FI58137C - I WASH FORMBAR ACRYLIC SHEETS FOR FOUNDATION - Google Patents

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Patent- och refistaratyralaan AnaBkanutiagdoehutUkriftanpublic · »* 29.08.80 (32) (33) (31) privilege — 8« gtrt prlorltat 02.06.72

England-England (GB) 25867/72 '(71) Imperial Chemical Industries Limited, Imperial Chemical House, Millbank,

London SW1, England-England (GB) (72) Brian George Price, Westerhope, Northumberland, England-England (GB) (7 ^) Oy Kolster Ab (5 ^) Thermoformable acrylic sheet and method for its production - I värme formbar akrylskiva och This invention relates to a thermoplastic sheet and, more particularly, to a thermoplastic acrylic sheet having improved shaping properties when thermoformed into shaped bodies.

Methods for forming polymerizable, ethylenically unsaturated materials, such as methyl methacrylate, into sheets are well known. Such methods include extrusion or casting polymerization using a polymer-monomer syrup. The casting process may be a method known as "mold casting" in which the syrup is cast into a mold consisting of a pair of rigid plates with a ring seal which allows shrinkage to occur during polymerization. In this process, it is common to pour a low-viscosity polymer-in-monomer syrup containing a free-radical catalyst between the sheets and cause the material to polymerize under the influence of heat and possibly a certain pressure. Alternatively, the polymerization can be carried out in a continuous manner by a method known as "moving-belt casting". According to this method, the monomer or polymer-in-monomer syrup is cast and polymerized between a pair of continuously moving strips, which strips are provided with compressible seals at their edges.

2 58137

When a thermoplastic sheet (especially an acrylic sheet) is used for molding purposes under high temperature and vacuum or pressure, it is often found that the complexity of the body to be molded is limited by the flow properties of the molten polymer. For example, when forming an "angular" body with corners, additional thinning may occur in the corners of the plate. "Angle" means a convexity or other hollow portion on the side of the interior of the shaped body where lateral stretching of the sheet is necessary, and in particular where the sheet has to be bent laterally by up to 90 ° during shaping. Thus, for "angularity", the cross-section of the mold is larger than the cross-section at the mouth of the mold.

A further problem is that the flow properties of the molten polymer limit the speed at which the moldings can be made- Although the viscosity of the molten polymer can decrease when elevated temperatures are used in thermoforming, the thermal decomposition of the polymers can cause further temperature rise · Some problems can be overcome by incorporating plasticizing a sheet made under conditions that give the polymer a low molecular weight. The use of such solutions results in a deterioration of other properties of the board, such as the mechanical properties of the board and its resistance to tearing. It has now been found that an acrylic sheet can be made which has improved thermoforming properties at widely varying temperatures but still retains the better properties of a high molecular weight sheet by producing a sheet containing a mixture of certain crosslinked and linear fractions of acrylic polymers.

The present invention provides an acrylic sheet having improved thermoforming properties, which sheet is a close mixture of two different fractions having different average molecular weights. These consist essentially of a relatively low molecular weight linear fraction and a small amount of cross-linked fraction with a naturally high molecular weight.

Although it has previously been known to include crosslinking agents in acrylic sheet polymerization processes, it has now been found that if a crosslinking agent is added to monomer or polymer-monomer syrup at concentrations with very narrow limits to be determined, the mixture is polymerized under conditions to be determined. that certain amounts of substantially linear and cross-linked fractions are obtained, a material with greatly improved thermoforming properties is obtained while maintaining the advantageous properties of the high molecular weight sheet.

There is thus provided a process for producing a thermoformable acrylic sheet, which method is characterized in that the fully polymerized sheet has a viscosity number of 1.5 to 0.1 when prepared without a crosslinking agent, and that the insoluble acrylic polymer fraction contains 0.02 to 3.0 weight-crosslinking agent based on the weight of the finished sheet · 3,581 37 "Acrylic" monomer means alkyl methacrylates in which the alkyl group contains 1-U carbon atoms, and in particular methyl methacrylate containing up to 20% by weight of other copolymerizable ethylenically unsaturated monomers. , and the "acrylic" polymer is a polymer of such an "acrylic" monomer. The Kb monomer, if used, is preferably selected from other alkyl methacrylates, alkyl acrylates, it may also be styrene, ot-methylstyrene or acrylonitrile.

The term "viscosity number" as used throughout the application means a viscosity slip as measured in chloroform containing 1 g of polymer per 1000 cm of solution. It is expressed in dl / g in this application.

Although the materials can be obtained according to the invention by a casting process in which a crosslinking agent is added to a monomer, such a process presents practical difficulties and it is much more advantageous to use a polymer-monomer-syrup.

The sheet of the present invention is most preferably prepared using the casting methods described above, and in particular using a two-step process of first preparing a polymer-monomer-syrup having a low polymer content and then fully polymerizing in the cell to give the product in sheet form.

In a preferred process, it has been found that a sheet having the desired properties is prepared when the polymerizable acrylic-polymer-acrylic-monomer-syrup used as a starting material contains about 5 to about 30% of an acrylic polymer having a viscosity number of 0.1 + -8.0, preferably 0, 1 + -3.5, preferably 0.8-2.0, and the syrup is polymerized in the presence of 0.02-3.0% by weight of a crosslinking agent, under conditions such that the reduced viscosity of the final polymer of the sheet prepared without the crosslinking agent would be 1.5-1 + .0, preferably 2.0-3.5 · The value of the viscosity number of the polymer prepared without the crosslinking agent may, of course, be lower or higher than in the polymer syrup and is the average which is determined from the molecular weight samples that make up the final polymer.

The most suitable concentrations of crosslinking agent to be used in the process of the invention are selected by determining the stretching properties of a fully polymerized sheet containing various amounts of crosslinking agent. These tensile properties are suitably determined from tensile measurements of a test specimen, the dimensions of which are defined on page 293 in the book "Encyclopedia of Polymer Science", Vol. 7, Wiley and Son, 1967, in an article entitled "Fracture", subtitled "Short Term Phenomena", the sample is cut from an acrylic sheet about 3 mm thick. The tensile properties of such a specimen can be determined by placing the specimen vertically in a Davenport elongation tester placed in an oven that can be operated at a temperature of 165 ° C + 1 ° C. The sample is allowed to stand for 15 min. time to reach equilibrium *> 58137, after which it is stretched at a speed of 1.25 cm / min.

The load on the specimen during stretching is measured with a load cell based on electrical resistance and strain gauge strips. The signal from the load cell is fed to a plotter, which gives a continuous curve for the load as a function of time. From this information, a curve can be easily constructed showing the elongation at break as a function of load.

In an improved method for determining the tensile properties of these polymers, an apparatus: "Instron Universal Testing Instrument" can be used in connection with a cross-section compensator, whereby it is possible to determine a stress-fracture as a function of curve. This can be easily converted to a fractional elongation curve. (In both experiments, the elongation is set on the abscissa axis and the load or stress on the ordinate axis). The experiment differs from the previously presented experiment (Davenport) only in that the sample is stretched slightly more slowly (1.0 cm / min.) And that the obtained curve is compensated for any changes in the cross-sectional area of the sample during the experiment. Typical test results obtained with an Instron instrument using polymethyl methacrylate plates with varying viscosity numbers but no crosslinking agent are shown in Figure 1. It is noted that the stress required to stretch a sample having a viscosity number of 5 , 2, increases steadily to its maximum, which is reached at 100% elongation, before it decreases and the specimen finally breaks with a fracture stress servo, which is reached at an elongation value of about 200%. For a material with a low molecular weight (viscosity number 1.2), the required maximum stress is achieved by 100% elongation, with the required stress then maturing uniformly to about 1 + 00% elongation. Such behavior is due to a phenomenon known as "narrowing" in which the cross-section decreases rapidly in a small portion of the sample without fracture. In practice, this means that the sheet should not be stretched more than 100% during thermoforming if it is desired to avoid non-uniform thinning of the thermoformed sheet. The sheet produced by the method according to the invention, on the other hand, has a much higher extensibility and requires a small load to achieve a given elongation compared to a conventional sheet.

