CH642980A5 - Process for the preparation of a copolymer latex - Google Patents

Description

The invention is illustrated by the following examples.

60

Example 1

87.0 g of distilled water are introduced into a reactor having a water circulation jacket, equipped with a thermometer, an agitator, a condenser and three ampoules with taps. 65 The following are introduced into the ampoules: (1) 71.25 g of acrylamide (1.0 mole) in 166.0 g of distilled water, (2) 3.75 g of dimethyldiallylammonium chloride (DMDAAC, 0.023 mole) in 8.75 g of distilled water and (3) 1.88 g of persulfate

7

642,980

ammonium (0.008 mole) in 35.6 g of distilled water. The contents of the reactor are heated to 85-89 ° C and the contents of the three stopcock bulbs are added dropwise over three hours. After an additional 15 minutes of heating, the solution is cooled to room temperature (about 23 ° C). The solution produced contains 21.9% solids and has a specific viscosity reduced by 0.32 (1% solution in 1 M NaCl at 25 ° C).

493.0 g of distilled water and 54.4 g of liquid are introduced into a reactor having a water circulation jacket, equipped with a thermometer, an agitator, a condenser and three ampoules with taps. a 10% solids solution of the above copolymer (5.44 g of dry copolymer). The following are introduced into the ampoules: (1) 164.0 g of a 10% solution of total solids of the above copolymer (16.4 g of dry copolymer), (2) 218.0 g of styrene and (3) 6.0 g of ammonium persulfate in 24.2 g of distilled water. The contents of the reactor are stirred and heated to 88 ° C. The contents of the three ampoules are added over three hours while maintaining the reactor temperature between 88 and 93 ° C. After an additional 15 minutes of heating, the product is cooled to room temperature. The product is a white latex with a solids content of 25.2%. About half of the latex is dialyzed with a 48 Å regenerated cellulose membrane to remove the unreacted water-soluble prepolymer.

5 A sample of 240.0 g of the dialyzed latex (50.0 g of dry polymer, 0.056 mole of acrylamide) is introduced into a reactor and the pH is adjusted between 4.2 and 9.1 with 0.9 ml of 1 M sodium hydroxide solution 16.2 g of a 40% aqueous solution of glyoxal (0.112 mole) are added and the pH is adjusted from 6.2 to 9.0 with 0.8 ml of a 1 M solution of sodium hydroxide. 56 ml of water are added to reduce the solids content. The mixture is heated for 4 hours at 50 ° C. and then the pH is lowered to 2.0 with 0.5 ml of concentrated hydrochloric acid. The final product contains 18.2% solids.

Examples 2 to 5 Four additional latexes are prepared according to the method described in Example 1, except that the ratio of acrylamide to DMDAAC is modified as indicated in Table 1 below.

Table 1

Prepolymer

Initial latex

Eg Acryl-

DMDAAC

(NH4) 2-

Report

%

Solution

Sty

(NH4) 2-

% of material- Amide size

s2o8

molar

befor

rein

S208

res solid particles

Acrylamide /

polymer

Pro- Dia- Jim

(g)

(g)

(g)

DMDAAC

S.T.

VSR

at 10% (g)

(g)

(g)

duit lysé (1)

1,71.25

3.75

1.88

97.75 / 2.25

21.9

0.32

218.4

218

6.0

25.2 20.8 0.4-0.6

2 67.5

7.5

1.88

95/5

21.7

0.37

218.4

218

6.0

25.9 21.3 0.4-0.6

3 60.0

15.0

1.88

90/10

21.6

0.28

218.4

218

6.0

26.1 19.7 0.4-1.0

4 56.3

18.7

1.88

87/13

21.4

0.24

218.4

218

6.0

26.0 18.3 0.5-0.8

5 37.5

37.5

1.88

70/30

21.3

0.18

218.4

218

6.0

25.2 17.6 0.8-1.26

Modified Latex modified

Ex.

Latex

40%

Water

Total of

dialysis

Glyoxal

materials

solids of

(g)

(g)

(g)

product

1

240.0

16.2

56.0

18.2

2

234.0

13.9

60.0

18.2

3

253.0

12.2

39.0

18.3

4

218.0

9.2

14.0

18.3

5

226.6

5.8

2.0

17.9

(g) = grams

(1) The particle size is measured by transmission electron microscopy.

S.T. = total solids

VSR (reduced specific viscosity) measured in 1% solution in 1M NaCl at 25 "C.

Example 6

The compositions of Examples 1 to 5 are evaluated as fillers for paper. Test sheets are prepared with a Noble & Wood apparatus. The pulp is made of a 50/50 mixture of bleached hardwood pulp and bleached softwood pulp, refined to a standard Canadian draining level of 300 ml. The paper is made at a pH of 4.5 (sulfuric acid, no alum). The latexes are evaluated with additive contents of 4% and 8% (in dry value). The witnesses consist of a paper without load and a paper loaded with 10% or 20% kaolin clay. To retain the clay, 1% of alum and 0.05% of a retention aid consisting of a cationic polyacrylamide of raised molecular weight are used. The results of the paper test results are collated in Table 2 below.

Table 2 Load (%)

None Kaolin clay

Retention adjuvant

Alum

(1%)

more

(10) Cationic polyacrylamide (20) (0.05%)

Area weight (g / m2)

64.1

Opacity (1) (%)

73.6

68.2 72.6

80.3 84.5

Dry tensile strength

(da N / cm) 3.26

2.63 2.36

Resistance to

bursting Mullen (bar)

2.23

1.77 1.54

642,980

8

Table 2

Charge (%)

Example 1 Example 2 Example 3 Example 4 Example 5

Retention adjuvant

(4) -

(8) -

(4) -

(8) -

(4) -

(8) -

(4) -

(8) -

(4) -

(8) -

Area weight (g / m2)

64.4 65.9

65.1

66.2 65.2 67.4 65.4 67.7 65.4 66.4

Opacity"'(%)

74.3 75.1 78.0

82.7

80.0

85.1 81.5 86.3 79.3

83.8

Dry tensile strength

(da N / cm)

3.43

3.47

3.48 3.54 3.57 3.47 3.36 3.33 3.45 3.22

Resistance to

bursting Mullen (bar)

2.50 2.36 2.57 2.63 2.57 2.38 2.36 2.34 2.36 2.34

(1) Opacity measured according to the Tappi T-425 standard (Opacity Meter Hunter

Examples 7 to 10 Four latexes are prepared according to the procedure described in Example 1 with 10% of various copolymers of acrylamide and DMDAAC. Latexes are not reacted with glyoxal. The latex synthesis conditions are shown in Table 3.

Example 11

The graft copolymers of Examples 7 to 10 are evaluated as fillers for paper according to the procedure described in Example 6. The results of the tests are collated in Table 4.

EXAMPLES 12 to 16 Several latexes are prepared according to the procedure described in Example 1 except that the water-soluble prepolymers used to prepare the graft copolymers are copolymers of acrylamide and methacryl methyl sulfate. loyloxyethyltrimethylammonium (MTMMS). Conditions

Table 3

The water soluble reaction prepolymers are grouped in Table 5. The latexes are not reacted with glyoxal.

Example 17

The graft copolymer particles of Examples 12 to 16 were evaluated as fillers for paper according to the procedure described in Example 6. In this experiment, a commercial polystyrene latex was used as an additional control. The particles of polystyrene latex carry negative charges and therefore a retention aid is used as indicated.

Example 18

A clay and a commercial polystyrene latex were evaluated as fillers for paper according to the procedure described in Example 6. The two fillers were evaluated with and without a retention aid consisting of a cationic polyacrylamide. The results of the tests are collated in Table 7.

Latex

Ex.

Acryl-

DMDAAC

(NH4) 2

Report

%

Solution

Sty

(NH3) 4) 2

% of my

Cut

amide

s2o8

molar

at 10% rein

S2Og all

Acrylamide /

copoly-

particu

(g)

(g)

(g)

DMDAAC

S.T.

