KR100226186B1 - Process for making molded polymeric product with multipass expansion of polymer bead with low blowing agent content - Google Patents

Abstract

2 to 4.4 weight percent blowing agent is used to produce low density (12.82 (0.8) to 17.62 kg / m ³ (1.1 lb / ft ³ )) of polymeric foam. This manufacturing process uses polymers with special polydispersity, average molecular weight and Mz: Mn characteristics and 2 to 5 foaming steps, which have greater foamability than conventional polymers. This manufacturing process requires about half of the amount of blowing agent used in the general process for producing polystyrene foam. This manufacturing process can be used with or without the forming step.

Description

[Name of invention]

Process for producing a molded polymeric article using a small amount of blowing agent and multi-stage foaming the polymer beads

Detailed description of the invention

The present invention relates to a process for producing a polymeric foam article. This manufacturing method relates to the production of low density foam articles by reducing the amount of blowing agent. This is achieved by using together (1) a small amount of blowing agent, (2) a plurality of preforming foaming steps and (3) a polymer with a high degree of foamability and a specific molecular weight distribution. In conclusion, the method not only reduces costs by using fewer blowing agents, but more importantly reduces the amount of environmentally harmful volatile organic compounds (VOCS) released to the atmosphere. The polymer is preferably polystyrene. When producing shaped polystyrene products, it is necessary to prepare intimate mixtures of polystyrene polymers and blowing agents. By conventional manipulations, the intimate mixtures are generally solid beads (relatively dense beads) of relatively small size (about 0.2 to 4 millimeters in diameter). The beads are then foamed (through the process of heating the mixture) to produce a foamed polystyrene product. Generally, this foaming process is carried out by heating the beads above their softening point and above the boiling point of the blowing agent (usually pentane) and the blowing agent will evaporate (the blowing agent will have a boiling point lower than the softening point of the mixture of polymer and blowing agent). Must have). As the blowing agent evaporates, the beads foam and form individual foam particles. In general, the foaming process is carried out in the first foaming step, and then the foamed fine particles (hereinafter referred to as prepuff ') are further foamed by aging and shaping and reheating, and because of the limited volume, a single Fuse to form a foam. Under optimum conditions, the bond formed between the individual prepuff particles is stronger than the bond formed by the individual prepuff particles themselves. That is, if the finished moldings are subjected to enough pressure to break them, the moldings are broken, with the fracture pattern occurring throughout the individual prepuff particles rather than at the junctions and gaps of the prepuff particles.

The basis for foaming operations is that the polymer contains a blowing agent. In conventional conventional manufacturing methods, the beads are heated using steam, which vaporizes the blowing agent to form bubbles in the polymer. Bubbles expand as the internal pressure increases. Since most bubbles are trapped, a foam is formed. Since the majority of the interior space of the foam is occupied by bubbles, the resulting foam is less dense than the non-foamable polymer / foaming agent mixture. The blowing agent also diffuses over time.

Most foam polystyrenes currently produced have a density of 0.8 lb / ft ³ to 1.1 lb / ft ³ . Generally, materials in this density range are used for insulation and / or protective packages of buildings. In order to obtain said density value, the manufacturing method of low-density foamable polygolistyrene which mix | blends about 6-8 weight% pentane with a polystyrene polymer has been performed. Beads are formed through suspension polymerization during or after pentane is introduced into the beads. These beads are then heated in a single preform foaming step, where the beads are foamed to a volume with a foaming rate of about 40 (ie, a density of about 1.0 lb / ft ³ ). The pre-foamed prepuff is now further foamed and molded in a molding state where it is equilibrated by cooling the pre-foamed bead (prepuff) and diffusing air into the bead and then reheating. The fusion causes the prepuff particles to bind to each other.

U. S. Patent No. 2,884, 386 describes a method for providing a foamed structure of thermoplastic organic materials. This method relates to a process for preparing an intimate mixture of thermoplastic resin and blowing agent and to foaming the mixture to produce a thermoplastic foam. In the detailed description of the disclosed method, reference is made herein to the fact that, when the foaming operation is repeatedly performed, the prepuff fine particles are further foamed. However, the patent 2,884,386 does not describe any explanation as to how much preforming foaming step should be used.

No. 2,884,386 makes no mention of the amount of blowing agent used in the production process. However, the patent document claims that the preferred first blowing agent is dichlorodifluoromethane, and in the examples, only halogenated methane is used as blowing agent. In Example 1 of this patent document, 2 wt% of dichlorodifluoromethane was used with 8 foaming steps to obtain the density of the final product, which was not described. In Example 2 of this patent document, 8.11% by weight of dichlorodifluoromethane was used with nine foaming steps to obtain a 150-fold volume increase (final density of the final product was not disclosed). In Example 4, 20% by volume of dichlorodifluoromethane was used in three foaming steps to ensure that the final product had a density of 0.938 lb / ft ³ . Compared with the production process according to the invention, these embodiments (including the remaining examples of US Pat. No. 2,884,386) used a high concentration of blowing agent (and / or many foaming steps), and the production process according to the invention Neither disclosed nor taught.

In addition, the above patent document discloses that as a surprising result of the present invention, when using 2 to 4.4% by weight of blowing agent, a relatively low density of 0.8 to 1.1 lb / ft ³ can be produced through 2 to 5 foaming steps. It is not starting. The patent document discloses the general concept of using a plurality of foaming steps to obtain a volume increase larger than the theoretical increase which can be obtained by using only blowing agents. According to the patent document, this increase in volume is achieved by cooling the second, more permeable second blowing agent (e.g., air) and then diffusing into the foam to further foam the second blowing agent in a further heating / foaming step. do. Although the above-mentioned mechanism is used to increase the degree of foaming in the production method of the present invention, the method of the present invention uses not only the above mechanism but also a low concentration (2 to 4.4 wt%) of blowing agent, and together with 2 to 5 times Foaming step and certain types of polymers ((1) polydispersities of about 1 to less than 2.5, (2) weight average molecular weights of 180,000 to about 300,000, (3) Mn: Mn of about 2 to about 4.5, and (4) Polymer in that it is branched from 0 to 5% by weight. It should be noted that the patent document does not disclose a polymer having the above characteristics.

In addition, the method according to the invention separates a special area which is advanced compared to the contents described in US Pat. No. 2,884,386. The process according to the invention relates to the use of thermoplastic polymer beads containing from about 2 to about 4.4% by weight hydrocarbon blowing agent. Surprisingly, the beads were subjected to bead with a small amount of blowing agent during only 2 to 5 foaming stages (or during 2 to 4 pre-foaming stages prior to forming) and the final density was about 0.8 to 1.1 lb / ft. It was found that it could be foamed to ³ . U. S. Patent No. 2,884, 386 does not describe a method for producing a final product having this density using such a small amount of blowing agent.

Several important advantages have been found in the use of small amounts of blowing agents, among which are the following (1) to (3).

(1) the cost is reduced by reducing the amount of blowing agent consumed, and (2) small amounts of blowing agent (typically volatile organic compounds, abbreviated as VOCs) are released into the environment during the manufacturing process and consumer use. Environmental pollution is reduced, (3) (a) less shrinkage in the molding step, (b) faster cooling time in the molding step, and (c) aging time between pre-expanding steps And a shorter aging time between the last prefoaming step and the forming step, and (d) an advantage in the processing process that can be easily molded with acceptable fusing and dimensional stability to molding during low concentrations of blowing agent. have.

US Pat. No. 4,839,396 describes a method for preparing expandable alkenyl aromatic polymer particulates. In the process described, the microparticles can use a smaller amount of blowing agent to obtain the same bulk density as that obtained by the microparticles containing the excess blowing agent. This is achieved by using a density modifier of 0.005 to 0.5% by weight. Patent 4,839,396 describes density modifiers as compounds which provide thermal stability to alkenyl aromatic polymers under extrusion and foaming conditions, and also as liquid plasticizers under foaming conditions. These density modifiers include octadecyl 3,5-di-t-butyl-4-hydroxyhydrocinnamate and ethylene bis (oxyethylene) bis (3-t-butyl-4-hydroxy-5-methylhydrocinnamate ).

US Pat. No. 4,839,396 generally describes the use of volatile fluid foaming (ie blowing agents) in an amount corresponding to about 5 to about 15% of the total composition weight. In the examples of patent 4,839,396, 8.8 to 10.3% by weight of blowing agent was used. These examples achieve a final density value as in the case of using larger amounts of foaming agent (10.0 to 10.3% by weight), while the amount of blowing agent is from 10.0 to 10.3% by weight to about 8.8% by weight (the amount of foaming agent is about 12 to 15%). Is reduced).

