JP2008255293A - Expandable resin particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an expandable resin particle that comprises a thermoplastic resin composition containing a maleimide copolymer composed of an aromatic vinyl, an unsaturated dicarboxylic anhydride and an N-alkyl substituted maleimide, has a high expansion ratio, and can obtain a pre-expanded particle suitable for bead method internal mold foaming. <P>SOLUTION: This expandable resin particle comprises the thermoplastic resin composition produced by mixing a copolymer (A) composed of the aromatic vinyl, the unsaturated dicarboxylic anhydride and the N-alkyl substituted maleimide as monomers with a copolymer (B) composed of the aromatic vinyl and a vinyl cyanide as monomers, an expanding agent, and a nucleating agent. The expandable resin particle comprises at least one of polyethylene wax or ethylenebisstearylamide, as the nucleating agent, of 0.005-0.5 pt.wt. based on the thermoplastic resin composition of 100 pts.wt. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to expandable resin particles having heat resistance.

  Polystyrene foam is inexpensive and can be easily obtained as an in-mold foam-molded product, so it is widely used as a cushioning material. However, it is not suitable for automotive applications where the temperature is relatively high.

  On the other hand, it is known that a maleimide copolymer obtained by copolymerizing an aromatic vinyl with an unsaturated dicarboxylic acid imide monomer and an unsaturated dicarboxylic acid anhydride has heat resistance. A thermoplastic resin obtained by copolymerizing an aromatic vinyl monomer and a vinyl cyanide monomer to the copolymer is disclosed.

  As described above, the resin having heat resistance is foam-molded in the bead method, so that it is expected to be used as a member having various shapes, for example, an automobile member. When applying the resin to bead-method in-mold foam molding, adjusting the magnification of the pre-expanded particles is one of the important requirements.

  However, the aromatic vinyl monomer and the vinyl cyanide monomer are mixed with the maleimide copolymer obtained by copolymerizing the aromatic vinyl, unsaturated dicarboxylic imide monomer, and unsaturated dicarboxylic anhydride described in Patent Document 1. It is difficult to obtain pre-expanded particles having a high expansion ratio from expandable resin particles obtained by adding a foaming agent to a thermoplastic resin obtained by copolymerizing a body. It is disclosed that the apparent magnification of pre-expanded particles obtained from expandable resin particles made of a polymer comprising 20 parts of a copolymer, 20 parts of acrylonitrile and 60 parts of styrene is 10 times. This is a much lower magnification for pre-expanded particles. Further, when the amount of styrene is increased without using acrylonitrile (Example 5) or the amount of maleimide copolymer is decreased (Example 6), the foaming ratio increases, but the heat resistance tends to decrease.

Patent Document 2 describes the production of a foamed molded product in which the prefoamed particles are completely fused at the boundary surface in the foaming molding process, the particle gap is small, the foamed cells are uniform and fine, the surface hardness is high, and there is no shrinkage. For the purpose of providing expandable styrenic resin particles that enable styrene resin particles, 1 to 20 parts by weight of easily volatile foaming agent and 0.01 to 1.0 parts by weight of polyethylene wax with respect to 100 parts by weight of styrene resin particles Expandable styrenic resin particles comprising a layer containing a particle and the particle surface layer of which does not foam are disclosed.
Japanese Patent Laid-Open No. 4-345639 JP-A-6-122781

  An object of the present invention is a foamed particle comprising a thermoplastic resin composition comprising a maleimide copolymer comprising an aromatic vinyl, an unsaturated dicarboxylic anhydride, and an N-alkyl-substituted maleimide, and has a high foaming ratio. Another object of the present invention is to provide expandable resin particles from which pre-expanded particles suitable for in-mold foam molding of a bead method are obtained.

  As a result of intensive studies, the present inventors did not impregnate and polymerize an aromatic vinyl or vinyl cyanide on a maleimide copolymer comprising an aromatic vinyl, an unsaturated dicarboxylic acid anhydride and an N-alkyl-substituted maleimide. By using a thermoplastic resin composition obtained by mixing a copolymer composed of aromatic vinyl and vinyl cyanide, and further adding a predetermined amount of polyethylene wax or ethylene bisstearyl amide to obtain expandable resin particles, The inventors have found that the expansion ratio is increased when the pre-expansion ratio is set, and the present invention has been completed.

  That is, the present invention comprises a copolymer (A) comprising an aromatic vinyl, an unsaturated dicarboxylic acid anhydride, and an N-alkyl-substituted maleimide as monomers, and an aromatic vinyl and vinyl cyanide as monomers. A foamable resin particle containing a foaming agent and a nucleating agent in a thermoplastic resin composition obtained by mixing a copolymer (B), wherein at least one of polyethylene wax or ethylenebisstearylamide is used as the nucleating agent. Further, the present invention relates to an expandable resin particle characterized by containing 0.005 to 0.5 parts by weight with respect to 100 parts by weight of the thermoplastic resin composition.

As a preferred embodiment,
(1) The aromatic vinyl is styrene.
(2) The unsaturated dicarboxylic acid anhydride is maleic anhydride,
(3) The N-alkyl-substituted maleimide is N-phenylmaleimide.
(4) The vinyl cyanide is acrylonitrile.
(5) The nucleating agent is polyethylene wax.
It relates to the expandable resin particles described above.

  Thermoplastic formed by mixing copolymer (A) of aromatic vinyl-unsaturated dicarboxylic acid anhydride, N-alkyl-substituted maleimide and copolymer (B) of aromatic vinyl-vinyl cyanide Expandable resin particles made of a resin composition can provide pre-expanded particles having a high expansion ratio. Since the pre-expanded particles of the present invention have heat resistance, they can be suitably used as automobile members.

  The thermoplastic resin composition constituting the expandable resin particles of the present invention is a copolymer (A) (hereinafter referred to as copolymer A) composed of aromatic vinyl, unsaturated dicarboxylic anhydride, and N-alkyl-substituted maleimide. In some cases) and a copolymer (B) composed of aromatic vinyl and vinyl cyanide (hereinafter sometimes referred to as copolymer B).

  Examples of the aromatic vinyl unit constituting the copolymer (A) composed of aromatic vinyl, unsaturated dicarboxylic anhydride, and N-alkyl-substituted maleimide include styrene, α-methylstyrene, ethylstyrene, isopropylstyrene, dimethylstyrene, Examples include bromostyrene, chlorostyrene, vinyl toluene, and vinyl xylene.

  Among these, from the viewpoint of compatibility with the copolymer B and ease of polymerization, styrene and α-methylstyrene are preferable as the aromatic vinyl, and styrene, which is inexpensive in price, is optimal.

  Further, examples of the unsaturated dicarboxylic acid anhydride include maleic anhydride, itaconic anhydride, and citraconic anhydride. Maleic anhydride is preferred from the viewpoint of compatibility with the copolymer B, ease of polymerization, and low cost. It is.

  Further, as N-alkyl substituted maleimide, N-methylmaleimide, N-butylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-4-diphenylmaleimide, N-2-chlorophenylmaleimide, N-4-bromophenyl Examples thereof include maleimide and N-1-naphthylmaleimide, and N-phenylmaleimide is optimal from the viewpoint of compatibility with the copolymer B, ease of polymerization, and low cost.

  In copolymer A, when the total amount of aromatic vinyl, unsaturated dicarboxylic acid anhydride, and N-alkyl-substituted maleimide is 100% by weight, N-alkyl-substituted maleimide is 40% by weight in view of heat resistance. The content is preferably 80% by weight or less, and considering the water absorption and moisture absorption resistance, the unsaturated dicarboxylic acid anhydride is preferably 0.1% or more and 5% or less.

  The copolymer (B) comprising aromatic vinyl and vinyl cyanide used in the present invention comprises aromatic vinyl and vinyl cyanide. In the copolymer B, as the aromatic vinyl, as described above, styrene and α-methylstyrene are preferable from the viewpoint of compatibility with the copolymer A and ease of polymerization, and are inexpensive in price. Styrene is the most suitable. Moreover, it is preferable from the surface of compatibility that the aromatic vinyl used for the copolymer A and the copolymer B is the same.

  In copolymer B, examples of vinyl cyanide include acrylonitrile, methacrylonitrile, and α-chloroacrylonitrile, and acrylonitrile is preferred from the viewpoint of compatibility with copolymer A and ease of polymerization. In view of compatibility with the copolymer A, ease of polymerization, and low cost, the copolymer B is preferably a copolymer of styrene and acrylonitrile. The composition ratio of aromatic vinyl and vinyl cyanide in copolymer B is preferably 67% to 85% by weight of aromatic vinyl and 15% to 33% of vinyl cyanide in the copolymer. .

  The thermoplastic resin composition in the present invention is obtained by mixing copolymer A and copolymer B.

  The weight ratio of the copolymer A and the copolymer B in the thermoplastic resin composition is such that the copolymer A is 30% by weight to 80% by weight and the copolymer B is 20% by weight to 70% by weight. Further, it is preferable that the copolymer A is 35 wt% or more and 70 wt% or less, the copolymer B is 30 wt% or more and 65 wt% or less, and the copolymer A is 40 wt% or more and 65 wt% or less. It is more preferable that the amount of the copolymer B is 35% by weight or more and 60% by weight or less. It exists in the tendency for the heat resistance of the thermoplastic resin composition obtained as it is in the said range to be favorable.

