JPH0987332A - Styrene/(meth)acrylic acid copolymer and its composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a styrene/(meth)acrylic acid copolymer that gives a foamed sheet improved in primary foamability/extrudability and excellent in printability. SOLUTION: This styrene/(meth) acrylic acid copolymer is a styrene/(meth) acrylic acid copolymer wherein the weight-average molecular weight Mw in terms of polystyrene measured by the gel permeation chromatography is 150,000 to 400,000, the Mw/Mn is from 1.5 to 3.5, the amount of the (meth)acrylic acid units in the copolymer is 1 to 30wt.%, and the degree of acid condensation of the (meth)acrylic acid units is 0.3 to 2.0.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a styrene- (meth) acrylic acid copolymer having excellent heat resistance and good foaming extrusion molding characteristics. Furthermore, it relates to a copolymer suitable for food containers and the like.

[0002]

Demand for thermoplastic resins consumed for food packaging containers and bento containers has been increasing year by year, but in recent years the popularity of microwave ovens at homes and sales of bento at convenience stores have increased. With the increase, the demand for heat-resistant containers that can be heated in microwave ovens has increased significantly.

Generally, food containers and lunch containers are produced by thermoforming a resin sheet or a foam sheet. Conventionally, filler-reinforced polypropylene has been known as a resin material for a foam sheet having excellent heat resistance. But,
The food container molded using this polypropylene sheet containing a filler has a low heat retaining effect, and the heat of the contents is transferred to the human body through the container, so it may be difficult to remove the container with bare hands immediately after heating the microwave oven. In addition, since it contains a filler, it has a defect that the filler is broken during sheet extrusion and mechanical strength is lowered.

On the other hand, polystyrene is known as a resin for a foamed sheet which is excellent in transparency and processability and can be obtained at low cost. The container molded using the expanded polystyrene sheet has a characteristic of being excellent in heat retention. However, polystyrene has a limit in heat resistance, and the molded article is greatly deformed under heating by a microwave oven or the like, and therefore, it is necessary to increase the wall pressure of the molded article.

The styrene- (meth) acrylic acid copolymer is excellent in heat distortion resistance and heat retention and is lightweight. This property is used to make a foamed sheet. In particular, its use is expanding to improve heat resistance of food containers and the like. As a method for producing a styrene- (meth) acrylic acid-based copolymer, for example, a method based on a continuous process (JP-A-56-161409).
Japanese Laid-Open Patent Publication No. 9-8518).
Various methods such as Japanese Patent No. 4) have been proposed. Further, a food container (Japanese Patent Laid-Open No. 62-94539) molded from a foamed sheet of a styrene- (meth) acrylic acid-based copolymer is disclosed.

However, with the conventional resin, when the extrusion speed is increased during the primary foaming, unevenness of foaming occurs inside and on the surface of the foam, and the surface condition of the foam does not become smooth. Was not fully satisfied. Further, depending on the extrusion conditions, pressure fluctuations may occur during extrusion, which makes it difficult to control the thickness of the foamed sheet, and in that respect also, productivity was not sufficiently satisfied. In addition, since these defects cause uneven printing when printing on the foamed sheet,
It was necessary to sufficiently control the extrusion rate of primary foaming.

[0007]

DISCLOSURE OF THE INVENTION The present invention relates to a styrene- (meth) acrylic acid-based copolymer having improved primary foaming extrusion processability and styrene- (meth) acrylic acid present in a foamed sheet having excellent printability. A system copolymer and a composition thereof are provided.

[0008]

[Means for Solving the Problems] That is, the present invention has a polystyrene-equivalent weight average molecular weight MW of 150,000 to 400,000 as measured by gel permeation chromatography.
w / Mn is 1.5 to 3.5, and the (meth) acrylic acid unit in the copolymer is 1 to 30% by weight,
The acid condensation degree of the (meth) acrylic acid unit is 0.3 to 2.0%.
Is a styrene-based monomer- (meth) acrylic acid-based monomer-based copolymer.

A styrene- (meth) acrylic acid-based resin containing 0.1 to 20 parts by weight of a styrene-based thermoplastic elastomer based on 100 parts by weight of the styrene-based monomer- (meth) acrylic acid-based monomer copolymer. A copolymer composition is preferred, and the styrene-based thermoplastic elastomer is preferably crosslinked. The styrene-based monomer- (meth) acrylic acid-based monomer-based copolymer of the present invention can improve the surface condition of the foam and the primary foaming extrusion stability. Alternatively, by using a foamed sheet obtained by extrusion-molding a styrene-based monomer- (meth) acrylic acid-based monomer-based copolymer composition, an effect of improving printability can be obtained. Excellent as a polymer or copolymer composition.

