MXPA99002332A - Acrylic sheet having uniform distribution of coloring and mineral filler before and after thermoforming - Google Patents

Abstract

The present invention is drawn to a composition and thermoformable sheets and articles made therefrom. In the present invention, ranges of chain-transfer agents, thixotropic agents, and mineral filler content are balanced to minimize migration or maldistribution of coloring matter and mineral filler during curing of methyl methacrylate in a syrup and also during subsequent heating and deformation in thermoforming, to achieve constancy of impact resistance and improve stability of patterns even in deformed portions of formed sheets.

Description

ACRYLIC SHEET THAT HAS A UNIFORM DISTRIBUTION OF COLOR AND MINERAL LOAD, BEFORE AND AFTER THE THERMOFORMING RELATED APPLICATION This application is a continuation in part of our co-pending application of the same title, Series No. 740,380, filed on November 4, 1995, which is a continuation in part of Series No. 720,164, filed on September 1996, which is a continuation in part of Serial No. 620,510 filed on March 22, 1996, Patent No. 5,567,745, which is a Divisional of Serial No. Application No. 392,650, filed on February 23, 1995, Patent No. 5,521,243, which is a continuation in part of the Serial No. 157,253 filed on November 26, 1993, currently abandoned.

TECHNICAL FIELD This invention relates to the manufacture of acrylic sheets or plates, ie sheets or plates of polymethyl methacrylate ("PMMA"), of the type of those that are applied or designed in architectural uses as kitchen countertops and more complex forms . These "sheets or plates contain significant amounts of flame retardants of mineral origin, typically trihydrate alumina and almost P1170 / 99MX always contains dyes, often in imitation of natural minerals such as onyx, marble or similar synthetics with a solid color appearance or those with designs that have particles that are not visibly distinguishable. This invention discloses a sheet which can be heated and bent at a 90 ° closed angle and / or which can be heated and formed in a curved vacuum at a closed angle of 90 ° and / or which can be heated and vacuum formed at forms such as sinks and bowls without significant sacrifice of aesthetics. In addition, the sheets or plates of this invention exhibit physical properties and other specific properties such as low flammability and minimal color changes after thermoforming; The even distribution of the flame retardant significantly improves the consistency of impact resistance.

BACKGROUND OF THE INVENTION The sheets and plates of synthetic material with mineral appearance are now commonly used as kitchen countertops and exterior and interior covers of all kinds for buildings such as banks, air terminals, stores and the like. These applications often require that the material be manufactured to fit the areas designed by the client, which in turn require that the plates or P117- / 99 X sheets are assembled together with these or otherwise joined so that they are juxtaposed to a cross section with a normal surface of 90 °. The manufacturing process requires a lot of time and specially trained craftsmen to complete it successfully, since special tools and procedures are necessary. If a part of a part in the form of continuous or monolithic material is desired, that part can be produced only by molding in a molding cavity under special conditions. In addition to the high costs of such a process and the installation of the parts (adjust, stick it in place to a flat and / or finished sheet, for example) there are often color differences between the molded bowl, for example and the flat plate of the same material. The sheet (the terms "sheet" and "plate" will be used here indistinctly) of our invention can provide a relatively complex finished part by a simple thermoforming operation - that is, the sheet is heated and then pulled into a mold vacuum of concave cavity (or convex), in which it is left to cool, to conserve its new form. That mold can be made in the shape of a toilet cover, with a rear wall of 90 ° splashing, with a blunt tip front end of 1.0 inch radius and a toilet bowl. After forming, P1170 / 99MX cooling and roughing, the part can be installed directly on site, without requiring additional manufacturing. It is said that only a contemporary commercial product (Corian® by DuPont) is susceptible to bending with heat. However, its operation is not suitable, for example, to make a rear splattering wall with a 90 ° angle, since the minimum radius of curvature specified by the Corian literature is 3.0 inches. To our knowledge, the use of alumina trihydrate in polymethyl methacrylate articles ("PMMA") was first proposed by Stevens et al. in the U.S. Patent 3,563,939 (col 4, lines 28-29) and Duggins in Canadian Patent 916,337. Its flame retardant properties are now well known and accepted and the alumina trihydrate ("ATH") is currently widely used as a filler in different resinous products. Some more detail for the construction of synthetic mineral products is provided by Duggins in U.S. Patent 3,847,865; where, for example, the crosslinking agents are mentioned. Release agents and viscosity reducers such as aliphatic acids are also proposed. Buser et al., In U.S. Patents 4,085,246 and 4,159,301 address the problem of P1170 / 99MX the sedimentation rates of various particles used in the manufacture of imitation granite having a polymerizable methyl methacrylate ("MMA") matrix having PMMA dissolved therein. See column 7, lines 42-62 of the '301 patent. They use PMMA to adjust the viscosity, which in turn controls the sedimentation rates of the larger particles - see the Examples, in particular Example 5 of US Patent 4,159,301, lines 31-34. They also use chain transfer agents as accelerators for the polymerization-col. 8, lines 58-68 of the same patent. Uniformity in color is mentioned as a goal in U.S. Patent 4,413,089 to Gavin et al., Wherein the iron oxide pigment of 10 microns or less is evenly distributed in a MMA / PMMA syrup that it is cured later; Prolonged storage of this syrup is not recommended (col 2, lines 50-64). In addition to facing the aforementioned challenges, for example, a material intended to be used as a back cover for kitchen must have a surface that is easily repairable and restorable to recover its original appearance, for example by sanding and polishing, which is protected against flammability and that it has good resistance to temperature despite being thermoformable.

