JPH0364337A - Latex composition - Google Patents

Abstract

PURPOSE:To obtain an excellent blistering resistance and adhesive strength necessary for an adhesive compsn. for carpet backing by compounding a specific copolymer latex with an org. high molecular heat sensitizer and a bicarbonate salt. CONSTITUTION:100 pts.wt. (solid base) copolymer latex is compounded with 0.01-30 pts.wt. org. high molecular heat sensitizer and 0.03-5 pts.wt. bicarbonate salt. The copolymer latex is obtd. by emulsion polymerizing a monomer mixture comprising: 25-70wt.% at least one monomer selected from the group consisting of an aliph. conjugated diene, 2-10C alkyl acrylate, and 6-14C alkyl methacrylate; 0-5wt.% ethylenically unsatd. carboxylic acid; and 25-75wt.% other monomer copolymerizable with these two monomers. The copolymer latex has a glass transition temp. of +30 to -55 deg.C, a mean particle diameter of 600-2500Angstrom , and a gel content of 40-99wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a latex composition, and more particularly to a latex composition useful for manufacturing nonwoven fabrics, artificial leather, soaked rubber products, various foam products, carpets, and the like. especially,
The latex composition of the present invention has excellent blister resistance and adhesive strength, and is suitable as an adhesive composition for carpet lining.

(Conventional Technique Wl) Tufted carpets, which are a typical type of carpet, are generally made of a primary base fabric of polypropylene, crimped nylon yarn,
A carpet lining composition is applied to the back side of a gray fabric obtained by tufting tufted yarn such as polyester crimped yarn, and the carpet lining composition is directly heated and dried, or after the lining composition is applied, it becomes rough. It is manufactured by laminating a secondary base fabric such as a synthetic fiber nonwoven fabric and drying it with hot air.

The above carpet lining composition is made by adding an inorganic filler and, if necessary, a dispersant, an anti-aging agent, an antifoaming agent, a foaming agent, a crosslinking agent, etc. to a copolymer latex, and then adjusting the viscosity to an appropriate level with a thickener. Manufactured by adjusting.

The properties required for carpet lining compositions include:
(υThe removal strength of the tufted yarn in the manufacturing process or the product and the peeling strength between the primary base fabric and the secondary base fabric are high, (
2) Good drying efficiency in the drying process and good blister resistance (no blistering).

In particular, in recent years, in order to increase productivity in the carpet processing and manufacturing process, a drying method has been adopted in which large dryers (modular type) are used to dry the carpet at high speed under high temperature and high air volume conditions. However, in this method, blister resistance is particularly important.

As a method of increasing blister resistance, a method of increasing the solid content concentration in the composition has been proposed, but increasing the solid content concentration decreases the fluidity of the composition, the dispersibility of the filler, and the viscosity stability. Moreover, the blister resistance has not necessarily been sufficiently improved. Furthermore, this method requires a high concentration of the copolymer latex, which causes problems in the production of the copolymer latex. That is, in order to increase the concentration of the composition, for example, it is necessary to increase the particle size of the copolymer latex constituting the composition and lower the viscosity, but as a result, coagulation occurs and the polymerization process becomes a big problem.

Another method for improving blister resistance is to blend organic polysiloxane into polymer latex (
JP-A No. 56-44191), a method of blending starch (JP-A-54-126242), a method of blending an organic polysiloxane and an aromatic sulfonic acid-formaldehyde condensate (JP-A-62-167337). Public bulletin)
Although such methods have been proposed, they have not yet achieved sufficient blister prevention, and there are problems with the stability of carpet lining compositions over time, decomposition, etc., and they are still unsatisfactory.

(Problems to be Solved by the Invention) The present invention solves the above conventional problems and provides a latex composition with excellent blister resistance and adhesive strength, particularly a latex composition suitable for carpet lining. .

(Means for Solving the Problems) As a result of studying the mechanism of blister generation in carpets, the present inventors found that blister generation is caused by migration of the carpet lining composition after it is applied to the carpet,
In other words, the latex and the inorganic filler separate due to a decrease in the viscosity of the composition due to a sudden rise in temperature during the drying process, which causes the surface of the latex phase to form a film, and the water that has no place to escape boils and forms blisters. I found out.

The present inventors have discovered that a latex composition with excellent blister resistance and adhesive strength can be obtained by blending a specific amount of an organic polymer heat sensitizing agent with a cloud point and bicarbonate into a copolymer latex, and has found that a latex composition with excellent blister resistance and adhesive strength can be obtained. The present invention was completed based on the findings.

That is, the present invention provides at least one compound selected from (a) an aliphatic conjugated diene, an acrylic acid alkyl ester having an alkyl group having 2 to 10 carbon atoms, and a methacrylic acid alkyl ester having an alkyl group having 6 to 14 carbon atoms; Seed monomer 25~
70% by weight, (b) 0-5% by weight of ethylenically unsaturated carboxylic acid,
and (c) a 99% by weight copolymer latex obtained by emulsion polymerization of a monomer mixture consisting of 25 to 75% of other monopolymers copolymerizable with (a) and (b) above. and 0 organic polymer heat-sensitizing agent per 100 parts by weight (solid content basis) of the copolymer latex.
．． The present invention relates to a latex composition containing ~30 parts by weight of OI and 0.03 to 5 parts by weight of bicarbonate.

The present invention will be explained in detail below.

Component (a) of the monomer mixture used in the production of the copolymer latex in the present invention is an aliphatic conjugated diene, an acrylic acid alkyl ester having an alkyl group having 2 to 10 carbon atoms, and an acrylic acid alkyl ester having an alkyl group having 6 to 14 carbon atoms. At least one monomer selected from methacrylic acid alkyl esters having an alkyl group.

As the aliphatic conjugated diene, 1,3-butadiene,
Examples include isoprene, 2-chloro-1,3-butadiene, and the like. Among these, 1,3-butadiene is preferred. Examples of the acrylic acid alkyl ester having an alkyl group having 2 to 10 carbon atoms include ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate.

Examples of the methacrylic acid alkyl ester having an alkyl group having 6 to 14 carbon atoms include 2-ethylhexyl methacrylate and lauryl methacrylate.

The above monomer (a) is an essential component for imparting appropriate flexibility and adhesive strength to the obtained copolymer, and its usage ratio is 25 to 70% by weight of the monomer mixture. , and the pulp content is 30 to 65% by weight. Usage rate is 25% by weight
If it is less than 70% by weight, the resulting copolymer will have poor flexibility and adhesive strength, while if it exceeds 70% by weight, the carpet produced using the resulting copolymer latex will be too soft, have low peel strength, and have poor blister resistance. Deteriorate.

Component (b) of the monomer mixture is an ethylenically unsaturated carboxylic acid, such as itaconic acid, acrylic acid, methacrylic acid, fumaric acid, maleic acid, and the like. These ethylenically unsaturated carboxylic acids can be used alone or in combination of two or more. In particular, it is preferable to use acrylic acid and methacrylic acid in a suitable ffi combination. The proportion of component (b) used is 0 to 5% by weight, preferably 0.2 to 4.5% by weight of the monomer mixture.

If this proportion exceeds 5% by weight, the copolymer latex will have a high viscosity and will be impractical.

Component (c) of the monomer mixture is the above components (a) and (b).
Examples of other monomers that can be copolymerized with the monomer include aromatic vinyl compounds, vinyl cyanide compounds, vinyl acetate, acrylamide, and methacrylic acid alkyl esters in which the alkyl group has 1 to 5 carbon atoms.

Specific examples of the aromatic vinyl compounds include styrene,
Examples include α-methylstyrene, ρ-methylstyrene, vinyltoluene, and chlorostyrene. Among these, styrene is particularly preferred. Specific examples of vinyl cyanide compounds include acrylonitrile and methacrylonitrile. Among these, acrylonitrile is particularly preferred. Among the above alkyl methacrylate esters, methyl methacrylate is particularly preferred. These other monomers can be used alone or in combination of two or more.

The proportion of component (c) used is 25 to 75% by weight, or 30 to 70% by weight of the monomer mixture. If the amount used is less than 25% by weight, the obtained copolymer latex is used. The texture of the leftover carpet becomes too soft, while if it exceeds 75% by weight, it becomes too hard, making it difficult to handle, and the main physical properties of the carpet, such as thread removal strength and peel strength from the secondary base fabric, are poor. . Furthermore,
Blister resistance also deteriorates.

The copolymer latex in the present invention is obtained by emulsion polymerization of the above monomer mixture. Emulsifiers used in this emulsion polymerization include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium diphenyl ether disulfonate, sodium dialkyl succinate sulfonate, sodium rosinate, potassium oleate, and sodium salt of alkylnaphthalenesulfonic acid-formaldehyde condensate. One or more types of anionic emulsifiers such as, or nonionic emulsifiers such as polyoxyethylene alkyl ester and polyoxyethylene alkyl allyl ether can be used. In the present invention, anionic emulsifiers are effective, and a combination of sodium diphenyl ether disulfonate and a sodium salt of an alkylnaphthalene sulfonic acid-formaldehyde condensate is particularly suitable from the viewpoint of polymerization stability.

The amount of emulsifier used is usually 14 monomers: 0.2 to 0.2 of the mixture.
The content is 4%, and particularly preferably in the range of 0.5 to 3%. If the amount of emulsifier used is less than 0.2% by weight, coagulation will occur during the production of the copolymer and polymerization stability will deteriorate, while if it exceeds 4% by weight, the average particles of the copolymer latex obtained will decrease. The diameter becomes smaller, and the dispersibility of the filler described later becomes worse when preparing a carpet lining composition.
After blending, viscosity changes over time.

Examples of chain transfer agents used to lower the degree of polymerization in the emulsion polymerization reaction and to cause an ideal chain transfer reaction include t-dodecyl mercaptan, octyl mercaptan, n-tetradecyl mercaptan, and t-hexyl mercaptan. Mercaptans such as mercaptan and n-hexyl mercaptan, halogen compounds such as carbon tetrachloride, ethylene bromide, methylene bromide, and bromoform, α-methylstyrene dimer, terpinolene, ethylxanthogen disulfide, diisopropyl xanthogen sulfide,
Aminophenyl disulfide, tetraethylthiuram disulfide, etc. 1 or 21! The above can be used in combination. The amount of emulsifier used is usually 00 to 5% by weight of the monomer mixture.

Examples of the polymerization initiator in the emulsion polymerization include persulfate initiators such as potassium persulfate, sodium persulfate, and ammonium persulfate, 811w compounds such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, and benzoyl peroxide; Hydrogen peroxide and the like can be used. The amount of polymerization initiator used is 0.03 to 2.5% by weight of the monomer mixture, preferably 0.
．． 05 to 2%.

In order to promote emulsion polymerization, for example, sodium pyrobisulfite, sodium Vtite, sodium hydrogen sulfite, ferrous acid, glucose, formaldehyde, sodium sulfoxylate, L-ascorbic acid, sodium hydrogen sulfite, etc. reducing agent, glycine, alanine,
A chelating agent such as sodium ethylenediaminetetraacetate can also be used in combination.

There are no particular restrictions on the emulsion polymerization method in the present invention, and in addition to the above-mentioned emulsifier, chain transfer agent, polymerization initiator, etc., various electrolytes, pi (preparative agents, etc.) may be used in combination as necessary.
This may be done by a conventionally known method.

For example, 100 parts by weight of the monomer mixture to 100 parts by weight of water.
300°C, an emulsifier, a chain transfer agent, a polymerization initiator, etc. are used in the amounts within the above range, and the temperature is 5 to 80°C, preferably 30°C.
Emulsion polymerization may be carried out at a temperature of ~50°C for 19 to 30 hours.

The glass transition temperature (T8) of the copolymer constituting the copolymer latex in the present invention is +30°C to -55°C, preferably +25°C to -50°C.

When the glass transition temperature of the copolymer is within the above range,
A carpet with good texture, carpet workability, peel strength, thread extraction strength, and blister resistance can be obtained.

The glass transition temperature (T8) in the present invention is a value calculated by the following formula.

W (i) = weight fraction of monomer (i) in the copolymer T g (i) = value of Tg of the homopolymer of monomer (i) expressed in absolute temperature. The glass transition temperature of the homopolymer is as follows. Poly(1,3-butadiene) = 1 at I83°
Polystyrene = 373''K, polymethyl methacrylate = 378''K, polymethacrylic acid = 501''K, polyitaconic acid = 553'K, polyacrylic acid = 37''
9"K, polyacrylonitrile = 376"K, and polyacrylic acid 2-ethylhexyl = 203' have poor blister resistance and also cause carpet backing.
Unfavorable in terms of price. Furthermore, the fluidity of the carpet lining composition is reduced, resulting in poor workability.

The average particle diameter of the above copolymer was determined by treating the copolymer latex with osmic acid, taking an electron micrograph at a magnification of 30,000 times, measuring the diameters of 100 particles, and averaging them by number. Ta.

The gel content of the copolymer latex in the present invention is 40~
It is 99% by weight, particularly preferably 45 to 98% by weight.

If the gel content is less than 40% by weight, the resulting carpet backing composition will have poor blister resistance, and the flIllff strength of the primary base fabric and secondary base fabric of the carpet will decrease.

- On the other hand, if it exceeds 99fffffi%, the texture of the carpet will become hard and the workability will deteriorate.

The gel content of the above copolymer latex was measured as follows. That is, the copolymer latex was adjusted to pl (8), the copolymer in the latex was coagulated with isopropanol, then washed and dried, and the obtained solid content of 0.38 was immersed in toluene 100 at room temperature for 20 hours. and then 120
The weight ratio of the residual solid content obtained by filtration through a mesh wire mesh to the total solid content was defined as the gel content.

The gel content of the copolymer latex can be easily adjusted by selecting the type and amount of the chain transfer agent, which is a molecular weight regulator. For example, when carbon tetrachloride or methyl bromide is used as a chain transfer agent, it may be used in an amount of about 2 to 5% by weight of the monomer mixture. Further, t-dodecylmercaptan or n4-decylcaptan may be used in an amount of about 0.05 to 2% of the monomer mixture. others,
The gel content of the copolymer latex can also be adjusted by appropriately selecting the polymerization initiator used/TIJffi, the polymerization initiation temperature, etc.

As the organic polymer heat sensitizing agent in the present invention, any organic polymer heat sensitizing agent that can impart heat sensitivity to latex can be used. Agents are preferably used. Cloud point is 3
Examples of organic polymer heat sensitizing agents at 5 to 80°C include alkylene oxide adducts of alkylphenol-formaldehyde condensates, polyvinyl methyl ether, polyether polyformals, organopolysiloxanes, starches, water-1-volume polyamides, methyl cellulose, etc. can be mentioned.

Specific examples of alkylene oxide adducts of the alkylphenol-formaldehyde condensate include compounds represented by the following general formulas (1) to (1v).

CI) (■) (II) (IV) (wherein R represents an alkyl group, preferably an alkyl group having 6 to 12 carbon atoms, a and b each represent an integer, preferably an integer of 3 to 200, EO represents an ethylene oxide group, PO represents a propylene oxide group, and n represents an average degree of condensation, preferably an average degree of condensation of 2 to 20).

Among the above-mentioned 81 polymeric heat sensitizing agents having a cloud point of 35 to 80°C, alkylene oxide adducts of alkylphenol-formaldehyde condensates and organopolysiloxanes are preferably used.

For example, as organopolysiloxane, commercially available TP
A4390. TPA4380 (manufactured by Toshiba Silicon Co., Ltd.), F474 (manufactured by Shin-Etsu Silicon Co., Ltd.), etc. can be used.

Note that if an organic polymer heat sensitizing agent with a cloud point of less than 35° C. is used, the storage stability will be poor, while an organic polymer heat sensitizer with a cloud point of more than 80° C. will have a weak effect in preventing blistering.

The cloud point in the present invention is 10% of the organic polymer heat sensitizing agent.
The temperature was determined by diluting the solution to 100%, heating it gradually, and measuring the temperature at which the entire solution became cloudy.

The amount of the organic polymer heat-sensitizing agent used in the present invention varies somewhat depending on the type of organic polymer heat-sensitizing agent, but is usually 100 Mm parts of the above-mentioned copolymer latex (0.01 to 100 mm per solid content group (t()). The amount is 30 parts by weight. If this amount is less than 0.01 parts by weight, the blister resistance will be poor, while if it exceeds 30 parts by weight, the stability over time of the carpet lining composition will deteriorate, which is not preferable. The amount of the alkylene oxide adduct of the alkylphenol-formaldehyde condensate used is 0.01 to 3 parts by weight, preferably 0.03 to 3 parts by weight.
The amount of polyvinyl methyl ether used is 0.05 to 5 parts by weight, preferably 0.1 to 4 parts by weight, and the amount of polyether polyformal or organopolysiloxane used is 0.03 parts by weight. -2 parts by weight, preferably 0.05-1 parts by weight, and the amount of starch used is 1-2 parts by weight.
30 parts by weight, preferably 3 to 28 parts by weight, and the amount of water-soluble polyamide or methyl cellulose used is 0.5 to 28 parts by weight.
10 parts by weight, preferably 0.7 to 8 parts by weight.

The above organic polymer heat sensitizers can be used alone or in combination of two or more.

As the bicarbonate in the present invention, ammonium bicarbonate, potassium bicarbonate, sodium bicarbonate, and the like can be used alone or in combination of two or more. Among these, ammonium bicarbonate is preferred.

The amount of bicarbonate used is 0.03 to 5 parts by weight, preferably 0.05 to 4 parts by weight, based on 100 parts by weight of the copolymer latex (based on solid content). The amount of bicarbonate used is 0.0
If it is less than 3 parts by weight, the blister resistance of the carpet backing composition will be poor, while if it is added in an amount exceeding 5 parts by weight, no commensurate effect will be obtained, and the stability of the composition over time will worsen.

The latex composition of the present invention may further include a dispersant, an antifoaming agent, a crosslinking agent, a foaming agent, a coloring agent, a flame retardant, a preservative, an anti-aging agent, a stabilizer, a vulcanization accelerator, and an antistatic agent, as necessary. agent, p
An H adjuster and the like can be added.

The latex composition of the present invention can be used not only as a carpet backing composition but also in the production of nonwoven fabrics, artificial leather, dipped rubber products, various foams, and the like.

(Example> Hereinafter, the present invention will be explained in more detail with reference to Examples.

Note that parts and percentages are based on weight.

Example 1 [Production of copolymer latex] Monomer mixture consisting of 48 parts of butadiene, 2 parts of acrylic acid, 45 parts of styrene and 5 parts of methyl methacrylate, 1.3 parts of sodium diphenyl ether disulfonate as an emulsifier, and a chain transfer agent. 0.3 parts of t-dodecyl mercaptan and 0.7 parts of potassium persulfate as a polymerization initiator.
In addition to 0.0 parts of sodium ethylenediaminetetraacetate
1 part and 200 parts of water were placed in a stainless steel reactor having an internal volume of tool, and emulsion polymerization was carried out under stirring at 45 to 60°C for 20 hours to obtain a copolymer latex (A). Although the polymerization was carried out by batch charging, the polymerization conversion rate was 99.0% or more, the polymerization stability was also good, and there was almost no coagulum.

Table 1 shows the polymerization rate, average particle diameter, gel content, and glass transition temperature of the copolymer latex (A). Note that the average particle diameter, gel content, and glass transition temperature were measured by the method described above.

[g of carpet backing composition! A carpet lining composition was prepared using the above-mentioned copolymer latex manufactured by Coeco Co., Ltd. manufactured by Co., Ltd. 4 according to the following formulation.

Copolymer latex (A) 100 parts (solid content) Potassium bicarbonate 0.3 parts Alkylene oxide adduct of alkylphenol-formaldehyde condensate (Latemul NP-5150, Kao Corporation prototype) 0.3
Part heavy calcium carbonate 350 parts Potassium birophosphate 0.8 part Polyoxyethylene nonylphenol ether (Emuldan 9101 Kao Corporation)
(manufactured by Sumilizer S, Sumitomo Chemical Co., Ltd.) 0.5 parts Styrenated phenol (Sumilyzer S, manufactured by Sumitomo Chemical Co., Ltd.) 1.0 parts Heavy calcium carbonate as a filler is added last, and after thorough dispersion, the viscosity is about 25,000 ~ 30,000c
A carpet backing composition was prepared by adjusting the viscosity with a thickener and water so that the composition had a viscosity of 1.5 ps (measured using a Brookfield viscometer, BM type No. 4, at 6 rpm).

[Evaluation of Performance of Composition] The blister resistance and adhesive strength of the above carpet lining composition were measured by the following method.

1.5 kg (wetfl)/m2 of the above carpet lining composition with a solid content concentration of 75% was applied to a gray fabric made of a primary base fabric made of blister-resistant polypropylene tufted with nylon crimped yarn, and then 75 kg (wetfl)/m2 of the above carpet lining composition with a solid content concentration of 75% was applied as a secondary base fabric. The ounce jutes were bonded together by pressure, and dried in a hot air dryer at 180°C. Blisters generated during drying were visually observed and evaluated on a five-point scale from 1 to 5. Note that 1st grade means that no blisters were generated, and 5th grade means that blisters were generated all over the surface.

Peel strength Measured according to JIS L-1021 rug test method.

That is, the above-mentioned carpet lining composition having a solid content concentration of 75% was applied to a gray fabric made of a primary polypropylene base fabric tufted with nylon crimped yarn, and then 7 oz. After drying at ℃ for 20 minutes, the peel strength between the secondary base fabric and the gray fabric was measured.

Stability of viscosity over time After the composition was left at 40° C. for 7 days, the viscosity was measured in the same manner as in the above [Preparation of carpet lining composition] to evaluate the stability of viscosity over time.

The results are shown in Table 2.

Examples 2 to 5, Comparative Examples 1 to 14 Copolymer latexes (B) to (D) of the present invention were produced in the same manner as in Example 1 except that the raw material composition was changed as shown in Table 1. ) and comparative copolymer latexes (E) to (L) were prepared.

Table 1 shows the polymerization rate, average particle diameter, gel content, and glass transition temperature of these copolymer latexes.

Using these copolymer latexes (B) to (L), Table 2
A carpet lining composition was prepared in the same manner as in Example 1 except for the formulation shown in , and its performance was evaluated. The results are shown in Table 2. From the results in Table 2 (blank below), it is understood that the latex compositions of the present invention (Examples 1 to 5) have good blister resistance, peel strength, and stability at &1. Ru.

On the other hand, in Comparative Example 1.2, the proportion of aliphatic conjugated diene in the charged monomer mixture was outside the scope of the present invention, and in Comparative Example 3, the proportion of ethylenically unsaturated carboxylic acid in the charged monomer mixture was outside the scope of the present invention. In Comparative Example 4.5, the average particle diameter of the copolymer was outside the range of the present invention, and in Comparative Example 6.
In Example 7, the gel content of the copolymer latex was outside the range of the present invention, and in Comparative Example 12, the glass transition temperature of the copolymer was outside the range of the present invention, and both had poor blister resistance.
Peel strength is also low. Moreover, in Comparative Example 3.4, the stability of viscosity over time is also poor.

Comparative Example 8 is an example in which no bicarbonate was used, Comparative Example 9 is an example in which the amount of bicarbonate used is outside the scope of the present invention, and Comparative Example 13 is an example in which another compound is used instead of bicarbonate. All of these examples have poor blister resistance and low peel strength.

Comparative Example 9 also has poor viscosity stability over time.

Comparative Example 10 is an example in which no organic polymer heat sensitizing agent was used, and Comparative Example 11 is an example in which the amount of organic polymer heat sensitizing agent used is ii! of the present invention. Both have poor blister resistance and low peel strength. Comparative Example 11 also has poor viscosity stability over time.

Comparative Example 14 is an example in which only an alkylene oxide adduct of an alkylphenol-formaldehyde condensate was used as an organic polymer heat sensitizing agent without using a bicarbonate, and the blister resistance was poor.

(Effects of the Invention) The latex composition of the present invention is a copolymer latex having a specific glass transition temperature, average particle size, and gel content obtained by emulsion polymerization of a monomer mixture with a specific composition. It is made by combining a curing agent and bicarbonate,
For example, when used as a carpet lining, it has superior sub-blister properties, peel strength, and viscosity stability over time compared to conventional products. As a result, it is possible to increase the running speed during carpet drying, and it can be applied to high-productivity drying systems that use large dryers at high temperatures and large air volumes.

Claims (1)

[Claims] (1) (a) At least one member selected from aliphatic conjugated dienes, acrylic acid alkyl esters having an alkyl group having 2 to 10 carbon atoms, and methacrylic acid alkyl esters having an alkyl group having 6 to 14 carbon atoms. mass 25
~70% by weight, (b) 0 to 5% by weight of an ethylenically unsaturated carboxylic acid, and (c) 25 to 75% by weight of another monomer copolymerizable with (a) and (b) above. A copolymer obtained by emulsion polymerization of a polymer mixture has a glass transition temperature of +30 to -55°C, an average particle diameter of 600 to 2500 Å, and a gel content of 40 to 99.
% by weight of a copolymer latex, and 0.01 to 30 parts by weight of an organic polymer heat sensitizing agent and 0.03 to 5 parts by weight of a bicarbonate per 100 parts by weight (based on solid content) of the copolymer latex. A latex composition characterized by: