JPS6017405B2 - Method for producing multilayered acrylic polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for making multilayer acrylic polymers.

More specifically, the present invention relates to a method for producing a multilayered acrylic polymer for improving the impact resistance, solvent resistance, and whitening resistance of hard amorphous synthetic resins. Hard amorphous synthetic resin such as acrylic resin, methyl methacrylate (
Polymers (hereinafter abbreviated as MMA) are widely used both indoors and outdoors due to their excellent transparency, weather resistance, beautiful appearance, and ease of molding.

However, ordinary acrylic resin has an impact strength of 4.
It has drawbacks such as low resistance to solvent cracking (craze, cracking), and improvements have been desired. Methods of improving solvent resistance using normal polymerization methods include methods using additives (Kokai No. 49-131241) and methods using special copolymerization (Special Publications No. 7792-1982 and Koichi No. 9919). However, these methods cannot improve impact resistance. As a method for improving impact resistance, a method has been proposed in which particles with a special multilayer structure are manufactured by emulsion polymerization and blended (Jiko Sho 55-127576).
In this method, hard-soft-
It is explained that impact resistance is improved by forming a hard three-layered granular crosslinked polymer and blending it with ordinary acrylic resin. According to detailed research conducted by the inventors,
Although this method could improve impact resistance, it could not improve solvent resistance and was not suitable for our purpose. On the other hand, Japanese Patent Application Laid-Open No. 53-58554 discloses stress whitening of acrylic resin by using a modifier composition obtained by providing an intermediate layer whose hardness (European scale) changes at a constant rate between hard, soft, and hard layers. They claim that it can improve sexuality. Also,
Samurai Publication No. 55-194917 claims that blending a soft-hard-soft-hard four-layer polymer with an acrylic resin is effective in improving stress whitening resistance. However, all of these conventional technologies have advantages and disadvantages, such as impact resistance, solvent resistance,
It was not recognized that the four factors of stress whitening resistance and hot water whitening resistance were improved at the same time, and the above four drawbacks of impact resistant acrylic resins still remained without being improved at the same time.
The inventors of the present invention have conducted intensive research to simultaneously improve the four drawbacks of acrylic resin, and as a result, they have discovered a technology that can simultaneously improve the four drawbacks of acrylic resin without impairing its transparency, wear resistance, and processability. The invention was completed. That is, the present invention comprises, as the first layer, methyl methacrylate alone or a monofunctional monomer copolymerizable with methyl methacrylate in an amount of 3 parts by weight or less out of 10 parts by weight of a mixture of methyl methacrylate and a monomer. Emulsion polymerization of a monomer mixture consisting of
A hard polymer having a temperature of 0° C. or higher, and a second layer containing at least one alkyl acrylate whose alkyl group has 1 to 8 carbon atoms in 100 parts by weight of the monomer polymer.
5. 0 parts by weight of monofunctional monomer copolymerizable with these
-4 parts by weight of a polyfunctional crosslinking agent, 0.05 to 5 parts by weight of a polyfunctional crosslinking agent, and 0.05 to 1 part by weight of a polyfunctional grafting agent, when polymerized alone, a polymer with a Tg of 40 qo or less The monomer polymer to be formed is emulsion polymerized in the presence of the first layer polymer, at which time a pseudo layer structure of three or more stages is formed inside the third layer, and a pseudo layer in contact with the first layer is formed. In , the concentration of the crosslinking agent in 100 parts by weight of the monomeric mixture is 0 to 2.
The concentration of the grafting agent was set to a minimum value of 5 parts by weight and a maximum value of 10 to 0.5 parts by weight, and the concentration of the crosslinking agent was gradually increased as it moved away from the first layer, and the concentration of the grafting agent was decreased. After the crosslinking agent concentration in parts by weight reaches a maximum value of 0.5 to 5 parts by weight and the grafting agent concentration reaches a minimum value of 0 to 2.5 parts by weight, gradually reduce the crosslinking agent concentration and reduce the grafting agent concentration. Then again, the crosslinking agent concentration in 100 parts by weight of the monomer mixture is the minimum value of 0 to 2.5 parts by weight, and the grafting agent concentration is 1.
A multi-stage pseudo layer structure/partially crosslinked polymer designed to have a maximum value of 0 to 0.5 parts by weight, as the third layer,
At least one alkyl acrylate whose alkyl group has 1 to 8 carbon atoms, or up to 3 parts by weight of methyl methacrylate alone or a mixture of methyl methacrylate and a monomer in 10 parts by weight, Consists of a monofunctional monomer copolymerizable with methacrylate or both, and when polymerized alone, has a Tg of 50qC
The monomer or monomer mixture forming the above polymer is subjected to emulsion polymerization in the presence of the polymer consisting of the first and second layers to obtain a hard polymer, and the monomer for producing the polymer is Based on the total weight, the monomer mixture for producing the first layer is 5 to 3% by weight, the monomer mixture for producing the second layer is 30 to 85% by weight, and the monomer or monomer for producing the third layer is The present invention is a method for producing a multilayered acrylic polymer, characterized in that the amount of the acrylic polymer is 10 to 6% by weight.