  In the present invention, it is necessary that the expandable resin particles contain at least one of polyethylene wax or ethylenebisstearylamide as a nucleating agent. The nucleating agent is used in an amount of 0.005 to 0.5 parts by weight, preferably 0.01 to 0.2 parts by weight, based on 100 parts by weight of the thermoplastic resin composition. If it is less than 0.005 parts by weight, the effect of increasing the magnification cannot be obtained, and if it exceeds 0.5 parts by weight, it becomes difficult to knead the nucleating agent into the thermoplastic resin composition.

  The nucleating agent is at least one of polyethylene wax or ethylene bisstearylamide, and the use of these can improve the expansion ratio. When pre-expanded particles having a more uniform cell structure are obtained, it is desirable to use polyethylene wax.

  The polyethylene wax used in the present invention is a wax mainly composed of ethylene as a monomer composition, and a commercially available polyethylene wax can be used. The molecular weight is preferably 300 to 3000, and more preferably 500 to 1500.

  In the present invention, the thermoplastic resin composition may contain a stabilizer, a lubricant, a flame retardant, an antistatic agent, a plasticizer, a water-absorbing material, a radiation inhibitor, etc., as necessary, in addition to the nucleating agent. You may mix | blend an additive, unless the effect of this invention is impaired.

  As the foaming agent to be contained in the thermoplastic resin composition, a chemical foaming agent or a physical foaming agent can be used.

  Examples of the chemical foaming agent include inorganic chemical foaming agents such as sodium bicarbonate and ammonium carbonate, and organic chemical foaming agents such as azodicarbonamide and N, N′-dinitrosopentamethylenetetramine. .

  Examples of the physical blowing agent include hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, neopentane, cyclopentane, and hexane; 1,1-difluoroethane, 1,2-difluoroethane, 1,1,1-trifluoroethane, 1,1,2-trifluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane, 1,1,1, Fluorinated hydrocarbons such as 2,2-pentafluoroethane, difluoromethane, trifluoromethane; inorganic gases such as carbon dioxide, nitrogen, water, argon, helium; dimethyl ether, diethyl ether, methyl ethyl ether, isopropyl ether, n-butyl ether And ethers such as diisoamyl ether. Among them, it is preferable to use n-butane because it has high solubility in the thermoplastic resin composition and pre-expanded particles having a high expansion ratio can be obtained.

  These foaming agents can be used alone or in admixture of two or more. Although the addition amount of a foaming agent changes according to the foaming ratio desired, it is preferable to make it contain 1-20 weight part with respect to 100 weight part of thermoplastic resin compositions. When a chemical foaming agent is used, it is preferable to add the foaming agent so that the amount of gas generated falls within the above range.

  The expandable resin particles of the present invention can be obtained by a known method. For example, a copolymer (A) composed of aromatic vinyl, unsaturated dicarboxylic acid anhydride and N-alkyl-substituted maleimide and a copolymer (B) composed of aromatic vinyl-vinyl cyanide as a monomer are mixed. When the thermoplastic resin composition is melt-kneaded, the polyethylene wax is melt-kneaded together to form pellet-shaped resin particles, and then the obtained resin particles are dispersed in an aqueous suspension system, A method of impregnating a resin particle with a foaming agent by adding to the dispersion system and stirring to make a foamable resin particle, the resin particles are pressurized in a pressure vessel and dispersed in a liquid foaming agent A method of impregnating a resin particle with a foaming agent to form a foamable resin particle; in the process of melt-kneading the thermoplastic resin composition and polyethylene wax, a physical foaming agent is pressed into the extruder and impregnated; There is by kneading a chemical blowing agent, a method like that extruded with expandable resin beads pellet shape.

  The foamable resin particles of the present invention obtained as described above can be prefoamed by a known method, for example, foamed with pressurized steam or superheated steam to obtain prefoamed particles. .

  Thus, the bulk magnification of the pre-expanded particles obtained from the expandable resin particles is preferably 10 to 90 times.

  The bulk magnification is a value obtained from the magnification of the apparent volume of the pre-expanded particles.

  The pre-expanded particles obtained as described above can be subjected to in-mold foam molding by a known method. Fill the pre-expanded particles in a closed mold with a number of small holes in the wall having the desired shape, and spray the heating medium such as water vapor from the small holes to heat the pre-expanded particles above their softening temperature. Then, the particles are fused together and cooled to obtain a foam molded article.

  Hereinafter, although the thermoplastic resin foam of this invention is demonstrated in detail by a specific Example, this invention is not limited only to this Example. Unless otherwise specified, “parts” and “%” are based on weight.

-How to measure bulk magnification The weight of the expandable resin particle before foaming was measured, and the volume was calculated by dividing by the density of the resin composition as a raw material. Pre-expanded particles obtained by pre-expanding the expandable resin particles were placed in a graduated cylinder, the volume was measured, and how many times the volume was increased was calculated as the bulk magnification.