In addition, the process of the present invention aims to reduce the amount of blowing agent used in the preparation of foamable polymers. However, compared to US Pat. No. 4,839,396, the amount of blowing agent used in the process of the present invention is reduced by at least about two times (e.g., most preferably, from about 6% to about 3.5% by weight, so the reduction rate Approximately 40%). The method of the present invention greatly reduces the amount of blowing agent through a method different from that of US Pat. No. 4,839,396. The process of the invention initially uses a low concentration of blowing agent (2 to 4.4% by weight) while using a plurality of preforming steps. Although US Pat. No. 4,839,396 describes a method of using a plurality of preforming steps before the forming step, the patent document does not show any relationship between the use of small amounts of blowing agent and the use of a plurality of preforming steps. It does not disclose, does not describe the amount of blowing agent used, and only very broadly. In addition, the patent document proposes to use a relatively large amount of foaming agent (in the embodiment limited to 8.8 to 10.3% by weight, but optically 5 to 15%).

U.S. Pat. Nos. 4,520,135 and 4,525,484 (partial application of the above patents 4,520,135) disclose polystyrene particulates containing a blowing agent, wherein the polystyrene has improved foamability. More specifically, these polystyrene particulates contain a polymer having a molecular weight of about 130,000 to about 180,000. Patent 4,525,484 discloses a variety of methods for preparing polymers using chain transfer agents and oligomers or polymerizing in the presence of a blowing agent. Patent No. 4,525,484 discloses that the produced polystyrene fine particles can be foamed by conventional methods (eg, vapor foaming). Patent 4,525,484 discloses that a blowing agent can generally be provided at 3 to 12% by weight (preferably 5 to 8% by weight, in the examples of Patent 4,525,484 using about 7% by weight pentane). . However, the patent 4,525,484 does not disclose any explanation regarding the use of a plurality of preformed foaming steps. In contrast, the process of the present invention employs a polymer that differs from the polymer disclosed in Patent 4,525,484 and exhibits three different properties from this polymer. An important fact in this difference is that the weight average molecular weight of the polymer used in the process of the invention is greater than the weight average molecular weight of the polymer disclosed in US Pat. No. 4,525,484. Surprisingly, such large molecular weight polymers have at least as high foaming properties as the polymers disclosed in the above patent 4,525,484. In addition, in the process of the present invention, it is necessary to use 2 to 4 preforming foaming steps, while the above patent 4,525,484 discloses no use of a plurality of foaming steps with or without forming steps.

U. S. Patent No. 4,485, 193 describes a process for preparing elastic foam particulates and molding slightly crosslinked polymers, which may be styrene polymers. This method involves the use of low permeability volatile fluid blowing agents for polymers and also utilizes a plurality of foaming steps to produce low density foams suitable for molding. In the process disclosed in patent 4,485,196, the once-expanded particulates are placed in atmospheric conditions of 3 atmospheres or more and the pressurized particulates are further foamed by heating above the glass transition temperature of the polymer after returning to normal atmospheric pressure.

No. 4,485,193 does not describe any description of the amount of blowing agent used in the disclosed process. However, out of 43 samples disclosed in patent 4,485,193, samples 1 to 17 used about 20 to about 30% by weight of blowing agent, and samples 18 to 21 were foams prepared in accordance with those disclosed in patent 4,485,196. The amount of blowing agent used in the preparation of this foam was not exemplified, Sample 22 is a foam prepared in accordance with the conditions of Sample 2 (Sample 2 uses 28.9% by weight of blowing agent) and Samples 23-38 are 6.12- 7.0 wt% blowing agent was used, samples 39-41 did not exemplify any description of the amount of blowing agent, but exemplified that the blowing agent diffused into the pre-foamed beads, while Sample 42 and Sample 43 showed at least 11 wt% blowing agent. Is used. In summary, the patent 4,485, 193 shows that it uses a significantly larger amount of blowing agent than is used in the process of the present invention.

U. S. Patent No. 3,639, 551 describes a circulation method for producing low density polystyrene foam beads which are foamed in a plurality of foaming steps. However, the gist of patent 3,639,551 is to reheat partially foamed beads between the foaming steps so that most of the lost volume (the volume lost immediately after cooling after the beads are foamed) is recovered. This reheating step will precede the next foaming step. By this method shrinking of the beads is prevented from substantially affecting the final degree of foaming obtained.

U. S. Patent No. 3,639, 551 does not disclose the amount of blowing agent used to foam the beads. Patent 3,639,551 discloses one embodiment, which according to this embodiment contains a low boiling hydrocarbon promoter (pentane) therein and has a diameter of about 1/64 to about 1/32 inch. A pound of commercial grade acrylonitrile styrene copolymer is stored in a hopper and this is a Bucaneer prefoam (Lebanon, Ohio) with a foam chamber substantially as described above. Sold by Sales Co.). Patent 3,639,551 does not disclose the amount of low boiling accelerator (pentane) contained in the beads.

In contrast to the patent 3,639,551, the process of the present invention uses a low concentration (about 2 to about 4.4% by weight) of blowing agent in combination with multistage foaming to produce a product having a density of about 0.8 to 1.1 lb / ft ³ . use. Patent 3,639, 551 does not disclose the use of such small amounts of blowing agent. In addition, in the process of the present invention, it is necessary to use a special polymer which is not described anywhere in the above-mentioned patent 3,639,551.

U.S. Patent No. 3,631,133 describes a process for foaming polystyrene beads to produce beads having exceptionally low densities (i.e., 5 kg / m ³ or less, equivalent to about 0.3 lb / ft ³ or less). . The foaming method disclosed in Patent No. 3,631,133 is composed of the following steps.

(1) spraying (i.e., pre-foaming the partially foamed product to produce a partially foamed product) containing the blowing agent, which step is carried out with steam at approximately atmospheric pressure, with the result that the granules are partially Foaming, (2) conditioning the partially foamed granules at atmospheric pressure, (3) treating the partially foamed granules (in the defined space) with steam at a pressure of about 150 g / sq.cm Step, and (4) recovering the foamed granules to the condition of atmospheric temperature and atmospheric pressure.

The gist of patent 3,631,133 is that a plurality of foaming steps are used in combination with a control step to ultimately produce a low density product. Patent No. 3,631,133 does not disclose the amount of blowing agent used in the above process, and defines the blowing agent as follows. The starting material consisting of polystyrene granules contains the pentane petroleum fraction as blowing agent (see column 2, lines 61-63).

In stark contrast to the above patents 3,631,133, the process of the present invention uses a low concentration of blowing agent with multistage foaming to produce a product having a density of about 0.8 to 1.1 lb / ft ³ . Patent 3,631,133 does not disclose the use of such small amounts of blowing agent. In addition, Patent No. 3,631,133 does not disclose features of polystyrene polymers whose foamability is different from existing levels.

U. S. Patent No. 3,598, 769 discloses a process for foaming polystyrene, which comprises the following steps (1) to (5).

(1) treating the polystyrene granules with low pressure steam (for several minutes), (2) conditioning the granules for several hours at about 20 ° C. to 40 ° C., and (3) high temperature foamed granules. Reheating to about 100 ° C. with air, (4) treating the granules with steam for 30-40 seconds, and (5) conditioning the granules for 1 to 24 hours.

The purpose of this patent 3,598,769 is to provide a process for producing polystyrene beads having an apparent specific gravity of less than 7 kg / m ³ (ie, density less than about 0.44 lb / ft ³ ). The gist of patent 3,598,769 is to provide a very unique process that uses two foaming steps and one conditioning step after each foaming step. In addition, the patent 3,598,769 performs this process on a continuous conveyor belt.

Like Patent No. 3,631,133, Patent No. 3,598,769 also does not describe the amount of blowing agent used in the process.

In contrast to the patent 3,598,768, the process of the present invention uses a low concentration of blowing agent in combination with multistage foaming to produce products having a density of 0.8 to 1.1 lb / ft ³ . No. 3,598,769 does not disclose the use of such small amounts of blowing agents, nor does it disclose the use of polymers with exceptional foaming properties.

U.S. Patent No. 3,126,432 describes a process for producing ultra low density thermoplastic foams, i.e., polystyrene foams. The process disclosed in the above patent No. 3,126,432 foams polystyrene fine particles containing an evaporable liquid expander (butane or pentane), so that the expanded fine particles are aged at atmospheric pressure, and then for several hours at a pressure above atmospheric pressure (2 to 8 atmospheres). It is a step of aging again. Exposing the foamed microparticles to air above atmospheric pressure causes the second blowing agent to enter the foamed microparticles. Thereafter, within 5 hours of the release of the pressure, the particulates are heated in a closed mold. Thus, the gist of patent 3,126,432 is pumped up by exposing the foamed particulates to air above atmospheric pressure and then undergoing a second foaming step by the relatively high internal pressure of the particulates immediately after they are released from the pressure chamber. It is. The patent 3,126,432 makes no mention of the amount of blowing agent used in the production of polystyrene foams. Of the five embodiments described in patent 3,126,432, only Examples 1, 3, and 5 describe the amount of blowing agent used in the process. In each of these examples, the blowing agent used is pentane and the pentane is present in 6 weight percent polystyrene spheres. Thus, it is evident that Patent 3,126,432 does not teach a process using less than 6% by weight of blowing agent.