The purpose of the present invention is mainly to achieve transparency, which is a characteristic of acrylic resin.
An object of the present invention is to provide a method for producing an acrylic polymer for blending, which improves impact resistance, solvent resistance, stress whitening resistance, and hot water whitening resistance without impairing properties, weather resistance, and processability.

The multilayer structure polymer according to the present invention can be produced by a combination of known emulsion polymerization methods.

In this case, it is necessary that no new particles be generated when performing the second and subsequent polymerizations, and for this purpose, a so-called seed polymerization method is employed. That is, when performing the second stage and subsequent polymerizations, it is necessary not to add a new emulsifier, or even if it is unavoidably added, it is necessary to keep it to a small amount within a range where new emulsified particles are not generated. The first layer of the multilayer structure polymer emulsifies MMA alone or a mixture of MMA and a monofunctional monomer copolymerizable with 30 parts by weight or less out of 100 parts by weight of the total first layer monomers. Obtained by polymerization.

It is a hard acrylic resin with a Tg of 5,000 or more, preferably 7,000 or more, and has a non-crosslinked structure. That is, the polymer must be made from a monomer mixture in which no polyfunctional monomers, such as dipinibenzene or allyl methacrylate, which are commonly used as crosslinking or grafting agents, are added to this part. be. Use of such a polymer is extremely effective in maintaining compatibility with the polymer layers in the second and subsequent stages. It is particularly preferred that the average molecular weight of the first layer polymer is between 10,000 and 300,000.
It is desirable that the polymer constituting the second stage (the first pseudolayer in the second layer) be chemically covalently bonded to the polymer constituting the first layer. , the first layer polymer must retain double bonds. In the prior art, for this purpose, a polyfunctional grafting monomer such as allyl methacrylate, which has double bonds at both ends that have mutually different reactivities, is usually blended into the first layer. However, such polyfunctional monomers also act as crosslinking agents, so in order to make the first layer polymer a crosslinked polymer, the first layer polymer does not have free entanglement with the second step polymer. It is presumed that this occurs and prevents the development of stronger interlayer adhesion, which does not give good results for the purposes of the present inventors. As a result of detailed research by the present inventors, a surprising phenomenon has been found that when the polymerization initiator concentration and polymerization temperature are appropriately controlled, excellent physical properties can be achieved without adding a polyfunctional grafting monomer to the first layer. It has been found that, in particular, stress whitening resistance can be obtained. The reason for this is presumed to be that the adhesion between the first layer and the second layer progresses firmly. Although the mechanism is not clear, among the polymerization termination reactions, there are termination reactions that leave double bonds at the ends of polymer chains, that is, unmeltification termination reactions due to chain transfer between polymers, and chain transfer to monomers. When polymerization is carried out under conditions where the termination reaction is larger than the chain transfer to the chain transfer agent or initiator, a double bond remains at the end of the polymer, and this double bond is later Since the added second-stage monomer reacts, it is presumed that a strong grafting effect can be obtained even if no grafting agent is present in the first layer. (For the type of polymerization termination reaction and terminal double bond, for example, P
．． J. Flory, translated by Oka and Kanamaru, Polymer Chemistry, Maruzen,
1955 etc.), the present invention is based on this estimation,
There are no restrictions. In order to achieve the purpose of the present invention, the polymerization conditions for the first layer include a polymerization temperature of 4 to 9,000;
More preferably, it is set in the range of 55 to 860, and the initiator concentration is 0.015 molar ratio to the amount of monomer used.
~3.0%, more preferably 0.10~2.0%, gives good results in balancing the above four properties. Under these conditions, polymerization is carried out using a monomeric mixture prepared with or without the addition of the required amount of chain transfer agent to control molecular weight. The basic composition forming the second layer is at least one alkyl acrylate whose alkyl group has 1 to 8 carbon atoms.
．． and 0 to 4 parts by weight of a monofunctional monomer copolymerizable with these, and 0.05 to 5 parts by weight of a polyfunctional crosslinking agent.
Parts by weight and 0.05 to 10 parts by weight of a polyfunctional grafting agent (total 10 parts by weight), and the Tg of the polymer obtained when polymerized in the absence of the first layer is 40oo or less. The lower the Tg, the better the impact resistance and solvent resistance at low temperatures of the resulting resin composition.

