DK144335B - PROCEDURE FOR MANUFACTURING FORMED BODIES BASED ON EXPANDED POLYSTYR - Google Patents

Description

(19) DENMARK (Jf)

Ip (12) PUBLICATION ON 144335 B

DIRECTORATE OF THE PATENT AND TRADEMARKET SYSTEM

(21) Application No. 2653/74 (51) IntCI.3 C 08 J 9/22 (22) Filing date 15 May 1974 C 08 F 12/08 (24) Running day 15 May 1974 C 08 F 2/44 ( 41) Aim. available Nov. 19 1974 (44) Posted Feb 22 1982 (86) International Application No. ~ (86) International Filing Day "(85) Continuation Day ~ (62) Master Application No. -

(30) Priority May 18, 1973. 24272/73 * IT

(71) Applicant MONTEDISON S.P.A., Milan, IT.

(72) Inventor Gianfranco Biglione, IT: Antonio Al vares, IT: Guido

Bertazzoni, IT.

(74) Associate Engineer Hofraan-Bang & Boutard.

(54) Process for the production of shaped bodies based on expanded polystyrene.

The invention relates to a process for the production of shaped bodies based on expanded polystyrene, of the kind set forth in the preamble of claim 1.

It is known that it is possible to obtain shaped bodies, on the basis of foamed polymers of styrene, by forming in fine molds (not gaseous), fine particles of polymer containing gaseous -O or liquid expanding agents by work at a temperature exceeding the boiling point of the foaming agent and the softening point of the polymeric material.

* □ 2 144335 According to a method generally followed, the polymer particles containing the foaming agent are first heated (pre-expansion) in either a closed or open container until a predetermined apparent density is reached and then there after one. appropriate aging period, a further expansion by heating in a form (not gas tight) that is pressure resistant.

Because of this heating, the particles sinter into a body of the same shape as the mold.

After molding, the molded body is allowed to cool in the mold for a period long enough to avoid distortions of the molded body, once removed from the mold.

It is known to produce shaped bodies by polymerizing styrene in the presence of an expanding agent, expanding the particles produced, aging and finally forming into a pressure resistant but not gas tight form.

It is also, e.g. from French Patent Specification No. 2,075-4-92, known that the cooling time in the mold after molding can be shortened by adding an elastomer in the polymerization step.

It is an object of the invention to provide a method of the kind set forth in the preamble of claim 1 for the production of expandable polystyrene particles to obtain expanded bodies whereby the residence time in the mold is particularly short, the molded bodies exhibiting only a very small shrinkage, whereby the shaped bodies exhibit a high degree of sintering.

The method according to the invention, which is of the kind set forth in the preamble of claim 1, is characterized by the method of claim 1. The object of the invention is thus fulfilled.

In fact, it has surprisingly been found that the shaped, expanded bodies, especially the blocks made according to the method of the invention, simultaneously exhibit the following characteristics: a) a short residence time in the mold which is generally equal to or even lower than 50% of the time needed to cool the blocks made from pre-expanded particles which do not contain the polymeric elastomeric materials used in the process of the invention; the block (as thickness) · ζ1%, and c) a high degree of sintering.

A particularly preferred embodiment of the method according to the invention is characterized by the characterizing part of claim 2. This results in a particularly short residence time in the mold.

A particularly preferred embodiment of the method according to the invention is characterized by the characterizing part of claim 3. This results in a particularly short residence time in the mold.

A particularly preferred embodiment of the method according to the invention is characterized by the characterizing part of claim 4. This results in a particularly short residence time in the mold, a very low shrinkage and a very high degree of sintering.

Particularly suitable results can be obtained, as indicated, when using ethylene-propylene copolymers containing between 10 and 90% by weight ethylene units and having a logarithmic viscosity number, measured in a 0.25% solution of polymer in tetralin at 135 ° C, which is between 0.25 and 4.

Similarly, as indicated, suitable results can be obtained with alkenic, elastomeric terpolymers containing between 40 and 50% by weight ethylene units, between 50 and 40% by weight propylene units, and up to 15% by weight units of diene hydrocarbons such as dicyclopentadiene, 1,4-hexadiene, methyl norbornene, methyl tetrahydroindene, ethylidene norbornene, butenyl norbornene and the like.

A preferred elastomer is as mentioned ethylene-propylene-ethylidene-norbornene polymer (weight ratio: 50/47/3) with a logarithmic viscosity number (measured in a 0.25% solution of polymer in tetralin at 135 ° C) of about . 1.8.

4 144335

These alkenic elastomers are generally admixed to styrene prior to polymerization or during polymerization, optionally in admixture with expanding agents.

The term "styrene polymers" means both homopolymers of styrene and copolymers of styrene and other vinyl and / or vinylidene monomers containing at least 50% by weight of chemically bonded styrene.

Examples of such comonomers are: alpha-methylstyrene, styrene halogenated in the nucleus, acrylonitrile, methacrylonitrile, esters of acrylic and / or methacrylic acids with alcohols containing from 1 to 8 carbon atoms, N-vinyl compounds such as vinylcarbazole. Copolymers may also be used which, in addition to styrene and possibly the above-mentioned vinyl and / or vinylidene monomers, also contain small amounts of monomers containing several double bonds, such as e.g. divinylbenzene.