In contrast to the above patents 3,126,432, the method of the present invention uses a low concentration of blowing agent with multistage foaming to produce a product having a density of 0.8 to 1.1 lb / ft ³ . Patent 3,126,432 does not disclose the use of such small amounts of blowing agent nor does it disclose a polymer exhibiting the properties according to the invention.

US Patent No. 3,056,753 discloses a process for preparing expandable polymer microparticles having a foamed polymer structure. This process includes the steps of (1) to (3) below.

(1) partially foaming the polymer fine particles, (2) pulverizing the fine particles, and (3) partially foaming the fine particles again.

The gist of patent 3,056,753 is that by reducing the molding cycle time the molded article can be removed from the mold after passing through a shorter cooler. Patent 3,056,753 does not disclose any explanation as to the amount of blowing agent used in this process. In fact, the patent document does not describe the amount of blowing agent used in the examples.

In contrast to the patent 3,056,753, the process of the present invention uses a low concentration of blowing agent with multistage foaming to produce a product having a density of 0.8 to 1.1 lb / ft ³ . Patent 3,056,753 does not disclose the use of such small amounts of blowing agents nor does it disclose polymers having the features of the polymers of the present invention.

US Pat. No. 4,721,588 discloses a ring closure process for making foamed polystyrene foam. This process includes the following steps (a) to (d).

(a) prefoaming a polystyrene bead raw material containing a blowing agent in a prefoaming container; (b) storing the beads in one or more closed reservoirs so that the internal pressure of the foamed beads is substantially atmospheric pressure; (c) shaping the foamed beads with steam until the desired shape is obtained in a closed mold, and (d) removing the foamed article from the mold and placing it in a maturing chamber. The blowing agent released from the beads in each of the above steps is recovered and separated from any residual vapor by a condensation system and then introduced into the burner of the steam generator to be used as fuel for the process.

As can be seen from the foregoing steps, the gist of the process described in patent 4,721,588 is that the blowing agent is recovered and reused as fuel in the heating step. This provides a dual effect of (1) reducing the amount of volatile organic compounds released to atmospheric pressure and (2) reusing the blowing agent released from the polystyrene during the pre-expanding and forming steps. Further, the patent 4,721,588 discloses that the blowing agent can be pentane or a mixture of normalpentane and isopentane (up to 25% by weight isopentane). In addition, the Patent No. 4,721,588 describes that the amount of the initial blowing agent of the expandable polystyrene beads may be 4 to 8% by weight, but low density polystyrene foams can be produced when using less than 5% by weight of blowing agent. The thing is not disclosed. In fact, except that it discloses that 4 to 8% by weight of blowing agent can be used, the above-mentioned patent 4,721,588 does not disclose the density of the actual foam or the amount of blowing agent in the actual composition. Consequently, the patent 4,721,588 does not disclose the use of a plurality of preforming foaming steps, but only discloses performing a molding step after performing a single preforming foaming step.

In contrast to the patent 4,721,588, the method of the present invention uses a low concentration of blowing agent with multistage foaming to produce a product having a density of 0.8 to 1.1 lb / ft ³ . The patent 4,721,588 does not disclose the use of less than 5% by weight of blowing agent with multistage foaming to produce products having a density of 0.8 to 1.1 lb / ft ³ and is also used in the process of the present invention. There is no disclosure of the use of a polymer having the characteristics of the resulting polymer.

Currently, the issue of volatile organic compounds (VOC) emissions to the atmosphere is under strict inspection by the US Environmental Protection Agency, a state and local air quality control department mandated by the US Air Cleansing Decree in 1977. Since hydrocarbons are released into the atmosphere causing photochemical smog, the expanded polystyrene industry using pentane as a blowing agent has been under pressure to limit the use of blowing agents and / or the release of pentane.

Since the beginning of 1990, the inventors have found that more than 3 million pounds of foams foamed at 0.8 to 1.1 lb / ft ³ can be produced on a commercial scale in the United States only by the method proposed by the inventors. The amount of expandable polymer of is about 96% by weight based on the total weight of the formulation. Thus, not only the formulations used to carry out the process but also all of the processes have achieved great commercial success.

For many years BASF Corporation has produced and sold a number of expandable polystyrene compositions having about 6% by weight of pentane. Typically these compositions contain a polymer having a polydispersity of 2.2 and a weight average molecular weight of about 190,000 and about 3.5 Mz: Mn. In contrast, the compositions of the present invention contain a polymer having a polydispersity of less than 1 to 2, a weight average molecular weight of about 200,000 to about 300,000, and a Mz: Mn of less than about 2-3.

One polymer that has been commercially available for many years has a polydispersity of about 1.9, a weight average molecular weight of about 190,000, and Mz: Mn of 3.04. In addition, this polymer was prepared only in formulations containing about 6% by weight of blowing agent. In contrast, the polymers of the present invention have different characteristics (polydispersity, weight average molecular weight and Mz; Mn) from the commercially available polymers. In addition, from about 2% to about 4.4% by weight blowing agent is used in the composition of the present invention.

[Overview of invention]

The method of the present invention relates to the production of a foamed thermoplastic resin article in an independent bubble form, wherein the beads are foamed through a foaming step of 2 to 5. This bead includes a blowing agent and a polymer. The blowing agent is uniformly dispersed in the polymer, and generally this blowing agent is a hydrocarbon that is a gas or liquid at standard temperature and pressure, does not dissolve the styrene polymer and boils at a temperature lower than the softening point of the styrene polymer. The blowing agent includes azo compounds, pentane, cyclopentane, neopentane, isopentane, pentane petroleum distillate fraction, propane, butane, isobutane, hexane, and hexane which can decompose at the thermoplastic temperature to form a polymer. Isomers, 2-methylpentane, 3-methylpentane, methylcyclopentane, cyclohexane, methylcyclohexane, heptane, propylene, 1-butylene, 2-butylene, isobutylene, absolute molecular weight of 42 or more and 760 millimeters It is preferably selected from the group consisting of water, carbon dioxide and ammonium carbonate, mixtures of one or more aliphatic hydrocarbons having a boiling point of up to 95 ° C. under pressure.

The blowing agent is present in the beads in an amount of about 2% to about 4.4% by weight based on the weight of the beads.

The polymer constituting the beads is one or more polymers made from one or more various monomers. The monomer is selected from the group consisting of styrene, styrene derivatives, vinyltoluene, monohalogenated vinyltoluene and polyhalogenated vinyltoluene to form linear polymers, acrylonitrile and methacrylates. The polymer is present in the beads in an amount of about 93% to about 98% by weight based on the weight of the beads. This polymer has the following characteristics: (1) polydispersity of about 1 to less than 2.5, (2) weight average molecular weight of about 180,000 to about 300,000, and (3) Mz: Mn of about 2 to about 4.5. In addition, the polymer is branched to 0 to less than 5% by weight.

The foaming steps are carried out in a foamer at substantially atmospheric pressure, resulting in a finally foamed bead. Foaming of the polystyrene beads is carried out in such a way that the density of the finally foamed beads is from about 0.8 to about 1.1 lb / ft ³ . After each foaming step, it is common for the foamed beads to age for 1 to 80 hours.

In addition, the process is carried out so that the amount of blowing agent discharged in the foaming step is about 0.3 to about 1.5% by weight based on the weight of the beads. This foaming step produces the finally foamed beads, and the foaming of the beads is performed such that the density of the finally foamed beads is from about 0.8 to about 2 lb / ft ³ .

The method also relates to a method for producing a thermoplastic resin molded article foamed in an independent form. The method foams the beads in two to four prefoaming steps, after which the beads are further foamed in the molding step and fused into a single foam. In this method, the foaming step preceding the molding step is called a "preliminary foaming" step. It should be noted that in general, the beads pre-released in the forming step are foamed at least several more times because they are bonded to each other (fusion).

The beads include a blowing agent and a polymerizing agent. In general, the blowing agent may be one described above, but azo compounds, pentane, cyclopentane, neopentane, isopentane, pentane petroleum distillate fraction, propane, which may decompose at the thermoplastic temperature at which the polymer is formed to form a gas. Butane, isobutane, hexane, hexane isomer, 2-methylpentane, 3-methylpentane, methylcyclopentane, cyclohexane, methylcyclohexane, heptane, propylene, 1-butylene, 2-butylene, isobutylene, molecular weight Is preferably selected from the group consisting of water, carbon dioxide and ammonium carbonate, a mixture of one or more aliphatic hydrocarbons having a boiling point of at least 95 and a boiling point of 95 ° C. or lower at an absolute pressure of 760 millimeters.

The blowing agent is present in the beads in an amount of about 2 to 4.4 weight percent based on the weight of the beads.

