8</td><td>75.4</td><td>74.2</td><td>75.6</td><td>74.4</td>

<td>Drainage time (S)</td><td>7.5</td><td>5.2</td><td>5.8</td><td>6.1</td><td>8.8</td>

<td>porosity (s / 100 cm³ Air)</td><td>10.8</td><td>2.0</td><td>2.8</td><td>4.8</td><td>8.9</td>

<td>Tearing length (m)</td><td>2229</td><td>1606</td><td>1773</td><td>2012</td><td>2235</td>

<td>spec. Bursting Strength</td><td>11.4</td><td>4.6</td><td>5.5</td><td>7.2</td><td>13.4</td>

The results obtained and reported in Table I above show that addition of about 5% Kraft gel to achieve good tensile strength while maintaining sufficient paper stock draining and arch porosity advantages is optimal.

While, as can be seen, with the addition of 5% gel, some of the good drainage and porosity properties are lost as compared to the lower additives

- 4 Nr.383382

Compensation at the same time significantly improves the tensile strength of the webs. However, using amounts above 5% will unduly reduce the benefits of dewatering and porosity while further degrading the desired properties.

Examples 6 to 11

In Examples 6 to 11, additional sheets were made using a formulation of essentially 70% paper fibers, 25% mineral fibers and 5% gel, as well as various amounts of latex and flocculant additives. The latex used was a product of Dow under the designation Latex Dow XD-30374, a styrene-butadiene copolymer. The flocculant used was a Dow product called Polymer PC-XD 30440. Both

Products are further described in U.S. Patent No. 4,225,383 to Dow Chemical Company. The aim of the use of latex and flocculant was to obtain an agglomerate of paper, gel and mineral fibers, whereby the pellets of the mineral fiber are well suspended in the pulp. The considerable extent of shot-suspension shows two advantages: elimination of the shot from the equipment and paper machines and maximum incorporation of the shot

Shots in the mineral fiber / paper fiber sheet according to the invention.

Table II below sets forth the values ​​of the various blends made according to Example 6 bis and the properties of the handsheets made therefrom.

The results obtained in Table II show that the sheets produced have improved tensile strength, drainage and porosity through the use of latex. Thus, the 5% latex handsheets made in Example 9 were comparable in their tensile strength to 100% paper fiber handsheets. However, the formulation with 2.5% latex and 0.1% flocculant appeared to be suitable for suspension of the shot in the slurry recipe used for commercial products. This result was obtained by visual observation of beakers containing various pulp agglomerates. The substances of Examples 6 and 7, in the form of the 0.15% slurry formulation, showed some settling of the shot at the bottom of the beakers. In marked contrast, Examples 8, 9 and 10, with a comparable 0.75% bulk density, showed excellent dispersion of the slurry in the slurry with no evidence of settling of the shot at the bottom of the beakers.

As mentioned above, one of the problems encountered in prior art attempts to produce a mineral fiber-containing paper is the presence of shot. According to the invention, this problem can be solved by using a combination of latex and one or more flocculants to keep the shot suspended and to avoid contamination of the paper machines. Among the used

Latexes gives a styrene-butadiene copolymer excellent results. These and other substances are described in U.S. Patent No. 4,225,383 to Dow Chemical Company. Other polymers may also be used, such as polyvinyl alcohol, which are generally known in the art as binders. The flocculant may be selected from the starches, polymers such as Dow Chemical Polymer PC-XD (a preferred substance),

Alum and others such as polyacrylamides. The aim of using the latex flocculant combination is to obtain a paper mineral fiber agglomerate in aqueous solution to uniformly and discreetly incorporate the mineral fiber shot in the web. By achieving a pulp system to incorporate the shot in the paper, contamination of tanks, stock and mix tubes and machine wires is discouraged. It also avoids the need for a method of removing the shot. In addition, the latex adds strength to the paper-mineral fiber product.

Nr.383382

Table II

<td>11</td><td>100% paper fibers</td><td>fr- "Φ fr-</td><td>W</td><td>10.8</td><td>2229</td><td>r-1 approx</td>

<td>© t-4</td><td>sisgiUeKj 3 Ϊ ä ^8th S! 5 = 1 S fc,</td><td>75.15</td><td>5.8</td><td>" τί</td><td>2340</td><td>11.17</td>

<td>0)</td><td>g «1 g 2 1 Ü es ® j&gt; let r? 03 "2 fl) TO ΙΟΣ * * · rS⁵⁰ 0-d ^N fi 8 &amp; s J ° 0 rat- &lt;h iS ^MS Ix,</td><td>76.93</td><td>6.0</td><td>lß</td><td>2278</td><td>9.86</td>

<td>00</td><td>gisgisäsääl 3 Ϊ i ^8th I i S '3 ° ί S fe</td><td>IO "sH fr-</td><td>5.8 i</td><td>CO τί</td><td>2103</td><td>8.84</td>

<td>fr-</td><td>ι ¹ ε t. ? 53 L * Φ X^ω &amp; J ^N .5 &lt;2 g 3 o 8 S £ l,</td><td>75.2</td><td>6.0</td><td>00</td><td>1975</td><td>in</td>

<td>CO</td><td>g ί I gg | s s g. 8 - § 3 "I o. S</td><td>75.6</td><td>H CO</td><td>4.8</td><td>2012</td><td>&lt;N fr-</td>

<td>Examples</td><td>Check (TAPP1 220)</td><td>N ε ω **&gt; * 1 c Φ rC 43 Q : rt&gt; pH Φ Ck bss</td><td>Drainage time (s)</td><td>porosity (s / 100 cm³Air)</td><td>Tearing length (m)</td><td>spec. Bursting Strength</td>

Nr.383382

The second problem attempted by the invention is the loss of web strength which can be caused by the presence of mineral fibers. This problem is reduced by the use of limited amounts of mineral wool fibers along with selected amounts of kraft / newsprint gel and latex. These substances allow the production of paper webs with good strength, while not losing the benefits of rapid dewatering, good porosity and rapid drying.

The use of Kraft / Newsprint Gel also provides better dispersibility of the mineral fibers and mechanical protection of the fragile mineral fibers prior to the turbulence of the mixing motion. When using the gel, the detrimental effect on slowing the drainage and reducing the porosity of the web by careful selection. The share of mineral wool and gel avoided and you can get the optimal properties of the substances. An optimum composition of the components is given below in percent dry weight of the total composition. The percentages of Kr / Ztg gel, latex and flocculant were corrected for the original water content.

<td>paper fibers</td><td>64.8%</td>

<td>Mineral wool asper n</td><td>25%</td>

<td>Power / newspaper gel</td><td>5%</td>

<td>latex</td><td>5%</td>

<td>flocculants</td><td>0.2%</td>

While it has been found that the above proportions are optimal, suitable papers for making gypsum boards can also be obtained from the following ranges of proportions:

Wt .-%

Paper fibers 65 - 95

Mineral fibers 5 - 40

Kraft / Newsprint Gel 1 - 10

Latex 1 - 10

Flocculant 0.05 - 0.5

The following examples were conducted to examine the effect of using mineral fibers on the speed of web drying.

Example 12

An aqueous slurry of 1.2% pulp consistency with 25% mineral wool fibers, 64.8% paper fibers (70% Altwellpappe and 30% newsprint) and 5% kraft / newsprint gel was prepared. After mixing to obtain good fiber dispersion, 5% latex (Dow XD-30374) was added and the slurry stirred again for 5 minutes. Finally, flocculation of the latex with Dow Polymer PC-XD 30440 (0.2%) produced a fiber agglomerate. Then, handsheets were made in the TAPPI hand bow form at a stock consistency of 0.15%. After normal TAPPI Gautschen, the sheets were weighed to determine the moisture content. After this weighing, the sheets were passed through a Noble and Wood bow dryer several times at 116 ° C (240 ° F) dry drum temperature and rechecked for moisture content after each pass.

Example 13

For comparison, paper sheets of 100% paper fiber (70% corrugated and 30% newsprint) were slurried, shaped, skinned, weighed, dried, and weighed again by the same procedure as described above in Examples 1-5.

The results of the tests on the sheets of Examples 12 and 13 are shown in the table below

III cited. The results are mean values ​​of 5 test pieces of about 1.5 g each (70 g / m²).

Nr.383382

<td rowspan="2">3. dryer passage</td><td>% Fiber</td><td>100</td><td>100</td>

<td>Weight (g)</td><td>1.51</td><td>1.53</td>

<td rowspan="2">2nd dryer passage</td><td>% Fiber</td><td>O O ί-1</td><td>94.4</td>

<td>Weight (g)</td><td>1.51</td><td>1.62</td>

<td rowspan="2">1st dryer - passage</td><td>% Fiber 1</td><td>65.6</td><td>47.9</td>

<td>Weight (g)</td><td>2.30</td><td>cn CO</td>

<td rowspan="2">Gautschpressen .....</td><td>1 | % Fiber</td><td>32.4</td><td>26.5</td>

<td>Weight (g)</td><td>99'F</td><td>5.77</td>

<td colspan="2">arc</td><td>Example 12 *</td><td>Example 13 **</td>

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Nr.383382

The above-mentioned test results of the products of Examples 12 and 13 show the improved dewatering rates in the press molding and the improved drying rates which can be achieved by using the composition of Example 12 according to the invention. The results show a 22% improvement in press drainage and a 36% improvement in the first dryer pass. This clearly results in considerable energy savings.