The compounds to be used as expanding agents for the styrene polymers can be selected from a wide range of compounds whose properties are known to those skilled in the art.

Particularly suitable are aliphatic hydrocarbons, alone or in appropriate mixtures, and containing between 2 and 6 carbon atoms such as: propane, butane, pentane, hexane and cyclohexane, and the halogenated derivatives of aliphatic hydrocarbons containing from 1 to 3 carbon atoms such as f. eg. chlorofluoro derivatives of methane, ethane and ethylene.

In addition to the expanding agents, other additives such as e.g. flame extinguishing agents, organic and inorganic fillers, dyes, antistatic agents, anti-coagulants to prevent the formation of crumbly particles in the pre-expansion step, plasticizers and other compounds of similar nature.

The polymerization of styrene, preferably in an aqueous suspension, the addition of the expanding agent, preferably during the polymerization, the pre-expansion of the resulting expandable particles, aging and the conversion of the pre-expanding and aged pairs into shaped bodies, by forming into closed molds are carried out in accordance with methods known to those skilled in the art, such as those detailed in "Rigid Plastics Foams" by TN Ferrigno, Reinhold Publishing Corp., New York - USA, (1963).

The following examples are provided to better illustrate the essential features of the invention.

EXAMPLE 1

Various tests were performed with an aqueous suspension polymerization, using mixtures consisting of: - monomeric styrene 100 - deionized water 100 - polymerization initiator (1) 0.20 - suspending agent (2) 0.05 - NaCl 0.1 - alkenic elastomer copolymer (3) 0.1 (1) mixture of tert, butyl peroxide and tert.-butyl perbenzoate (2) acrylic acid / 2-ethylhexyl acrylate copolymer (weight ratio 89/11).

(3) various types of alkenic elastomeric copolymers, namely: (a) ethylene / propylene copolymer containing 50 wt% chemically bonded ethylene units, with a logarithmic viscosity number measured at 135 ° C in 0.25 wt% solution of polymer in tetralin, equal to 0.96.

(b) ethylene / propylene copolymer containing 50% by weight ethylene units having a logarithmic viscosity number of 0.6.

(c) ethylene / propylene / ethylidene norbornene elastone} is alkenic terpolymer (weight ratio: 50/47/3), with a logarithmic viscosity number of 1.8.

(d) polybutadiene gamma of the type known commercially as "Intene NF35A".

Compounds a), b) and c) are in accordance with the invention, while compound d) is indicated for comparative reasons.

The polymerization was carried out at temperatures ranging from 100 ° C to 140 ° C for a total of 20 hours.

6 144335

During the polymerization, 8 parts by weight of an expansion agent consisting of a mixture of n-pentane and isopentane (weight ratio = 70/30) was added.

After cooling to room temperature, filtering, washing with water and drying for 7 hours at 35-40 ° C, the polymer was screened so that expandable polystyrene particles having a diameter ranging from 0.9 to 1.6 mm were obtained.

These particles carried an expanding agent content of about 6% by weight.

To the expandable particles, a conventional anti-caking agent was added in amounts equal to 0.15% by weight.

The mixing was carried out in a SAGA screw mixer at room temperature for approx. 1Q minutes.

The expandable particles thus treated were fed to a pre-expansion apparatus (Erlenbach Mod. K2) which was of the type comprising a screw inlet on the bottom and an outlet of the pre-swelled material from the top, thereby pre-expanding the particles. -dated for approx. 5 minutes with steam at 95-100 ° C.

The pre-expanded particles were then allowed to age in air at room temperature for approx. 24 hours.

The pre-expanded and aged particles were then introduced into a block-making press of the Rauscher type until the 100 x 100 x 50 cm cavity of the mold was filled. The molding was conducted with steam at a pressure of 1 atm.

The cooling time for the blocks is the time required for the pressure inside the blocks to drop to zero after the steam treatment is interrupted.

After 48 hours of molding, the shrinkage and sintering degree of the blocks were determined. This last property was evaluated on a 2 cm thick plate obtained by hot flushing from the central portion of the block and it was determined as the percentage of the expanded particles that were broken when the plate was broken.

7 144335

The properties of the expandable particles and of the resulting shaped blocks are recorded in the following table.

TABLE

- Type of elastomer, alkenic copolymer a b c d -% by weight - 0.1 0.1 0.25 0.1

Properties of the_formed_block - Density in kg / cm ^ 20 20 20 20 20 - Cooling of blocks, in minutes 60 30 27 30 45 - Shrinkage of block 41 41 41 41 * 41 (as thickness),% - Degree of sintering, in% 70 70 70 70 70

As can be seen from the preceding table, blocks with low cooling time can only be produced when using elastomers, alkenic copolymers and terpolymers of types a), b) or c) according to the invention, while in other cases blocks with significantly higher cooling times.