The polymer constituting the beads is one or more polymers prepared from one or more various monomers. The monomer is selected from the group consisting of styrene, styrene derivatives, vinyltoluene, monohalogenated vinyltoluene and polyhalogenated vinyltoluene to form linear polymers, acrylonitrile and methyl methacrylate.

The polymer is present in the beads in an amount of about 93 to about 98 weight percent based on the weight of the beads. This polymer has the following characteristics: (1) polydispersity of about 1 to less than 2.5, (2) weight average molecular weight of about 180,000 to about 300,000, and (3) Mz: Mn of about 2 to about 4.5. In addition, the polymer is branched by weight percent of 0 to less than 5.

The preliminary foaming steps are carried out in a foamer at substantially atmospheric pressure. Upon completion of the prefoaming steps, a “finally prefoamed” bead is formed. Finally the prefoamed beads are molded, further foamed and fused. Both the prefoaming step and the forming step are performed so that the density of the forming foam is about 0.8 to 1.1 lb / ft ³ .

It is an object of the present invention to reduce the amount of blowing agent used in the preparation of thermoplastic resin articles foamed into low density, self-contained foams.

It is an object of the present invention to reduce the degree of environmental pollution involved in the production of low density, self-contained foamed thermoplastic articles (ie, reducing the emissions of VOCs).

It is an object of the present invention to provide a method for reducing the degree of shrinkage during molding in the production of a thermoplastic resin article foamed into an independent foam.

It is an object of the present invention to provide a method of shortening the cooling time required between any foaming step (and pre-expanding step) as well as in any molding step employed.

It is an object of the present invention to provide a method of effectively using polystyrene polymers having a high degree of foaming.

It is also an object of the present invention to provide a method of using the expandable polystyrene composition in the manufacture of foamed polystyrene products.

It is also an object of the present invention to use less polystyrene polymers as well as compositions for making foamed polystyrene products, so that less blowing agent is discharged to the atmosphere and / or pollution reduction facilities.

It is also an object of the present invention to provide a process for producing foamed polystyrene products in which more resin is present per unit pound of composition, using a composition having a higher ratio of resin: foaming agent.

It is also an object of the present invention to provide a process for producing polystyrene foam with reduced molding cycle time, shrinkage during molding and aging time between foaming steps.

It is also an object of the present invention to provide a process for producing foamed polystyrene products having reduced sensitivity to losses during processing.

It is also an object of the present invention to provide a process for the preparation of foamed polystyrene beads which has a long shelf life before the molding step since the loss rate of the blowing agent is reduced.

It is also an object of the present invention to provide a process for the preparation of foamed polystyrene products which reduces the sensitivity to steam during the foaming and molding step, resulting in a more extensive molding process with respect to the use of steam in the pre-expanding and molding step, Affects fusion, cycle time and dimensional stabilization immediately after molding.

Each of the above objects can be understood to provide respective advantages to the method of the present invention. Although the object to be treated is shown as polystyrene above, it is to be understood that the object to be applied applies to all polymers that can be used in the process of the invention.

[Detailed Description of Preferred Embodiments]

The process of the invention relates to foaming a substantially solid thermoplastic polymer to produce a foam. Foaming of the polymer causes the polymer particulate to foam while the blowing agent is intimately mixed with the polymer, and then the mixture is heated so that the foaming agent vaporizes in the polymer particulate. Evaporation of the blowing agent occurs by applying heat, which likewise softens the polymer. Sufficient heat must be applied so that the temperature of the polymer is above its softening point. By evaporation of the blowing agent in the softened polymer the mixture foams to form a foam. The foam is then cooled while maintaining a substantially foamed state.

During cooling, the internal pressure of the foam bubbles is reduced due to the condensation and cooling of the blowing agent. This causes gases (e.g., air, steam, etc.) that can penetrate the polymer to enter the bubble and somewhat recover the relatively low internal pressure (e.g. atmospheric pressure). Although components in the atmosphere (i.e., oxygen, carbon dioxide, nitrogen, etc.) diffuse to some extent into the bubbles, when the vapor is used as a heat source in the foaming (or forming) phase, the most permeable gas is generally It diffuses into the bubble. As soon as the cooled foam reaches a substantial equilibrium state (where the internal pressure of the bubble becomes equal to atmospheric pressure), it can be heated again and further foamed. Accordingly, volume increase may occur continuously by multi-stage circulation or multi-stage passes such as foaming, cooling, and aging.

The foam may optionally be further foamed and fused to form a molded article. In the forming step, the pre-foamed beads are placed in a mold and sealed to have a substantially limited volume, so that the pre-foamed beads are further foamed to occupy the internal volume of the mold and fuse together (combine with each other). Heat.

Generally, in the process of the present invention without a forming step, the blowing agent is discharged in an amount of about 0.3 to about 1.5 weight percent based on the total weight of the beads. Preferred emissions of blowing agent are from about 0.5 to about 1.2 weight percent, and more preferably from about 0.6 to about 0.7 weight percent of blowing agent. The discharge means the maturation period between the foaming steps and the total amount of blowing agent discharged to the atmosphere during the foaming step.

In general, the amount of blowing agent in the process of the invention comprising the forming step is from about 1 to about 2.5% by weight based on the total weight of the beads. Preferred emissions of blowing agent are from about 1.5 to 1.9% by weight, and more preferably from about 1.6 to about 1.8% by weight of blowing agent. The above discharge means the total amount of blowing agent discharged in the pre-expanding step, the maturing period after each pre-expanding step and the molding step.

The method of the present invention aims to provide a commercially viable method of reducing the emissions of volatile organic compounds (VOCs) as compared to the presently prepared methods. In part, the process for achieving this object is achieved by using a smaller amount of blowing agent than that used in the prior art processes. This process is carried out by using from 2 to 4.4% by weight of blowing agent, based on the weight of the polymer. One or more various blowing agents can be used in the process of the present invention. These blowing agents are hydrocarbons that are gaseous or liquid under normal conditions, do not dissolve the styrene polymer and boil below the softening point of the polymer. Examples of preferred blowing agents used in the process include pentane isomers and pentanes such as azo compounds, pentanes (cyclopentane, methylcyclopentane, neopentane, isopentane, etc.) that can decompose at the thermoplastic temperature at which the polymer is formed to form a gas. Petroleum distillate fractions), propane, butane, isobutane, hexane, isomers of hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, methylcyclopentane, cyclo Hexane, heptane, propylene, 1-butylene, 2-butylene, isobutylene, a mixture of one or more aliphatic hydrocarbons having a molecular weight of 42 or more and a boiling point of 95 ° C. or less at an absolute pressure of 760 millimeters, water, carbon dioxide and ammonium carbonate Can be mentioned.

Examples of more preferred blowing agents used in the process include pentane, cyclopentane, methylcyclopentane, neopentane, isopentane, pentane petroleum distillate fraction, 2-methylpentane, 3-methylpentane, propane, butane, isobutane, iso Butylene, hexane, isomer of hexane, cyclohexane and heptane.

The blowing agent may be introduced into the polymer before, during or after the polymerization reaction. In the process of the present invention, the blowing agent is introduced into the polymer in an amount of 2 to 4.4% by weight based on the total weight of the beads. The preferred amount of blowing agent introduced into the polymer is from about 2.5 to about 4.4 weight percent, more preferably the amount of blowing agent is from about 3 to about 4 weight percent, and the most preferred amount of blowing agent is about 3.5 weight percent. Most preferred blowing agent is pentane (a mixture of pentane or an isomer of n-pentane and pentane). It is preferred to add pentane to the polymer during the polymerization reaction, and more preferably add pentane when 20 to 60% of the styrene is converted.

The process of the present invention is carried out on unfoamed beads. In this specification, unfoamed beads are defined as discrete particulates comprising a polymer and a blowing agent.

According to the method of the present invention, the unfoamed beads are foamed through two to five foaming steps. In a preferred method of the present invention, two or three prefoaming steps are carried out followed by a shaping step. That is, two to three preforming foaming steps are required to produce the final pre-foamed beads. Most preferably, the method utilizes only two prefoaming steps.

In the case of manufacturing the non-molded product using the method of the present invention, the method preferably performs two to three foaming steps to prepare the finally foamed beads, most preferably only two foaming steps. It is done.

If the beads foam but do not fuse into the molded article, the beads are referred to herein as finally foamed beads. However, when the beads are ultimately fused into the molded article, the foaming steps are referred to as prefoaming steps. Once the beads are finally prefoamed, they are then refoamed and fused into the molded article in the forming step serving as the final foaming step. Whether the beads are foamed or pre-foamed, the total number of foaming stages (including the pre-foaming stage) according to the method of the present invention is 2 to 5 times. Surprisingly, it has been found that final products having a density of 0.8 to 1.1 lb / ft ³ can be produced using 2 to 4.4% by weight of blowing agent. Foams with densities in this range are useful for insulation and / or protective packages.