P1170 / 99MX The prior art has neglected more or less the goal of the thermoformability or the ter occurrence of the solid surface sheets, since the products of the prior art were generally designed to reproduce the appearance of the flat sheets, with base mineral, natural.

BRIEF DESCRIPTION OF THE DRAWINGS Figure IA is a more or less hypothetical illustration of the bending of a half inch thick "Corian" sheet of the prior art. Figure IB is an idealized similar illustration of the bending of a sheet of the present invention.

SUMMARY OF THE INVENTION The present invention is directed to the manufacture of PMMA sheets with mineral charge which: - can be bent with heat at relatively closed angles, - can be thermoformed into shaped articles without losing uniform appearance and properties of upper surface, - can be vacuum thermoformed inside a mold of simple profile, concave or convex and do not require a set of two molds, - they have only minimal color changes and P1170 / 99MX tolerable through the complete finished part, either lower than Delta E = 2.0 by Cielab or not easily noticeable to the naked eye, - have a low thermoforming temperature sufficient to avoid any significant loss of water from the ATH charger during thermoforming, as is common in the case of other thermoplastic materials, - have a Flame Propagation Index, through the ASTM E-84 Tunnel Test, less than 75 and a Smoke Index of 350 or less, - have the same resistance to impact by a method of falling a weight, determined both from the upper side and the side of the bottom. Our invention provides the stability of the suspension of alumina trihydrate or other mineral filler, in a methyl methacrylate syrup having methyl polymethacrylate dissolved in it by keeping the following ingredients within the indicated ranges (by weight): - Content of PMMA dissolved in MMA / other monomers: 0-30% by weight, preferably 10-25%. - ATH in the total composition: 20-60% by weight, preferably, 25-40%. - Thixotropic agent (preferably fuming silica) in the monomeric / j moiety fraction of the mixture: .10-3.5% or as necessary for P1170 / 99MX obtain a viscosity between 1,000 and 10,000 centipoises (preferably between approximately 2,000 and 5,000 centipoises) after mixing and measuring by the Brookfield Viscometer Model RVTDV-II, Needle No. 2, 10RPM. - Crosslinking agent as% by weight of the total monomer content: greater than 1% and up to about 12%. Chain transfer agent as% by weight of the total content of monomers related to the amount of crosslinking agent "x": when 1 < x < 6, 0.01 < and < (1.07x + 0.3) and when 6 < x < 12, 7.0 > _ Y_ > _ (0.545x - 3.23), when n-dodecyl mercaptan is used. A convenient way to compare the effects of chain transfer agents is to compare the molecular weights obtained by polymerizing MMA in the presence of the chain transfer agent and in the absence of the crosslinking agents. MWW and MWn should be similar to those obtained with n-dodecyl mercaptan. In addition to the ingredients identified in the above, dyes and pigments may be present, polymerization initiators will be necessary and other conventional ingredients known in the art may be used. However, we do not use particulates that are visibly distinguished in the finished product. The P1170 / 99 X Most synthetic granites contain visibly distinguishable particles of various compositions and colors varying between approximately 150 and 500 microns - that is, they will pass through a sieve having 500 micron openings and will be retained in one having 150 micron openings (Although the largest particles in the technique of synthetic minerals are not rare). We have found that our goal of uniform particle distribution can be thwarted by the use of those large particles of various compositions and therefore, we restrict our particle size to smaller particles than those that are retained in a sieve with openings of 90 microns and preferably smaller than those retained in a sieve with openings of 60 microns. These particle size specifications are applied in our invention to particulates of any composition with a function of flame retardants of mineral origin such as ATH, for example, or synthetic resin or other fillers. The ingredients set forth above may be further described as follows: The PMMA that is used herein is a polymethyl methacrylate having a molecular weight range (average weight) between about 30,000 and 60,000 which has no crosslinked polymer chains to remain soluble in MMA. East P1170 / 99MX is typically made in situ by partial polymerization of the methyl methacrylate but can be prepolymerized and dissolved in the MMA. MMA is methyl methacrylate. The syrup described herein is comprised of PMMA dissolved in monomers comprising at least about 60% MMA and preferably at least about 80% MMA and of course the crosslinking agent, the chain terminator, the initiator and the thixotropic agent are also present in the amounts indicated herein as well as variable amounts of dyes and / or pigments; in addition, amounts of other optional capolis erizables monomers, mainly butyl acrylate may be present in the syrup as is known in the art. We prefer to use a syrup that contains between approximately 15% and 25% PMMA. By referring to syrup and MMA herein, it should be understood that they may include these additional materials. Alumina trihydrate is well known in the synthetic mineral manufacturing art. In the examples, we use it with a particle size range of about 9 microns on average, although the size of the particulate can vary widely. As noted above, the ATH as well as any other particles that are potentially visually distinguishable (if they are sufficiently large) P1170 / 99MX in the finished product should be able to pass through a sieve having openings of 90 microns and preferably pass through a sieve having openings of 60 microns, to ensure that they will not be visually distinguishable. In quantity, the ATH can vary between about 20% and 60% by weight (preferably between 25% and 50%) of the finished product. Our invention contemplates a solid surface material in which the effects