The present invention will be described in detail below. The degree of acid condensation of the (meth) acrylic acid unit used in the present invention is 0.3 to 2.0%. When the acid condensation degree is less than 0.3%, the elasticity at the time of melting is insufficient, and the foam extrusion stability effect is low. If it exceeds 2.0%, melt fracture tends to occur during primary foaming extrusion, which is not preferable. If acid condensation further proceeds, there will be excessive cross-linking, causing gelation and making molding difficult. The degree of acid condensation can be controlled by controlling the residence time and temperature of the solvent degassing layer, which is the latter step of the polymerization reaction.

According to the present invention, a foam having a good surface condition with less breakage and unevenness of foaming during primary foaming extrusion was obtained. It has been found that this is obtained with a resin having a high relaxation elastic modulus in the molten state. In order to improve the elasticity at the time of melting, it is easily conjectured that the average molecular weight is increased to a high molecular weight, but simply increasing the molecular weight increases the viscosity and impairs the fluidity, so the discharge rate decreases during primary foam extrusion. Therefore, it is not preferable in terms of productivity. In addition, in order to increase elasticity while maintaining viscosity during melting, it is possible to consider widening the molecular weight distribution as an option, but there is a problem that the physical properties and transparency decrease due to the composition distribution, which makes it difficult to widen the molecular weight distribution. .
In response to such difficulty, it was found that the elasticity at the time of melting is improved by acid-condensing the carboxylic acid groups of the (meth) acrylic acid unit of the styrene- (meth) acrylic acid-based copolymer, and the primary foam extrudability is An improved foam with less surface breakage and uneven foaming and a good surface condition was obtained.

The Mw of the styrene- (meth) acrylic acid type copolymer of the present invention is in the range of 150,000 to 400,000, more preferably 180,000 to 300,000. If the Mw exceeds 400,000, the viscosity of the melt may be increased, the extrusion moldability, the processability, etc. may be extremely reduced, and the productivity may be deteriorated. Again 15
If it is less than 10,000, the strength of the foam will decrease. Also, Mw
The range of / Mn is 1.5 to 3.5. When it exceeds 3.5, the distribution becomes too wide in the low molecular weight region and the strength of the foam decreases. If the composition is less than 1.5, it becomes difficult to supply the composition by the bulk polymerization, suspension polymerization or emulsion polymerization method, which is industrially excellent in productivity.

When the composition of the present invention is blended with a cross-linking rubbery polymer, after dissolving the sample in tetrahydrofuran,
The sample solution is obtained by filtering the crosslinked rubbery polymer with a sample pretreatment filter for liquid chromatography, and the solution sample is used as a matrix for the composition of the present invention. The liquid chromatograph sample pretreatment filter used at that time is a non-aqueous non-sterile filter having a pore size of 0.45 μm.

The (meth) acrylic acid unit in the copolymer of the present invention is 1 to 30% by weight, more preferably 5 to 15% by weight.
It is. When the (meth) acrylic acid unit in the copolymer exceeds 30% by weight, the viscosity of the melt becomes high, the extrusion moldability, the processability, etc. are deteriorated, and the productivity is deteriorated. Sometimes, a gel composition may be produced in a large amount. When the amount is less than 1% by weight, the effect of improving the heat resistance of the copolymer is insufficient.

The styrene-based monomer of the present invention is an aromatic vinyl-based monomer such as styrene, α-methylstyrene, ethylstyrene, isobutylstyrene, tert-butylstyrene, bromostyrene, chlorostyrene,
Vinyl toluene and the like. Of these, styrene is preferable because of its excellent reaction with (meth) acrylic acid.
Examples of the (meth) acrylic acid-based monomer include acrylic acid and methacrylic acid, and methacrylic acid is preferable from the viewpoint of easy production of the copolymer.

The styrenic thermoplastic elastomer in the present invention is a block copolymer having polystyrene in the hard segment, such as styrene-butadiene block copolymer (SB), styrene-butadiene-styrene block copolymer (SBS) and styrene-isoprene. Block copolymer (SI), styrene-isoprene-styrene block copolymer (SI)
S), styrene-ethylene / butene block copolymer (SEB), styrene-ethylene / butylene-styrene block copolymer (SEBS), styrene-ethylene / propylene block copolymer (SEP), styrene-ethylene / propylene-styrene block A copolymer (SEPS) etc. are mentioned. Further, a part or all of these double bonds may be hydrogenated.

When the amount of the styrene-based thermoplastic elastomer added exceeds 20 parts by weight, the heat resistance of the foamed product is largely lowered, and it is difficult to secure the desired heat resistance, which is not preferable. The crosslinkable rubbery polymer or the crosslinkable rubbery polymer generally used for high impact polystyrene (HIPS), polybutadiene, polyisobutylene, polyethylene / butadiene (partially hydrogenated polybutadiene), etc. Examples of the polymer include: The composition containing the cross-linking rubbery polymer can be obtained by generally using a method for producing high-impact polystyrene and changing a part of the monomer from styrene to (meth) acrylic acid.

The content of the cross-linked rubbery polymer is 20% by weight.
When it exceeds the above range, the heat resistance of the foam is largely lowered, and it is difficult to secure the desired heat resistance, which is not preferable. Here, the content of the cross-linked rubbery polymer is calculated by dissolving 1 g of the composition in 50 ml of methyl ethyl ketone, centrifuging and drying the insoluble matter, and calculating the dry weight thereof. Moreover, the polymerization method of the composition in the present invention includes bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization and the like.

Examples of the copolymer composition containing the cross-linking rubbery polymer include bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization. Further, additives commonly used in styrene resins, such as antioxidants, lubricants, plasticizers, colorants, etc., may be added within a range that does not impair the object of the present invention. Further, a vinyl monomer copolymerizable with styrene may be copolymerized with the copolymer of the present invention within a range not impairing the object of the present invention.

Vinyl monomers copolymerizable with styrene include (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate; and (meth) acrylonitrile. Examples include vinyl cyanides.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The measuring conditions such as physical properties are shown below.
In the present invention, Mw and Mn are the polystyrene-equivalent weight average molecular weight and number average molecular weight of the styrene- (meth) acrylic acid copolymer, respectively, and are determined by the RI method using gel permeation chromatography.

In the present invention, the RI method is a differential refractive index detection method, which is measured by gel permeation chromatography using tetrahydrofuran as a solvent. The molecular weight Mw at each elution time may be calculated from the elution curve of a similarly prepared monodisperse polystyrene solution sample of known molecular weight, and the polystyrene-equivalent Mw may be calculated. Measuring machine: Tosoh HCL8020, sorting column: Tosoh TS
K-gel-GMH-XL (2 lines), solvent: tetrahydrofuran, sample concentration: 20 mg of sample is dissolved in 20 ml of solvent, temperature: 38 ° C, flow rate: 1 ml / min.

Sample pretreatment filter for liquid chromatograph: non-aqueous non-sterile 13N manufactured by GL Sciences
0.45 μm. Expansion ratio = specific gravity of styrene resin / specific gravity of molded product Melt flow rate: according to 1SO-R1133. Vicat softening point: according to ASTM-D1525.

The amount of (meth) acrylic acid units in the copolymer is determined by dissolving 0.5 g of the copolymer in 30 ml of methyl ethyl ketone and titrating with a 1/10 normal potassium hydroxide ethanol solution. From the volume of the 1/10 normal potassium hydroxide ethanol solution consumed up to the end point and the 1/10 normal potassium hydroxide ethanol solution volume consumed for the blank, the moles of carboxylic acid groups of (meth) acrylic acid were calculated. The quantity is obtained and the weight of the (meth) acrylic acid unit is obtained by multiplying the molecular weight of the (meth) acrylic acid.

An automatic potentiometric titrator manufactured by Mitsubishi Chemical was used for the titration. Drop rate: 50 μl / sec, minimum drop rate: 10 μ
1 / drop, maximum dropping amount: 300 μl / drop, stirring time after dropping: 5 seconds, and the maximum value (or minimum value) of potential difference / change amount of sample volume (δE / δV) was set as the end point. Further, as a blank, a sample of a solvent alone was titrated, and a titration amount exceeding pH 13 was used as an end point of the blank to correct the actual titration amount.

The weight% of the (meth) acrylic acid unit in the composition was calculated by determining the ratio of the weight of the (meth) acrylic acid unit to the weight of the sample used for the measurement. The measurement was performed 3 times and the average value was shown. The molar quantity of acid anhydride bond was determined by dissolving 1.0 g of the copolymer in 50 ml of methyl ethyl ketone, adding 31 ml of a 1/20 normal n-butylamine solution in methyl ethyl ketone, and after 5-10 minutes, 1
Immediately titrate a sample solution containing 30 ml of a / 20 N hydrochloric acid ethanol solution with a 1/100 N hydrochloric acid ethanol solution.

An automatic potentiometric titrator manufactured by Mitsubishi Chemical was used for the titration. Drop rate: 50 μl / sec, minimum drop rate: 10 μ
1 / drop, maximum dropping amount: 300 μl / drop, stirring time after dropping: 5 seconds, potential difference / change amount of sample volume (δE / δ)
The maximum value (or minimum value) of V) was set as the end point. In addition, as a blank, a methyl ethyl ketone solution of 1 / 20N in 31 ml of 50 ml of methyl ethyl ketone was used as a blank.
1 was added, and 5 to 10 minutes later, a solution containing 30 ml of 1/20 N hydrochloric acid ethanol solution was titrated.

The measurement was carried out three times, and the average value was shown. The measurement temperature is room temperature. The molar quantity of acid anhydride bonds was calculated as follows from the difference in volume between the blank solution consumed by the end point and the sample-containing solution 1 / 100N ethanolic hydrochloric acid solution. Molar amount of acid anhydride bond = (blank consumed titrant volume-consumed titrant volume of the sample solution) x specified concentration of the titrant (mol / l) The acid condensation degree is contained per unit weight of the composition. The ratio of the molar quantity of acid anhydride bond to the molar quantity of carboxylic acid group of (meth) acrylic acid.

The content of the crosslinkable rubbery polymer was determined by dissolving 1 g of the composition in 50 ml of methyl ethyl ketone (MEK), centrifuging and drying the insoluble matter to obtain the dry weight. As the centrifuge, Hitachi ultra high speed centrifuge CR20 was used. The measurement conditions are: rotation speed: 20000 rpm, rotation time: 1 hour, drying temperature: 160 ° C., drying time: 45 minutes.

Regarding the surface condition of the foam, the condition of the foam surface and the cross section is observed, and the degree of its appearance is visually judged by using the degree of the phenomenon of unevenness of foaming called as a standard. The smaller the amount of the barn and the smaller the size of the barb, the better. The discharge fluctuation of the foam is judged by the fluctuation frequency based on the fluctuation of the die pressure during foam extrusion. The smaller the fluctuation range of the die pressure at the time of extrusion, and the smaller the fluctuation frequency and the constant frequency, the better.

The flexural strength is the flexural strength of a foam, which was measured using a tensile compression tester manufactured by Minebea Co., Ltd. after cutting the foam into 15 mm squares. The conditions are as follows.
Distance between spans: 101.6 mm, bending speed: 20 mm /
Minutes, measurement temperature: 23 ° C., measurement humidity: 50%.

[0032]

[Example 1] "Production of styrene-methacrylic acid copolymer" A mixture of styrene 72.1% by weight, methacrylic acid 5.4% by weight, ethylbenzene 20% by weight, and 2-ethylhexanol 2.5% by weight. A polymerization solution prepared by adding 0.01 part by weight of 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane to 100 parts by weight was added to a 5.0 liter completely mixed reactor. 1.00 for polymerization equipment
Charge continuously at liter / hr. Adjust the temperature of the fully mixed reactor to 135 ° C. The polymer solution continuously discharged from the polymerization reactor was taken out, retained for 2 hours in the devolatilization layer depressurized to 10 to 20 torr and heated to 200 ° C., and then introduced into an extruder heated to 220 ° C. and pelletized. To do.

To this styrene-methacrylic acid copolymer, 1 part by weight of a foaming nucleating agent and 3 parts by weight of a foaming agent were added to a resin, and a 30 mm extrusion equipped with a T die having a width of 30 mm was added. Using a foaming machine, foam extrusion is performed to produce a foam. Resin melting zone temperature 180-200 ° C, rotary cooler temperature 150-160 ° C, T-die temperature 14
Adjust to 0-150 ° C. Liquid butane gas is used as the foaming agent, and Mistron vapor manufactured by Nippon Mistron is used as the foam nucleating agent.

The results are shown in Table 1.

[0035]

[Example 2] "Production of styrene-methacrylic acid copolymer" A copolymer was produced under the same conditions as in Example 1 except that the residence time of the devolatilization layer was changed to 4 hours.

[0036]

[Examples 3 and 4] "Production of styrene-methacrylic acid copolymer" Same as Example 1 except that the temperature of the devolatilizing layer was changed to 220 ° C and the residence time of the devolatilizing layer was changed to 0.5 and 2 hr. A copolymer was produced under the conditions of.

[0037]

[Example 5] A copolymer was produced under the same conditions as in Example 1 except that the temperature of the devolatilization layer was changed to 240 ° C.

[0038]

[Comparative Example 1] "Production of styrene-methacrylic acid copolymer" A mixed solution of 72.1% by weight of styrene, 5.4% by weight of methacrylic acid, 20% by weight of ethylbenzene and 2.5% by weight of 2-ethylhexanol. A polymerization solution prepared by adding 0.01 part by weight of 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane to 100 parts by weight was added to a 5.0 liter completely mixed reactor. 1.00 for polymerization equipment
Charge continuously at liter / hr. Adjust the temperature of the fully mixed reactor to 135 ° C. The polymer solution continuously discharged from the polymerization reactor was introduced into an extruder heated at 220 ° C. having a vent port whose pressure was reduced to 20 to 30 torr, and pelletized after volatilization.

[0039]

[Comparative Example 2] "Production of styrene-methacrylic acid copolymer" A copolymer was produced under the same conditions as in Example 1 except that the residence time was changed to 0.5 hr.

[0040]

[Comparative Example 3] "Production of styrene-methacrylic acid copolymer" A copolymer was produced under the same conditions as in Example 1 except that the temperature of the devolatilization layer was changed to 220 ° C and the residence time was changed to 4 hours.

[0041]

[Comparative Example 4] "Production of styrene-methacrylic acid copolymer" Styrene 35.0% by weight, methacrylic acid 32.5% by weight, ethylbenzene 20% by weight, 2-ethylhexanol 2.5
1,1-bis (t
-Butylperoxy) 3,3,5-trimethylcyclohexane was added in an amount of 0.01 parts by weight to prepare a copolymer under the same conditions as in Example 1, except that acid condensation was conducted. The reaction proceeded excessively and production was impossible.

[0042]

Comparative Example 5 “Production of GP polystyrene” 77.5% by weight of styrene,
0.01 parts by weight of 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane was added to 100 parts by weight of a mixed solution of 20% by weight of ethylbenzene and 2.5% by weight of 2-ethylhexanol. A polymer was produced under the same conditions as in Example 1 except that the resulting polymerization liquid was used.

[0043]

[Comparative Example 6] "Production of styrene-methacrylic acid copolymer" A mixed liquid of 71.3% by weight of styrene, 6.2% by weight of methacrylic acid, 20% by weight of ethylbenzene and 2.5% by weight of 2-ethylhexanol. A polymerization solution prepared by adding 0.01 part by weight of 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane to 100 parts by weight was used, and the temperature of the complete mixing type reactor was 100 ° C. A copolymer was produced under the same conditions as in Example 1 except that the above conditions were adjusted.

[0044]

[Comparative Example 7] "Production of styrene-methacrylic acid copolymer" A mixed liquid of styrene 66.6% by weight, methacrylic acid 5.9% by weight, ethylbenzene 25% by weight, and 2-ethylhexanol 2.5% by weight. A polymerization solution prepared by adding 0.01 part by weight of 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane to 100 parts by weight was used, and the temperature of the complete mixing type reactor was 140 ° C. A copolymer was produced under the same conditions as in Example 1 except that the above conditions were adjusted.

[0045]

Comparative Example 8 “Production of Styrene-Methacrylic Acid Copolymer” Styrene 64.3% by weight, methacrylic acid 5.7% by weight, ethylbenzene 27.5% by weight, 2-ethylhexanol 2.
A polymerization solution prepared by adding 01 parts by weight of 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane to 100 parts by weight of a 5% by weight mixed solution was added to 150 parts by weight.
A polymerization apparatus 1 having a 5.0 liter perfect mixing type reactor adjusted to 0 ° C. is continuously charged at 1.00 liter / hr. Separately, with respect to 100 parts by weight of a mixed solution of 71.3% by weight of styrene, 6.2% by weight of methacrylic acid, 20% by weight of ethylbenzene and 2.5% by weight of 2-ethylhexanol, 1,1-bis (t-butylperoxide) was added. Oxy) 3,3,5
-The polymerization solution obtained by adding 0.01 parts by weight of trimethylcyclohexane is continuously charged at 0.8 liter / hr into the polymerization apparatus 2 having a 5.0 liter perfect mixing type reactor adjusted to 100 ° C. . The polymerization reactors 1 and 2 were connected in parallel, and the polymer solution continuously discharged from both was stirred by a mixer, and then the pressure was reduced to 10 to 20 torr.
The mixture was supplied to the devolatilization layer heated to 0 ° C., retained for 2 hours, then introduced into an extruder heated to 220 ° C., and pelletized.

The copolymers or polymers obtained in Examples 2-5 and Comparative Examples 1-8 were foamed and extruded in the same manner as in Example 1,
A foam was produced. Table 1 shows the results. 1 in the table)
Is an evaluation of the surface condition. "Slightly good" is a level where uneven glossiness is sometimes caused partially, "poor" is uneven glossiness as a whole, and "melt" is a level where melt fracture causes uneven thickness.

2) in the table is the evaluation of the discharge fluctuation. "Slightly large" causes uneven thickness in some areas. "Many" means
This is a level that causes uneven thickness on the whole.

[0048]

[Table 1]

[0049]

[Example 6] "Production of styrene-methacrylic acid copolymer" Example 1
Asahi Kasei styrene-butadiene block copolymer "Tafprene 12" per 100 parts by weight of the polymer obtained in
5 "5 parts by weight were blended and extruded and blended with a biaxial extrusion kneader heated to 180 to 220 ° C to produce a copolymer composition.

[0050]

[Example 7] "Production of styrene-methacrylic acid copolymer" A mixed solution of 73.7% by weight of styrene, 3.8% by weight of methacrylic acid, 20% by weight of ethylbenzene and 2.5% by weight of 2-ethylhexanol. To 100 parts by weight, 7 parts by weight of a rubbery polymer (Asaprene 720A manufactured by Asahi Kasei), 1,1-bis (t
-Butylperoxy) 3,3,5-trimethylcyclohexane (0.01 part by weight)
A polymerization apparatus having 2 liters of completely mixed reactors in series is continuously charged at 1.67 liters / hr. A mixed solution of 50% by weight of methacrylic acid and 50% by weight of ethylbenzene is added to the second reactor at 0.085 liter / hr. The temperature of the first stage reactor is adjusted to 125 ° C and the temperature of the second stage reactor is adjusted to 145 ° C. Take out the polymer solution continuously discharged from the polymerization reactor,
After being retained for 2 hours in a devolatilizing layer heated to 200 ° C. and depressurized to rr, it is introduced into an extruder heated to 220 ° C. and pelletized.

[0051]

Comparative Example 9 “Production of Styrene-Methacrylic Acid Copolymer” Comparative Example 1
A copolymer was produced under the same conditions as in Example 6 except that 100 parts by weight of the copolymer obtained in 1. was used.

[0052]

Comparative Example 10 Example 7 was repeated except that the polymer solution continuously discharged from the polymerization reactor was introduced into an extruder heated to 220 ° C. with a vent port having a pressure reduced to 20 to 30 torr and pelletized after volatilization. A copolymer was produced under the same conditions as above. The copolymers obtained in Examples 6 and 7 and Comparative Examples 9 and 10 were foamed and extruded in the same manner as in Example 1 to produce foamed products. The results are shown in Table 2.

In the table, 1) is the evaluation of the surface condition. "Slightly good" is a level at which uneven glossiness is sometimes caused partially. 2) in the table is the evaluation of the ejection fluctuation. "Slightly high"
Is a level at which uneven thickness is partially generated.

[0054]

[Table 2]

[0055]

EFFECT OF THE INVENTION By using the styrene- (meth) acrylic acid type copolymer of the present invention or the copolymer composition thereof, a foam having a good surface condition can be stably produced.

Claims (4)

[Claims] 1. A polystyrene-equivalent weight average molecular weight MW of 1 measured by gel permeation chromatography.
5 to 400,000, Mw / Mn is 1.5 to 3.5, and the (meth) acrylic acid unit in the copolymer is 1
To 30% by weight, and the degree of acid condensation of (meth) acrylic acid units is 0.3 to 2.0%. Polymer. 2. A styrene-based thermoplastic elastomer is contained in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the styrene-based monomer- (meth) acrylic acid-based monomer-based copolymer according to claim 1. A styrene-based monomer- (meth) acrylic acid-based monomer-based copolymer composition. 3. A styrene-based monomer- (meth) acrylic acid-based monomer-based copolymer composition, wherein the styrene-based thermoplastic elastomer according to claim 2 is crosslinked. 4. The styrene-based monomer- (meth) acrylic acid-based monomer-based copolymer or the styrene-based monomer- (meth) acrylic acid-based monomer-based copolymer composition according to claim 1 or 2. Foamed sheet made of objects.