Typically, the bead foaming process is carried out in a closed vessel of a closed pulverulent foamer in which steam is injected. Examples of foaming machines are Tri 502, Tree 905, Weiser VN400, Kurtz KV1000, Dingledein VA2000. Foaming of the beads is carried out by passing the beads through the foamer, from which the beads are heated and softened sufficiently to foam due to the elevated pressure by evaporation of the blowing agent and other internal gases. In general, the amount of beads to be foamed is determined by the flow rate of the beads through the foamer. Therefore, as the flow rate of the beads passing through the foamer decreases, the amount of heat transferred to the beads increases, thereby increasing the degree of foaming. However, for any given bead formulation there is a maximum amount of foaming that can occur in either foaming step. Thus, the flow rate of the beads through the foamer is expressed in pounds per hour / feet cubic (lb / hr. / Ft ³ ) and is generally about 5 to about 120 lb / hr. / Ft ³ . At flow rates less than about 5 lb / hr. / Ft ³ , the beads stay in the foamer for a long time and are inefficient because agglomerate crystals are produced. At flow rates above about 120 lb / hr. / Ft ³ , no satisfactory foaming occurs because the beads do not stay in the foamer for a time sufficient to foam at an effective level. A flow rate of about 7 to about 100 lb / hr. / Ft ³ is preferred, with a most preferred flow rate of about 12 to about 80 lb / hr. / Ft ³ .

The method of the present invention can be carried out with or without a forming step. The following description relates to the molding steps used in the process of the invention. This step places the prepuff (pre-foamed bead) into a cuts vacuum block molder with a interior of about 48 × 96 × 33, pre-vacuum the vacuum to about 0.5 bar absolute, and steam for about 3 seconds. Then, cross steam through the block for about 3 to 6 seconds, pressurize and heat for 3 to 8 seconds to reach a maximum foam pressure of about 0.5 to 1.0 bar, wherein the vacuum is about 0 to 0.1 vacuum is applied to the blocks in the mold to cool the blocks to a pressure of bar, and the blocks are removed from the molding machine without post-foaming or shrinking.

As mentioned above, short aging times allow for more efficient processes by completing the process in less time. In addition, the amount of blowing agent discharged to the environment is further reduced by using a small amount of blowing agent while completing the process in a shorter time.

In general, the aging time after each first foaming (or first prefoaming) is about 1 to 80 hours. A more preferred aging time is about 2 to about 6 hours, or about 1.2 to 8 hours, and the most preferred aging time is 1.5 to about 2.5 hours.

In addition, polystyrene beads can be used to reduce antistatic agents, stabilizers, colorants, lubricants, fillers, zinc stearate, melamine formaldehyde concentrate or silica, which prevents agglomeration in pre-foaming, and molded part uptime during the final foaming process. It contains additives that impart certain properties to the foamed article, such as glycerol esters or hydroxycarboxylic acid esters, which are substances. Depending on the desired effect of the additives, the additives may be uniformly diffused in the microparticles or present as a surface coating.

About 0.7 parts by weight (based on 100 parts by weight of styrene) of the free radical initiator is added to the organic phase at the start of the polymerization reaction. Preferred initiators are mixtures of benzoyl peroxide, dicumyl peroxide, t-butyl perbenzoate. While benzoyl peroxide acts as a low temperature initiator, t-butyl benzoate acts as a high temperature initiator. In addition, any excess dicumyl peroxide (dakumil peroxide remaining after the polymerization reaction) acts as a synergist for the flame retardant.

In the method of the present invention, poly-n-vinylpyrrolidone may optionally be used as the protective colloid to coat the beads. Poly-n-vinylpyrrolidone is added at a time when the beads become a certain size during the polymerization reaction. Poly-n-vinylpyrrolidone coats the beads so that the beads do not adhere to each other to prevent the beads from growing so that the size of the beads is fixed. The preferred amount of poly-n-vinylpyrrolidone added to the reaction mixture is about 0.3% by weight based on the weight of polymer present.

In general, the polymers used in the process of the invention can be prepared from one or more of a wide variety of monomers. This monomer comprises a monovinyl compound which gives a linear polymer via an addition polymerization reaction. The polymer is preferably capable of forming a crosslinked structure with a predetermined degree of polymerization when the polymerization is carried out in the presence of a crosslinking amount of a polyvinyl compound (eg, ethylene glycol, dimethacrylate, divinylbenzene, etc.). Do. Examples of monovinyl compounds useful in the process of the invention include styrene (including styrene derivatives), vinyltoluene, monohalogenated vinyltoluene and polyhalogenated vinyltoluene to form linear polymers, acrylonitrile, methyl methacrylate and vinyltoluene. have.

Preferred monomers are those selected from the group consisting of styrene and styrene derivatives. The most preferred polymer used in the process of the invention is polystyrene. Although pure polystyrene is the most preferred polymer for use in the process of the invention, monomers referred to as styrene derivatives can be used and polymerized in the process of the invention, examples of which are alpha-methylstyrene, o-methylstyrene , m-methylstyrene, p-methylstyrene, ar-ethylstyrene, ar-vinylxylene, ar-chlorostyrene and ar-bromostyrene or divinylbenzene, methyl methacrylate or acrylonitrile There are solid copolymers in which small amounts of possible olefin compounds and two or more alkenyl aromatic compounds are mixed.

In the method of this invention, it is necessary to use the polymer which shows three characteristics of (1) polydispersity within a prescribed range, (2) weight average molecular weight within a prescribed range, and (3) Mz: Mn within a prescribed range. In addition, the polymer used for the method of this invention is determined by weight average molecular weight (Mw), number average molecular weight number (Mn), and Z-average molecular weight (Mz). The number average molecular weight is an arithmetic mean obtained by dividing the sum of the molecular weights by the number of molecules. The weight average molecular weight is the second average molecular weight in the polydisperse polymer. Z-average molecular weight is the third average molecular weight in the polydisperse polymer. A broader description of these molecular weights is described in Billmeyer, FW Jr., Textbook of Polymer Science, 2nd Edition, 1971, Wiley-Interscience, NY, NY, pages 6, 66, 78 and 92. Which is hereby incorporated by reference.

In the process of the present invention, the inventors have found that low density, ie, 0.8 to 1.1 lb / ft ³ foams can be produced by using 2 to 5 foaming steps and using a small amount of blowing agent and at the same time using the polymer. It was.

The method of the present invention uses a polymer having features derived from the molecular weight distribution curve of the polymer. The molecular weight distribution curve is measured by gel permeation chromatography. This method is specified in detail in G.Glockler, Polymercharakterisierung, chromatographische Methoden, Volume 17, published in 1982 by Huthig, Heidelberg, which is incorporated herein by reference.

It is the polydispersity, which is the first characteristic of the polymer, which is determined by analyzing the molecular weight distribution curve for the polymerization reaction product. Polydispersity is the weight average molecular weight divided by the number average molecular weight. Thus, polydispersity is a measure of the width of the molecular weight distribution curve. Generally the polymer has a polydispersity of about 1 to less than 2.5. Preferred polydispersities of the polymers are less than about 1 to 2.0, more preferably less than about 1.5 to 2.0, and most preferably about 1.7 to 1.98. Example 7 to be described later shows a method for analyzing a polymerization product, which shows a method for measuring weight average molecular weight, number average molecular weight and Z-average molecular weight. Thus, this analytical method provides data from which the polydispersity, weight average molecular weight Mz: Mn ratio can be calculated.

The second characteristic (ie, weight average molecular weight) of the polymer is generally about 180,000 to about 300,000, and the weight average molecular weight of the preferred polymer used in the process of the present invention is at least 190,000 to about 250,000. Most preferably about 200,000 to about 220,000. Like polydispersity, a weight average molecular weight is measured by the analysis method shown in Example 7 mentioned later.

A third feature of the polymer is the ratio of Z-average molecular weight: number average molecular weight (Mz: Mz). This ratio is related to the slope of the top end slope of the molecular weight distribution curve. Generally, the polymer has a Mz: Mn ratio of about 2.5 to about 3.3. Most preferred Mz: Mn ratio is about 2.7 to about 3.0. As with polydispersity and weight average molecular weight, the ratio of Mz: Mn can be calculated based on the analytical method according to Example 7. Of course, the molecular weight distribution curve is obtained by the analytical method according to Example 7, from which the weight average molecular weight, number average molecular weight and Z-molecular weight are determined. With this value the polydispersity can be calculated as well as the ratio of Mz: Mn.