of the particles not greater than 90 microns can be seen. Our material does not simulate granite, in that it is not coarse grain, as it is sometimes described. Rather, if the effects of the particulates in our material can be perceived somewhat, they can be described as essentially fine-grained (which we specifically define as having particles or grains smaller than 90 microns - that is, they do not have particles that more than 90 microns are visibly distinguished individually). With the term "essentially fine-grained" we try to include materials in which there are no grains or particles visibly distinguishable individually. Any number of cross-linking, di-functional or tri-functional agents can be used. Examples of suitable crosslinking agents are ethylene glycol dimethylacrylate, propylene dimethylacrylate, polyethylene glycol dimethylacrylate, dimethylacrylate P1170 / 99MX propylene, polyethylene glycol dimethyl acrylate, divinyl benzene, diallyl phthalate, 1,3-butanediol methacrylate, 1,4-butanedimethacrylate ethylene glycol or neopentyl glycol dimethacrylate as di-functional crosslinking agents and trimethylol propane trimethacrylate, triallyl cyanurate , pentaerythritol tetramethacrylate, allyl methacrylate, hydroxyethyl methacrylate or hydroxypropyl methacrylate as tri-functional crosslinkers. Ethylene glycol dimethacrylate is preferred with greater convenience. The crosslinking agents are maintained at concentrations greater than 1.0. Preferably, between 1.0 and 12.0 pph of di-functional crosslinkers based on the MMA in the syrup or as a component of the finished product, based on the crosslinked polymer. More preferably, the content is 6.0 > x > 1.0. The combination of crosslinking agent and the chain termination in the appropriate amounts guarantees the appropriate polymer network more sensitive to thermoformability. Chain terminators or chain transfer agents, such as octyl mercaptan, isododecyl mercaptan, thiurams, dithiocarbamates, dipenten dimercaptan, 2-mercapto ethanol, allyl mercapto acetates, ethylene glycol dimercaptoacetate, trimethylolethane trithioglycolate, pentaerythritol tetrathioglycolate, usually make the function of regulating the molecular weight of the MMA polymerization, P1170 / 99 X which in turn is known to affect the plastic behavior of the polymerized mixture. According to our method, chain terminators or chain transfer agents are used to regulate the length of polymer chains and thus obtain the most convenient polymer matrix for thermoformability, as will be seen from the data in Example 3. These they should be used in preferred amounts between about .01 and 7.0 pph of the total monomers present when n-dodecyl mercaptan is used. More preferably, 0.01 < 7 and < (1.07x + 0.3). Although we can use a conventional thickening agent as well as a thixotropic agent, the thixotropic agents we use here proved particularly convenient for present purposes. It seems that they reinforce the tendency of inertia of a particle to remain stationary in the suspension of the matrix. We prefer to use fumed silica. By fumed silica we identify the product formed by the hydrolysis of the silicon tetrachloride vapor in a flame of hydrogen and oxygen to produce solid particles in the range of 7-30 millimicrons. Very different types of fuming silica are available. To carry out most of our experimentation, we selected CAB-O-Sil M5, which has a surface area of 200 meters P1170 / 99MX square / gram. However, any conventional fuming silica will have a beneficial effect on our invention. The surface of fuming silica is hydrophilic since it has an abundance of hydroxyl groups, which make it capable of being bound by means of hydrogen with appropriate molecules. The moisture absorbed in silica or in the other components has a great effect on the final viscosity of the suspensions containing fuming silica and usually decreases it. The same effect occurs with other substances that may be more or less capable of forming bonds through hydrogen. If the fumed silica and / or ATH are dried to remove the absorbed moisture, the final viscosity of the suspension will be greater than when commercial products are used directly from the containers in which they are sold. The drying of the ATH above 200 ° F can cancel out its primary utility as a flame retardant by depleting its water content. In our preferred compositions, the amount of fumed silica is selected in such a way that the preferred viscosity is obtained, without taking into account the variations in the other ingredients. The preferred method to obtain a suitable viscosity is as follows: A. Mix all the ingredients (MMA, PMMA, ATH, pigments, other additives, catalysts, P1170 / 99MX chain transfer agents and crosslinking agents) of the formulation except fuming silica and measure the viscosity as indicated below. If necessary, adjust the MMA (monomer) content of the syrup to obtain a viscosity between 800 and 1,500 centipoise. B. Repeat step A including a quantity of fuming silica and measure the viscosity. C. Repeat step B to bring the viscosity to a level between 1,000 and 10,000 centipoise, preferably between 2,000 and 5,000 centipoise. As previously indicated, the stability of our syrup is considered important and this is especially so when the sheet or plate is formed in a continuous steel strip forming machine such as that described in U.S. Patent 3,371,383 to Hellsund and U.S. Patent 3,376,371 to Opel, which is incorporated herein by reference in its entirety, as these references represent our preferred method. Although the formation of the sheets or plates between two continuous steel bands that move is the preferred procedure, it is important to realize that these machines are "necessarily prone to vibration and micro-adjustments that tend to result in an almost inevitable shock from the particulates in the syrup, the concentrations of the crosslinking agents, P1170 / 99MX chain terminators, fuming silica and PMMA prepolymer are important for stabilizing ATH and / or other solids that contribute to a uniformly distributed fine grain appearance.

DETAILED DESCRIPTION OF THE INVENTION With reference to Figure IA, the recommended minimum bending radius (DuPont Corian Technical Bulletin CTDC-110, October 1987) of three inches for a half inch thick flat sheet of the prior art is illustrated as the radius of the curve in the internal curve from the point of vertical extension A to the point of horizontal extension B. Applying the simple formula C = IID, the circumference of a hypothetical circle of three inches would be 18.8496 inches and a quarter of the circle AB could measure 4.7124 inches. Applying the same formula to the external curve for a 0.5-inch-thick sheet, for example using a radius of 3.5, would give a quarter-circle of 5.4953, a 16.6% difference in internal curvature. Such distortion would tend to cause a flow of hot ingredients from the internal curve compressed to the expanded exterior and longitudinally towards points A and B from the curved part. The flow of the ingredients has a tendency to distort the decorative or visual design; therefore, the prior art has minimized the alterations P1170 / 99MX of the material using a relatively large radius for the curvature, for example, 3 inches. Figure IB illustrates the feasible curvature of a sheet of the present invention, wherein the radius of the curve is rather one-half inch than three inches from that of the section of Figure IA. In this case, the theoretical circumference of the exterior of the curved section CD is 100% greater than that of the interior of the curve. It is easily observed that by allowing that forming capacity, the present invention resolves a more severe displacement of material in a relatively smaller volume. The relatively more severe displacement of material means a greater potential for the distortion of the aesthetic design, but we avoid or neutralize that distortion and thus achieve a continuity of the design that was not feasible before under it. thermoforming effort. A test has been devised to evaluate thermoformability, which is a primary object of the present invention. The test consists of holding a 4-7 / 8"square test specimen having the desired thickness on a steel plate in which a 3-inch diameter hole has been made, then a polished stainless steel plunger that has a radius of one inch and is lowered at a rate of five inches per minute without taking into account the resistance.

P1170 / 99MX of the test at a convenient temperature. As the plunger moves, a load cell generates a signal representing the amount of resistance in pounds, which can be recorded. The moment the specimen breaks, the plunger stops and the distance that has been displaced is measured. It is recommended to average the tests of four specimens of each sample. This test will be referred to herein as TP-0085.

Example 1 A syrup was made by the partial polymerization of MMA to obtain a viscosity of 3 Poises and a PMMA content of about 20% by weight. Butyl Acrylate, Cab-O-Sil M5, Trihydrated Alumina (ATH) with stirring were added to the syrup. Its proportions are indicated below, together with the chemical substances necessary to obtain a complete polymerization and a good demolding of the cellular molding plates: P1170 / 99MX TABLE 1 % by weight Syrup 1-3 (80% MMA) 57.20 Butyl Acrylate 2.00 Cab-O-Sil M5 0.53 ATH 39.92 Wetting Agents 0.35 Per hundred parts of rubber Pigment Paste What is needed Mold Release Agents What is needed Catalysts What is needed? Chain Transfer Agent See Table 2 Plasticizer See Table 2 The mixture of ingredients was first stirred under vacuum for 15 minutes, to eliminate the dissolved gases and to avoid bubbles in the resulting sheet. It was then used to fill a cell mold unit, large enough to produce a sheet of approximately 12 x 12 x 0.5 inches. Curing was obtained by immersing the cell mold unit in a 180 ° F water bath for one hour, followed by one hour post-cure in a circulating air oven at 250 ° F. After cooling to room temperature, the cell mold unit was opened to remove the plastic sheet and the physical test described in the text was performed after conditioning at room temperature.

P1170 / 99MX Table 2 shows the combinations that were used of the chain transfer agent and the crosslinker and the results of the test. The first group of data (PL-8, PL-11, PL-12, PL-14, PL-16, PL-19, PL-24, PL-25, PL-28 set forth in Table 2) represent the compositions which were vacuum thermoformed to a much greater extent than the compositions of the known art. These were also thermally stable to provide flawless forms. The second group of data (PL-10, PL-13, PL-20, PL-23) represents the compositions that did not pass the thermal stability tests at 340 ° F. Sample PL-23 did not show visible evidence of blister test failure, but the specimens were broken during the H.D.T. and its stability was evaluated as not completely satisfactory. The third group of data (PL-12, PL-22, PL-27) represents formulations that provide sheets with a dubious thermoformability. PL-22 and PL-27 represent the demarcation between good formability above them and little formability below them. The mold forming test V referred to in Table 2 was developed to determine what type of composition could give a sheet that was an improvement over the prior art. For example, a 12-inch x 12-inch Corian blade does not stretch P1170 / 99MX to a significant degree under vacuum. (Approximately 0.2 inches). Therefore, a sheet of the present invention is an improvement over the prior art if the stretch that is observed is greater than 0.2 inches.