Examples 14 and 15

In Examples 14 and 15, attempts were made to compare the resulting fiber lengths of the mineral fibers in the paper made using cellulose gel in accordance with the present invention with those in paper made according to U.S. Patent No. 3,562,097.

The handsheets of Example 15 of the present invention were made according to the method of Examples 1-5 using 25% mineral fibers, 65% paper fibers, 5% cellulose gel, and 5% latex flocculant. In Example 14, the composition contained 25% mineral fibers and 65% paper fibers, but the method used to make the handsheets was U.S. Patent No. 3,562,097. After forming and drying the handsheets, mineral fibers were removed by moistening and gently separating the fibers of an unsized and shaped handsheet to determine fiber length. The mineral fibers obtained from a handpiece according to the invention obtained according to Example 15 measured 6.4 to 12.7 mm. In comparison, the length of the mineral fibers made from the handsheets according to Example 14 produced according to US Pat. No. 3,562,097 was only 0.8 to 1.6 mm. The greater fiber length of the mineral fibers is important for achieving both maximum incorporation of mineral fiber and shot and improved web formation.

Production of plasterboard

Using the recipe of Example 4, multilayer handsheets of 4.8 grams were prepared by the method TAPPI T-205 as used in Examples 1-5 above. The multilayer bows consisted of four individual layers of 200 cm each², The 4.8 g multilayer sheets corresponded to a standard commercial product having a bow weight of 23.59 kg / 92.90 m² or 253.9 g / m²). An aqueous slurry of commercial calcium sulfate hemihydrate was prepared. The recipe of the kernel 92,90 m each² The plates consisted of 657.71 kg stucco, 2.72 kg core starch, 1.81 kg calcium sulfate dihydrate as accelerator and 0.91 kg K₂SO₄, The determined Vicat values ​​were about 8 min. The slabs made by applying the slurry between two handsheets were dried at 171 ° C to 70% of their wet weight, and then at 43 ° C for 16 hours. The densities of the plates were 736.8 to 768.9 kg / m³,

All the panels produced showed excellent wet, dry and wet bond strength between the paper sheets and the gypsum core without exception.

Comparative test

For comparison, laboratory plates were made using common commercial gypsum board papers and the same recipe for the gypsum core. The bond strength results were comparable to those of mineral fiber-containing sheets made with paper of the invention and showed excellent wet, dry and wet bond strength.

The main difference between the two types of panels was a somewhat rougher texture for the mineral fiber panel. However, this can be compensated by using an additional surface layer of fibers on plasterboard paper made on a rotary screen machine. By using mineral fibers in the paper, less energy was used to dry the paper during the manufacturing process. Due to the higher porosity of the paper, less energy is needed to set and dry the finished panels.

The process and product of the invention show a number of advantages over those of the prior art. When mixing the mineral and paper fibers with the kraft or cellulose gel, the mineral fiber structure remains intact and the web strength is increased.

In prior art processes, the fibers are significantly shortened when the shot

Nr.383382

- 9 is removed, simultaneously with a loss of drainage and a reduction in paper strength. Furthermore, in prior art processes, if the meal is not removed, this meal falls out of the slurry and contaminates the paper machines.

In addition, as in the invention, when the mineral fibers, cellulosic fibers and gel components are flocced and / or agglomerated with latex and a flocculant, the pulp dewatering time, the web porosity and the sheet strength are further improved. The addition of latex and flocculant also additionally promotes more effective suspension of the mineral fiber meal in the slurry and better incorporation of the shot in the web. In addition, the use of mineral fibers, gel and the latex / flocculant additive gives better results in drying and thus leads to energy savings.

In summary, the invention provides effective suspension and incorporation of the shot in the web by addition of a cellulose gel and latex / flocculant without the need to remove the shot and without the disadvantages of shot contamination. Further advantages result from faster pulp dewatering, improved web porosity, higher web stability and better pressing and drying properties.

The invention should not be limited to the precise details of the illustrated and described formulations, process conditions, substances or mixtures, as obvious modifications and equivalents will be apparent to those skilled in the art.