Significant improvements in thermoforming are achieved over conventional sheets when the conditions used in the process are such that the viscosity number of the sheet when prepared without a crosslinking agent, the viscosity of which is hereinafter referred to as the polymer body viscosity number, does not exceed i *, 0. Although significant improvements over a conventional sheet are obtained with a viscosity number of the polymer body of less than 1.5, it is desirable to achieve a value of at least 1.5 so that the properties of the sheet do not differ significantly from those of a conventionally made sheet. For example, the present invention provides a sheet which has improved elongation properties but still retains the excellent weather resistance and crack resistance of a conventionally made cast acrylic sheet. In addition, a property such as impact strength, for example, does not change significantly with ordinary cast acrylic sheets. Significant improvements over a conventional plate are observed in practice when the plate has an elongation at break of at least βΟΟ% and the stress required for 600% elongation is greater than the load or the stress at 100% elongation, although significant advantages over a conventional plate can be obtained for a plate with an elongation at break of less than 600%. . It is preferred that the plate have an elongation of at least 600% and that the slope of the elongation at break curve be positive at an elongation value of $ 600, i.e. at 600% elongation the required load or stress is still increasing.

It is to be understood that the terms "load", "stress" and "elongation at break" as used in this application are used exclusively to refer to standardized stretching tests using either a "Davenport" tensile tester or an "Instron" tensile tester.

"In order to produce an acrylic sheet according to the present invention having certain stretching properties, the concentrations of crosslinking agent should be within very narrow limits. These limits are primarily determined by the crosslinking agent effectiveness already in the polymerization step, the polymerization conditions used in the presence of crosslinking agent. elongation with a strong crosslinking agent is lower than with a less effective crosslinking agent, and in the case of a particular crosslinking agent, slightly more of this agent is required when the reaction ratios used are such that a low viscosity value is obtained unless a crosslinking agent is used. than when the reaction conditions are such that a high viscosity value is obtained unless a crosslinking agent is used.

Limits are determined experimentally for each crosslinking agent. Using a strong crosslinking agent such as glycol dimethacrylate, hereinafter referred to as GDM, it has been found that an acrylic sheet with suitable extensibility is prepared using at least 0.02% by weight of GDM syrup. Preferably, the concentration of GIM or other crosslinking agent should not be so high as to cause too high a degree of crosslinking, resulting in a plate elongation at break of less than 600% (determined as follows). The upper limit of the concentration of crosslinking agent has been found to be 0.2% t when using GIM or another strong crosslinking agent, this when a value of elongation at break of at least 600% is desired. The preferred concentration range is 0.0 ^ -0.15% GDM, most preferred 0.0 ^ -0.08%.

The concentration limits required to ensure that the board has the desired properties, e.g., a value of elongation at break of at least 600%, can be readily determined experimentally for which money-crosslinking agent. When a less effective crosslinking agent, such as triallyl cyanurate, is used, it has been found that a plate with at least 600% elongation at break is obtained when about 0.1-1.0% triallyl cyanurate is used. Correspondingly, a useful concentration range for di-allyl phthalate is about 0.3-1.5%. · Other suitable crosslinking agents include allyl methacrylate, allyl acrylate, triallyl phosphate, diallyl maleate dimethyl acrylate, dimethyl acrylate, vinyl methacrylate, divinyl ethylene, divinyl benzene, divinyl benzene.

Depending on the crosslinking agent used, the concentration providing improved lime shaping properties may be 0.02-3.0% by weight of the finished sheet.

When the polymerization of a monomer or polymer-in-monomer syrup is carried out in the presence of a crosslinking agent, a small portion of the polymer formed in the presence of the crosslinking agent is linear in nature and not significantly crosslinked. the lowest when the concentration of the cross-linking agent used is the highest and when the cross-linking agent used is strong. Thus, if 0.06% of a crosslinking agent, such as glycol dimethacrylate, is added to a syrup containing 15% linear polymer (based on the weight of the syrup), the final polymerized product may contain about 25-60%, depending on the polymerization conditions used, a linear polymer that can be extracted with a solvent, e.g. chloroform, and which can be considered substantially linear. When 0.2% glycol dimethacrylate is used, but under otherwise similar conditions, the fully polymerized sheet has less solubility than 0.06% crosslinking agent, but still not the polymer content of the original syrup. When a less effective crosslinking agent such as triallyl cyanurate is used at low concentrations, e.g. 0.1%, even higher amounts of extractable polymer can be formed. In order to obtain products with significant advantages in terms of thermoforming properties, the concentration and quality of the crosslinking agent and the reaction conditions used must be such that at least 5% by weight of the fully polymerized sheet is in an insoluble fraction, as determined by the standard test below. determining the amount of soluble polymer in the sheet.