TABLE 2 Sample. (I). (I) Plast (2) HDT (3) TP-0085 (-) Ampoule Mold (6) in. / v (5) pounds in. Temp. F PL-8 1.44 1. .44 5.2 / 112 2.5 P PL-11 2-88 2. .88 3.6 / 110 P PL-12 4.80 4. .32 2.4 / 125 2.4 P PL-14 2.88 1. .20 2.0 / 187 P PL-16 2.16 0. .48 2.1 / 192 P PL-19 4.80 2. .40 1.88 P PL-24 6.72 5. .76 157 2.3 / 71 P PL-25 8.64 3. .84 178 1.1 / 90 PL-28 11.50 3. .00 171 0.7 / 38 PL-10 1.44 2.40 6.9 / 23 F PL-13 2.88 3.60 Ampoule F PL-20 4.80 5.28 2.7 / 55 F PL-23 7.68 6.72 P PL- 18 4. 80 0. 48 197 1.5 / 148 0.8 P PL-22 6. 72 0. 96 0.55 P PL-27 11. 50 3. 00 187 .54 / 68 P P1170 / 99MX (1) Per hundred parts of crosslinker rubber x and chain transfer agent y_ per 100 parts of monomers in the formulation of Example 1 (2) Per hundred parts of plasticizer DINP (diisononyl phthalate) used. (3) Distortion heat temperature, at 264 psi; by ASTM D-648. (4) Thermoforming test described in U.S. Patent No. 5,521,243. The samples are heated for 40 minutes in an oven at 340 ° F before the test is started. (5) V mold forming test. (6) Aristech test method; visual observation to determine if blisters are formed in a 4"x 4" sample after 40 minutes in a 340 ° F oven; P = indicates that the test passes; F indicates that the test does not pass.

P1170 / 99 X

Claims (7)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property: 1. A composition comprising: (a) a syrup comprising methyl methacrylate, the syrup is dispersed therein, x parts by weight of a crosslinking agent and, and parts by weight of a chain terminator, per hundred parts by weight of methyl methacrylate and wherein x is greater than 1.0 and when 1.0 <1. x < 6.0, 0.01 < and < (1.07 x + 0.3), and when x > 6.0 7.0 > and > (0.545 x -3.23); and (b) a plurality of solid particulates that will pass through a sieve having openings of 90 microns, the solid particulates comprise between about 20% and 60% of a mineral charge, based on the weight of the final composition.
2. 2. A composition according to claim 1, wherein 0.01 < x < 12.0.
3. 3. A composition according to claim 1, wherein 0.01 < x < 6.0
4. 4. A composition according to the claim 1, where 6.0 < x < ^ 12.0.
5. 5. A composition according to the claim P1170 / 99MX 1, where the particulates will pass through a mesh that has an opening of 60 microns. 6. A composition according to claim 1, wherein the mineral filler is alumina trihydrate. 7. A thermoformed article comprising a polymerized composition which before polymerization comprises: (a) a syrup comprising methyl methacrylate, the syrup has dispersed therein, x parts by weight of a crosslinking agent and, and parts by weight of a chain terminator, per one hundred parts by weight of methyl methacrylate and where x is greater than 1.0 and up to about 12.0 and when 1.0 <1. x < 6.0, 0.01 < and < (1.07 x + 0.3), and when x > 6.0, 7.0 > and > (0.545 x -3.23); and (b) a plurality of solid particulates that will pass through a sieve having openings of 90 microns, the solid particulates comprise between about 20% and 60% of a mineral charge, based on the weight of the final composition. 8. An article according to claim 7, wherein 0.01 < x < 12.0. 9. An article according to claim 7, wherein 0.01 < x < 6.0 10. An article according to claim 7, wherein 6.0 < x < 12.0. P1170 / 99MX 11. A thermoformable article according to claim 7, wherein the particulates will pass through the sieve having an aperture of 60 microns. 12. A thermoformable article according to claim 7, wherein the mineral filler is alumina trihydrate. 13. A thermoformable article according to claim 7, wherein the article is a thermoformable sheet. 14. A process for making a thermoformable article comprising the steps of: (a) making a composition comprising: a syrup comprising methyl methacrylate, the syrup is dispersed therein, x parts by weight of a crosslinking agent, and and parts by weight of a chain terminator, per hundred parts by weight of methyl methacrylate and where x is greater than 1.0 and when 1. Q < x < 6.0, 0.01 < and < (1.07 x + 0.3), and when x >
6. 6.0,
7. 7.0 > and > (0.545 x -3.23); and (b) making a thermoformable sheet from that composition; and (c) thermoforming that sheet in the article. P1170 / 99MX