The polymer used in the process of the present invention is a substantially unbranched linear polymer. Generally the polymer has a degree of branching of from 0 to 5% by weight. Branched from 0 to less than 5% by weight. The phrase means that at least 95% by weight of the molecular weight of the polymer moiety is a linear chain of molecular moieties. When calculating the weight percent of branched polymers (except for the linear portion of the polymer molecule), carbon atoms not belonging to the main polymerization chain are considered to be branched, and likewise any atom bound to the branched carbon atoms is attached to the branched portion of the polymer. It is considered to belong. Non-carbon atoms bonded to carbon atoms of the linear polymer backbone (they do not form part of the backbone) are considered substituents rather than branched. However, when a substituent atom binds directly or indirectly to a second carbon atom not belonging to the linear polymer backbone, this substituent and any atoms bonded thereon (not belonging to the polymer backbone) are considered to be branched. The polymer is preferably branched to less than 0-2% by weight, most preferably from 0-1% by weight.

It is preferred that the polymer is a polystyrene polymer that is substantially homopolymerized. That is, the polymer is preferably derived from a single monomer whose monomer is styrene. Substantially homopolymerized polymer is defined herein as a polymer wherein at least 99% of the monomer units (reacted to form polystyrene) are single monomers. It is preferred that at least 99.9% of the monomer units reacted to form the polymer are single monomer species.

Preferred polymers are substantially unsubstituted polymers. Substantially unsubstituted polymer herein refers to a polymer having a carbon backbone and branch with less than 2% of the positions at which atoms other than hydrogen are substituted. More preferably, they have a degree of substitution of less than 0.5% based on the polymer having 35 total substitution positions.

Preferred polymers of the present invention are characterized by (1) polydispersities of less than about 1.5 to 2.0, (2) weight average molecular weights of 190,000 to about 250,000, and (3) Mz: Mn of about 2.5 to about 3.3. In addition, the preferred polymers are branched at 0% by weight to less than 2. In conclusion, these preferred polymers are substantially homopolymerizable and unsubstituted polymers.

More preferred polymers of the present invention are characterized by (1) polydispersities of about 1.7 to about 1.98, (2) weight average molecular weights of about 200,000 to about 220,000, and (3) Mz: Mn of about 2.7 to less than about 3.0 Indicates. Further preferred polymers are branched at 0% by weight or less. In conclusion, these more preferred polymers are substantially homopolymerizable and unsubstituted polymers.

In addition, preferred formulations of the present invention contain chain transfer agents. Chain transfer agents having a transfer constant (K) (Vollmert, Grundriss der Makromolekularen chemie, Springer Publication, 1962, pages 52 and 71) of 0.1 to 50, preferably 1 to 30, are used. Examples of suitable chain transfer agents for use are shown below.

n-dodecyl mercaptan (K = 19)

t-dodecyl mercaptan (K = 3)

n-butyl mercaptan (K = 22)

t-butyl mercaptan (K = 3.6)

Carbon bromide (K = 2.2)

Pentaphenylethane (K = 2.0)

Alternatively (preferably), the method of the present invention uses a flame retardant in the mixture of the components making up the expandable bead formulation. Generally, the flame retardant is an organobrominated flame retardant or an organochlorinated flame retardant present in an amount of about 0.2 to about 2 weight percent based on the total weight of the formulation. More preferably, the flame retardant is a brominated hydrocarbon flame retardant present in about 0.5 to about 1.5 weight percent based on the total weight of the formulation. More preferred flame retardants for the formulations are at least one selected from the group consisting of trisdibromo-propylphosphate, hexabromocyclododecane and bisalkyl ethers of tetrabromo-bis-phenol A and the total weight of the formulation Present in an amount from about 0.6 to about 1.2 weight percent.

In addition, preferably (optionally), the formulation contains a flame retardant synergist, which is one or more compounds that increase the effectiveness of the flame retardant in combination with the flame retardant. This flame retardant synergist is at least one member selected from the group consisting of organic peroxides and dicumyl peroxides having a half-life of 1 hour at temperatures of about 110 ° C to about 150 ° C.

In addition, the formulation may further contain additional additives that impart particular properties to the foamable article. Examples of the additives include flame retardants such as organic bromide or organic chlorides such as trisdibropropyl phosphate, hexabromocyclodecane and chloroparaffin as main components, dicumyl peroxide and other organic peroxides decomposed at high temperature, Antistatic agents, stabilizers, colorants, lubricants, fillers, zinc stearate, melamineformaldehyde concentrate or silica, which prevents agglomeration during prefoaming, and glycerol, a reagent for reducing the take-out time of molded parts during final foaming Esters or hydroxycarboxylic acid esters. The additives may be uniformly dispersed in the microparticles or present as a surface coating, depending on their desired effect.

Unfoamed beads comprise, as a main component, one or more polymers having the abovementioned characteristics. It is preferable that the said polymer is a polymer or polystyrene manufactured by superposing | polymerizing the monomer which is a derivative of polystyrene. Generally, the beads include polymers present in an amount of about 93 to about 98 weight percent based on the total weight of the beads. Preferably, the beads consist of a polymer present in an amount of about 94 to about 97.5 weight percent, more preferably a polymer present in an amount of about 95 to 97 weight percent, most preferably about It consists of 96% by weight of polymer.

If crosslinkable polyvinyl compounds are present, they should not be present so much that too many crosslinks are formed. This is because the polymer does not foam when the degree of crosslinking is too high. As a crosslinking agent which can be used for the method of this invention, divinylbenzene, diethylene glycol dimethacrylate, diisopropenylbenzene, diisopropenyl diphenyl, diallyl maleate, diallyl phthalate, allyl acrylate , Allyl methacrylate, allyl fumarate, allyl itaconate, alkyd resins, butadiene or isoprene polymers, cyclooctadiene, methylene norbornylene, divinyl phthalate, vinylisopropenylbenzene, divinyl biphenyl and polymerization Bifunctional compounds or polyfunctional compounds known to be used as crosslinking agents in the functional vinyl addition composition.

Example 1 (Method for Producing Polymer)

A mixture consisting of 87 parts of water, 0.16 parts of sodium pyrophosphate and 0.27 parts of magnesium sulfate hexahydrate was reacted with stirring at ambient temperature in a stainless steel pressure vessel. 100 parts of styrene, 0.14 parts of benzoyl peroxide, 0.32 parts of t-butyl perbenzoate, 0.62 parts of hexabromocyclododecane and 0.21 parts of dicumyl peroxide were added to the mixture while stirring. The reaction vessel was heated at 85 ° C. for at least 2 hours at a constant rate, and then at 115 ° C. for 4.5 hours. After 65 to 75 minutes have elapsed since the temperature of the reaction vessel reached 80 ° C., 2.9 parts of 10% poly-n-vinylpyrrolidone aqueous solution was added to the reaction mixture. Then, after 100 to 120 minutes had elapsed, a solution containing 0.10 parts of a chain transfer agent in 4.7 parts of n-pentane was added to the reaction vessel. After the temperature of the reaction vessel reached 115 ° C., it was kept constant at this temperature for 3 hours and cooled to ambient temperature over 3 hours.

Example 2

Polystyrene polymers were prepared as described in Example 1. This polymer contained about 3.1% pentane (foaming agent). The resulting expandable polystyrene beads were analyzed according to the procedure of Example 7 and found that the polymer contained in the beads exhibited a polydispersity of 1.82, a weight average molecular weight of 202,000 and Mz: Mn of 2.70. The beads were shielded to a diameter of 0.6 to 1.3 millimeters, dried to remove moisture from the surface, and coated with 0.12% by weight of a mixture of powdered lubricants and anti-crystals commonly used as shielding aids and anti-crystals in industry. . The pentane content in the beads exiting the polymerization reactor was 3.41 wt%. However, since about 0.3% by weight of pentane is usually lost during subsequent processing, the actual pentane content in the foaming step was 3.1% by weight.

Coated beads were foamed in a tree manufacturing model 502 foamer. The inlet steam temperature was about 211 ° F. and the steam inlet rate was about 74 pounds per hour. The first foaming rate was about 208 pounds per hour and the outlet density of the prepuff was about 1.9 lb / ft ³ . The prepuff was cooled with a fluid bed dryer (generally for industrial use) and the resulting prepuff was partially stabilized. The fluid bed dryer has a blower that fluidizes the beads at ambient temperature. The prepuff was air transferred into a storage bag and aged at ambient temperature and humidity for about 3 hours. After aging, the prepuff is foamed again in the same foamer operated under the same conditions so that the resulting prepuff has a density of about 1.10 lb / ft ³ and the amount of prepuff processed in the foamer is about 217 pounds per hour. to be. The resulting prepuff was passed through a fluid bed drier again. The air was transferred back to the reservoir and aged for about 3 hours, after which the prepuff was transferred to a cuts vacuum block molder (4 'x 8' x 34) and molded. The molding cycle was pretreated at an absolute pressure of about 0.5 bar, then cross steamed and pressurized with steam. The block that went through the molding cycle was cooled until the foam pressure stabilized. The pressure relief time is about 30 seconds, the resulting blocks have an average of 10% fusion, 1% shrinkage (actual block shrinkage length after 24 hours after molding for actual mold length), 1.6% collapse (compare to actual mold thickness). The actual thickness shrinkage of one block), and the bulk density of 1.10 lb / ft ³ (weight of the block divided by the volume of the actual molded part).