It is not possible to determine the properties of a sheet prepared by the process of this invention by the solution viscosities of molanp's essential parts when a crosslinking agent is used, because although the soluble and probably substantially linear fraction can be extracted with a suitable solvent and determined by its viscosity number, not crosslinked found a treatment method by which its molecular weight could be determined.

7,581 37

The final sheet can be characterized by fiber sulfur by measuring its stretching behavior under the special conditions described above. Using the experimental conditions shown, it has been found that the fracture-tensile value of a sheet made by the method according to the invention is e.g. at least 600%, and the tension or load required at 600% elongation is higher or not substantially lower than the load at 100% elongation. Preferably, the plate has an elongation at break value of at least 600% and the direction of the elongation at break curve is positive at 600% elongation.

Thus, a thermoformable acrylic sheet is prepared which is characterized in that it is a thorough mixture containing about 10-95% (by weight of the fully polymerized sheet), preferably 15-50% of a soluble acrylic polymer fraction having a viscosity number of not more than 4.0 , preferably 0.8-2.0 and about 90-5%, preferably 85-50% of an insoluble slightly crosslinked polymer fraction, wherein the fully polymerized acrylic sheet has an elongation at break of at least 600% as measured at standard diol ratios. Preferably, the 600% elongation stress or load is greater or not significantly less than the 100% elongation stress or load, because a sheet with these properties has a much lower tendency to shrink or thin during stretching.

The viscosity number of the soluble acrylic polymer fraction can be determined as described above by extraction as a suitable solvent and then by determining the viscosity number measured at 25 ° C in a chloroform solution containing 3 l of polymer per 1000 cm of solution and expressed in dl / g. In practice, it has been found that it is not possible to extract all the soluble polymeric material in the plate quantitatively. For example, when preparing a linear polymer having a high viscosity number in the first syrup step, it has not been found possible to isolate the soluble fraction containing this high viscosity linear polymer by repeated solvent extraction. The term "soluble acrylic polymer if fraction" is therefore defined as a polymer not extracted under the standard experimental conditions defined below. Using these particular conditions, it has been found that in order for the final sheet to have an elongation at break of at least 600%, the viscosity number of the "soluble acrylic polymer fraction" should not exceed 4.0, preferably between 0.8 and 2.0.

The methods used to make the board are well known in the art to those skilled in the art. In the two-step process described, a polymerizable syrup containing a preformed acrylic polymer can be prepared either by dissolving a suitable polymer prepared by any conventional method, such as batch, granular or emulsion polymerization, in an acrylic polymer to give an acrylic polymer, or a partial polymer. -syrup. When a syrup containing less than 5% by weight of polymer is used in casting processes, difficulties may occur due to the low viscosity syrup leaking past the ring seal or other sealing devices. On the other hand, if the viscosity of the syrup is too high, difficulties may occur due to the difficulty of filling the pouring vessel with such syrup. It is usually impractical to use a syrup with a polymer content greater than about 30% in casting processes. A sheet with satisfactory stretching properties can be prepared by a method in which a crosslinking agent is added after 30% of the polymer has been formed, but as discussed above, the manufacture of such a sheet by the casting method is limited by practical limitations.

When using a two-step process, the viscosity ti in the polymerizable syrup of the polymer should be 0.1 U-8.0, preferably 0.8-2.0, regardless of the method of preparation of the syrup, before the crosslinking agent is added.