If the amount of the polyfunctional crosslinking agent is out of the range of 0.05 to 5 parts by weight, or if the amount of the polyfunctional grafting agent is out of the range of 0.05 to 10 parts by weight, the impact resistance and stress whitening resistance will decrease. The properties and hot water whitening resistance did not reach the target. Furthermore, if the amount of alkyl acrylate is less than 45 parts by weight, the impact resistance decreases. Tg is measured by a Jintong differential calorimeter. Alkyl acrylates generally have a lower refractive index than MMA polymers, so if a transparent product is required, transparency can be improved by copolymerizing a monomer that provides a polymer with a higher refractive index. be able to. The role of the second layer is to form rubber elastic particles that suppress stress concentration and stress propagation applied to the final product (acrylic resin blended with the modifier composition of the present invention, etc.). Therefore, it is necessary to have an appropriate crosslinked structure.

Therefore, the monomer that should constitute the second layer contains a crosslinking agent. However, adhesion with the central hard first layer or the outer hard third layer is a very important factor for the purpose of the present invention, and if the degree of crosslinking agent in the second layer is excessive, molecular movement at the adhesive interface is As a result, physical properties (such as stress whitening resistance and hot water whitening resistance) are deteriorated, which is presumed to be insufficient adhesion with the first or third layer, while the degree of crosslinking is If it is too small, impact resistance and solvent resistance will decrease. In order to overcome this trade-off, the present inventors have conducted detailed research and found that it is extremely important to make the second layer an aggregate of even thinner pseudo-layers and to create differences in the degree of crosslinking between the pseudo-layers. In other words, the center side of the second layer has the highest crosslinking density, and the first hard layer (the center of the whole particle) and the third hard layer (the outer layer of the whole particle) are closer to each other. Very good results can be obtained by designing the composition of the pseudo layer so that the crosslinking density becomes smaller. In order to realize this, after the formation of the first hard layer, when polymerizing the second layer, multi-stage polymerization is performed again. That is, with respect to the basic composition of the second layer, a monomer mixture with a different concentration of crosslinking agent (and grafting agent) is prepared, and polymerization is performed to first form the first layer and first pseudo layer. Next, a second layer and a second pseudo layer are formed, and the second layer and n-th pseudo layer are formed in the same manner to complete the reaction of the second layer.
At this time, the concentration of the crosslinking agent in the monomer mixture is varied as initially designed. Of course, this multi-stage reaction polymerization may be carried out continuously using some automated method. That is, equivalent results can be obtained by dropping the monomer mixture in a manner that gradually changes the crosslinker concentration over time. Regarding the control of the degree of crosslinking in the second layer, good results are obtained by providing a difference of 2:1 or more, preferably 3:1 or more, between the maximum and minimum values of the crosslinking agent concentration. The crosslinking agent concentration may be 0 at the minimum value, but in that case, the grafting agent described below is necessarily present, and the grafting agent partially functions in the same way as the crosslinking agent, so the entire second layer As such, it is presumed that there is no part that is not crosslinked at all. In order to maximize the effects of the present invention, it is important to obtain an integral bond between each pseudo layer inside the second layer, and an effective method for this purpose is to combine double bonds with different reactivities. The method is to add a grafting agent having a plurality of such functional groups to the raw material monomer compound of each pseudo layer of the second layer.