Mother VSR (g)

(g)

(g)

Solid them (um)

7

60.0

15.0

1.88

90/10

21.6

0.28 218.4

218

6.0

26.1

0.4-l, 0 <'>

8

56.3

18.7

1.88

87/13

21.4

0.24 218.4

218

6.0

26.0

0.5 — 1.0t, J

9

46.9

28.1

1.88

79/21

21.3

0.24 218.4

218

6.0

25.7

~ 0.5 <2)

10

37.5

37.5

1.88

70/30

21.3

0.18 218.4

218

6.0

26.2

0.8-1.26 (l)

The particle size is measured by transmission electron microscopy (2) The particle size is evaluated by light microscopy (g) S.T. grams total solids

VSR (reduced specific viscosity) measured in 1% solution in 1 M NaCl at 25 ° C. Table 4

Charge (%)

Adjuvant of

Surface weight

Opacity (I) (%)

Resistance to

Resistance to

retention retention (g / m2)

traction at

bursting

dry

Mullen

(da N / cm)

(bar)

None

_

66.2

75.2

2.85

2.16

Clay

Alum (1%) more

kaolin type

(10)

Polyacrylamide

69.5

79.1

2.57

1.82

(20)

cationic (0.05%)

72.1

81.0

2.68

1.72

Example 7

(4)

-

67.8

80.2

2.96

2.07

(B)

-

69.8

84.5

2.75

1.94

642,980

Table 4

Load (0; .j

Adjuvant of

Surface weight

Opacity "'(%)

Resistance to

Resistance to

retention retention (g / m2)

dry traction

(da N / cm)

bursting

Mullen

(bar)

Example 8

(4)

-

67.7

81.7

2.75

2.07

(8)

-

69.6

86.0

2.66

1.83

Example 9

(4)

-

68.0

81.6

2.68

1.98

(B)

-

69.8

86.3

2.47

1.78

Example 10

(4)

-

67.0

79.3

2.71

1.93

(8)

-

68.2

82.9

2.64

1.92

(l)

Opacity measured according to Tappi T-425 standard (Opacity Meter Hunter)

Table 5

Water soluble prepolymer

Latex

Eg Acryl-

MTMMS

(NH4) 2

Report

%

Solution

Sty

(NH4) 2

% of

Amide size

s2o8

molar

at 10% re2s2

medium materials

Arylamide /

copolymer

party solids

(g)

(g)

(g)

MTMMS

S.T.

VSR

(g)

(g)

(g)

cules ^ '(um)

12 120.0

180.0

22.5

70/30

21.6

0.16

2402

2398

66.0

26.0

0.8

13,150.0

150.0

22.5

78/22

21.6

0.154

2402

2398

66.0

25.6

0.8

14,201.0

99.0

22.5

88/12

21.8

0.187

2402

2398

66.0

25.6

0.7

15,225.2

74.8

22.5

9/9

21.7

0.143

2402

2398

66.0

25.6

0.8

16,255.0

45.0

22.5

95/5

21.7

0.168

2402

2398

66.0

24.7

0.8

(g) grams

01 The particle size is evaluated by turbidimetry according to the A.B. Loebel method (Officiai Digest, 200, February 1959). S.T. total solids

VSR (reduced specific viscosity) measured in 1% solution in 1 M NaCl at 25 "C.

Table 6

Charge (%)

Adjuvant of

Surface weight

Opacity (1)%

Resistance to

Resistance to

retention retention (g / m2)

traction at

bursting

dry

Mullen

(da N / cm)

(bar)

None

64.9

79.6

3.19

2.10

Clay

Alum (1%) more

kaolin type

(10)

Polyacrylamide

72.4

86.0

2.43

1.48

(20)

cationic (0.05%)

79.6

89.4

2.03

1.14

Example 12

(4)

-

66.1

85.0

3.06

2.00

(8)

-

68.5

89.4

2.59

1.68

Example 13

(4)

-

66.2

85.1

3.13

2.09

(8)

-

67.4

89.1

2.80

2.27

Example 14

(4)

-

66.4

83.9

3.01

2.03

(8)

-

67.4

88.0

2.70

1.83

Example 15

(4)

-

64.4

81.0

3.22

2.14

(8)

-

66.1

83.9

3.20

2.20

Example 16

(4)

-

64.4

78.3

3.03

2.25

(8)

-

64.3

78.5

3.13

2.12

Polystyrene

(4)

Alum (1%) plus Poly

Trade

(8)

acrylamide catio

66.5

86.5

2.71

1.65

picnic (0.05%)

70.0

90.6

2.47

1.37

(1) Opacity measured according to the Tappi T-425 standard (Opacimeter Diano).

642,980

10

Table 7

Charge (%)

Kaolin-type clay Kaolin-type clay

Commercial polystyrene (4) Commercial polystyrene (4)

Retention adjuvant

(10) Alum (1%)

Alum (1%) plus (10) Cationic polyacrylamide (0.05%)

Alum (1%) Alum (1%) plus Cationic polyacrylamide (0.05%)

Area weight (g / m2)

65.6

69.6 64.8

Opacity '"(%)

75.9

80.4 76.3

66.4 80.5

(1) Opacity measured according to the Tappi T-425 standard (Opacity Meter Hunter).

Dry tensile strength

(da N / cm)

2.84

2.84 3.31

3.20

Bursting resistance Mullen (bar)

1.99

1.84 2.11

2.03

Example 19

157 g of dimethylaminoethyl methacrylate are added dropwise to 98 g of 37% hydrochloric acid. Cooling is necessary to keep the temperature below 30 ° C. 38 ml of water and 12.2 ml of isopropanol are added to obtain a 30% solution. This solution is heated to 50 ° C, nitrogen is diffused therein for 30 minutes, it is heated to 75 ° C and 3.6 ml of 0.1 M FeS04.7H20 is added, then 10.9 ml of hydroperoxide tert-butyl (90%). When the addition of the catalyst is complete, the solution is stirred for 30 minutes and cooled to room temperature. The viscous solution is diluted to 15.85% solids. VSR = 0.53 (1 M NaCl, 1%, 25 ° C).

269 ml of distilled water are introduced into a 2 liter reactor having a water circulation jacket, fitted with a thermometer, an agitator, a condenser and three ampoules. The following are introduced into the ampoules:

(1) 183 g of an aqueous solution at 12.3% of the poly (methacryloyloxyethyldimethylammonium chloride) prepared above,

(2) 225 g of styrene and (3) 6 g of ammonium persulfate in 25 ml of distilled water. The contents of the reactor are stirred and heated to 88 ° C under nitrogen. The contents of the ampoules are added dropwise over two hours while maintaining the reactor temperature at 88-95.5 ° C. After an additional 15 minutes of heating, the product is cooled to room temperature. The final product is free of styrene and has a total solids content of 36.4%.

Example 20

Poly (methacryloyloxyethyldi-methylammonium chloride) is prepared as in Example 19, except that the solution is diluted to 30% solids instead of 15.85%. 161.5 g of this 30% solution are introduced into a reactor with 359 g of distilled water. The pH of the solution is adjusted between 1.9 and 1.0 with 3.6 ml of concentrated hydrochloric acid. 34.7 g of epichlorohydrin are introduced into the reactor in order to obtain a concentration of reactive solids of 15%. This mixture is stirred for 6.5 hours after which the pH rises to 7.6. The pH is then adjusted to 0.5 with 13.7 ml of concentrated hydrochloric acid. Total solid content: 12.3%.

269 ml of distilled water are introduced into a reactor having a water circulation jacket fitted with a thermometer, an agitator, a condenser and three ampoules. Is introduced into the ampoules (1) 183 g of an aqueous solution at 12.3% of the prepolymer modified with epichlorohydrin, soluble in water prepared above, (2) 225 g of styrene and (3 ) 6 g of ammonium persulfate in 25 ml of water

20

distilled. The contents of the reactor are stirred and heated to 89 ° C under nitrogen. The contents of the ampoules are added dropwise over two hours while maintaining the reactor temperature between 89 and 97 ° C. After 15 minutes of additional heating, the product is cooled to room temperature. The final product does not contain styrene and has a total solids content of 36.8%.

Example 21

30 130 g of distilled water and 145.5 g of a 51.95% aqueous solution of poly (methyldiallylammonium chloride) are introduced into a reactor. The contents of the reactor are heated to 87 ° C. under nitrogen. 228 g of poly (methyldiallylam-35 monium chloride) are added simultaneously dropwise over two hours in 1,597 g of distilled water, 3,040 g of styrene and 83.7 g of ammonium persulfate in 338 g of distilled water, the temperature is maintained at 87-100 ° C. The contents of the reactor are stirred for another 15 minutes, cooled to room temperature and filtered through a 0.15 mm or 40 mesh screen. The latex obtained has a total solid content of 37.2% and the particle size measured according to the Loebel method (see Table 5) is 0, 5 µm 806.5 g of the above latex (300 g solids) is introduced into a reactor and the pH is adjusted from 1.6 to 1.1 with 8.8 ml of concentrated hydrochloric acid. 34.2 g of epichlorohydrin are added and the mixture is then stirred at room temperature. As the reaction progresses, the pH rises to 7.3 and is then adjusted to 1.55 with chl acid concentrated hydride. The latex obtained has a solids content of 37%.

50

Example 22

200 g of distilled water, 0.24 g of acetic acid, 3.64 g of sodium acetate and 1 g of isopropanol are introduced into a reactor. The mixture is heated to 60 ° C. under nitrogen and maintained at this temperature for 15 minutes. 40 g of methylolacryl amide in 160 g of distilled water, 13.3 g of methyldiallylammonium chloride in 53.1 g of distilled water and 0.8 g of persulfate are added dropwise simultaneously over approximately 1.8 hours. of ammonium in 20 g of distilled water and then stirred 60 for one hour. The viscous copolymer solution is cooled to room temperature and the pH is adjusted from 5.0 to 7.2 with 1.4 ml of 5 M sodium hydroxide. The total solids content of the reaction mass is 12 , 8%. To synthesize the latex, 493 g 65 of distilled water, 54.4 g of a 10% aqueous solution of the copolymer prepared above are introduced into a reactor and the mixture is heated to 89 ° C. under nitrogen. 164 g of a 10% aqueous solution of the copolymer prepared above are added simultaneously over two hours, 218 g of

11

642,980

styrene and 6 g of ammonium persulfate in 24.2 g of distilled water. The temperature is adjusted between 89 and 96 ° C. After 15 minutes of stirring, the latex is cooled to room temperature and filtered through a sieve with a 0.15 mm mesh opening. The filtered latex has a solids content of 26%.

Example 23

200 g of distilled water, 0.24 g of acetic acid, 3.64 g of sodium acetate and 1.5 g of isopro-panol are introduced into a reactor. The mixture is heated to 60-62 ° C. under nitrogen and this temperature is maintained for 15 minutes. 40 g of methylolacrylamide in 160 g of distilled water, 13.3 g of dimethyldiallylammonium chloride in 53.1 g of distilled water and 0.8 g of ammonium persulfate in 20 g are added simultaneously dropwise over 2 hours. distilled water and then stirred for one hour. The copolymer solution, which has a solids content of 12.3%, is cooled to ordinary temperature and its pH is adjusted to 7.3 with 0.5 ml of 5 M sodium hydroxide. 439 is introduced into a reactor. g of distilled water, and 54.4 g of a 10% aqueous solution of the above copolymer. The contents of the reactor are heated to 88-90 ° C under nitrogen. 164 g of a 10% aqueous solution of the above copolymer, 218 g of styrene and 6 g of ammonium persulfate in 24.2 ml are simultaneously added dropwise over approximately 2 hours to the contents of the reactor. distilled water. When the addition is complete, the contents of the reactor are stirred for 15 minutes and cooled to room temperature. The latex obtained has a solids content of 25.4%.

Example 24

170 ml of distilled water are introduced into a reactor and the mixture is heated to 85 ° C. while diffusing nitrogen. After 15 minutes of nitrogen diffusion, 110.3 g of acrylamide in 257.3 ml of distilled water, 133.2 g of a 29.8 aqueous solution are simultaneously added dropwise over 1.75 hours. % methyldiallylammonium acetate and 7.5 g of ammonium persulfate in 71.3 ml of distilled water then stirred for 15 minutes and cooled. The total solid content is 20.4% and the specific viscosity reduced by 0.35 (1 M NaCl, 1%, 25 ° C).

To synthesize the latex, 798 ml of distilled water and 1308 g of a 10% aqueous solution of the copolymer prepared above are introduced into a reactor. The mixture is heated to 93 ° C. under nitrogen. At the same time, 1308 g of styrene, 14.6 g of tert-butyl hydroperoxide and 127.6 g of distilled water and 14.4 g of sodium formaldehyde sulphoxide are added dropwise over 3 hours. 127.8 ml of distilled water and then stirred for 15 minutes and cooled to room temperature. The latex is filtered through a sieve with a 0.15 mm mesh opening. The total solid content is 39.7% and the particle size measured by the Loebel method (see Table 5) is 0.65 µm.

Example 25

The latex of Example 24 is modified as follows by glyoxal. 214 g of this latex are introduced into a reactor and the pH is adjusted between 4.9 and 8.5 with 1.4 ml of sodium hydroxide 5 M. 9.3 g of glyoxal are added to 13.9 g of distilled water to obtain a pH of 6. The pH is readjusted to 8.5 with 1.3 ml of 5 M sodium hydroxide. the mixture of la-25 tex and glyoxal while maintaining the pH at 8.5 and periodically adding a total of 0.2 ml of 5 M sodium hydroxide. After about 30 minutes, the viscosity increased from 31 to 60 cP. To stop the reaction, 0.4 ml of concentrated sulfuric acid is added. The total solids content is 30 39.2%.

Example 26

The latexes of Examples 24 and 25 are evaluated as fillers for paper according to the method described in Example 6. The results are shown in Table 8 below.

Table 8 Load (%)

Weight over-

facique

(g / m2)

Tensile strength (da N / cm)

Bursting resistance Mullen (bar)

Opacity "'%

None

65.7

3.10

2.13

79.4

Example 24

(4)

67.0

3.05

2.24

86.2

Example 24

(8)

68.8

2.63

1.89

89.2

Example 25

(4)

67.5

3.41

2.47

86.3

Example 25

(8)

68.8

3.08

2.13

89.3

Clay

kaolin type *

(10)

71.9

2.66

1.52

86.2

(20)

IIA

2.21

1.23

89.4

* Use is made, as retention adjuvant, of clay of the kaolin type, 0.05% relative to the weight of the paper of a cationic polyacrylamide.

(1) Opacity measured according to the Tappi T-425 standard (Opacimeter Diano).

Example 27

30.0 g of distilled water, 0.6 g of liquid are introduced into a reactor having a water circulation jacket, equipped with a thermometer, an agitator, a condenser and four ampoules with taps. acetic acid, and 0.85 g of sodium acetate. Is introduced into the ampoules (1) 60.0 g of styrene, (2) 6.0 g of chitosan, 6.0 g of acetic acid and 114.0 g of distilled water, (3) 0.65 g of a 20% aqueous solution of tert-butyl hydroperoxide and 25.0 g of distilled water and (4) 0.65 g of sodium formaldehyde desulfoxylate and 25.0 g of distilled water. The contents of the reactor are stirred and heated to 88 ° C. The contents of the four ampoules are added dropwise over 4 hours while maintaining the temperature at 60 ° C. After an additional 30 minutes of heating, the product is cooled to room temperature and since all the styrene has not reacted, the residual styrene is removed with a rotary evaporator. The product is a latex with a solids content of 28.8%. The particles of this latex are evaluated as a filler for paper according to the procedure of Example 6. The results are shown in Table 9 below.

60

65

642,980

12

Table 9

Charge (%)

Area weight (g / m2)

Opacity'

ité.O

Tensile strength (da N / cm)

Bursting resistance Mullen (bar)

None

66.1

80.0

Example 27

(4)

66.4

84.1

Example

(8)

68.2

86.6

Clay

kaolin type *

(10)

72.6

85.7

(20)

75.3

87.5

Polystyrene

Trade

* (4)

66.7

83.5

(8)

67.0

86.1

3.29 2.20

3.24 1.98

3.10 1.96

2.66 1.58

2.33 1.28

3.10 1.95

2.85 1.81

* 0.05% relative to the weight of the paper of a cationic polyacrylamide is used as a charge retention aid.

(i) Opacity measured according to the Tappi T-425 standard (Opacity Meter Hunter).

The remarkable advantages of the organic pigments of the invention appear particularly on examining Tables 1 and 2. The organic pigments added at a rate of 4% and 8% are compared with kaolin-type clay added at a rate of 10%. and 20% (which is equivalent in volume to 4% and 8% of organic pigments of the invention). Alum and a cationic polyacrylamide of high molecular weight are used as retention aids for kaolin clay. A retention aid is not used with the organic pigments of the invention. The opacity of the loaded paper is a measure of the retention of the charge in the paper.

The dry tensile strength and the bursting Mullen, the values of which appear in table 2, show the advantages relating to the mechanical resistance which the organic pigments of the invention provide. It can be seen that kaolin-type clay reduces the mechanical resistance properties compared to unloaded paper by around 20 to 30%. On the contrary, the organic pigments of the invention which produce the maximum opacity (compositions of Examples 3 and 4) also improve the mechanical resistance by approximately 5 to 15% compared to the unfilled paper. When we compare these organic pigments with clay, we see that they give an opacity equivalent to that of clay and that in addition the mechanical resistance properties are 20 to 50% higher than those obtained with clay.

Another advantage of the fillers (organic pigments) of the invention appears from the examination of Table 2. The paper containing a clay charge is considerably heavier than the control while the paper containing the charge of the invention is not only slightly heavier than the witness.

In Tables 3 and 4 are gathered the values of the evaluation of a similar series of organic pigments stabilized with copolymers of acrylamidodi-methyldiallylammonium chloride as cationic prepolymers soluble in water but which one does not have reacts with glyoxal. As the particles do not contain reactive functionality, the mechanical resistance properties are weaker in this experiment than in the previous experiment.

Tables 5 and 6 combine the data from a similar experiment in which organic pigments are prepared with various copolymers of acrylamide and methacryloyloxyethyltrimethylammonium methylsulfate as the cationic water-soluble prepolymer. As the particles do not have a reactive functionality, the values of the mechanical resistance are in some cases slightly lower than those of the control but they are always significantly higher than those of paper with a clay charge. In this experiment, to establish a complementary comparison, a commercial polystyrene latex is evaluated. The particles of this latex are anionic charges and therefore alum and a polymeric retention aid are used. The results show that the polystyrene particles lead to a paper before an opacity slightly greater than that obtained with the organic pigments of the invention but whose weight is also increased. The polystyrene particles reduce the mechanical strength of the paper, although this reduction is not as great as that observed with clay.

The values in Table 7 show that to obtain optimal performance with conventional fillers such as clay and polystyrene, it is necessary to use retention aids. In both cases, in the absence of retention aid, the opacity is very low. As shown in Tables 2, 4 and 6, the organic pigments of the invention per-4o provide good opacity without the use of any retention aid.

Example 28

89 g of distilled water are added to a reactor having a water circulation jacket, 45 fitted with a thermometer, an agitator, a condenser and a tap bulb, and 436 g of a 10% aqueous solution of poly (methyldiallylammonium chloride). The solution obtained is heated to 87-88 "C by circulation of hot water through the reactor envelope so. 425.2 g of styrene and 10.9 g of di-vinylbenzene are mixed and introduced into the 13.3 g of a 90% aqueous tert-butyl hydroperoxide solution and 108 g of distilled water are introduced into a burette and 13.6 g of so bisulphite are introduced into another burette. -55dium dissolved in 124.5 g of distilled water, the mixture of styrene and divinylbenzene, the tert-butyl hydroperoxide solution and the bisulfite solution are added dropwise simultaneously over 2 hours to the contents of the reactor. After 20 minutes of stirring, a slight odor of 6ostyrene is observed, an additional quantity of tert-butyl hydroperoxide solution (3.4 g of tert-butyl hydroperoxide dissolved in 27 is added to the reaction mass. g of distilled water) and an additional quantity of sodium bisulfite solution (3.4 g of dissolved sodium bisulfite in 31 g of "distilled" water) and the reaction mass is stirred for another 20 minutes. The latex obtained is cooled to ordinary temperature and filtered through a sieve with a 0.15 mm mesh opening. The total solids content is 27.7%. The

13

642,980

particle size measured with a Coulter Gounter is of a concentrated solution of hydrochloric acid (0.19 mole)

0.8 | im. in 200 g of distilled water and (2) 2.5 g of ammonium persulfate

As previously indicated, the mononium can be used in 100 g of distilled water. The content of the polyethylenically unsaturated mothers such as the divinylben- reactor is heated to 80 ° C. and the content of the zenes, mixed with monomers containing mono-bulbs, is added dropwise over 2 hours and 25 minutes while maintaining the temperature. -

ethylenic to obtain copolymer particles of ture between 80 and 85 ° C. After an additional 30 minutes of cross-linked transplant. Examples of other mono-heating which may be mentioned are that the solution is cooled to ordinary polyethylene unsaturated mother temperature which can be used at (approximately 23 ° C.). The solution obtained contains 21.6% of ma-

this effect, diallyl phthalate, ethyl dimethacrylate solids and has a reduced specific viscosity of 0.34 (solu-

neglycol, 1,3-butylene glycol dimethacrylate, 1% dimeter in 1 M NaCl at 25 ° C).

1,6-hexanediol thacrylate, polyethyl dimethacrylate.

leneglycol, polypropylene glycol dimethacrylate, water triulation, fitted with a thermometer, a stirrer, a vinylbenzene, divinylnaphthalene, diallyl maleate, the refrigerant and three tap bulbs, 503, 4 g distilled water

diallyl fumarate, trimethylolpropane trimethacrylate and 26.6 g of the above copolymer solution (5.7 g of and pentaerythritol tetraacrylate. The unsatu-15 copolymer dry copolymers). 79.8 g of the polyethylene ration which is preferred and which is called the above copolymer solution (17.2 g of dry copolymer) are introduced into the ampoule (1) and

also crosslinking monomers are divinylbenzene, 120 g of distilled water, in the ampoule (2) 230 g of styrene and diallyl phthalate, ethylene glycol dimethacrylate and the in the ampoule (3) 5.1 g of ammonium persulfate in 1,3-butylene glycol dimethacrylate. 120.0 g of distilled water. The contents of the reactor are stirred and

Although the organic pigments of the invention are heated to 78 ° C. The particularly useful as fillers for paper are added dropwise simultaneously, ampoules may be contained. Add the contents of the bulbs (1)

also use them in paper coatings with and (2) within four hours. Add the contents of the bulb (3)

an appropriate binder. In addition, they can be used in paints in four hours and 15 minutes. The temperature is maintained tures, inks and the like. They can be applied under the reactor at 78-84 ° C during the additions. The coating form is cooled with a suitable binder to product surfaces at room temperature and the pH is adjusted from 2.0 to

glass, metal, wood, plaster and the like. 4.6 with a 10% solution of sodium hydroxide. The product is filtered through a sieve with a 0.15 mm mesh opening. The

Example 29 product is a white latex containing 25.8% of solids

In a reactor with a water circulation jacket, totals and having an average particle size of 0.45

equipped with a thermometer, an agitator, a condenser and 30 µm (Loebel method, Officiai Digest, 200, February 1959). three ampoules at tap, 75.0 g of distilled water are introduced.

The following are introduced into the ampoules: (1) 35.0 g of acrylamide (0.49 Example 31

mole) in 70.0 g of distilled water, (2) 15.0 g of chloride 200 g of distilled water are introduced into a reactor having vinylbenzyltrimethylammonium (0.07 mole) in 60.0 g a flow envelope of water, fitted with a thermometer,

distilled water and (3) 1.25 g of ammonium persulfate in a stirrer, a condenser and two ampoules

50.0 g of distilled water. The contents of the reactor are heated to clean. The following are introduced into the ampoule: (1) 69.0 g of acrylamide

80 "C and the contents of (0.97 mole) and 31.0 g of methacrylamidopropyltri chloride are added dropwise over 2.5 hours.

bulbs keeping the temperature between 80 and 85 ° C. methylammonium (0.14 mole) in 200 g of distilled water and

After an additional 30 minutes of heating, it is cooled in the vial (2) 2.5 g of ammonium persulfate in solution at room temperature (about 23 ° C). The solu- 40 100 g of distilled water. The contents of the reactor are heated to

tion produced contains 22.0% solids and has a screw- 77 ° C and the contents of the ampoules are added dropwise with a reduced specificity of 0.27 (1% solution in chloro 2.5 hours in now the temperature at 77-85 ° C. After 15

1 M sodium rure at 25 ° C). additional minutes of heating the solution is cooled to

In a reactor having a jacket with circulation of water the ordinary temperature (approximately 23 ° C). The solution obtained equipped with a thermometer, an agitator, a condenser and 45 contains 22.7% of solid matter and has a specific viscosity.

three ampoules, tap 503.8 g of distilled water which is reduced by 0.52 (1% solution in sodium chloride and 26.2 g of the above copolymer solution (5.8 g of co- 1 M at 25 ° C).

dry polymer). 78.6 g of the above copolymer solution (17.3 g of dry copolymer) are introduced into the ampoule (1). It is introduced into a reactor having a circular envelope.

and 120.0 g of distilled water, in the bulb (2) 230.0 g of 50 culation of water provided with a thermometer, a stirrer, a styrene and in the bulb (3) 5.1 g of refrigerant ammonium persulfate and three ampoules, 504.7 g of distilled water

in 120.0 g of distilled water. The solution and 25.3 g of the above copolymer solution are added dropwise (5.7 g of keeping the three ampoules in 4 hours while keeping the temperature copolymer dry). 76.1 g of the ture of the reactor are introduced into the bulb (1) at 79-88 ° C. After 15 minutes additional solution of the above copolymer (17.3 g of dry copolymer) and heating, the product is cooled to room temperature 55 120.0 g of distilled water, in the ampoule (2) 230, 0 g of styrene and the pH is adjusted from 1.9 to 7.5 with a solution and in the ampoule (3) 5.1 g of ammonium persulfate in 25% sodium hydroxide. The product is filtered through a ta- 120 g of distilled water. The contents of the reactor are stirred and put in 0.15 mm mesh size. The product is a latex heated to 79 ° C. The contents of the ampoules are added simultaneously.

white containing 25.1% total solids and having a drop-by-drop size. We add the contents of the amp

average particle size of 0.62 jim (method by A.B. Loebel, 60 les (1) and (2) in 4 hours. Add the contents of the bulb (3)

Officiai Diges t, 200, February 1959). in 4 hours and 15 minutes. The reactor temperature is maintained at 79-87 ° C during the additions. We cool the pro-

Example 30 is added at room temperature and the pH is adjusted from 2.1 to 8.0

200 g of distilled water are introduced into a reactor having with a 25% solution of sodium hydroxide. Filter a water circulation envelope provided with a thermometer, 65 produced on a sieve of 0.15 mm mesh opening. The value of an agitator, a condenser and two ampoules for the product is a white latex containing 25.5% of total net solids. 77.0 g of acrylamide and having an average particle size of 0.47 μm are introduced into the ampoules (1)

(1.08 mole), 17.1 g of vinyl-4 pyridine (0.16 mole) and 16.0 g (method of Loebel, Officiai Digest, 200, February 1959).

642980

Example 32

200 g of distilled water are introduced into a reactor having a water circulation jacket provided with a thermometer, an agitator, a condenser and two ampoules with taps. 67 g of acrylamide (0.94 mole) and 33 g of methacryloyloxy-3-hydroxy-2-hydroxypropyltrimethylammonium chloride (0.14 mole) are introduced into the ampoule (1) in 200 g of distilled water and in ampoule (2) 2.5 g of ammonium persulfate in 100 g of distilled water. The contents of the reactor are heated to 80 ° C and the contents of the ampoules are added dropwise over 2 hours and 25 minutes while maintaining the temperature at 80-84 ° C. After an additional 15 minutes of heating, the solution is cooled to room temperature (about 23 ° C). The solution obtained contains 21.3% solids and has a reduced specific viscosity of 0.46 (1% solution in 1M NaCl at 25 ° C).

503 g of distilled water and 27 g of the copolymer solution are introduced into a reactor having a water circulation jacket, equipped with a thermometer, an agitator, a condenser and three ampoules with taps. above (5.8 g of dry copolymer). 81 g of the above copolymer solution (17.3 g of dry copolymer) and 120 g of distilled water are introduced into the ampoule (1), 230 g of styrene and into the ampoule (2). ampoule (3) 5.1 g of ammonium persulfate in 120 g

14

distilled water. The contents of the reactor are stirred and heated to 77 ° C. The contents of the ampoules are added dropwise and simultaneously. The contents of the ampoules (1) and (2) are added over four hours. The contents of the ampoule (3) are added in 5 hours and 15 minutes. The reactor temperature is maintained at 77-88 ° C during the additions. The product is cooled to room temperature and the pH is adjusted from 1.9 to 6.5 with a 25% solution of sodium hydroxide. The product is filtered through a sieve with a 0.15 mm mesh opening. The product is a white latex containing 25.5% total solids with an average particle size of 0.8 µm (Loebel method, Officiai Digest, 200, February 1959).

15

Example 33

The compositions of Examples 29 to 32 are evaluated as fillers for paper. Test sheets are prepared with a Noble & Wood apparatus. The pulp is made from a 50/50 mixture of bleached hardwood pulp and bleached softwood pulp ripened to a standard Canadian draining rate of 2,500. The paper is made at a pH of 4.5 (sulfuric acid, no alum). The latexes are evaluated with addition contents of 4% and 8% (dry values). The witness is unloaded paper. The results of the paper tests are collated in Table 10 below.

Table 10

Charge (%)

Weight

Opacity (1)

Brillance®

Resistance to

Resistance

surface

(%)

(%)

traction

to burst

(g / m2)

dry mullen

(da N / cm) (3)

(bar) (3)

None

64.4

73.4

80.2

3.36

2.14

Example 29

(4)

65.7

78.4

81.6

3.40

2.24

(8)

66.7

83.0

82.6

3.17

2.11

Example 30

(4)

68.5

79.2

83.6

3.83

2.31

(8)

66.5

83.0

85.5

3.76

2.27

Example 31

(4)

67.7

78.3

82.8

3.43

2.12

(8)

67.5

81.4

83.1

3.68

2.29

Example 32

(4)

63.9

75.3

79.8

3.61

2.14

(8)

67.7

80.8

83.6

3.76

2.16

(1) The opacity is measured according to the Tappi T-425 (Opacity Meter Diano) standard, mean of 4 tests.

(2) The gloss is measured according to the Tappi T-452 standard (Brightness Meter Diano); average of 4 trials.

(3) Average of 8 tests.

The new organic pigments obtained according to the invention can be used separately or in combination with other organic pigments and / or mineral pigments as fillers and coatings for paper.

VS

Claims (10)

642,980 2 CLAIMS 1. Process for preparing a latex of graft copolymer particles, characterized in that it consists in carrying out a graft copolymerization in an aqueous medium and in the presence of a radical initiator of (1) at least one monomer to ethylenic unsaturation and (2) a water-soluble cationic prepolymer, so that the prepolymer fraction of the graft copolymer particles is present on the surfaces of the particles, and in that the monomer (1) is chosen from methyl a-chlo-roacrylate, ethyl a-chloroacrylate, methyl methacrylate, isopropyl methacrylate, phenyl methacrylate, vinyl chloride, acrylonitrile, methacrylonitrile and monomers corresponding to the formula: X (III) whereR „R2, R3andX mule (I), have the same definition as in the form- 20 -C = CH. where R represents a hydrogen atom or a methyl radical, Y represents a methyl or chloro radical and n is equal to 0.1.2 or 3, and in that the prepolymer (2) has a specific viscosity reduced from 0.1 to 2.5 in solution at 1% by weight in 25 NaCl 1 M at 25 ° C and is the product of polymerization by addition of at least one cationic monomer (a) or is the product of copolymerization by addition of at least 5 mol% J of said cationic monomer (a) with at plus 95 mole% of at least one nonionic monomer (b), the cationic monomer where R], R3 and X ~ than (a) being chosen from those of formula: (I) (IV) N + R. have the same definition as in the formula Ri 1 CH2 = CCOOC2H4N ' R7 —R, X " R, laughed I (I) 35CH2 = CCONH (CH2) nNH R2 r3 -R, X- (v) where R] represents a hydrogen atom or a radical where R15 R2, R3 and X ~ have the same definition as in methyl formula, R2 represents a hydrogen atom or a radical 40 (I) and n is equal to 1, 2 or 3 and C 1 -C 4 alkyl, R3 represents a hydrogen atom or a OH R, i i ^ r2 alkyl radical in C, -C4, -CH2CHCH2Y where Y represents a CH2 = CCOOCH2CHCH2N + ^ —R2 X "(VI) _ 45 I R3 / 0 \ OH hydroxy or halo radical, -CH2CHCH2, and CH2CH20) nH where n is an integer equal to or greater than 1 where Ri, R2, R3 and X ~ have the same definition as in the drill X- is an anion, mule (I) and the nonionic monomer (b) being chosen from soN-vinylpyrrolidone, the ethylenically unsaturated monomers having an amide functionality and the ethylenically unsaturated monomers having a hydroxy functionality, and in CH n CH n only the amount of prepolymer (2) used to prepare the It ^ graft copolymer particles is between 1 part C — R 55 and 25 parts by weight per 100 parts by weight of monomer 1 I I 1 (1) used. çpj (II) 2. Method according to claim 1, characterized in that the 2/2 monomer (1) is styrene and component (b) of the mother prepoly (2) is a monoethylenically unsaturated amide, the N s 60 quantity of prepolymer (2) used to prepare the particles I \ ^ the graft copolymer being between 2 parts and 10 R 0 '3 parts by weight per 100 parts by weight of the monomer (1) used and the specific viscosity of the prepolymer being from 0.1 to 1.0. where R] represents a hydrogen atom or an alkyl radical es 3. Process according to claim 2, characterized in that in C, -C4, R2 represents a hydrogen atom or a radical amide with monoethylenic unsaturation (b ) is acrylamide. alkyl or substituted alkyl and R3 and X- have the same definition 4. Method according to one of claims 1,2, and 3, charac- that in formula (I), terized in that the prepolymer fraction of the particles is united 2 II R x CH. 3,642,980 chemically to an aldehyde group capable of reacting with it also indicates that a mu dispersion can be formed lulose. of microcapsules and cellulosic and transforming fibers 5. Method according to claim 1, characterized in that the whole in a fibrous mat and that the microcapsules are subsequently reacted with the particles of polymer copolymer behave as opaque agents not grafted with a compound which provides groups capable of reacting abrasives which give high opacity to the cellulosic substrate with the cellulose on the surface of the particles. that ultimately formed. 6. Use of the latex of copolymer particles of One of the aims of the invention is to provide graft or pigments obtained by the process according to one of claims 1 to ganics which can be used as fillers for pa- 5 as an external or internal opacifying agent in light manufacturers and which give the paper opacity, glossiness of the paper, respectively by coating the paper or i0et and surface regularity without harming its mechanical resistance by addition to pulp. picnic; and another object of the invention is to provide organic pigments which are self-retained during the papermaking process, i.e. organic pigments which are well retained on the pulp fibers without use The present invention relates to the preparation of a latex 15 conventional retention juices. new organic pigments which are particularly suitable. The invention therefore relates to the process defined in the resale as charges for paper. dication 1, for the preparation of a latex of co-particles The mineral fillers such as graft polymer suitable for organic pigments are often added to the paper, and clay, calcium carbonate or ti dioxide in particular as fillers for the paper. tane. The mineral fillers have the effect of increasing opacity when the graft copolymer particles are obstructed from paper and of avoiding "transparency"; low opacity held according to the invention suspended in water for allowing to see through the pages of printed works such as sence of cellulose pulp fibers, they are attracted to books, magazines and newspapers. Although the anionic charms of the surface of the fibers and adhere to the mineral fibers fill this role very well for a relatively low pulp price. During the manufacture of the paper which comprises the weak event, they also have drawbacks. 25 dripping water from a pulp fiber suspension, the parts- First of all they greatly reduce the strength of cationic mechanisms remain with the pulp fibers and are only paper. This defect can cause problems when well retained in the paper. subsequent use but above all the poor mechanical resistance. The graft copolymer particles prepared with leaf nicks may require that the speed of the water-soluble prepolymers containing an opti-paper machine content be reduced. The second disadvantage is that the male charges in cationic functions, are self-contained during the mineral have relatively high densities (2.5-4.0) this papermaking; so when we put these particles in which increases the weight of the loaded paper. This defect is further suspended with the pulp fibers prior to the formation of the most undesirable due to the increased costs of the sheet, the particles strongly adhere to the anionic fibers when printed materials such as pulp and are very little or not lost when the water is eli-zines, so that more and more papers are used in the manufacture of paper. It is therefore not necessary. Therefore, the paper industry is looking for a way for paper to use a retention aid to maintain the opacifiers at low density which does not harm the resistance of the particles to the pulp fibers. However, you can use paper. ser if desired for the production of paper additives The use of latex particles as known light retention charges. In addition, paper loaded with particles of paper is known in the art. Latexes of graft copolymer prepared according to the invention are marketed with propolystyrene useful for this purpose. Like mineral fillers, properties of mechanical resistance generally equivalent, and these polystyrene latexes consist of anionic particles, sometimes better, than those of an unfilled paper as well as those which require cationic retention adjuvants by weight. Papers loaded with mineral pigments such as ar- so that good retention is obtained on the pa- bile fibers or titanium dioxide, have anionic piercing resistance properties. In addition, the fillers made of mechanical polystyrene latex considerably lower than those of unloaded reene paper reduce the mechanical resistance of the corresponding well loaded paper. that this reduction is less than that caused by the monomers used to prepare these particles are mineral fillers. as they polymerize with grafting onto the prepolymer ca Water soluble ionic fillers have also been used as paper fillers to form a copolymer of small particles of urea-formaldehyde resin. 50 water insoluble grafts have been reported. It is this insolubility of the copoly that these particles are light and that when used as a graft mother which allows the formation of separate particles as fillers for the paper, they improve the opacity, the essentially spherical in suspension in the water. The brilliant role, the surface regularity and the bulk of the paper; this initial of the cationic prepolymer soluble in water is during they have a detrimental effect on the mechanical resistance stabilize the suspension and avoid the coagulation of the particles of the paper although one indicates that this effect is less than this 55 individual. After the graft copolymerization it loads mineral. initial is performed, some homopolymerization of the US Patent No. 3,824,114 describes microcapsules having monomer can occur inside the particles. According to a solid polymer wall and a solid polymer core which is not the invention, essentially stable sticky latexes are prepared which are grafted onto the polymer wall. It is possible to coat graft copolymer particles without the presence of one of the cellulosic substrates of these microcapsules or to incorporate 60 additional stabilizers being necessary. The particles of co-microcapsules with such substrates and then performing a polymeric graft fusion prepared according to the invention must be satisfied in order to obtain cellulosic substrates united to a film to do two main conditions. They must (1) be insoluble and have increased mechanical strength. This same fad in water and (2) having a melting point or ramol-patent indicates (column 3, lines 29-40) that one can form smoothing sufficiently high to be practically not microcapsules containing a polymer having a diameter 65 deformed under temperature and / or pres-medium conditions of between about 0.5 and about 1.0 µm. It is indicated to which they are subject during use. The use that also that particles can impart a strong filler to paper requires that the particles de-opacity to surface coatings of various substrates. We die distinct and essentially spherical during the forma- 642,980 4 mation of the fibrous mat, drying and calendering. Preferably the graft copolymer should have a second order transition temperature (glass transition temperature, Tg) of about 75 "C or higher. All graft copolymers prepared in the examples below have a glass transition temperature above 75 ° C. Any monomer which co-polymerizes with grafting onto the cationic water-soluble prepolymers described below can be used in the invention to form graft copolymer particles satisfying the above conditions. Suitable monomers are monoethylenically unsaturated monomers, such as for example acrylic esters such as methyl α-chloroacrylate and ethyl α-chloroacrylate, methacrylic esters such as methyl methacry-late, isopropyl methacrylate and phenyl methacrylate, and monomers corresponding to the formula: r, Ri CH, = CCOOC2H4N + —R2 X " r3 (I) In formula (I), R] represents a hydrogen atom or a methyl radical; R2 represents a hydrogen atom or a C1-C4 alkyl radical such as methyl, ethyl, propyl or butyl; R3 represents a hydrogen atom or a radical OH I alkyl in'C] -C4, -CH2C HCH2Y where Y represents a radical AT hydroxy or halo, such as chloro or bromo, -CH2CHCH2 and <- (CH2CH20) nH where n is an integer at least equal to 1, preferably from 1 to 20; andX ~ is an anion such as Cl ", Br ~, 20 CH3OSO3 - and CH3COO -. where R represents a hydrogen atom or a methyl radical, Y represents a methyl or chloro radical and n is equal to 0.1,2 or 3. Mention may be made, as examples of such monomers, of styrene, α-methylstyrene , monochlorostyrene, dichlorostyrene, trichlorostyrene, monomethylstyrene, di-methylstyrene, and trimethylstyrene. Other suitable monomers are vinyl chloride, acrylonitrile and methacrylonitrile. Mixtures of two or more monoethylenically unsaturated monomers can be used in the invention, provided that the graft copolymer particles obtained are isolated in water and have a glass transition temperature of about 75 ° C or more. Polyethylenically unsaturated monomers, such as divinylbenzene, can also be used in admixture with monoethylenically unsaturated monomers to obtain crosslinked graft copolymer particles. Among the aforementioned monoethylenically unsaturated monomers, styrene, vinyl chloride, acrylontrile and methyl methacrylate are preferred. The water-soluble cationic prepolymer can be chosen from various polymers. The main criterion for choice is that the optimum cationic charge is obtained for good retention in the paper of the graft copolymer particles produced. For example, in a latex prepared with approximately 10% of prepolymer relative to the weight of the monomer used, the opacity is maximum when the molar percentage of the cationic monomer fragments of the water-soluble prepolymer is between approximately 5 and 50, the optimal range being between about 10 and about 30 mol%. Of course, these ranges depend on the content of the water-soluble cationic prepolymer used to prepare the latex. Thus when about 5% of water-soluble prepolymer is used relative to the monomer, the range is between about 10 and about 100 moles% of cationic monomer fragments and the optimal range is between about 20 and about 60 moles %. For other contents of the water-soluble polymer, similar corrections can be made which are within the competence of the specialist. The water-soluble cationic prepolymers which are particularly suitable for the invention are addition polymers prepared from cationic ethylenically unsaturated monomers corresponding to formulas (I), (II), (III), (IV), (V) and (VI) below: The monomers of formula (I) are quaternary ammonium salts and acid salts of aminoacrylates such as dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate. Mention may be made, as characteristic quaternary salts of monomers corresponding to formula (I), methacryloyloxyethyltrimethylammonium methyl sulfate and methacryloyloxyethyltrimethylammonium chloride. As characteristic examples of monomeric acid salts corresponding to formula (I), mention may be made of methacryloyloxyethyldimethylammonium chloride and demethacryloyloxyethyldimethylammonium acetate. CH. R1 ~ C 45 50 CH_ 'Y XN, fH-Il * C-R. I * CH_ (ii) Y R., R3 In formula (II), R] represents a hydrogen atom or a Q-C4 alkyl radical and R2 represents a hydrogen atom or an alkyl or substituted alkyl radical. R2 can typically represent alkyl radicals containing 1 to 18 carbon atoms and preferably 1 to 6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, tert-butyl, hexyl, octyl, decyl radicals , dodecyl, tetra-decyl, and octadecyl. R2 may also represent a radi-60 cal alkyl substituted by any suitable substituents which do not interfere with the polymerization via a vinyl double bond. Typically, the substituents can be carboxylate, cyano, ether, amino (primary, secondary or tertiary), amide, hydrazide, 65 and hydroxy functions. R3 and X- have the same definition as in formula (I). The monomers of formula (II) are quaternary ammonium salts or acid salts of a diallylamine corresponding to the formula: 5 642,980 CH 0 CHn Rr (r C-R. r. i CH2 = CCONH (CH2) nNH R, r3 -R, X " (v) CH n CH / R. In formula (V), Rb R2, R3 and X ~ have the same definition as in formula (I) and n is equal to 1.2 or 3. We can cite as a characteristic example of monomer of formula 10 (V) , methacrylamidopropyldimethylam chloride- monium. where R] and R2 have the same definition as above. Mention may be made, as characteristic examples of quaternary ammonium salts monomers corresponding to formula (II), of dimethyldiallylammonium chloride and of dimethyl-diallylammonium bromide. Mention may be made, as characteristic examples of monomeric acid salts corresponding to formula (II), of methyldiallylammonium acetate, diallylammonium chloride, N-methyldiallylammonium bromide, 2,2-dimethylchloride N-methyldiallylammonium , N-ethyldiallylammonium bromide, N-iso-propyldiallylammonium chloride, N-butyldiallylam-monium bromide, N-tert-butyldiallylammonium chloride, N-hexyldiallylammonium chloride, N-octa-decyldiallylammonium chloride , N-acetamidodiallyl ammonium chloride, N-cyanomethyldiallylammonium chloride, N-ß-propionamidodiallylammonium bromide, N-acetoxyethyldiallylammonium chloride, N-ethoxymethyldiallylammonium bromide, Np-ethylammonium chloride N-hydroxyethyl-diallylammonium bromide and N-acetylhydrazinodiallyl-ammonium chloride. "■ î X 15 ch2 = c cooch2c hch2n + I R, OH —R, X- (VI) C = CH, ! i (III) CH. In formula (III), Rb R2, R3 and X- have the same definition as in formula (I). As characteristic examples of monomers of formula (III), mention may be made of vinylbenzyltrimethylammonium chloride and vinyl-benzyltrimethylammonium bromide. C = CH0 (IV) P .. In formula (IV), Rb R3 and X ~ have the same definition as in formula (I). As characteristic examples of monomers of formula (IV), mention may be made of 2-vinylpyridinium chloride and 2-vinylpyridinium bromide. In formula (VI), R ,, R2, R3 and X ~ have the same definition as in formula (I). As a characteristic example of a monomer of formula (VI), mention may be made of 3-methacryloyloxy-2-hydroxypropyldimethylammonium chloride. The water-soluble cationic prepolymer used in the invention may also be a natural polymer such as casein or a derivative of a natural polymer such as chi-tosane. As previously indicated, there is an optimal content of the cationic charge of the polymer particles which makes it possible to obtain good retention in the paper. In the case of a cationic homopolymer, the quantity of homopolymer used to prepare the graft copolymer latex can be adjusted to obtain the optimum charge. It is preferred, however, to adjust the cationic charge, to use a copolymer of at least one cationic monomer and at least one nonionic unsaturated monomer capable of addition polymerization. Examples of non-ionic monomers that may be mentioned are monoethylenically unsaturated amides monomers such as acrylamide, methacrylamide, N-acetamidoacrylamide, N-acetamidomethacrylamide, N-40 methylolacrylamide, diacetoneacrylamide, diacetonamide-thacrylamide. N, N-dimethylacrylamide and N-methyl-acrylamide. Other suitable nonionic monomers are vinyl acetate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and N-vinylpyrrolidone. The vinyl acetate copolymers are subsequently hydrolyzed to replace essentially all of the acetate groups with hydroxy groups. The water-soluble cationic prepolymers used in the invention may be (A) homopolymers of the cationic monomers illustrated by formulas (I) to (VI); (B) copolymers of two or more of these monomers illustrated by formulas (I) to (VI); and (C) copolymers of at least one of the monomers illustrated by formulas (I) to (VI) and of at least one other ethylenically unsaturated monomer, preferably a nonionic monomer. Therefore, the preferred water-insoluble cationic prepolymers consist essentially of approximately 5 mol% to 100 mol% of at least one monomer illustrated by the formulas (I) to (VI) and of approximately 95 mol% to 0 mole% of at least one other nonionic ethylenically unsaturated monomer. Very satisfactory cationic water-soluble prepolymers useful for preparing the graft copolymer particles of the invention are (1) prepolymers prepared from about 70 mole% to about 98 mole%, preferably about m 82 mole% to about 90 mole% of acrylamide and from about 30 mole% to about 2 mole%, and preferably from about 18 mole% to about 10 mole% of dimethyldiallylammonium chloride; (2) prepolymers prepared 642,980 6 from about 67 mole% to about 98 mole%, preferably from about 67 mole% to about 89 mole%, of acrylamide and from about 33 mole% to about 2 mole% and preferably from about 33 mole% to about 11 mole%, of methyldiallylammonium chloride; (3) prepolymers prepared from approximately 70 mol% to approximately 98 mol%, preferably from approximately 82 mol% to approximately 91 mol%, of acrylamide and from approximately 30 mol% to approximately 2 mol%, preferably from about 18 mole% to about 9 mole%, of methyldiallylammonium acetate, and (4) the prepolymers prepared from about 70 mole% to about 95 mole%, preferably from about 70 mole% to about 88 mole% acrylamide and about 30 mole% to about 5 mole%, preferably about 30 mole% to about 12 mole%, of methacryloyloxyethyltrimethylammonium methyl sulfate. The water-soluble cationic prepolymers are easily and quickly prepared by simultaneously introducing the desired monomers, in the desired amounts and in aqueous solution, and a water-soluble radical polymerization initiator in aqueous solution, a reactor containing water maintained at a temperature of about 80 ° C to about 90 ° C. Suitable radiolocal polymerization initiators are those used to prepare the graft copolymer particles of the invention and which are described below. The amount of initiator used is such that it is sufficient to obtain cationic water-soluble prepolymers having a specific viscosity reduced from about 0.1 to about 2.5 and preferably from about 0.1 to about 1.0, measured as a 1% solution in 1M NaCl at 25 ° C. In some cases it is desirable to have reactive functionality, i.e. reactive groups, on the surface of the graft copolymer particles. In general, the reactive groups increase the binding properties of the graft copolymer particles. Preferred reactive groups are those which react with cellulose. Reactive groups can be introduced into the cationic monomer before preparation of the prepolymer or introduced into the prepolymer after its preparation or introduced into the graft copolymer particles after their preparation. Groups reacting with cellulose can be introduced by reacting an epihalohydrin, such as epichlorohydrin, with polymers comprising a secondary amine function and / or a tertiary amine function. The reactive groups provided by the epihalohydrin can be epoxy groups, the halohydrin form of the epoxide or an azetidinium group. The reactive groups can be introduced by means of an aldehyde such as formaldehyde, glyoxal or glutaraldehyde in the case of polymers containing an amide function such as the prepolymers prepared by copolymerization of a cationic monomer and of acrylamide or polymers containing a secondary amine function such as prepolymers prepared from diallylamine salts. When dialdehydes such as glyoxal are used, the reactive group is an aldehyde group. When formaldehyde is used, the reactive group is the N-methylol group. The amount of the agent which is used to introduce reactive groups on the graft copolymer particles of the invention is between approximately 0.25 mole and approximately 3 moles, preferably between approximately 1 mole and approximately 2 moles per mole of amide or amine function. The reaction is carried out at a temperature of about 20 ° C to about 60 ° C at a pH of about 8 to 10 except in the case where formaldehyde is used to form the reactive groups, in which case it is operated with a pH around 2 to 3. Reactive groups can improve the mechanical strength of the paper by allowing the graft copolymer particles to react with the cellulose fibers. Conventional fillers generally reduce the mechanical strength of the paper because they interfere with the union between the cellulose fibers. The use of graft copolymer particles having groups reacting with cellulose makes it possible to increase the mechanical resistance of the paper by mutual union of the fibers via the reactive functional groups of the particles. The amount of prepolymer which is used to prepare the graft copolymers in accordance with the invention can vary between approximately 1 part and approximately 25 parts by weight per 100 parts by weight of the monomer used. The preferred range is from about 2 to about 10 parts of prepolymer per 100 parts of monomer. To carry out the graft copolymerization, the monomer is added to an aqueous solution of the water-soluble cationic prepolymer in the presence of a radical polymerization initiator. The water-soluble prepolymer may be present in its entirety in the reactor at the start of the reaction or it may be added all or part of it at the same time as the monomer. The initiator is generally added continuously with the monomer. The total reaction time can vary between about 1 and about 24 hours and the preferred time is about 2 to 6 hours. The latexes prepared according to the invention have solids contents of approximately 15% to approximately 60%. Preferably the amount of water which is used to prepare the latexes is such that latexes having a solids content of from about 25% to about 55% are obtained. In some cases the latex can be dehydrated in the form of a fine powder. In this case, the powder can be redispersed in water and then added to the pulp suspension before the paper is formed. It is generally not possible to dehydrate the latex as a fine powder when the graft copolymer particles have reactive functionality. The final product is a stable suspension of essentially spherical graft copolymer particles in water. According to the invention, graft copolymer particles can be prepared having a size of between about 0.1 µm 40 and about 2 µm. A wide variety of chemical polymerization initiators can be used to prepare the latexes of the invention, and peroxy-type compounds are particularly useful. It is preferred that the initiator is water soluble. Suitable water soluble initiators are those which are activated by heat such as sodium persulfate and ammonium persulfate. With these initiators, the polymerizations are generally carried out at temperatures of 70 to 95 ° C. Other suitable water-soluble initiators are solox redox initiator systems such as ammonium persulfate-sodium bisulfite-ferrous ion systems and sodium tert-butyl formaldehyde sulfoxylate hydroperoxide systems. The redox initiators are activated at relatively low temperatures and polymerizations can be carried out with these systems at temperatures of about 20 to 80 ° C. The amount of initiator used is known in the art. Generally, about 0.1 part is used, around 5 parts by weight of initiator per 100 parts by weight of monomer used.