The molecular weight of the polymer in such a pre-syrup is adjusted according to the type and amount of catalyst used, as well as the chain transfer agents used and the polymerization temperature. It is preferred to use a free radical catalyst with a half-life of less than six minutes as measured at 85 ° C in the syrup step and to use it at concentrations that ensure that the polymer has a viscosity number of 0.8-2.0 at a suitable polymerization temperature. Such catalysts include peroxide carbonates such as diisopropyl, di-n-iso-butyl, diisobutyl, dicyclohexyl or bis- (U-t-butylcyclohexyl) peroxide carbonate and t-butyl perpivalate. These can be used in concentrations of 0.008 to 2% by weight, based on the weight of the monomer used. Most preferred are diisopropyl peroxydicarbonate and bis- (t-t-butylcyclohexyl) peroxydicarbonate. Although the preferred catalysts have a half-life of less than six minutes at 85 ° C, conventional catalysts such as azodiisobutyronitrile can also be used. It is best to use a concentration such that the catalyst is substantially depleted when a polymer of the required viscosity number is formed. This concentration depends on the catalyst used and can be conveniently determined by conventional routine experiments.

The syrup used in the casting process can be prepared, for example, by heating a mixture of monomer and catalyst at a western temperature of 70-90 ° C, which temperature is maintained until the polymer contained in the syrup has a viscosity number in the required range. In this case, the syrup can be cooled to stop the reaction until the polymerization is completed.

According to the process of the invention, which may be the second step following the in situ preparation of the syrup, the crosslinked polymer fraction is prepared by polymerizing the syrup in the presence of a crosslinking agent.

The molecular weight of the material prepared in the second step can be adjusted according to the type and concentration of crosslinking agent used and reaction conditions such as catalyst concentration, polymerization temperature and the use of materials known as chain transfer agents which limit the chain length of the polymer prepared. by.

In order to obtain the acrylic sheet of the present invention, the polymerization conditions used in the second step of the polymerization must be such that the fully polymerized polymer of the sheet has a viscosity number of 1.5 to * +, 0 prepared without crosslinking agent * The catalyst used can be any of the conventional free radical catalysts. , e.g. lauryl peroxide, benzoyl peroxide, o (.04'-azodiisobutyronitrile or one of the aforementioned peroxide carbonates. The concentration to be used depends on the temperature at which the second polymerization step is carried out. The second polymerization step can be suitably carried out at 60-120 ° C and catalyst concentrations of 0.005-0.3% are usually used.

Any conventional chain transfer agent can be used to limit the chain length of the polymer being prepared. Examples of suitable compounds are sulfur-containing compounds, such as alkyl or aryl mercaptans, in particular octyl, lauryl and n-, s- and t-dodecyl mercaptans, esters of mercaptoacetic acid, such as glycol dimer captoacetate and isooctyl thioglycollate. On the other hand, the chain transfer agent may be a hydrocarbon such as benzene, toluene, triphenylmethane, limonene, terpinolene, O (-, fo- or γ-terpinene or 1- * + cyclohexadiene. Further chlorinated compounds such as chloroform, carbon tetrachloride, carbon tetrachloride, The concentration of chain transfer agent used depends on the efficiency of the chain transfer agent and is generally used in concentrations of 0.002-0.2% based on the total weight of monomer used. * The sheets of this invention can be used for various purposes requiring excellent physical properties of acrylic sheets. with good thermal design properties Areas of use include internally illuminated arrangements or shields, sanitary - * t .......

tare products, decorative interior or exterior door-mounted architectural arrangements and any glazed arrangements where curved surfaces are required in a window or ceiling dome.

The production of the sheet according to the present invention has advantages not only in obtaining more or less shaped articles with better accuracy than previously possible with a high molecular weight acrylic sheet, but also in obtaining considerable savings in manufacturing costs due to reduced manufacturing time made possible by improvements in design properties. at widely varying design temperatures.

The invention is illustrated by the following examples in which parts and percentages are expressed by weight and by weight.

Example 1

A syrup was prepared by adding 0.003 parts of azodiisobutyronitrile and 0.1 part of lauryl mercaptan to 100 parts of methyl methacrylate and heating.