The functional group of the grafting agent with greater reactivity with the monomer was first consumed in bonding with the monomer and bonded to the polymer (
Second) It leaves functional groups behind. This remaining functional group is
During the subsequent polymerization of the pseudo layer or the third layer, some of the monomers constituting them react with this to provide a strong adhesive interface between each pseudo layer and between the second and third layers. The grafting agent is
Since it works effectively at the interface between the first/second or second/third layers, it is necessary to maintain a concentration profile opposite to that of the crosslinking agent between the second and pseudo layers to give good results. The ratio between the maximum value and the minimum value of the grafting agent is 2:1 or more, preferably 3:1.
Maintaining the above concentration difference will give good results. If an excessive amount of grafting agent is inadvertently present in the center of the second layer, the physical properties of the final product will be abnormal (in the case of melt retention, the melt fluidity will decrease over time.The cause of this is Although it is unclear, it is presumed that the excess functional groups present inside the particles are exposed in some form to the outer surface of the particles. The concentration of the grafting agent can be controlled in exactly the same way as for the crosslinking agent, except that the concentration process is reversed. While the multiple pseudolayers forming the second layer have different degrees of crosslinking and grafting agent content, it is easy to leave the other compositions unchanged and gives good results, but it is not possible to vary them for other reasons. You can also do it.

That is, it is also possible to change the refractive index and Tg of the polymer of the pseudo layer by changing the copolymerization ratio, or to change the concentration of additives such as ultraviolet absorbers and plasticizers. T of each pseudolayer in the second layer
When varying g, it is necessary that the Tg of the polymer when the components of each pseudo layer are individually polymerized is 40°C or less, and preferably the average Tg of the entire second layer is It is effective for improving the impact strength at low temperatures that the Tg (approximately, the weighted average of the Tg of each pseudo layer) is 260 or less, more preferably 10° C. or less.

The third layer polymer is MMA alone or the entire third layer monomer 1
At least one alkyl acrylate whose alkyl group has 1 to 8 carbon atoms, or a monofunctional monomer copolymerizable with these, up to 3 parts by weight in 0 parts by weight or less or, if necessary, a monomer mixture consisting of both, and this polymer has a Tg of 50° C. or higher, preferably 70 qo or higher when polymerized in the absence of the first and second layers. Made of polymer.

This third layer has the effect of improving the compatibility between the elastic body and the matrix resin by graft bonding with the second layer, and also facilitates handling in industrial production by covering the elastic body. The weight ratio of each layer in the three-layer structure composition is 5 to 3 weight % for the first layer, 30 to 85 weight % for the second layer, and 10 to 6 weight % for the third layer.

If the amount of the first layer is less than 5% by weight, seed polymerization is difficult to complete, and uniform multilayer structured particles may not be obtained. On the other hand, if the amount is more than 3% by weight, the effect of improving solvent resistance cannot be sufficiently obtained. If the content of the third layer is less than 1% by weight, the multilayer structure particles become sticky, resulting in poor handling properties and poor compatibility with the matrix resin to be modified. If the amount is more than 6% by weight, the content of the elastic body in the whole decreases and the improvement effect is not exhibited. When producing multilayer polymer particles by emulsion polymerization, the particle size can be adjusted by adjusting the amount of emulsifier.

The particle size is measured by known methods such as electron microscopy, absorbance method, and light scattering method in the state of the emulsion after emulsion polymerization.
Measurable.

It is also possible to measure by electron microscopy in the state of a composition blended with the matrix resin to be modified. The multilayered acrylic polymer obtained by the method of the present invention can be blended by melt extrusion with a normal thermoplastic MMA polymer or copolymer, or can be dispersed in a monomer mixture for cast polymerization to perform cast polymerization. It can be used to modify acrylic resins by making it dispersed in products.

It can also be blended with other thermoplastic synthetic resins, such as vinyl chloride resin, polyamide resin, polyester resin, polystyrene resin, AS resin, ABS resin, polycarbonate resin, etc., to improve their properties. is possible. It is also possible to use a thermosetting resin such as a thermosetting polyester resin by blending it into the prepolymer. The alkyl acrylates whose alkyl group has 1 to 8 carbon atoms used in the present invention include methyl acrylate, ethyl acrylate propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, etc., and these can be used alone or as a mixture of two or more. It will be done.

Particularly preferred among these are n-butyl acrylate or 2-ethylhexyl acrylate. In addition, copolymerizable monofunctional monomers include aromatic unsaturated monobases represented by styrene, unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile, and pinyl monomers such as higher acrylates and higher methacrylates. Examples include mercury.

In particular, as a monomer for adjusting the refractive index, styrene phenyl methacrylate, naphthyl methacrylate, etc. are preferable. Examples of the polyfunctional grafting agent used in the second layer include allyl esters such as acrylic acid, methacrylic acid, maleic acid, and fumaric acid, with allyl acrylate and allyl methacrylate being particularly preferred.

The polyfunctional crosslinking agent used in the second layer includes polyalkylene glycol acrylic, methacrylic gester,
Examples include divinylbenzene.

As the polymerization initiator used for polymerizing the multilayer structure polymer of the present invention, radical polymerization initiators used in ordinary emulsion polymerization can be used, and redox-based polymerization initiators are particularly preferred.

Other additives that are usually added during polymerization, such as chain transfer agents and ultraviolet absorbers, may also be used freely. As the emulsifier, anionic surfactants are preferably used, but other emulsifiers commonly used in emulsion polymerization can also be used. Next, the present invention will be explained in more detail with reference to Examples.

The method for measuring grains in the examples was by electron microscopy.
Solvent resistance was determined by supporting an injection-molded dumbbell at one end with a fulcrum as a boundary, applying a load to the other end, dropping a solvent onto the fulcrum, and examining the time it took for the test piece to break. Impact resistance is ASTM
-The V-notched Izod strength of D256 was measured using a specimen obtained by injection molding. Stress whitening was performed using a tensile test dumbbell made by injection molding with a Tensilon tensile tester.
The results of visually inspecting the whitening state when stretched at a rate of 10% elongation were expressed in a 5-level scale. The molecular weight of the polymer was determined from the intrinsic viscosity of a chloroform solution using an Ostwald viscometer. Hot water whitening was determined by immersing a test piece in boiling water for 15 minutes, taking it out and observing the whitening after cooling and drying, which was expressed on a five-point scale.

The 5-level display is 5 No whitening at all.

4 Slight whitening.

3. Significant whitening.

2. Whitening.

1 strong (whitening)

Ranked in the following manner.

Physical property evaluations were performed at 23oo and 50% RH unless otherwise specified.

Example 1 5.7 volumes of distilled water, 121.0 volumes of sodium dioctyl sulfosuccinate as an emulsifier, and 1.2 volumes of Rongalit as a reducing agent were added to a 10-mL beaker equipped with a condenser and uniformly dissolved.

As a second layer, a homogeneous solution of 220 mL of MMA, 7.0 mL of n-butyl acrylate, 0.7 mL of n-octylcaptan, and 0.23 mL of diisopropylbenzene hydroperoxide was added and polymerized at 8,000 mL. (If the polymerization was completed without polymerizing the second layer, the polymerization would be completed in about 15 minutes, and the average molecular weight of the resulting polymer was about 8, and the Tg was about 100 qo.) In order to obtain union,
Ten minutes after the start of polymerization of the first layer, dropwise addition of the monomer component of the second layer is started. As a component of the second layer and first pseudolayer, n-
A homogeneous solution of 325 parts of butyl methacrylate, 75 parts of styrene, 3 parts of ethylene glycol diacrylate, 4 parts of allyl methacrylate, and 0.5 parts of diisopropylbenzene hydroperoxide was added dropwise over 2 minutes.

After the dropwise addition was completed, the reaction was allowed to proceed for 4 minutes to complete the reaction. Next, as the second layer second pseudo layer component, a homogeneous solution which is the same as the first pseudo layer component except that ethylene glycol diacrylate of the first pseudo layer component was used for 9 hours and allyl methacrylate for 1 hour was prepared for 20 minutes. After dropping, the reaction was allowed to proceed for 40 minutes to complete the reaction. Next, as the second layer and third pseudo layer, n-
Instead of 325 mm of butyl acrylate, a mixture of 203 mm of n-butyl acrylate, 150 mm of MMA, and 47 mm of Tastyrene was used, and other components similar to those of the second pseudo layer were added dropwise over a period of 20 minutes, and after the completion of the dropwise addition, the reaction was allowed to occur for 4 hours. The reaction was terminated. Next, as the second layer and fourth pseudo layer, n-phthyl acrylate 325 of the first pseudo layer components is
Instead of evening, n-butyl acrylate 244 evening and MMAI
Using a mixture of 56 parts of OO Tastyrene, 2 parts of ethylene glycol diacrylate and 6 parts of allyl methacrylate.
A mixed solution of the same components as those of the first pseudo layer was added dropwise over a period of 2 minutes, except that the mixture was mixed with the same ingredients as the first pseudo layer. Then, MMAI as the third layer
OOO, a homogeneous solution of 70 g of n-butyl acrylate, 4.0 g of n-octyl mercaptan, and 1.4 g of diisopropylbenzene hydroperoxide was added dropwise over 2 minutes, and polymerization occurred for about 4 minutes after the dropwise addition was completed. The reaction was terminated.

The reaction temperature was then raised to 95 qo and held for 1 hour. The particle size of the obtained polymer was 850A. The obtained emulsion was poured into a 0.5% aluminum chloride aqueous solution to collect the polymer, and the mixture was dehydrated, washed with warm water, and dried five times.
A multilayer structure polymer was obtained.

Tables 1-1 summarize the component compositions of each layer and each pseudo layer. Table 1-1 The numbers outside () are component amounts, and the numbers inside () are parts by weight (%).Acrylic resin beads with an average molecular weight of 100,000 and made of 97% MMA and 3% methyl acrylate obtained by a conventional suspension polymerization method ( A pellet (approximately 0.3 side) was melt-blended with the above multilayer structure polymer composition to form a pellet.

Using this, a test piece was produced by injection molding. The results of these physical property measurements are summarized in Tables 1-3.
Comparative Example 1 (Crosslinking agent, grafting agent) Example 1 except that the amount of crosslinking agent ethylene glycol dimethacrylate and the amount of grafting agent allyl methacrylate in the second layer and each pseudo layer were changed as shown in Table 1-2. All were conducted on the same machine as in Example 1.

The physical property evaluation results are summarized in Tables 1-3. Table 1-2 Table 1-3 Suspension polymerization MMA by conventional method used in Reference Example 1 and Example 1
The physical properties of the polymer itself were evaluated.

The results are shown in Table 1-3. Example 2, Comparative Example 2 The same procedure as in Example 1 was performed except that the particle size was adjusted by changing the amount of emulsifier, and the physical properties were evaluated.

The results are shown in Table 2. Table 2 Example 3 The same procedure as in Example 1 was conducted except that the second layer and fourth pseudo layer were omitted and the component compositions of each layer were as shown in Table 3-1.

The monster evaluation results are shown in Table 3-2. Comparative Example 3 The same procedure as in Example 3 was conducted except that the composition of the crosslinking agent and grafting agent was as shown in Table 3-2.

The physical properties are also shown in Table 3-23. Section 3-1 Table 3-2 Table 3-3

Claims (1)

[Claims] 1 As the first layer, methyl methacrylate alone or a monomer mixture consisting of methyl methacrylate and a monofunctional monomer copolymerizable in an amount of 30 parts by weight or less in 100 parts by weight of the monomer mixture is emulsion polymerized. Te, Tg
is a hard polymer having a temperature of 50° C. or higher, and the second layer contains at least one alkyl acrylate whose alkyl group has 1 to 8 carbon atoms in 100 parts by weight of the monomer mixture.
9 to 45.0 parts by weight, 0 to 40 parts by weight of a monofunctional monomer copolymerizable with these, 0.05 to 5 parts by weight of a polyfunctional crosslinking agent, and 0.05 to 10 parts by weight of a polyfunctional grafting agent. parts by weight and which, when polymerized alone, form a polymer with a Tg of 40°C or less, is emulsion polymerized in the presence of the first layer polymer, and at that time, the inside of the second layer is A pseudo layer structure of three or more stages is formed, and in the pseudo layer in contact with the first layer, the concentration of the crosslinking agent in 100 parts by weight of the monomer mixture is set to a minimum value of 0 to 2.5 parts by weight, and the concentration of the grafting agent is set to a minimum value of 0 to 2.5 parts by weight. 10 to 0
．． The concentration of the crosslinking agent was set at the maximum value of 5 parts by weight, and the concentration of the crosslinking agent was gradually increased as it moved away from the first layer, and the concentration of the grafting agent was decreased, and once the concentration of the crosslinking agent in 100 parts by weight of the monomer mixture was reduced to 0.5 to 5 parts by weight.
After the maximum value of parts by weight and the minimum value of the grafting agent concentration of 0 to 2.5 parts by weight, the crosslinking agent concentration is gradually decreased, and the grafting agent concentration is increased again to perform crosslinking in 100 parts by weight of the monomer mixture. A partially crosslinked polymer with a multi-stage pseudo layer structure designed to have a minimum concentration of the agent of 0 to 2.5 parts by weight and a maximum concentration of the grafting agent of 10 to 0.5 parts by weight, as the third layer. , 30 parts by weight or less of methyl methacrylate alone or methyl methacrylate and a monomer mixture in 100 parts by weight, at least one alkyl group having 1 to 8 carbon atoms.
consisting of a species alkyl acrylate or 30 parts by weight or less of a monofunctional monomer copolymerizable with methyl methacrylate, or both, and when polymerized alone, Tg
emulsion polymerization of a monomer or a monomer mixture that forms a polymer with a temperature of 50° C. or higher in the presence of a polymer consisting of a first and second layer to obtain a hard polymer, and a monomer for producing the polymer. The monomer mixture for producing the first layer is 5 to 30% by weight, and the monomer mixture for producing the second layer is 30 to 85% by weight, based on the total weight of the polymer.
A method for producing a multilayer acrylic polymer, characterized in that the monomer or monomer mixture for producing the third layer is 10 to 60% by weight.