・ Measurement method of the amount of foaming agent impregnation Measure the weight of the resin particles before impregnating the foaming agent, measure the weight of the foamable resin particles after impregnation with the foaming agent,
Weight after impregnation with foaming agent-The weight of resin before impregnation with foaming agent was taken as the amount of foaming agent, and the amount of foaming agent per 100 parts by weight of resin particles before impregnating with the foaming agent was taken as the amount of foaming agent impregnation.

Example 1
As Copolymer A, Denka IP MS-NA, Copolymer B, manufactured by Denki Kagaku Kogyo Co., Ltd., which is a copolymer of 49% styrene, 50% N-phenylmaleimide, and 1% maleic anhydride Using AS-XGS, manufactured by Denki Kagaku Kogyo Co., Ltd., which is a copolymer of 25% acrylonitrile and 75% styrene, the ratio of copolymer A / copolymer B is 60% by weight / 40% by weight. It mixed and was set as the thermoplastic resin composition. To 100 parts by weight of the thermoplastic resin composition, 0.05 part by weight of polyethylene wax (molecular weight 1000) as a nucleating agent is dry blended, supplied to a single screw extruder, melt kneaded, and the weight per grain is 0.00. 8 mg of resin particles were obtained.

  In a pressure-resistant reactor, 100 parts by weight of the obtained resin particles and 900 parts by weight of normal butane as a foaming agent were charged, and the temperature was adjusted to 160 ° C. and impregnation was performed for 4 hours to obtain expandable resin particles. The obtained foamable resin particles were foamed, and the bulk magnification was measured. The photograph of the cross section of the pre-expanded particle obtained in FIG. 1 is shown. The cell structure was uniform. The cell diameter was measured from the cross-sectional photograph. The cell diameter was 10-50 μm. The results are shown in Table 1.

(Example 2)
Pre-expanded particles were obtained under the same conditions as in Example 1 except that the amount of polyethylene wax was 0.1 parts by weight. The results are shown in Table 1. The cell structure was the same as in Example 1.

(Example 3)
Pre-expanded particles were obtained under the same conditions as in Example 1 except that 0.05 parts by weight of ethylene bisstearylamide was used as the nucleating agent. The results are shown in Table 1. A cross-sectional photograph of the pre-expanded particles is shown in FIG. In the cell structure, the cell diameter near the center of the particle was as large as 500 μm, and the cell diameter around the particle was 10 to 50 μm.

Example 4
Pre-expanded particles were obtained under the same conditions as in Example 1 except that 0.1 parts by weight of ethylene bisstearylamide was used as a nucleating agent. The results are shown in Table 1. The cell structure was the same as in Example 3.

(Comparative Example 1)
Pre-expanded particles were obtained under the same conditions as in Example 1 except that no nucleating agent was used. The results are shown in Table 1. A cross-sectional photograph of the pre-expanded particles is shown in FIG. The vicinity of the particle center had a cell diameter of 500 to 600 μm, the bubbles were broken and coalesced, and the periphery of the particle had a cell diameter of 30 to 50 μm and had a very uneven structure.

From the above results, copolymer (A) comprising aromatic vinyl, unsaturated dicarboxylic anhydride, N-alkyl-substituted maleimide and aromatic vinyl, cyanide using polyethylene wax or ethylenebisstearylamide as a nucleating agent. The expandable resin particles made of the thermoplastic resin composition obtained by mixing the copolymer (B) made of vinyl fluoride had a high bulk magnification when used as pre-expanded particles.

2 is a SEM photograph of a cross section of pre-expanded particles obtained in Example 1. FIG. 4 is a SEM photograph of a cross section of pre-expanded particles obtained in Example 3. FIG. 4 is a SEM photograph of a cross section of pre-expanded particles obtained in Comparative Example 1.

Claims (6)

  Copolymer (A) composed of aromatic vinyl, unsaturated dicarboxylic acid anhydride and N-alkyl-substituted maleimide as the monomer, and copolymer (B) composed of aromatic vinyl and vinyl cyanide as the monomer. ) In a thermoplastic resin composition comprising a foaming agent and a nucleating agent, wherein at least one of polyethylene wax or ethylenebisstearylamide is used as the nucleating agent in the thermoplastic resin composition. Expandable resin particles characterized by containing 0.005 to 0.5 parts by weight per 100 parts by weight of the product.   The expandable resin particle according to claim 1, wherein the aromatic vinyl is styrene.   The expandable resin particle according to claim 1 or 2, wherein the unsaturated dicarboxylic acid anhydride is maleic anhydride.   The expandable resin particle according to any one of claims 1 to 3, wherein the N-alkyl-substituted maleimide is N-phenylmaleimide.   The expandable resin particle according to any one of claims 1 to 4, wherein the vinyl cyanide is acrylonitrile.   The expandable resin particle according to any one of claims 1 to 5, wherein the nucleating agent is polyethylene wax.