Example 3

This example illustrates the foaming and molding of relatively large polystyrene beads containing 4.4 wt% pentane. The effect of insufficient aging time prior to the molding step was demonstrated in this example. In addition, comparisons were made to materials containing commonly used amounts of pentane. In addition, the effect of a very short aging time (after the second pre-expansion step before the molding step) on the pentane material containing a full dose (about 6% by weight) of pentane is also illustrated.

Kurt's KV1000 foamer with Kurt's automatic density control system containing an average of 4.40 weight percent pentane and foamed polystyrene beads having a bead diameter of 1.3 to 1.9 millimeters to control the amount of inlet vapor to achieve the desired prepuff outflow density. It was foamed at. Fluid bed dryers were used for both foaming steps. The first flow rate was 2000 lbs / hr and the density was 1.22-1.25 lbft ³ . After the aging for about 2 hours, the prepuff was refoamed at a flow rate of 3000 lbs / hr to a density of 0.88 to 0.90 lb / ft ³ . The prepuff was then molded in a cuts vacuum block molding machine (26 × 49.5 × 196). No preliminary vapor vacuum was used. The steam was added at a pressure of about 0.6 bar for about 6 seconds and then cross steamed with autoclave for about 10 seconds. Vacuum was used to cool the block in the molder. The quality of the block after maturing the prepuff only for one hour was poor. Ie poorly fused and deformed (poor dimension stability). After the prepuffs were aged for 3-4 hours, the blocks were molded to a maximum foam pressure of 0.7 bar to obtain good quality with a total cycle time of 160 to 170 seconds. Typical cycle times were 300 to 360 seconds after a typical pentane product was aged for 24 to 36 hours.

Example 4

This example illustrates how advantageous the use of 4.4% of the pentane composition is compared to using the conventional composition. As a result of the foaming and molding, cycle time, fusion and dimensional stability were achieved in 4.4% pentane compositions over conventional 6% pentane compositions.

Expandable polystyrene beads comprising an average of 4.40% pentane and beads ranging in diameter from 0.6 to 1.3 millimeters were foamed in a Wager VN400 foamer equipped with a fluid bed dryer. The first flow rate had a runoff density of about 1.20 lb / ft ³ to about 2600 lb / hr. After about four hours of maturation, the prepuff was re-foamed at a flow rate of about 4000 lb / hr and an outflow density of about 0.79 to 0.88 lb / ft ³ . After aging for 1 hour, the prepuff was molded in a Wager Bark Compact Block Molding Machine (196 × 49 × 31). Cycle time, fusion and dimensional stability were the same or better than the product having a typical pentane content (6%) aged overnight (ie at least 8 hours).

Example 5

This example illustrates, among other results, the advantageous performance of a formulation containing 3.6% pentane. It should be noted that with the high dimensional stability after the molding step, it has a desired molding cycle time and a desirable short aging time.

Expandable polystyrene bead products comprising an average of 3.58% pentane and beads ranging in diameter from 0.6 to 1.3 millimeters were foamed in a Waver VN400 foamer equipped with a fluid bed dryer. The first flow rate was about 3100 lb / hr at an effluent density of about 1.59 lb / ft ³ . After aging for about 4 hours, the prepuff was foamed again at an outflow density of about 0.84 to 0.86 lb / ft ³ and a flow rate of about 3400 lb / hr. After maturing for about 1 hour, the prepuffs were molded in a wafer back compact block molder. The pressure release (ie cooling) time was 29 seconds. All blocks were well fused and dimensionally stable.

Example 6

This example illustrates that formulations containing 3.63% pentane provide a 50% increase in productivity during the molding step due to shorter cycle times, while providing good fusion and dimensional stability.

Expandable polystyrene beads comprising an average of 3.63% pentane and beads ranging in diameter from 0.6 to 1.3 millimeters foamed the product in a Dingledine Herbert VA-K2000 foamer. The first flow rate was 3000 lb / hr at an outflow density of 1.66-1.75 lb / ft ³ . After aging for about 24 hours, the prepuff was foamed again at an outflow density of about 0.92 to 0.94 lb / ft ³ and a flow rate of about 4000 lb / hr. After aging for about 2 hours, the prepuff was molded in a 16 'tree manufacturing block molder. From this, well fused and dimensionally stable blocks were produced at about 15 speeds per hour, in contrast to 10 blocks per hour for beads with a typical pentane content.

Example 7 (molecular weight distribution curve measurement)

The following apparatus and analytical procedures were used to obtain molecular weight distribution curves for polystyrene polymers. The following analytical procedure was used to determine the molecular weight distribution of the polystyrene polymers of the invention as well as to analyze the products compared and contrasted with the polymers and formulations according to the invention.

[Chromatography Apparatus and Conditions]

The unit is equipped with a Waters 6000A pump with a U6K injector, a pulse damper from Biscotec, two 30 cm PLGel 5 μm mixed bed polystyrene columns, a Biscotec Model 100 Differential Viscometer (DV) and a Waters R401 Differential Refractometer (R1). Equipped. The data acquisition and analysis hardware consists of an IBM PC with wit 640kb RAM, 30 Mb fixed disk and two 5.25 floppy disk drives, a dot matrix printer and an HP 7475A construction device. Used software Ver uni knife to display the M _{Z + 1.} 3.11 (ASYST-Base Package), which was obtained from Biscotec.

Chromatography conditions are as follows.

Nominal flow rate: 1.0 ml / min

Solvent: High purity, non spectral grade THF

Sample injection volume: 0.100 ml

RI detector: Attenuation: 16x

Polarity: +

DV detector: Temperature: 31.0 ± 0.1 ℃

Full scale output: 50 pa

DPT Sensitivity: 0.2074

Data collection: Start time: 6 minutes

Stop time: 24 minutes

[Analysis procedure]

THF used as the mobile phase for the GPC system was filtered through a 0.45 μm frit filter and then degassed under aspirator vacuum for about 45 minutes. THF and flasks were transferred to a GPC system and THF was kept with helium pads. Samples with a concentration of 5 mg / ml were made and filtered through a Gelman Acrodisc CR FTEE 0.45 μm filter before injection.

Only freshly prepared solutions were used as polymers, and the aged solutions were degraded. All solutions were analyzed twice. EPS (foamed polystyrene) samples were not purified by precipitation prior to dissolution and analysis, whereas the purified raw EPS polymers showed no significant difference. To obtain the correct solution concentration for the non-precipitated EPS, the initial solution concentration was determined by gravity analysis by firing samples for volatiles, or total volatiles, as measured by GC and total meter analysis for pentane and moisture, respectively. Corrected for volatiles.

In order to correct for inconsistent flow rates, each chromatogram was normalized to the flow rate indicated during calibration. This is accomplished by calculating the ratio of the pore volume (total extraction volume, first negative peak in the chromatogram) of the calibration chromatogram to the sample chromatogram. The calibrated pore volume measured was 19.72 ml. This ratio is entered into the data analysis package as a calibrated flow rate.

[Examples 8 to 15]

The procedure of Example 1 is substantially the preparation of the polystyrene formulation according to the invention. This polymer formulation is identical to Table 1 (shown later) in Example 8. The polymer formulation of Example 9 contains about 3.5% by weight of blowing agent (pentane). This polymer was analyzed by the procedure according to Example 7. As a result, the number average molecular weight (Mn), the weight average molecular weight (Mw), and the Z-average molecular weight (Mz) were determined. Polydispersity (PD) and Mz: Mn were calculated from these values.

In addition, the analytical procedure of Example 7 was carried out on a variety of currently commercially available products (ie, Examples 9-14), which polymer formulations contained 5.5% to at least 7% by weight of blowing agent. The amount of blowing agent of Example 10 was about 6% by weight. From this analysis, the same molecular weight measurements were obtained. Table 1 (shown below) shows the results of analysis for both the formulations of the invention (Example 9) as well as commercially available formulations currently available.

As can be seen in Table 1 below, only the formulations according to the invention have three characteristics associated with the polymers according to the invention. Although each of the polymers belonged to the definition of a polymer used in the formulation of the present invention, none of these formulations had an amount of blowing agent used in the formulation of the present invention.

TABLE 1

[The polydispersity is calculated as Mw / Mn, and the ratio of Mz: Mw is Mz divided by Mn squared.]

[Examples 16 and 17]

In these examples, (1) total emissions and (2) emissions during the maturation period are exemplified for the expanded polystyrene prepared according to the procedure described in Example 1. Example 16 shows the emissions according to a conventional process in which 6% by weight of blowing agent (pentane) is used. Example 17 shows the emissions following a process using a formulation containing 3.5% by weight of pentane. In Example 16, the amount of blowing agent added during the polymerization reaction was about 6% by weight, while in Example 17, the amount of blowing agent added during the polymerization reaction was about 3.5% by weight. Table 2 (shown below) shows each foaming step, each maturing period and amount of blowing agent discharged during each molding step according to each example. The last row of Table 2 shows the total emissions during the entire foaming, aging and molding phase.

As can be seen in Table 2, the initial polystyrene low polystyrene (Example 17) showed only 42-79% of the emissions according to Example 16. In addition, the total emissions during the maturation time were about 17 to about 48% of the total emissions of Example 16. Thus, the formulations (and polymers) of the present invention show a substantial reduction in emissions and total emissions during the ripening period.

TABLE 2

Example 16 Example 17

Content of blowing agent 6% by weight 3.5% by weight

First firing step 0.76 0.45

Emission at First Ripening 2.0 0.12

First aging time 24 hours 4 hours

Second Foaming Step N / A 0.07

Emission amount at the time of the second ripening N / A 0.22

Second ripening time N / A (2 hours)

0.6 ~ 1.1 0.76% of emissions from molding stage

Total emissions 3.36-3.86% 1.62%

Example 18

[Measurement and calculation method of branch map]

Branching can be measured using a Biscotec differential viscometer and associated software according to the Zim and Stockmayer theory. A more detailed description of this theory is presented in Bill Meyer, Textbook of Polymer Science, 2nd Edition, 1971, Wiley-Interscience, NY, pages 89-90, which is incorporated herein by reference. For linear polystyrene samples, Mark-Houwink constants can be used to calculate the degree of branching per 100 monomer units, for a more detailed description of these constants (Bilmayer, Textbook). of Polymer Science, 2nd edition, 1971, Wiley-Interscience, NY, pages 86-87.

Claims (25)

A process for producing an independent foamed thermoplastic resin article comprising foaming the unfoamed beads in a foaming step of 2 to 5, wherein the bead formulation is prepared at a thermoplasticization temperature at which (A) polymer is formed. Azo compounds that can decompose to form gases, pentane, cyclopentane, neopentane, isopentane, pentane petroleum distillate fractions, propane, butane, isobutane, hexane, isomers of hexane, 2-methylpentane, 3-methylpentane , 2,2-dimethylbutane, 2,3-dimethylbutane, methylcyclopentane, cyclohexane, heptane, propylene, butylene, isobutylene, one species having a molecular weight of 42 or more and a boiling point of 95 ° C. or less at 760 millimeters absolute pressure At least one member selected from the group consisting of mixtures of at least aliphatic hydrocarbons, water, carbon dioxide and ammonium carbonate, in an amount of about 2 to about 4.4 weight percent based on the weight of the beads A blowing agent present in the foam beads, and (B) styrene, derivatives of styrene, vinyltoluene, monohalogenated vinyltoluene and polyhalogenated vinyltoluene forming a linear polymer, acrylonitrile and methyl methacrylate. A polymer prepared from one or more monomers, wherein the polymer is present in the beads in an amount of about 93 to 98 weight percent based on the weight of the beads, while (a) polydispersity of about 1 to less than 2.5 And (b) a weight average molecular weight of 180,000 to 300,000, and (c) Mz: Mn of 2 to 4.5, and also branched at a weight percent of 0 to less than 5, wherein the foaming steps are carried out in a foamer under substantially atmospheric pressure. Wherein the foaming steps are performed such that finally foamed beads are produced, and the foaming steps have a density of 0.8 to 1 finally foamed beads. .1 lb / ft ³ or by molding the finally foamed beads to be fused and further foamed so that the density of this molded foam article is from about 0.8 to about 1.1 lb / ft ³ . A method for producing a thermoplastic resin article foamed into an independent bubble type. The method of claim 1, wherein the blowing agent is present in an amount of 3 to 4% by weight. The method of claim 1, wherein the blowing agent is present in an amount of about 3.5% by weight. The method of claim 1, wherein the polymer is contained in an amount of 95 to 97% by weight based on the weight of the beads. The process for producing a foamed thermoplastic resin article according to any one of claims 1 to 3, wherein the foamed beads are prepared using two foaming steps. The method of producing a foamed thermoplastic resin article according to any one of claims 1 to 3, wherein the flow rate of the beads passing through the foamer is 5 to 120 lb / hr / ft ³ . The method for producing a foamed thermoplastic resin article according to any one of claims 1 to 3, wherein the flow rate of the beads passing through the foamer is 12 to 80 lb / hr / ft ³ . The foamed thermoplastic foam according to any one of claims 1 to 3, wherein the foaming steps are performed by exposing the steam heated to 200 to 220 ° F as soon as the beads enter the foamer. Method for producing a resin article. The method for producing a thermoplastic resin article foamed to an independent foam according to any one of claims 1 to 3, wherein the polydispersity is 1.7 to 1.98. The process for producing a thermoplastic resin article foamed to an independent foam according to any one of claims 1 to 3, wherein the weight average molecular weight is 190,000 to 250,000. The method of claim 1, wherein the Mz: Mn is from about 2.7 to about 3.0. The method of claim 1, wherein the polystyrene polymer is a substantially homopolymer. The method of claim 1, wherein the polystyrene polymer is substantially unsubstituted. 4. The method of claim 1, wherein the bead formulation further comprises a chain transfer agent. 5. The bead formulation according to any one of claims 1 to 3, further comprising a flame retardant which is an organic bromine flame retardant compound or an organic chlorine flame retardant compound in an amount of 0.2 to 2% by weight, based on the total weight of the composition. A method for producing a thermoplastic resin article foamed in an independent bubble form. The flame retardant of claim 15 wherein the flame retardant is at least one member selected from trisdibromopropyl phosphate, hexabromocyclododecane, and bisallyl ether of tetrabromo-bis-phenol A, wherein the flame retardant is selected from A method for producing a foamed thermoplastic resin article in the form of a self-contained foam which is present in an amount of 0.6 to 1.2% by weight based on the total weight. 16. The independent preparation of claim 15 wherein the bead formulation further comprises a flame retardant having a half-life of 1 hour at 110 ° C to 150 ° C and at least one member selected from the group consisting of dicumyl peroxide and other organic peroxides. A method for producing a thermoplastic resin article foamed into a bubble. In a method for producing an independent foamed thermoplastic resin article comprising foaming an unfoamed bead in two foaming steps, the bead formulation comprises: A) pentane, cyclopentane, neopentane, isopentane, Pentane petroleum distillate fraction, at least one member selected from the group consisting of propane, butane, isobutane, hexane, hexane, cyclohexane and heptane, in an amount of about 3.5% by weight based on the weight of the beads A blowing agent present in the foamed beads and a composite made from one or more monomers which are at least one member selected from the group consisting of B) styrene and styrene derivatives, wherein the polymer is based on the weight of the beads Present in the beads in an amount of about 96% by weight, (a) a polydispersity of about 1.7 to about 1.98, (b) a weight average molecular weight of about 200,000 to about 220,000, and (c) about 2.7 Mz: Mn to about 3.0, wherein the polystyrene polymer is branched at a weight percent of 0 to less than 1, wherein the foaming steps are carried out in a foamer at substantially atmospheric pressure, and the foaming steps are finally foamed ratio The foaming step is carried out so that the foaming steps are finally performed so that the density of the foamed beads is about 0.8 to about 1.1 lb / ft ³ , or finally, the pre-foamed beads are fused and molded to further foam. A process for producing a thermoplastic resin article foamed to an independent foam, characterized in that the molding foam is made to have a density of about 0.8 to about 1.1 lb / ft ³ . The method according to any one of claims 1 to 3, wherein the manufacturing method comprises performing a first pre-expanding step to prepare a pre-foaming bead, and (a) a first pre-foaming step of the foamed beads. Then aged for about 1 to about 80 hours, and (b) one to three additional stages in which the maturation period is about 1 to about 80 hours between each additional pre-expanding stage (s) in the first pre-expanding stage. By carrying out a prefoaming step, the finally prefoamed beads are formed as soon as the additional prefoaming step (s) is completed. 20. The method of claim 19, wherein the aging time after the first prefoaming step is about 2 to about 6 hours. 20. The method of claim 19, wherein the aging time between additional prefoaming step (s) is from about 1.2 to about 6 hours. The total amount of blowing agent discharged during the aging time after the first prefoaming step, additional prefoaming step (s), and each prefoaming step is about 0.3 to 1.4 weights based on the total weight of the beads. A process for producing a thermoplastic resin article foamed to an independent bubble type which is%. 23. The method of claim 22, wherein the total amount of blowing agent is about 0.6 to about 0.7 weight percent based on the total weight of the beads. 20. The method according to claim 19, wherein the total amount of blowing agent discharged during the first prefoaming step, the additional prefoaming step (s), the aging time after each prefoaming step and the forming step is based on the weight of the beads. About 2.5% by weight. The method of claim 24, wherein the total amount of blowing agent is from about 1.6 to about 1.7 weight percent based on the total weight of the beads.