In a patient at 90 ° C for two hours. To this syrup was added an additional 0.003 part of azodiisobutyronitrile and the temperature of the mixture was maintained at 90 ° C for another two hours. After cooling to 20 ° C, the polymer content was found to be 11.0% and the viscosity number of the polymer was 1.72-

To equal portions of the syrup were added 0.012 wt.% Azodiisobutyronitrile, 0.1% lauryl mercaptan and GDM in various concentrations ranging from 0.02 to 0.12 #, all percentages based on the weight of the syrup. These syrups were then poured into glass cells and polymerized by heating at 98 ° C for 100 min, followed by heating at 5 ° C for 1 min to give sheets with a thickness of about 3 mm. A comparative experiment performed under the same conditions, but without crosslinking agent, gave a plate with a viscosity number of 1.97. Samples of cross-linked plates were tested by the method described. The elongation at break curves were obtained by the elongation test described above using a Davenport elongation tester and are shown in Figure 2. Curves B, C and D from plates made using 0.0¾%, 0.06% and 0.10% GDM show elongation at break values above 0000 %, and have a positive direction when the value of elongation at break is 600%. Curve A obtained from a plate made using 0.02% shows an elongation of U00% and the plate does not have the required thermoforming properties. It can be concluded that materials with the desired thermoforming properties and containing more than 0.1% GDM can be prepared using, in a second step, reaction conditions which, without the crosslinking agent, would give a product having a viscosity number of less than 1.97.

Example 2 (i) A syrup having a polymer content of 8% was prepared by adding 0.002 parts of azodiisobutyronitrile to 100 parts of methyl methacrylate and heating to 80 ° C. After the polymer content reached 8 #, the syrup was cooled to 20 ° C. The viscosity number of the polymer was 2.99 ·

To the syrup were added 0.2% bis (U-t-butylcyclohexyl) peroxydicarbonate, 0.003% azodiisobutyronitrile and 0.08% GDM. The syrup was polymerized between glass plates for 100 minutes at 90 ° C and then for 30 minutes at 115 ° C.

(ii) The procedure was repeated using as starting material a syrup prepared by adding 0.01¾% bis (i + t-butylcyclohexyl) peroxydicarbonate to 100 parts of methyl methacrylate and heating at 80 ° C until the polymer content reached 16%.

The plate prepared in these two experiments was tested according to the experiment used in Example 1. A plate having an elongation at break of 830% and a positive direction of the curve at an elongation value of 600% were obtained for the plate prepared according to Experiment 1. The plate prepared according to Experiment (ii) had a elongation at break of 700% and the direction of the curve was positive at an elongation value of 600%.

11 58137

Example 3 100 parts of methyl methacrylate and 0.01 part of diisopropyl peroxydicarbonate were mixed in a stirred vessel and heated to 90 ° C to start the pedal difference. When the polymer content of the mixture reached 17% t the contents of the vessel were cooled to 25 ° C, the viscosity number of the polymer in the syrup was 0.9 · To this syrup were added 0.035 parts of diisopropyl peroxydicarbonate and 0.06 parts of GDM and the syrup was polymerized using the same method as in Example 1. A comparative experiment performed under the conditions described, but without the crosslinking agent, gave a viscosity number of 1.7. A sample of a fully polymerized crosslinked sheet was tested by the stretching method of Example 1 and was found to have an elongation at break of more than 600% and a positive elongation at break of 600%.

- Example U

A series of experiments were performed to determine the required triallyl cyanurate to give the product the desired shaping properties. A syrup batch was prepared by heating with stirring 100 parts of methyl methacrylate and 0.01 part of bis (U-t-butylcyclohexyl) peroxydicarbonate at 80 ° C. The temperature of the mixture was maintained at 80 ° C until the solids content of the syrup reached 15% and then cooled to about 25 ° C. The viscosity number of the polymer in the syrup was 1.30. The following additives were added to the samples taken from this syrup: "Perkadox" 16 0,2%

Triallyl cyanurate ranges from 0-0.75%

Each syrup sample was poured into a polymerization cell and polymerized using a period of 100 minutes at 90 ° C, followed by a period of 15 minutes at 115 ° C. After cooling, translucent plates with a thickness of about 3 mm were removed from the mold. Under the same conditions, but without the crosslinking agent, a plate with a viscosity number of 1.98 was obtained. Specimens were cut from plates with crosslinks and tested according to the methods described previously.

The elongation results obtained using the test method of Example 1 are detailed in the following table.

Triallyl cyanurate Elongation at break Curve .direction 600 Jo ·. Concentration (Jo) (Jo) with elongation 0.2 580 0.3 870 positive 0.5 6k0 positive 0.75 390 12 5 81 37

Example 5

The example was repeated! a method for determining the concentration range of triallyl phosphate required to obtain a sheet of the invention using Example! polynerization conditions * The following table shows the elongation values obtained according to the experiment of Example 1.

Triallyl phthalate Elongation at break Direction of curve 600% · .η concentration (%) (%) with elongation 0.1 280 0.3 I58O positive 0.5 1000 positive 0.75 570 positive

Example 6 Using the example! the polymerization conditions shown were allyl methacrylate at 0.5 and 0.75%. Fully polymerized sheets were tested using the stretching test of Example 1. A sheet with an elongation at break of less than $ 600 was obtained using 0.5% allyl methacrylate. Using 0.75% allyl methacrylate, a plate with an elongation at break of 1250% was obtained.

Example 7 Using the polymerization conditions of Example k, the effect of diallyl phthalate in the concentration range of 0.3-1.0% was tested. Fracture elongation curves were obtained from completely polymer o it lux plates according to the method used in Example 1.

The values obtained are shown in the following table.

Concentration of diallyl phthalate Elongation at break Direction of curve at 600% elongation 0.3 215 0.6 720 negative 0.75 1035 negative 1.0 990 positive

Example 8

A syrup was prepared by adding 0.01 part of diisopropyl peroxydicarbonate and 0.1 part of lauryl mercaptan to 100 parts of methyl methacrylate and heating at 80 ° C until the polymer content reached 10.5%. The mixture was then cooled to 25 ° C.

To this syrup was added 0.2% Perkadox 16 and 0.06% GDM. To simulate the conditions used in the continuous strip casting process, the syrup was poured into a stainless steel cell and polynerized for 100 minutes at 85 ° C. The reaction temperature was then raised to 115 ° C and maintained at this temperature for 15 minutes. A comparative test performed without crosslinking agent, but under otherwise similar conditions, gave a plate having a viscosity number of 1.69. The tensile properties of a plate prepared in the presence of crosslinking agent were evaluated using the method described in the Instron Universal Testing Intrument. The elongation at break value of 6k0% was achieved and the direction of the elongation at break curve was positive at an elongation value of 600%.

Example 9

0.2 parts of “Perkadox” 16 and 0.06 parts of GDM were added to 100 parts of methyl methacrylate monomer. · The mixture was poured into a stainless steel cell and treated for 100 minutes at 90 ° C, followed by 30 minutes of treatment at 115 ° C. Comparative test without GDM gave a plate with a viscosity number of 2.1.17.

Example 10

A syrup was prepared by adding 0.01 part of diisopropyl peroxydicarbonate and 0.1 part of lauryl mercaptan to 100 parts of methyl methacrylate and heating at 55 ° C until the polymer content reached 16%. The mixture was cooled to below 25 ° C and had a viscosity number of 1.03.

To this syrup was added 0.08% GDM, 0.1% lauryl mercaptan and 0.05% azodiisobutyronitrile. The mixture was then poured into glass cells and polymerized for 5 hours at 68 ° C. The reaction temperature was then raised to 110 ° C and maintained at this temperature for 15 minutes. A comparative experiment performed under the same conditions, but without the crosslinking agent, gave a plate with a viscosity number of 1.8. A sample of a crosslinked plate was tested by the stretching method described in Example 1 and found to have an elongation at break of 800%. The direction of the elongation at break curve was positive at an elongation value of 600%.

Example 11

A syrup having a polymer content of 8% was prepared by adding 0.002 parts of azodiisobutyronitrile to 100 parts of methyl methacrylate at 80 ° C.

When the polymer content reached 8%, the syrup was cooled to about 25 ° C. The viscosity number of this polymer was 3.0.

"To this syrup were added 0.065% 2,2'-azobis (2, k-dimethylvaleronitrile) and 0.02% GDM. The mixture was poured into glass cells and treated for 100 minutes at 90 ° C, followed by 15 minutes of treatment at 115 ° C. without GDM gave a plate with a viscosity number of 3.7 · A plate with crosslinks had an elongation at break of 800% as measured by the experiment used in Example 8 and a curved direction with a positive elongation value of 600%.

The amount of soluble polymer in the fully polymerized sheet containing crosslinks was then determined by the following standard experiment:

About 2 g of a plate containing crosslinks, about 3 mm thick, was accurately weighed and placed in 150 ml of chloroform. This mixture was left to shake continuously for 2k on a mechanical shaker. The mixture was filtered. 1 Through Whatman filter paper as much as the chloroform solution easily separated from the swollen plate. This volume was measured (A ml). Evaporation to dryness at 100 ° C gave the weight of polymer in solution (x g).

The total amount of soluble polymer in the plate sample was obtained using the formula y = x 150, where y is the weight of the soluble fraction in the plate.

Using this experiment, it was found that the fully polymerized crosslinked plate contained 18% soluble material. The viscosity number of this material was 1.0.

Example 12

The polymerizations were performed as described in Example 11, using 0.1% and 0.2% triallyl cyanurate instead of GDM, respectively. The fully polymerized sheet containing 0.1% triallyl cyanurate had an elongation at break of 800% as measured by the experiment used in Example 8. The stress required at 600% elongation was about 2 5/5 less than the stress required at 100% elongation. Analysis of the soluble material performed according to the experiment described in Example 11 showed that 93% of the plate dissolved under the specified conditions.

The fully polymerized sheet prepared using 0.2% triallyl cyanurate had a tensile elongation value of 1000% and a tension of 600% elongation the same as required for 100% elongation. The final plate was found to contain 61+% soluble material according to the standard extraction method. The viscosity number of this soluble fraction was 2.0.

Claims (10)

15 581 37 Pat ent ive allowances: A thermoformable acrylic sheet comprising a mixture of 10 to 95% by weight of a soluble acrylic polymer fraction having a viscosity number of up to i +, 0, and 5 to 90% by weight of an insoluble slightly crosslinked polymer fraction, characterized in that the fully polymerized sheet has a viscosity number of 1,5-i +, 0 when prepared without a crosslinking agent, and that the insoluble acrylic polymer fraction contains 0.02 to 3.0% by weight of a crosslinking agent based on the weight of the finished sheet. Thermoformable acrylic sheet according to Claim 1, characterized in that the viscosities of the sheet without crosslinking agent have a viscosity number of 2.0 to 3.5. Thermoformable acrylic sheet according to Claim 1 or 2, characterized in that the sheet has an elongation at break of at least 600 #. Thermoforming sheet 1 according to one of Claims 1 to 3, characterized in that the tension required to stretch the sheet to 600 # elongation is not significantly less than the tension required for 100 # elongation. Thermoformable acrylic sheet according to one of Claims 1 to U, characterized in that the direction of the elongation at break is positive when the elongation is 600 °. A process for producing a thermoplastic acrylic sheet with improved stretching properties according to claim 1 by polymerizing methyl methacrylate in a mold or between moving belts, optionally containing up to 20% by weight of other copolymerizable ethylenically unsaturated monomers, characterized in that a preformed acrylic polymer having a viscosity number of 0.1 + -8.0 and 0.02-3.0 weight percent crosslinking agent based on the weight of the finished sheet and the reaction conditions under which the non-crosslinking agent would be obtained a product having a viscosity number of 1.5- ^ 1 +, 0 dl / g measured at 25 ° C in a chloroform solution containing 1 g of polymer 3 in 1000 cm of solution. Process according to Claim 6, characterized in that the viscosity number of the preformed acrylic polymer is 0.8 to 2.0. Process according to Claim 6, characterized in that the reaction conditions are chosen so as to obtain a product having a viscosity number of 2.0 to 3.5 in the absence of a crosslinking agent. Process according to Claim 6, characterized in that the polymerization is carried out in the presence of 0.02 to 0.2% of a strong crosslinking agent, such as glycol dimethacrylate. Process according to Claim 6, characterized in that the polymerization is carried out using 0.1 to 1.0 wt.% Of triallyl cyanurate. 16 5 81 3 7 Batent: